Ports are the bass cabinet honking at a low bass frequency. I prefer bigger sealed box drivers ,voice coils larger and dedicated sub amplifier (s), few short cuts to the desired (Your) system I may have to start or be an apprentice on a channel to help maturing audiophile diy.
I am retired,master photographer, 2nd class fcc,72, IBM ,Atlantic steel, designer, composite materials, gave it all away(lol,take nothing never look back, eyes forward on Him. I built my first car stereo in 1968, with horn tweeters, so I could hear gospel songs with windows down.
Why ask us if you should do and spl test in the car Of course do this test, and even go as far as having a friend see if he thinks box A B C was louder not tell8ng him what is what
A buddy of mine took third in modified wall at USACi finals by perfecting his small sealed side 4th order by putting poly fill in the sealed side. Completely manipulated the drivers to believe they were in larger volume and actually played lower than my fourth order using the same equipment having a larger sealed side. I've been a believer of it since
Slowing the movement of air makes driver think it's in a bigger box. That is one reason why stuffing is used. In ideal use would be to tweak a little bit too small enclosure size into more favourable. This comment is before watching the video, I'll be back if something changes my mind.
I have some vintage Klipsch KG-4s that had the original 1 inch foam panels tucked into the sides of the cabinet. Not fond of the bass response, I had to add a sub to get that low end resonance to the room. I removed the foam panels, lined the insides, top and bottom of the cabinet with felt and stuffed with 12 oz. of poly-fill. I only did one speaker at a time to test the results. Using my ears, which is the ultimate test IMHO, the bass response in the poly-filled speaker was smoother and did not cut out so quickly as the stock speaker, better low end resonance. I liked it, so I did both speakers and removed the sub from my system. Suits my ears just fine. These KG-4s are completely rebuilt now: titanium voice coils in the horns, xover has all poly caps, original inductors and 1 ohm resister instead of the .7 poly switch (to tone down the highs slightly), felt lined cabinet and 12 oz. poly fill. They sound amazing!
Found it!!! Thought you might find this interesting... I was taught long ago the primary purpose of "fill" in a speaker enclosure is to reduce internal cabinet resonance which muddies the bass response. 1965 A. R. Bailey did a series of tests published in the British audio magazine, Wireless World using various damping materials for a long quarter wave transmission line design. Various synthetic and organic materials were used. The test comprised of discharging a low inductance capacitor at 250 volts thru a fixed length fusible wire that was literally exploded within the cabinet with a repeatable impulse patterns. The rise and decay characteristics were close mic'ed and captured via O scope. I best results of all the materials used were found with long hair wool showing the smallest initial impulse rise and the quickest decay. I've two copies of the original article, but can't find anything online. An interesting read none the less.
SQ and SPL goals are muuuuch different. Polyfill and/or open-cell foam is used to mainly damp resonances and uncontrolled, peaky, runaway bass - it smooths out peaks in subs' and speakers' upper bass. It will make them less efficient, but when they're fed with more power/level boosts to normalize the FR from the upper bass losses and to the mids frequencies - the bass that's there will be deeper, tighter, and sound much better/smoother. SQ lovers don't like bass peaks followed by steep rolloffs - that's the antithesis of good bass......
Spot on. I'm focused on SQ at home and in my vehicle. I have a background in pro recording, ears spoiled by reference monitors for years- I only care about accuracy at this point. Losing 10db all around is fine by me if I gain accuracy as a result... clean amplification is cheap these days. Those crisp transients, damped internal reflections are worth it.
@@lllllllllllllllllllll1lll1 Same for me for decades; at home particularly in my 2-CH room, my vehicles. I like things louder than friends & family for sure, but definitely prefer tight responses and accurate (to me) reproduction. 👍
Back in the 80's we were stuffing boxes to dampen out the higher freqs because the crossovers at the time were not so great. In all the testing with the test equipment i had back then i was only able to determine there was a small drop in Spl, but it did sound better with the stuffing, so great for SQ.
I added stuffing when I made a cabinet for my bass woofer out of an old beat up Kustom brand cabinet that had one blown speaker out of the two, so I bought a book from RadioShack and as I started to understand the concepts, I became intimidated by the math, and the fact that I had no specs on the 15" woofer, so I used fiberglass lining and stuffed it with poly fill, both RadioShack products, and it sounded pretty good in a manageable package. I would love to make a special cabinet with the modern updates and the goal of making tight bass with no irritating peaks.
Yes, poly works to improve sound quality in ported enclosures. The goal of the poly is to smooth out sound quality rather than increase volume. For example, Kicker includes poly sheet inside their pre-fab combo units of a sub + ported enclosure@@anthonysandoval965
I love research and development!! I am currently going through a similar project in which I am trying to have an SPL/SQ system in my small truck. I've been doing this for 30 years, and I have done plenty. I think much deeper than most. Sound is truly a language, weapon, tool and art. Somewhere along the line, we lost that knowledge. Thanks for the RnD!
I don't understand all those charts and things but I do know after putting polyfil in my two very small enclosures it improved the sound quality to no end, not necessarily more bass but much improved sound quality.
This was not a sound quality test, it was a frequency response test. My goal was see if the polyfill would improve low end extension. I conclude that it did not.
@@DIYAudioGuy I just did a polyfil test today. Im building some medium size 3-way stand mounted speakers. 8" woofers with 10" passives. I have them mocked up for testing, so I added 1.5lbs of polyfil to one and left the other empty. I see why people think it adds lower extention. It's actually damping down the upper bass(120-200hz) which allows my ears to hear the lower bass notes more clearly. The empty box sounds much more "boxy" (for lack of a better term) at higher volumes than the stuffed one which sounds more natural.
Most of my builds I only use poly in the 2 inch mat. Just to reduce cabinet resonance. I use it sparingly where needed. I have been using rockwool in some recent builds with very good results. I try and build cabinets that don’t have too many box resonances but even then adding some well placed damping can tighten mid responses. It can definitely help smooth out some irregularities from internal reflections.
This could be another test - how does polyfill effect irregularities or random spikes? How flat is the curve in the + or - 3db range with and without polyfill?
@@DIYAudioGuy I would have to agree... I have never used polyfill for that application. Predictions modeled in software you can see the effect of fill in your box really does correspond with the measurements you took. Negligible changes in the lowest range with some reduced overall output.
I do similarly. I often use some Ultra-Touch Denim insulation on the walls torn in half thickness-wise in strategic locations, then lightly stuff with Polyfill just to help reduce the echos and sound bouncing around inside the cabinet. Similar to sounds echoing inside an empty room in a house... If you can hear an echo, that sound wave can interact with the rear of the driver cone and create additional, non-musical sounds. I don't think I've ever used it to try and make an enclosure 'appear' larger to a woofer or sub.
I do enjoy a good sealed enclosure. They are very easy to build and you really can't go wrong unless the enclosure is way too big or way too small for the subwoofer. As for the polyfill, I like to use the roll polyfill and line the inside of the box to break up the standing wave. The last sealed box I did was for a single 15" subwoofer. Without any polyfill it sounded dead and not very good. With polyfill it sounded much better and the lower bass was louder. I suppose it lowered the resonant frequency of the enclosure.
I added a LOT of rockwool to my ported UM12" by adding it to the walls. It cleaned up some resonances and lowered my tuning by 1Hz at no cost to my overall SPL. I'm getting flat output to 16Hz now. I know it's not polyfill but it was really cool to measure the before and after.
Great vid Justin. I appreciate these kind of tests that showcases the data that either supports or disproves a known practice or specific application technique. Videos like this helps Consumers and Hobbyists make informed decision for their own projects.
So I decided to add polyfill to my ported box. Wow what a difference it makes! It eliminated virtually all port noise, reduced box noise due to it's damping factor, and it lowered my tuning frequency from 40hz to 38hz. All while cleaning up the overall sound quality of the bass output. Only problem is it comes out of the ports a little. Next time I will use light applications of spray glue to help it hold together inside the box. Overall I'm very happy with the results. Wish I would have tried it sooner! I first tried it on a home sub I built. Again I was getting a ton of port noise which you could definitely hear inside the house way more than you can in a vehicle. I decided to to try the polyfill and it solved the problem. Made a world of difference. I won't build a ported box without it now.
Honestly just wanna say I genuinely enjoy your videos and I've been hooked on yours and toids podcasts/discussions. People like you guys and the people on your forums share an immense amount of knowledge for people like myself trying to dive into this
Yes, I just wrote a comment about the benefit of damping being to reduce cabinet resonances. Then I saw this comment said essentially the same thing that I said, so I removed my comment.
@@Roger_Gadd - I wrote something similar, then accidentally deleted it, then wrote it a second time. Here is a repost of my explanation. "This should not be how insulation in speakers is used. People make this mistake all the time. Insulation should be used to address standing waves and to absorb energy which can cause reflections on the driver, as well as absorb the energy to prevent it from setting the enclosure into a resonating state, which can effect sound quality and have a constant frequency being put off that is not part of the music. If you are doing it to make the enclosure "sound bigger," buy a different driver, one more suited to fit in the size that you intend to have the driver installed. That might mean saving up more. But you will be happier in the long run. Now, for sub frequencies, constrained layer damping is one of the best ways to stop the energy in the enclosure, with 2# MLV being able to drop the dB of the sub frequency range by up to 19dB (varies over the range). That makes it an excellent candidate if trying to address cabinet resonances while not trying to increase the enclosure size. If instead you want to go the insulation route, for subs, you MUST use 3.5" or thicker insulation, line the entire cabinet, and it should be denim, rockwool, or fiberglass. Polyfill, also called PET insulation, also called Dacron and Acousti-stuf (specific version with crimped polyester fibers that do inscrease its effects on frequencies) and other similar names, does practically nothing at the relevant FR for subs. As such, the use of poly outside of mids/woofers should stop. This can be seen in effectiveness charts in the loudspeaker design cookbook p.45 et seq. Insulation helps to smooth the frequency response of the speaker. It should not be used to gain low end extension. Instead, if it is used properly, you can have smoother bass. Look up Bobgolds website for absorption coefficient. This will show the only way to hit 125Hz or less is to use at least 4" insulation. With going deep, you may want 5.5" - 6". And there goes exploding the size of the enclosure. To do this experiment properly, it requires two boxes, both built to have the open space being the same volume in the end. That means the final open volume in the speaker enclosures must be the same, but one built with the extra thick insulation and one without it at all. Then, you are not trying to change the Q of the driver, instead you are trying to absorb the energy before it can effect the enclosure. Surely 4"-6" insulation is not practical as it greatly increases the size of the enclosure. But, it takes that to make insulation effective at smoothing at lower frequencies. Lowe's carries (although out right now) 3.5" and 5.5" UltraTouch Denim insulation which is a decent price. For Rockwool, you can get 3x 2'x4'x4" insulation for $65. That would be the thinnest I would recommend to have an effect on sub frequencies. At 0.15 absorption coefficiant, or 15%, this is negligible on performance. As such, anything showing 50% at 125Hz will be less than that by the time you reach 40Hz, or even 20Hz. That means you will need something reading near or at a coefficient of 1 at 125Hz if you have any hope to damp low frequencies. Hence the 3.5" being the minimum to consider, and 5"+ preferred for very low frequency damping. This was the second time I typed this, so lost some things, but I think this is enough to start with. I put no links because YT likes to delete my posts when I link things. So, hope you can find things I referenced."
Thanks for your analysis. What I saw from your charts appeared to benefit SQ listeners. Instead of focusing on where the enclosure is more efficient, focus on the slope of the roll off in the frequency range most listeners will run their subwoofers. If we’re not concerned about efficiency, level match these charts at say 40hz and see how without any additional EQ, you’ll get much more volume below 40hz without also boosting 80hz. Manufacturers have been using polyfill for years not because it’s louder at any given frequency but because it provides less of steep rolloff, and you’ll get your volume with more power or more excursion.
@@beakerwsw One of the boxes I used was a midsize box, same size that the manufacturer recommended. It's perfectly normal to put a 10-in subwoofer in an enclosure that is just under a cubic foot.
@@beakerwsw I think the box size is irrelevant. Manufacturers as well as DIY installers are constrained to the confines of a vehicle so box size is often limited to the space available. What we're trying to test here is the best use of the space we have. For SPL, clearly polyfill is a waste of money (and we see that in SPL lanes where builders rarely bother to fill their boxes) but for SQ installs using stealth boxes where you are going to level-match your subwoofer and midbass drivers at a particular crossover frequency, let's say 70-80Hz, it's pretty clear from these charts that you'll get way more low bass below that frequency with any amount of polyfill. Anyway, as I said before this just proves that polyfill does what people claim and the engineers at major manufacturers know what they are doing when they fill their boxes. Thanks again @DIY Audio Guy for taking the time. Your title and conclusion might have been clickbait, but your data was very useful.
Ive had sealed subs that sounded better with it (usually adding more than recommended), and others that sounded the same with or without it. Now I will say every ported full range speaker will benefit from a small amount of polyfil. Especially around the area of the port, but not blocking the port
Poly-fil is not a terrible idea, and even though you didnt see the results you were expecting in the graphs, you totally skipped the real world testing of how it actually sounds before coming to this conclusion. I've used it in both sealed and ported enclosures with noticeable results in the way it actually sounds. I dont use it to make small boxes sound bigger, but to make optimal enclosures sound better, and that is something that you probably won't see on the graphs.
I successfully used polyfil. I have measured the results with a Parts Express DATS. One pair of my New Large Advents have an F3 of 40Hz and a Q of .85. The original F3 is about 42 Hz. Considering the low cost and availability, I think polyfil is a good option.
Have rebuilt a pair of Realistic MACH1a series; famous/infamous vintage 1970s horn based 3-ways. Completely taken apart, I actually spray sealed the internal plastic horns (Twt & Mid) and added a high(!) volume (didn't weigh) of fiberfill in the interior cabinet and compared Left (with) to Right (w/out) as I rebuilt. The filled cabinet, w/ the light rubberized spray around the mid-high horns, we're audibly improved to me, so I completed project w/ replicating remaining Right CH speaker.
As efficiency at low frequencies is largely a function of box size, the results aren't too surprising. Polyfill changes the resonance and the behaviour around resonance, but it won't improve efficiency. Polyfill will also heavily damp resonances at higher frequencies, which can end up exaggerating distortion produced by the subwoofer driver, so it's not surprising that people who use it tend to report that their subwoofer sounds smoother and cleaner. Polyfill also works pretty decently in vented enclosures too, when you design the enclosure with the use of polyfill in mind. The end result is a lower Fb and shallower rolloff (less peaky around Fb), which can work great in both home audio and car audio environments.
So it's totally worth it to get a pillow or two and stuff my new sealed subs. I just bought dual 15" HO driver from Parts Express and the Denovo sealed enclosure. Havent built them yet. To get the best performance, I should use polyfil and a lot of it right?
Hey Justin great video. I agree with Blake that polyfill is probably more suited to higher frequency drivers than subwoofers, we might find we get a larger change of system resonance when it's initially higher anyways (but that's something I've not tested). Other materials like mineral wool or fibreglass should theoretically work better for lower frequencies due to the long fibres having more of a loss factor, but again, not something I've tested. I also imagine fill would be more effective when we have one long box dimension. This is because for low frequencies the absorption coefficient is greatly dependent on the thickness of the absorber, massively so. So perhaps a much less square box might show some different results too? Anyways, great bit of research, really nice methodology, and an amazing video! Thanks as always Justin 👍 - Elliott
@@DIYAudioGuy it's typically more important for frequencies a bit higher, but I do believe it plays a role in frequencies as low as these too. We've just started a thread in 14.4v talk discord about it, it's been very interesting
Lots of comments, maybe this has been covered as I didn't read through them all, but I'm more interested in how the curves compare than those DB plots. So I'd rather manipulate the plots just so they start at the same point up top (say 80 or 100hz), and then see how they look as they go low, for what I'll hear in my system. That will show the low-end poly improvement more, I care about the curve more than overall db. Done this to a few box/sub combos, always sounded deeper like I wanted. I play bass guitar and am a bit obsessive about the low end lol.
TYVM for testing this for us. For years I've suspected polyfill to be kinda pointless, better to stuff it with old mats/carpets and pillow fill, it seems. I've used polyfill many times over the years, never being able to tell any difference. I glued a thick old carpet on the inner walls at one point, much better
I see that you stuffed the polyfill. Would it have been different if the polyfill aligned the walls like a cover notwithstanding the 16 oz per cu? I see the Skar pre fab boxes and others, even home speakers, align the walls with polyfill.
Thank you so much. Your videos have humbled me in my knowledge. I've learned more, from 2 hours of your videos & and tutorials, than I acquired in my 26 years in car audio. Makes me feel for the people that came to me for advice and help 😮 thank you very, very much for your time and effort it must take to keep us entertained. Keep up the helpfull and super knowledgeable videos
I put polyfill in a JBL Charge 2+ (bluetooth speaker), because it was compressing/limiting on high volumes with much bass. Polyfill did smooth out and made it better. It is a passive radiator system
If I use polyfill I usually use the batting, works way better especially if you're using it in a ported box to help with resonance, and so not to worry about loose polyfill ...and you can glue it against the wall.... I mainly use it for aiding in the resonance of the enclosure... But helps with low end frequencies differently in each different box ,some more than others... So it kind of affects each different subwoofer enclosure differently.. I know on some subwoofer enclosures it had little improvement and on some of those uneven smaller subwoofer enclosures, it had pretty good improvements on the low end... I used polyfill many many times so I guess I did many tests LOL.. I tried five different amounts in one subwoofer box and they each yielded a different result.. I also put polyfill in my enclosures since I was younger and I'm almost 50 so like I said just from doing it on a bunch of different sealed enclosure I got alot of mixed/ different results...... .you also got to be careful on how much you put in because of heat issues and also loose polyfill can get into your spiders and onto your tinsel leads.. will it hurt it?... I don't know..
Like everything in life some people will swear by using polyfill and some people will call you out for using it. Thankfully you did the tests and showed the data 😎 all the polyfill does is change the density of the air inside the box making the sub behave as if it had more air behind it so I wouldn’t expect huge gains unless you really packed the polyfill in. I use polyfill when I have a slightly too small box due to space constraints and the sub needs a bigger box so I use the filler to overcome the space limitations that’s all it’s a simple fix.
I agree, there are benefits and disadvantages to putting poly-fill in a enclosure. I usually put them in sealed enclosures to help the bass output be a bit more balanced, but I don't cram alot of it into it. I usually buy the kind that looks like sheets and put them on the edges. I tried that in my ported enclosure as well for a JL Audio 12W7AE and the bass output reduced but sounded more balanced lol! So whoever decides to do this they will just have to play with the amount that best suits them. I Freaking LOVE your content my man. Keep them coming!!!! 😎👊
If there's anything I have learned about audio, it's that this thumbnail is completely clickbait and the only way to know for certain is to test it yourself. "Not much difference" is what everyone is working on.
@@DIYAudioGuy I do setup my own tests and that is how I know the impact of polyfill varies. I have never seen much difference stuffing an enclosure that is big enough for a 12",15", or 18" woofer. I have seen a noticeable difference in stuffing enclosures that are close to or smaller than the recommended size for 6.5" and 8" woofers. Especially when the enclosure is made of less than optimal materials to save weight. If you were racing you would be going after every tenth.
Thank you! I love that we can test equipment setups ourselves, for a reasonable cost these days. Obviously some Poly-Fill Lobbyist came up with the 1lb/cubic ft formula😎
A lot of people use it, does everybody use it because that is just what everybody does, or does it actually work? The tests I did do not tell us anything about sound quality.
I think the polyfill might have a more beneficial effect in larger, more normal acoustic suspension designs, i.e., a 12" woofer in a 2 cu. ft. cabinet. The idea of stuffing a cabinet full of insulation started with Edgar Villchur, who invented the acoustic suspension system and founded Acoustic Research. He used fiberglass. Later AR's (1980's forward) used polyfill. Advent, in their first systems ("The Advent Loudspeaker" (1969) and the "Smaller Advent" (1972)) used dense foam, like in couch cushions. The authorities I have read about for 40+ years all said the effect was never large, usually not more than a 10% change in effective cabinet volume. Cool video, good to see someone doing these tests.
@@DIYAudioGuy In my experience (granted, I haven't built a speaker in 20+ years) it did more to clean up midrange in two-way speakers than it did to improve bass. And fiberglass, though a pain to deal with, is way better than polyfill.
I think a mistake was using spl/output instead of a normalize frequency response. Think like WINISD transfer function magnatude. If you look at the *shape* of the stuffed curve they all appear slightly flatter so if you added some wattage to normalize spl at say 100hz I think you would see a net response gain lower down. And most people don't listen to their stuff at 100% wattage all the time so it stands to reason you could sacrifice spl for flatter response and then just turn the sub setting on your reveice/atreo up one to adjust for the overall lower output.
I think that is exactly why people believe polyfill works. It makes the upper frequencies, the stuff from 60 up to 100 Hertz, quieter. So they compensate by turning up the volume and thus gives the impression of improved low frequency extension.
@@DIYAudioGuy so what I think your saying is that poly fill does not ADD low end, it dampens high end (relative to this specific application ofc) but in the world of cheap wattage the net effect for the user is that they can add a little more volume and the net response in their experience is in fact added low end correct? Because in the end whether it mutes the mid and high range of the driver or truly adds to the low end is kind of semantics. If you can simply bump your subwoofer output by one and get a flatter frequently response that allows the total system to play lower overall and less peaky you're getting exactly what you want out of the polyfill aren't you? You're getting a cheap addition to an enclosure you're stuck with that allows you to play lower in the frequency range!
Great video. You showed the polyfill results for one driver. I have drivers with different QTS and VAS values where polyfill really can make a change that matters. Remember some drivers operate better in a ported enclosure(lower VAS driver) vs. a sealed enclosure (higher VAS driver - usually a cheaper driver).
24 years ago we all ran sealed boxes and they definitely sounded louder then the portered boxes of today. We all ran Polly fill in them. I think the box has to be 2 cubes or larger to see a difference not this tiny box you are running. but that's just my 2 cents.
Though the effect of adding poly fill can certainly be debated, I've never heard anyone that goes through the effort to build a subwoofer enclosure complain of how challenging or time consuming it is to put poly fill in a box before. Usually I've heard and even said the exact opposite. Poly fill is cheap and easy to try.
Polyfill is great for large speaker cabinets, but especially for 4th order bandpass subwoofers. It allows for precise tuning of the sub. Be careful not to have too much of it around the driver as this will kill output.
I use it in 12" Sica middbass woofer. I can hear 40hz shaking windows. Rrrrrr rrrrr. But not too much, cause it can kill the bass. Half of the cabinet filled.
My current tube has foam all around the internal walls. I did it due to I’ve heard it lowers the resonant frequency but I personally never noticed any difference. Wish I could have done some testing but taking the enclosure out once it’s in the car and the sub too is not an option. Lol
I have no test devices. But could tell audibly a difference. I built my own wedge shaped box to hold 3 DB Drive 10s for my regular cab S10. I built it only deep enough to give the sub maybe 4mm clearance from the back of the box. When I finished it, I wasn’t happy with the height. So I cut it down 6 inches, and added polyfill. The same higher bass note from a song played on the box when it was larger was now not as loud when played On the smaller box. I lost higher end but got the resonant frequency farther down in the lower end. Although, this modification did seem to narrow the loudest playable frequency range. I’d say the polyfill was worth the effort. And I didn’t use much of it either.
Great video! It would be more interesting to test it with pink noise. Just make a try! With certain speakers (speaker and cabinets) the difference can be interesting... Polyfill always used for reason. Resonancy control / shaping / tuning, in-box echo reduction, harmonic distortion reduction caused by box resonancy, etc... The difference can be more noticeable in ported boxes. For example, if I would remove the polyfil from my studio sub, it would make a plunky, "flat" knocking bass. With the originally installed polyfill it gives smooth, soft but deep and accurate bass. During the past so many years I found that the amount of fill really depends on the speaker, cabinet qualities. How they behave together. And, if something sounds good in an isolated environment might not sounding the same in another room. It is not as easy as 1 x 1.
I've been using Polyfill religiously for 30+ years which I was audibly sold on in the early 90's for sealed boxes. I've never noticed a tune difference on an RTA but I've been mesmerized my whole life on the audible differences in SQ. With that being said, I know it's sometimes hard to measure the psychoacoustics of what we hear especially with static frequency responses. Transient frequency testing is I believe where the differences could be measured. The "theory" is the Poly threads need to be able to absorb rear in-box sound waves, convert to kinetic energy and then dampen vibration as these fibers want to return to rest thus causing heat. Just know they can't absorb effectively if they are packed too tight, they need wiggle room per se. Probably why Kicker states "loosely half full". If this can be done most effectively in the sweet spot of compliance, we are essentially decreasing the pressure gradients (SPL) inside the box on a time scale. Testing should measure SPL inside a box over X amount of time. I think this is the effect of the psychoacoustic response we are hearing. If people want to call it bass in a small space, maybe that's the consensual audible perception? Audibly, I've felt the same way whether it can be measured effectively or not. Thanks for the video!!
I have a single 18 in my car with a sealed box & polyfill in it. My builder couldn't make the box big enough for the room my car has. I think it sounds great & puts out some nice spl. According to my audiocontrol epicenter in dash, I've hit 157. I don't know how accurate the spl meter built into the epicenter is though.
I use it in my pa company, remember magnet cooling problems with vented pole, make box bigger and use damping around outside of box, not this pillow stuffing, it's helps with quality of sound and standing waves, the cone won't be interrupted as much with damper,, use it in vented boxes also,,
I was always under the impression that people used Poly-Fil to cut down on cabinet resonances. Also another video idea for you, get the SVS sound isolation feet and measure the subwoofer to see if it makes a difference in output, They are like $50 for 4 of them. I use them on my subs mostly because I use to live in a apartment and they'd keep the walls from shaking.
To be honest what I thought would happen is that the higher bass would be attenuated and the lower bass also attenuated but more so, so it would sound "deeper" but you'd have to bump up the amp gain slightly to compensate. So I'm surprised at some gained efficiency on the lower bass notes, seeing as polyfill is taking up room in the box and making it smaller. The only thing I can think of is the polyfill simulating a longer coiled up tube in the box (as if you mounted the speaker in a funnel that went into an "intestine" with rigid walls with the other end closed off, or you made a long and skinny sealed box with a half wavelength at a low bass frequency), would it have some half wave resonance that boosted the output, even with the same total airspace?
Hey yeah if you want to do a spl comparison with polyfil that would be cool. Over the years I have bought loaded boxes from different manufacturers and many came with polyfil in them. I always thought it did make a difference, guess not. It'll be interesting to see if it is slightly louder.
I'll just have to wait and see if this video gets enough views to justify more testing. Give it a like and a share so that the algorithm will show it some love.
Thanks for linking me to this from your other video, and for taking the time to do all these tests. I work in pro audio - the big stuff. I've seen pro manufacturers like Meyer, L'Acoustics, EAW, etc. use batting in their boxes for decades, so I have to think it must serve a purpose. Otherwise they would get rid of it and save the money in manufacturing. One difference, is I've never seen polyfill. It's always fiberglass batting sheets. This leads me to wonder if the density of it would give you different results than poly. Sadly, I don't have the test equipment to do my own experiments.
The key thing to remember about the test in this video I was focused on one very specific hypothesis, or rather I was attempting to verify or bust one very specific myth. I have been told for decades that if my box is too small I can add polyfill and make the box behave as if it were larger. My results indicate that this is 100% BS. If you build the box wrong there's no magic trick to fixing it. How does the stuffing impact sound quality? I did not test that, I did not measure that. The thing to remember is that polyfill, rockwool, fiberglass batting, jute, eggshell foam are all used for the same reason. You're trying to break up the standing waves and you're trying to keep reflections from coming back through the cone. I think that these things work for that purpose, and I will continue to believe that until I'm able to prove that they don't.
@@DIYAudioGuy the different materials absorb different frequencies though. This I know from setting up a recording studio. 1.5" fiberglass is much more effective in taming mid frequencies than eggcrate foam. For bass traps you need even thicker and denser materials. I suspect the same is true in sub enclosures.
For years I use a trick that is to add some polyfill under the speaker cone, going around the speaker rim. You don't have to use much and you definitely have an extension on the lower frequencies and a better cone control. If you like that smooth bass go for this trick, specially on cheap subwoofers.
great test, i have been looking elsewhere for stuffing than polyfill for years. its not dense enough. i easily put 25 ounces in my 19 liter box with the stuff i use. even that i di not expect to much gain from it below 100hz, but 200hz and above you get nice absorption of the back wave frequencies.
My guess is that polyfill is not dense enough for the low frequencies without serious amounts. So something like rock wool, sheep wool or some hefty synthetic stuff would be better. But then again there are many types of polyester stuffing so some probably work better than others with low frequencies. I haven't done any analytical tests, but I have had the impression that adding fill does usually make the sound a bit smoother and less boomy. 3:35 I have a hard time as I tend to hear differences of 0.2 dB, at least when talking about stereo image and finding a suitable balance between left and right. When EQ'ing, I normally want to use gear with 0.5 dB increments or less, as I've noticed the sometimes massive effect of a 1 dB. But of course I am talking about single sine wave frequencies and I certainly couldn't point them out without using a signal generator. Lately, I've become blatantly aware about the importance of room acoustics and the horrific effects of hard, untreated surfaces. I've spent way too much time with a mic (and ears) trying to find a nice EQ curve with multiple speakers. From now on I should really focus on room acoustics.
I've got the walls in my dual 12" ported enclosure covered with polyfill and I couldn't tell a difference. I'm sure it's doing something but worth laying on my side scrunched in the back of the car to Uninstall and install 2 85lb subs? Um no. Not even going to bother pulling it out lol. Thankyou for shining light on the theory
This is maths, not science. Science establishes the cause of a natural phenomenon by formulation of hypothesis followed by systematic experimentation. Your tests were quantitive, science is qualitative. The difference is subtle, “what caused that to happen?” (Looks at rain) this can be put through the scientific method, to do so you assume a cause of the effect, vary it, and see if it causes it. In doing so you either validate the hypothesis or validate the null. Lastly science only deals with natural phenomenon, this is synthetic. Science seeks to illuminate the cause of an effect in nature, we know what the cause is when we measure how much…..with maths.
My understanding is that polyfill isn't necessary for subs but is useful for dampening higher frequencies. I don't use it in sub boxes but I do use it in bookshelf speakers.
This should not be how insulation in speakers is used. People make this mistake all the time. Insulation should be used to address standing waves and to absorb energy which can cause reflections on the driver, as well as absorb the energy to prevent it from setting the enclosure into a resonating state, which can effect sound quality and have a constant frequency being put off that is not part of the music. If you are doing it to make the enclosure "sound bigger," buy a different driver, one more suited to fit in the size that you intend to have the driver installed. That might mean saving up more. But you will be happier in the long run. Now, for sub frequencies, constrained layer damping is one of the best ways to stop the energy in the enclosure, with 2# MLV being able to drop the dB of the sub frequency range by up to 19dB (varies over the range). That makes it an excellent candidate if trying to address cabinet resonances while not trying to increase the enclosure size. If instead you want to go the insulation route, for subs, you MUST use 3.5" or thicker insulation, line the entire cabinet, and it should be denim, rockwool, or fiberglass. Polyfill, also called PET insulation, also called Dacron and Acousti-stuf (specific version with crimped polyester fibers that do inscrease its effects on frequencies) and other similar names, does practically nothing at the relevant FR for subs. As such, the use of poly outside of mids/woofers should stop. This can be seen in effectiveness charts in the loudspeaker design cookbook p.45 et seq. Insulation helps to smooth the frequency response of the speaker. It should not be used to gain low end extension. Instead, if it is used properly, you can have smoother bass. Look up Bobgolds website for absorption coefficient. This will show the only way to hit 125Hz or less is to use at least 4" insulation. With going deep, you may want 5.5" - 6". And there goes exploding the size of the enclosure. To do this experiment properly, it requires two boxes, both built to have the open space being the same volume in the end. That means the final open volume in the speaker enclosures must be the same, but one built with the extra thick insulation and one without it at all. Then, you are not trying to change the Q of the driver, instead you are trying to absorb the energy before it can effect the enclosure. Surely 4"-6" insulation is not practical as it greatly increases the size of the enclosure. But, it takes that to make insulation effective at smoothing at lower frequencies. Lowe's carries (although out right now) 3.5" and 5.5" UltraTouch Denim insulation which is a decent price. For Rockwool, you can get 3x 2'x4'x4" insulation for $65. That would be the thinnest I would recommend to have an effect on sub frequencies. At 0.15 absorption coefficiant, or 15%, this is negligible on performance. As such, anything showing 50% at 125Hz will be less than that by the time you reach 40Hz, or even 20Hz. That means you will need something reading near or at a coefficient of 1 at 125Hz if you have any hope to damp low frequencies. Hence the 3.5" being the minimum to consider, and 5"+ preferred for very low frequency damping. This was the second time I typed this, so lost some things, but I think this is enough to start with. I put no links because YT likes to delete my posts when I link things. So, hope you can find things I referenced.
As a previous owner of 3 Custom Audio Stores, I have to disagree. My main tools were LEAP and the LMS systems + Audio Control Spectrum (Former IASCA Judge). Dacron was the preferred fill back in the day. Filling is an artform to produce certain outputs. Especially in Sealed Enclosures . The use mostly reduces standing waves and other problematic issues within the Enclosure. Is much better for those who have limited space for Enclosure size as stuffing results in lowering the bottom end but also the SPL. Designing an Enclosure that geometrically cancels standing waves and internal issues is much more preferred, but a Dacron laced or filled enclosure will always produce a nicer tighter bottom end. If it doesn't , you're doing it wrong. my Bla bla bla... Previous Owner 'Audio Innovations inc, Sound Service inc, Mad Monster Customs inc.' drivers encluded, Dynaudio, Seas, Morel, Audax, Fostex, (many many others) and Drivers Custom made for me using my own Thiel Small Parameters, first batch copied Rockford Fosgate 12" Pro with tweeking.. A Simple Uncalibrated Spectrum Analysis always does not give you the true nature. You Have To Listen.
+1 for this! I have added fill to many small sealed boxes and it improves the sound greatly. Some boxes that have size limitations need the help. This analysis is very interesting, but it doesn't show what matters....how it sounds.
@@alejandronunez9796 Yes, the age old question. and the Survey says....... it's purely Subjective. My 60 year old ears do not hear what my 25 year old ears did. Everyone has their own 'Frequency Curve' . Some people hear better dynamic range... some higher frequencies.... and my Cat hates everything associated with my obnoxious Audio Systems.
Hope I'm not too late in posting this. I know the rule of thumb is content creators only read comments for the first hour. 🤷♂️ I'd like to point out a couple things you might try changing regarding how you're doing your testing. Though I will first admit I don't believe these will change your results but I've been proven wrong before so I figure it's worth pointing out. The first is the mic placement is an odd choice. I get that you were going for a Near Field measurement, which technically you were still within the near field of the speaker. But on low frequency drivers the standard procedure is to place the mic centered with the dust cap and just beyond its linear excursion, or 0.11r where r is the radius of the driver, preferably in cm's. This results in a measurement devoid of reflections and even baffle defraction and resonance. By placing it a foot back you're still getting all of those added acoustical affects in the measurements. To add to this being on carpet and repeatedly moving and replacing the subwoofer is highly likely to result in slight differences in both distance and focus (directional aim). When your looking at 0.5 decimal references even a cpl millimeters can result in a change. I would recommend placing the sub and mic on a wood panel and mounting stop blocks on the front and side of the sub (just short blocks obviously) allowing you to press the sub back in the exact same position every time. This would allow you to move the mic further up to a true near field low frequency testing position. I'm guessing that's a 10in Sub so that would roughly be 2.8 centimeters, assuming the driver truly measures at 10in. The other thought I had, and not knowing the model of the driver used I could be completely wrong on this, but just visually that 0.4 cubic ft box looked way too small for the driver you were using. I know the idea is that polyfill can make a smaller box function more like a correctly tuned box. But I've always heard that was only to a small extent, and again just going visually that box seemed excessively too small for that driver. Perhaps a better test would be to use a box sized closely to the reference tuning for the driver, and then test the effects of polyfill on that setup. Lastly, and this would really push the limits of your time so I wouldn't expect you to try this more than once, is the idea that the polyfill will shift and settle over time and use. So you could try doing a burn in on perhaps the recommended polyfill amount by running the sub for a while playing a constant square wave at first then perhaps some music for dynamics. This would give the polyfill time to shift and compress then run the measurement again and see if there's any difference. I'm definitely intrigued by this proof of concept. I think more investigating under different parameters is warranted and I hope you give this another go!! I wish I had the resources to try this myself but alas at this time I don't have any way to do that.
I jammed a small cloth bag of thermal foam in a really cheap ported subwoofer cab to stop it from distorting on very low notes. Not only did it eliminate the distortion, but I think it extended the low end a bit via slowing the air down to the port. The bass also sounds less boomy without significant output loss. Better all around for $15.
You created an Aperiodic enclosure. Its a cross between ported and sealed. An Aperiodic enclosure is one in which the woofer breathes through a resistive membrane to control it's cone characteristics. In laymen's terms, it makes a woofer in a tiny enclosure act as if it were in a large, sealed enclosure. Since you had ported stuffing made it more sealed lowering SPL slightly, tightening up the bass, and extending the low end.
Currently planning out a 3.75 cuft box for some 12s and decided on poly fill after lots of research, would be curious to see some tests with a larger volume setup. Great video.
Fun video! Great info! One suggestion: part of your charm is your gesticulation, just don't block your face. Keep your hands away from the lens itself. It's distracting and feels like I need to duck! lol Thanks for the content about speaker fill. Looks like I have some testing to do.
as a kid I would use coushom foam in speaker boxes to get the bass response. muck denser that poly fill and easy to salvage from discarded couches and chairs. LOL salvagd speakers from discarded stereo consoles that needed a fuse or a solder joint fixed maybe a broken wire. or one part of the whole console broke and others were fine but they wanted a new one. LOL literal "Trash to Treasure in stereo equipment and speakers. salvagd kitchen cabints for enclosures too... lol talk about cheap audio guy or rather kid.that was me at 10yo thru my teens
I like the video. You do some initial scientific testing, which you already say can be improved by using statistical techniques and doing the test dozens of times, etc. But you also mentioned another limitation which I always bring up in these kinds of videos: how does it sound to YOUR ears? It's one thing to use scientific measurements, but at the end of the day all that matters is how the sound is perceived by the human ear. One serious limitation is that your ear is different from mine, but I'd still lend that kind of analysis a lot of authority, especially if you consistently use parameters like the CheapAudioMan. Another, major limitation is the room. What you hear (or measure) in your room could be vastly different from my living room. This is a very good start, nevertheless.
Some years ago (15-25?), wool was the “preferred” stuffing for speakers enclosures. Curious if it is better than what everyone uses today since wool is not man made.
Fiberglass batting was also popular. I have pulled apart a few 70's era home speakers and found the walls lined with yellow fiberglass, the itchy stuff.
@@chrishuyler3580 Ahh yes I forgot about that itchy fiberglass! I’ve been in a few of those (regretted it for awhile! Lol) fiberglass filled speakers too 🔊 😬
My worry about this test is that the Polyfill will be mucho squashed - made much denser - so that would skew the results. The squashing would get more pronounced the more fill is inserted. Plus, there will be differences in the mechanical link between the driver and the bottom panel... and thus, the top panel... and thus, the frequency response/excursions of the driver at different frequencies. So altering the measurements. Hope this makes sense! Guy
I have been building speakers since the late 1970s. Point blank, Polyfil is crap. I line my DIY made cabinets and ammo can speaker builds with "BoomMat" carpeting (similar to old school automotive jute) and/or DynoMat (Mat66). The bass is deeper, richer, reduces cabinet resonances, and maintains internal cabinet volume space. For big wood subwoofers...I start with stapling in BoomMat on the back behind the sub and adding more to the sides to find the "sweet spot" by ear using a tone generator. Bass output can be tricky to master...it takes a good ear and proper placement to find what works for the listening environment.
I like to cram as many subs into a specified enclosure size as I can. Why? Because cone area is king. Also, you can kind of overcome the smallish enclosure size by not just adding in poly fill but also by increasing the power input
there is a lot of talk about poly fill used to make a small box seem bigger. but this test was the same box? i've always used poly fill but for the Dampening effect. not enclosure size, because i make my sealed enclosure to the recommended spec of my speaker. great test but didn't compare with different sized boxes.
Good video.! Geez this RUclips rabbit hole was deep. I'm voting for another video with different materials and a test for sound quality if that's possible? Fiberglass, Rock wool, ect. Testing the harmonics everything I've seen saying polyfill is useless but other materials make slight improvements on sound quality maybe even try some closed cell insulation. I'm going to be pulling my speakers and trying something but just going for highest sound quality possible not for spl or trying to help a small space
That's the problem with these kind of rabbit holes, a lot of people want more detailed tests, but when you start making the more detailed test people stop watching. I think I said toward the end of the video that if this video got a quarter million views that I would do more testing. So I'm sticking to that.
The output transistorsb are close to it's limit, they get hot. Oh the poly fill, I thought it may help offset the space taken up by the driver. I don't really know if the pillow stuffing helped extend the bottom end.
Poly fill or damping material has been used for ever i have built only 2 subs a 12 inch and 15 inch both ported both loaded with old fill from a pillow both sound perfect used measure from comercially sold subs using there size and put in port never tested with equiptment but to my ear sound good .i think stiffening box helps seal leaks
As far as the hearing of frequency. I can hear frequencies most can’t. I don’t know how that is! But I can and I’ve had expert I’ve proven wrong and they changed the tuning of their speaker box designs
I would be interested in the same test with a woofer that has a much higher QTS. At 0.49, while not terribly low, that is low enough that the Ultimax 10 is going to be fairly tolerant of varying box volume / fill. One of the ways around too small an enclosure is to use a woofer that will work well in a wider range of enclosures. Not arguing the results, just postulating.
The proper way is to line the inner walls especially the back inner wall with fiberglass and then stuff polyfill in the box. It can lower tuning up to 7hz.
Interesting! Yeah, I was wondering if I should do anything such as polyfill to the NVX 1.3 cu ft sealed enclosure that's coming with my new sub...tomorrow ***I am super happy with my new system. With the amp it sounds like I have a low power subwoofer already. ***Really enjoying it! ...and researching upgrading my other vehicles as well. I have confidence and more knowledge now. Gotta have it in all my cars!! 🤣
@DIY Audio Guy I heard the point of polly fill is to dampen standing waves and produce a cleaner sound. Could you test that? Also, did you listen to music at each fill just to see how it effects more than just a sweep?
Nice video, lots of good info, I do prefer the lower tones over the +70 hz range. Another measurement process is to do slower sweeps to get more data at frequencies at a slower rate. Another thought I've always wondered about using the "egg crate foam" that have peaks and valleys to break up the standing waves, similar to movie theater setups. Can you test that to see if it makes a difference?
Anything you put in the box to break up standing waves and cut down reflections will improve sound quality. The only thing this test shows is that you don't actually improve low end extension by adding polyfill to a box that is to small to begin with.
Poly fill works better in a full range speaker than a Subwoofer box. It helps resolve standing waves from the rear of the cone which can come thru the cone and muddy the sound. You put so much Poly fill inside that small box that it acted as a dampener against the back of the cone. (It doesn't have to touch to effect) Which made your results look the way they did. It's NEVER placed directly behind the cone that close as it affects the Qms (which is what happened to you)
Many years back I burned out a woofer. When I replaced it I replaced the scrawny internal crossover to woofer wire with a foot of 12 gauge. When I fired it up, oh, man, I blew the other woofer! No, not really. The other woofer worked as well as it ever had, but the woofer with one foot of 12 gauge was phenomenal. Try replacing that 18 gauge in the housing with 12 gauge. Then run 12 gauge all the way back to the amp, on one channel. You will think the other channel is dead. It all goes back to damping factor.
Great video and test. You did a nice job explaining everything as well. Is there any way I can talk you into comparing these results with a sealed box coated with expanding foam on the inside? Just squirt the expanding foam on a cheapo paintbrush then brush it on the inside surface of the box. When it cures it leaves a hard, not very thick, very bumpy surface. It's great for sound deadening and I'd love to see what would happen inside the box.
I've used pollyfill before and it worked! I didn't over stuff the box though! I lined the inside of the enclosure with a couple sheets but never stuffed a whole bag or two inside?
The standard recommendation is 1 lb per cuft. As you can see form the video when you weigh it out 1 lb per cuft means cramming a ton of polyfill in the box.
I made an FRFR cabinet for celestions 2 way FRFR speaker. They recommend stapling some sort of wadding to a wall but aren't very specific. I have tons of Roxul safe n sound, I don't know if I should mess with it...sounds like a studio monitor already, I can';t really imagine it any better
@@DIYAudioGuy I need to play with it some more. Its the closest I've ever had my live guitar rig sounding like it sounds in my studio control room, so I'm pretty happy. Maybe I'll hear something I don't like and need to fix it, but so far, loving it. If I build another, I'd like to make it slanted so its more aimed at where it matters, but not sure how to calculate the new dimensions, so I'll stick it on a speaker stand to tilt it. Oh, and next time I will build ONE! Not the insane dual I have now, its way more than loud enough if I unplug one of the speakers
also wouldnt running the sub repeatedly in the same box cause the air to heat up in the box regardless of the fill. how do you know its not the affect of the voice coil dumping heat.
DIY Guy.......Interesting test. of course you are just testing for SPL, there might be other issues the Poly fill improves? It might be interesting to test Fiberglass, Acousti-Stuff and the recycled blue jean information Lowes sells?
The first 1,000 people to use the link will get a 1 month free trial of Skillshare: skl.sh/diyaudioguy09221
Ports are the bass cabinet honking at a low bass frequency. I prefer bigger sealed box
drivers ,voice coils larger and dedicated sub amplifier (s), few short cuts to the desired (Your) system
I may have to start or be an apprentice on a channel to help maturing audiophile diy.
I am retired,master photographer, 2nd class fcc,72, IBM ,Atlantic steel, designer, composite materials, gave it all away(lol,take nothing never look back, eyes forward on Him. I built my first car stereo in 1968, with horn tweeters, so I could hear gospel songs with windows down.
I'm experimenting with the lawn fabric and shelf liner for unique covers. Or reducing pressure comb effect.
Why ask us if you should do and spl test in the car Of course do this test, and even go as far as having a friend see if he thinks box A B C was louder not tell8ng him what is what
@@UPsideDOWNworld321 still waiting on this video to get 200,000 views before I give that a try.
A buddy of mine took third in modified wall at USACi finals by perfecting his small sealed side 4th order by putting poly fill in the sealed side. Completely manipulated the drivers to believe they were in larger volume and actually played lower than my fourth order using the same equipment having a larger sealed side. I've been a believer of it since
Interesting, perhaps I'll need to build some bandpass enclosures and see what happens.
Slowing the movement of air makes driver think it's in a bigger box. That is one reason why stuffing is used. In ideal use would be to tweak a little bit too small enclosure size into more favourable.
This comment is before watching the video, I'll be back if something changes my mind.
Unpopular opinion- drivers don’t “think”.
@@robtaylor8907 Yes, just words we use. They don't "think" or "believe", they are working according to their specs considering surroundings.
@@robtaylor8907 sheesh ...mine do. I just trained a couple of 18's to clean my garage😂
I have some vintage Klipsch KG-4s that had the original 1 inch foam panels tucked into the sides of the cabinet. Not fond of the bass response, I had to add a sub to get that low end resonance to the room. I removed the foam panels, lined the insides, top and bottom of the cabinet with felt and stuffed with 12 oz. of poly-fill. I only did one speaker at a time to test the results. Using my ears, which is the ultimate test IMHO, the bass response in the poly-filled speaker was smoother and did not cut out so quickly as the stock speaker, better low end resonance. I liked it, so I did both speakers and removed the sub from my system. Suits my ears just fine. These KG-4s are completely rebuilt now: titanium voice coils in the horns, xover has all poly caps, original inductors and 1 ohm resister instead of the .7 poly switch (to tone down the highs slightly), felt lined cabinet and 12 oz. poly fill. They sound amazing!
Found it!!! Thought you might find this interesting...
I was taught long ago the primary purpose of "fill" in a speaker enclosure is to reduce internal cabinet resonance which muddies the bass response.
1965 A. R. Bailey did a series of tests published in the British audio magazine, Wireless World using various damping materials for a long quarter wave transmission line design. Various synthetic and organic materials were used.
The test comprised of discharging a low inductance capacitor at 250 volts thru a fixed length fusible wire that was literally exploded within the cabinet with a repeatable impulse patterns. The rise and decay characteristics were close mic'ed and captured via O scope.
I best results of all the materials used were found with long hair wool showing the smallest initial impulse rise and the quickest decay.
I've two copies of the original article, but can't find anything online. An interesting read none the less.
SQ and SPL goals are muuuuch different. Polyfill and/or open-cell foam is used to mainly damp resonances and uncontrolled, peaky, runaway bass - it smooths out peaks in subs' and speakers' upper bass. It will make them less efficient, but when they're fed with more power/level boosts to normalize the FR from the upper bass losses and to the mids frequencies - the bass that's there will be deeper, tighter, and sound much better/smoother. SQ lovers don't like bass peaks followed by steep rolloffs - that's the antithesis of good bass......
If I can get enough views on this video then I will be able to do more tests.
@@DIYAudioGuy 😂😂😂
Spot on. I'm focused on SQ at home and in my vehicle. I have a background in pro recording, ears spoiled by reference monitors for years- I only care about accuracy at this point. Losing 10db all around is fine by me if I gain accuracy as a result... clean amplification is cheap these days. Those crisp transients, damped internal reflections are worth it.
@@lllllllllllllllllllll1lll1 Same for me for decades; at home particularly in my 2-CH room, my vehicles. I like things louder than friends & family for sure, but definitely prefer tight responses and accurate (to me) reproduction. 👍
polyfill will do nothing for resonances, it has no mass.
Back in the 80's we were stuffing boxes to dampen out the higher freqs because the crossovers at the time were not so great. In all the testing with the test equipment i had back then i was only able to determine there was a small drop in Spl, but it did sound better with the stuffing, so great for SQ.
Cool
I remember my mother saying "Am I going nuts? Where did that pillow go?" - "Not so great" is being nice about it : )
I added stuffing when I made a cabinet for my bass woofer out of an old beat up Kustom brand cabinet that had one blown speaker out of the two, so I bought a book from RadioShack and as I started to understand the concepts, I became intimidated by the math, and the fact that I had no specs on the 15" woofer, so I used fiberglass lining and stuffed it with poly fill, both RadioShack products, and it sounded pretty good in a manageable package.
I would love to make a special cabinet with the modern updates and the goal of making tight bass with no irritating peaks.
Does poly work in ported enclosures? Great tutorial by the way 😎
Yes, poly works to improve sound quality in ported enclosures. The goal of the poly is to smooth out sound quality rather than increase volume. For example, Kicker includes poly sheet inside their pre-fab combo units of a sub + ported enclosure@@anthonysandoval965
I love research and development!! I am currently going through a similar project in which I am trying to have an SPL/SQ system in my small truck. I've been doing this for 30 years, and I have done plenty. I think much deeper than most. Sound is truly a language, weapon, tool and art. Somewhere along the line, we lost that knowledge. Thanks for the RnD!
I hope to do more in the future!
No need for research and development, it's already been done, just study the actual research from actual, researchers ,Thiel/Small , Butterworth, ect.
another benefit i could think of is the fact that tightly packed polyfil can stop the wire rattle (if unsecured/too long) inside the box :D
That's a real good point.
Hot melt to tac wire then liquid nails for no rattle or shift.
I don't understand all those charts and things but I do know after putting polyfil in my two very small enclosures it improved the sound quality to no end, not necessarily more bass but much improved sound quality.
This was not a sound quality test, it was a frequency response test. My goal was see if the polyfill would improve low end extension. I conclude that it did not.
@@DIYAudioGuy I just did a polyfil test today. Im building some medium size 3-way stand mounted speakers. 8" woofers with 10" passives. I have them mocked up for testing, so I added 1.5lbs of polyfil to one and left the other empty. I see why people think it adds lower extention. It's actually damping down the upper bass(120-200hz) which allows my ears to hear the lower bass notes more clearly. The empty box sounds much more "boxy" (for lack of a better term) at higher volumes than the stuffed one which sounds more natural.
Most of my builds I only use poly in the 2 inch mat. Just to reduce cabinet resonance. I use it sparingly where needed. I have been using rockwool in some recent builds with very good results. I try and build cabinets that don’t have too many box resonances but even then adding some well placed damping can tighten mid responses. It can definitely help smooth out some irregularities from internal reflections.
It may help with that, but I'm no longer convinced by the argument that polyfill will improve low frequency extension.
This could be another test - how does polyfill effect irregularities or random spikes? How flat is the curve in the + or - 3db range with and without polyfill?
@@ramonbmovies there are an infant number of variations that can be tested. One person can't do them all.
@@DIYAudioGuy I would have to agree... I have never used polyfill for that application. Predictions modeled in software you can see the effect of fill in your box really does correspond with the measurements you took. Negligible changes in the lowest range with some reduced overall output.
I do similarly. I often use some Ultra-Touch Denim insulation on the walls torn in half thickness-wise in strategic locations, then lightly stuff with Polyfill just to help reduce the echos and sound bouncing around inside the cabinet. Similar to sounds echoing inside an empty room in a house... If you can hear an echo, that sound wave can interact with the rear of the driver cone and create additional, non-musical sounds. I don't think I've ever used it to try and make an enclosure 'appear' larger to a woofer or sub.
I do enjoy a good sealed enclosure. They are very easy to build and you really can't go wrong unless the enclosure is way too big or way too small for the subwoofer. As for the polyfill, I like to use the roll polyfill and line the inside of the box to break up the standing wave. The last sealed box I did was for a single 15" subwoofer. Without any polyfill it sounded dead and not very good. With polyfill it sounded much better and the lower bass was louder. I suppose it lowered the resonant frequency of the enclosure.
I added a LOT of rockwool to my ported UM12" by adding it to the walls. It cleaned up some resonances and lowered my tuning by 1Hz at no cost to my overall SPL. I'm getting flat output to 16Hz now. I know it's not polyfill but it was really cool to measure the before and after.
Right, this stuffing works best in a box that's already been designed correctly. Trying to stuff a box to make it bigger is an exercise in futility.
Great vid Justin. I appreciate these kind of tests that showcases the data that either supports or disproves a known practice or specific application technique. Videos like this helps Consumers and Hobbyists make informed decision for their own projects.
That is the goal.
So I decided to add polyfill to my ported box. Wow what a difference it makes! It eliminated virtually all port noise, reduced box noise due to it's damping factor, and it lowered my tuning frequency from 40hz to 38hz. All while cleaning up the overall sound quality of the bass output. Only problem is it comes out of the ports a little. Next time I will use light applications of spray glue to help it hold together inside the box. Overall I'm very happy with the results. Wish I would have tried it sooner! I first tried it on a home sub I built. Again I was getting a ton of port noise which you could definitely hear inside the house way more than you can in a vehicle. I decided to to try the polyfill and it solved the problem. Made a world of difference. I won't build a ported box without it now.
I'm glad it worked for you.
Honestly just wanna say I genuinely enjoy your videos and I've been hooked on yours and toids podcasts/discussions. People like you guys and the people on your forums share an immense amount of knowledge for people like myself trying to dive into this
Thank you, I appreciate that.
Yeah, I find the larger benefit of polyfil to be damping standing waves. But that's not applicable at low frequencys
I would love to do some AB listening tests.
@@DIYAudioGuy After I moved on from entry level subs sheer output was never a goal it was always sq.
Nothing wrong with that.
Yes, I just wrote a comment about the benefit of damping being to reduce cabinet resonances. Then I saw this comment said essentially the same thing that I said, so I removed my comment.
@@Roger_Gadd - I wrote something similar, then accidentally deleted it, then wrote it a second time. Here is a repost of my explanation.
"This should not be how insulation in speakers is used. People make this mistake all the time. Insulation should be used to address standing waves and to absorb energy which can cause reflections on the driver, as well as absorb the energy to prevent it from setting the enclosure into a resonating state, which can effect sound quality and have a constant frequency being put off that is not part of the music.
If you are doing it to make the enclosure "sound bigger," buy a different driver, one more suited to fit in the size that you intend to have the driver installed. That might mean saving up more. But you will be happier in the long run.
Now, for sub frequencies, constrained layer damping is one of the best ways to stop the energy in the enclosure, with 2# MLV being able to drop the dB of the sub frequency range by up to 19dB (varies over the range). That makes it an excellent candidate if trying to address cabinet resonances while not trying to increase the enclosure size.
If instead you want to go the insulation route, for subs, you MUST use 3.5" or thicker insulation, line the entire cabinet, and it should be denim, rockwool, or fiberglass. Polyfill, also called PET insulation, also called Dacron and Acousti-stuf (specific version with crimped polyester fibers that do inscrease its effects on frequencies) and other similar names, does practically nothing at the relevant FR for subs. As such, the use of poly outside of mids/woofers should stop. This can be seen in effectiveness charts in the loudspeaker design cookbook p.45 et seq.
Insulation helps to smooth the frequency response of the speaker. It should not be used to gain low end extension. Instead, if it is used properly, you can have smoother bass.
Look up Bobgolds website for absorption coefficient. This will show the only way to hit 125Hz or less is to use at least 4" insulation. With going deep, you may want 5.5" - 6". And there goes exploding the size of the enclosure.
To do this experiment properly, it requires two boxes, both built to have the open space being the same volume in the end. That means the final open volume in the speaker enclosures must be the same, but one built with the extra thick insulation and one without it at all. Then, you are not trying to change the Q of the driver, instead you are trying to absorb the energy before it can effect the enclosure. Surely 4"-6" insulation is not practical as it greatly increases the size of the enclosure. But, it takes that to make insulation effective at smoothing at lower frequencies.
Lowe's carries (although out right now) 3.5" and 5.5" UltraTouch Denim insulation which is a decent price. For Rockwool, you can get 3x 2'x4'x4" insulation for $65. That would be the thinnest I would recommend to have an effect on sub frequencies. At 0.15 absorption coefficiant, or 15%, this is negligible on performance. As such, anything showing 50% at 125Hz will be less than that by the time you reach 40Hz, or even 20Hz. That means you will need something reading near or at a coefficient of 1 at 125Hz if you have any hope to damp low frequencies. Hence the 3.5" being the minimum to consider, and 5"+ preferred for very low frequency damping.
This was the second time I typed this, so lost some things, but I think this is enough to start with. I put no links because YT likes to delete my posts when I link things. So, hope you can find things I referenced."
Thanks for your analysis. What I saw from your charts appeared to benefit SQ listeners. Instead of focusing on where the enclosure is more efficient, focus on the slope of the roll off in the frequency range most listeners will run their subwoofers. If we’re not concerned about efficiency, level match these charts at say 40hz and see how without any additional EQ, you’ll get much more volume below 40hz without also boosting 80hz. Manufacturers have been using polyfill for years not because it’s louder at any given frequency but because it provides less of steep rolloff, and you’ll get your volume with more power or more excursion.
Good point!
@@DIYAudioGuy I also wonder if it would be more apparent if the box was bigger. Like if you put it in a "regular" sized box.
@@beakerwsw One of the boxes I used was a midsize box, same size that the manufacturer recommended. It's perfectly normal to put a 10-in subwoofer in an enclosure that is just under a cubic foot.
@@beakerwsw I think the box size is irrelevant. Manufacturers as well as DIY installers are constrained to the confines of a vehicle so box size is often limited to the space available. What we're trying to test here is the best use of the space we have. For SPL, clearly polyfill is a waste of money (and we see that in SPL lanes where builders rarely bother to fill their boxes) but for SQ installs using stealth boxes where you are going to level-match your subwoofer and midbass drivers at a particular crossover frequency, let's say 70-80Hz, it's pretty clear from these charts that you'll get way more low bass below that frequency with any amount of polyfill. Anyway, as I said before this just proves that polyfill does what people claim and the engineers at major manufacturers know what they are doing when they fill their boxes. Thanks again @DIY Audio Guy for taking the time. Your title and conclusion might have been clickbait, but your data was very useful.
Ive had sealed subs that sounded better with it (usually adding more than recommended), and others that sounded the same with or without it. Now I will say every ported full range speaker will benefit from a small amount of polyfil. Especially around the area of the port, but not blocking the port
Poly-fil is not a terrible idea, and even though you didnt see the results you were expecting in the graphs, you totally skipped the real world testing of how it actually sounds before coming to this conclusion. I've used it in both sealed and ported enclosures with noticeable results in the way it actually sounds. I dont use it to make small boxes sound bigger, but to make optimal enclosures sound better, and that is something that you probably won't see on the graphs.
That's the topic for another video.
I successfully used polyfil. I have measured the results with a Parts Express DATS. One pair of my New Large Advents have an F3 of 40Hz and a Q of .85. The original F3 is about 42 Hz. Considering the low cost and availability, I think polyfil is a good option.
Have rebuilt a pair of Realistic MACH1a series; famous/infamous vintage 1970s horn based 3-ways. Completely taken apart, I actually spray sealed the internal plastic horns (Twt & Mid) and added a high(!) volume (didn't weigh) of fiberfill in the interior cabinet and compared Left (with) to Right (w/out) as I rebuilt. The filled cabinet, w/ the light rubberized spray around the mid-high horns, we're audibly improved to me, so I completed project w/ replicating remaining Right CH speaker.
As efficiency at low frequencies is largely a function of box size, the results aren't too surprising. Polyfill changes the resonance and the behaviour around resonance, but it won't improve efficiency. Polyfill will also heavily damp resonances at higher frequencies, which can end up exaggerating distortion produced by the subwoofer driver, so it's not surprising that people who use it tend to report that their subwoofer sounds smoother and cleaner.
Polyfill also works pretty decently in vented enclosures too, when you design the enclosure with the use of polyfill in mind. The end result is a lower Fb and shallower rolloff (less peaky around Fb), which can work great in both home audio and car audio environments.
You always have good information.
So it's totally worth it to get a pillow or two and stuff my new sealed subs. I just bought dual 15" HO driver from Parts Express and the Denovo sealed enclosure. Havent built them yet. To get the best performance, I should use polyfil and a lot of it right?
Hey Justin great video. I agree with Blake that polyfill is probably more suited to higher frequency drivers than subwoofers, we might find we get a larger change of system resonance when it's initially higher anyways (but that's something I've not tested). Other materials like mineral wool or fibreglass should theoretically work better for lower frequencies due to the long fibres having more of a loss factor, but again, not something I've tested. I also imagine fill would be more effective when we have one long box dimension. This is because for low frequencies the absorption coefficient is greatly dependent on the thickness of the absorber, massively so. So perhaps a much less square box might show some different results too? Anyways, great bit of research, really nice methodology, and an amazing video! Thanks as always Justin 👍
- Elliott
Interesting, I've never really thought of the shape of the box as being that important.
@@DIYAudioGuy it's typically more important for frequencies a bit higher, but I do believe it plays a role in frequencies as low as these too. We've just started a thread in 14.4v talk discord about it, it's been very interesting
Lots of comments, maybe this has been covered as I didn't read through them all, but I'm more interested in how the curves compare than those DB plots. So I'd rather manipulate the plots just so they start at the same point up top (say 80 or 100hz), and then see how they look as they go low, for what I'll hear in my system. That will show the low-end poly improvement more, I care about the curve more than overall db. Done this to a few box/sub combos, always sounded deeper like I wanted. I play bass guitar and am a bit obsessive about the low end lol.
TYVM for testing this for us. For years I've suspected polyfill to be kinda pointless, better to stuff it with old mats/carpets and pillow fill, it seems. I've used polyfill many times over the years, never being able to tell any difference. I glued a thick old carpet on the inner walls at one point, much better
I see that you stuffed the polyfill. Would it have been different if the polyfill aligned the walls like a cover notwithstanding the 16 oz per cu? I see the Skar pre fab boxes and others, even home speakers, align the walls with polyfill.
Good question!
Thank you so much. Your videos have humbled me in my knowledge. I've learned more, from 2 hours of your videos & and tutorials, than I acquired in my 26 years in car audio. Makes me feel for the people that came to me for advice and help 😮 thank you very, very much for your time and effort it must take to keep us entertained. Keep up the helpfull and super knowledgeable videos
Glad I could help!
I put polyfill in a JBL Charge 2+ (bluetooth speaker), because it was compressing/limiting on high volumes with much bass. Polyfill did smooth out and made it better. It is a passive radiator system
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If I use polyfill I usually use the batting, works way better especially if you're using it in a ported box to help with resonance, and so not to worry about loose polyfill ...and you can glue it against the wall.... I mainly use it for aiding in the resonance of the enclosure... But helps with low end frequencies differently in each different box ,some more than others... So it kind of affects each different subwoofer enclosure differently.. I know on some subwoofer enclosures it had little improvement and on some of those uneven smaller subwoofer enclosures, it had pretty good improvements on the low end... I used polyfill many many times so I guess I did many tests LOL.. I tried five different amounts in one subwoofer box and they each yielded a different result.. I also put polyfill in my enclosures since I was younger and I'm almost 50 so like I said just from doing it on a bunch of different sealed enclosure I got alot of mixed/ different results...... .you also got to be careful on how much you put in because of heat issues and also loose polyfill can get into your spiders and onto your tinsel leads.. will it hurt it?... I don't know..
I definitely prefer the quilt batting to the loose fill.
To me a more flat response is just better at the cost of efficiency. Not to mention the dampening effects it is going to have, i call it a win.
Like everything in life some people will swear by using polyfill and some people will call you out for using it. Thankfully you did the tests and showed the data 😎 all the polyfill does is change the density of the air inside the box making the sub behave as if it had more air behind it so I wouldn’t expect huge gains unless you really packed the polyfill in. I use polyfill when I have a slightly too small box due to space constraints and the sub needs a bigger box so I use the filler to overcome the space limitations that’s all it’s a simple fix.
And I'm not saying that my test is going to settle the debate. Hopefully more people will make some videos showing off some more tests.
I'm a believer in the legitimately extremely huge box.
I agree, there are benefits and disadvantages to putting poly-fill in a enclosure. I usually put them in sealed enclosures to help the bass output be a bit more balanced, but I don't cram alot of it into it. I usually buy the kind that looks like sheets and put them on the edges. I tried that in my ported enclosure as well for a JL Audio 12W7AE and the bass output reduced but sounded more balanced lol! So whoever decides to do this they will just have to play with the amount that best suits them. I Freaking LOVE your content my man. Keep them coming!!!! 😎👊
Thank you!
@@DIYAudioGuy wow you sure got popular Justin, look at this other fake account trying to be you 😅
If there's anything I have learned about audio, it's that this thumbnail is completely clickbait and the only way to know for certain is to test it yourself.
"Not much difference" is what everyone is working on.
Not clickbait, after testing it myself I no longer recommend polyfill. You are welcome to set up your own test.
@@DIYAudioGuy I do setup my own tests and that is how I know the impact of polyfill varies. I have never seen much difference stuffing an enclosure that is big enough for a 12",15", or 18" woofer. I have seen a noticeable difference in stuffing enclosures that are close to or smaller than the recommended size for 6.5" and 8" woofers. Especially when the enclosure is made of less than optimal materials to save weight.
If you were racing you would be going after every tenth.
Thank you!
I love that we can test equipment setups ourselves, for a reasonable cost these days.
Obviously some Poly-Fill Lobbyist came up with the 1lb/cubic ft formula😎
I hope to do a few more tests. Since I'm going against conventional wisdom, I'll need a lot of data to back that up.
Hehehe nice!
Greetings from ph sir 🇵🇭🇵🇭🇵🇭 majority of the subs here are filled with poly fill now we know, this video is actually helpfull thankyou!
A lot of people use it, does everybody use it because that is just what everybody does, or does it actually work? The tests I did do not tell us anything about sound quality.
I think the polyfill might have a more beneficial effect in larger, more normal acoustic suspension designs, i.e., a 12" woofer in a 2 cu. ft. cabinet. The idea of stuffing a cabinet full of insulation started with Edgar Villchur, who invented the acoustic suspension system and founded Acoustic Research. He used fiberglass. Later AR's (1980's forward) used polyfill. Advent, in their first systems ("The Advent Loudspeaker" (1969) and the "Smaller Advent" (1972)) used dense foam, like in couch cushions. The authorities I have read about for 40+ years all said the effect was never large, usually not more than a 10% change in effective cabinet volume. Cool video, good to see someone doing these tests.
I'm not at all surprised to learn that Villchur did not find anything more than a 10% difference.
@@DIYAudioGuy In my experience (granted, I haven't built a speaker in 20+ years) it did more to clean up midrange in two-way speakers than it did to improve bass. And fiberglass, though a pain to deal with, is way better than polyfill.
I think a mistake was using spl/output instead of a normalize frequency response. Think like WINISD transfer function magnatude. If you look at the *shape* of the stuffed curve they all appear slightly flatter so if you added some wattage to normalize spl at say 100hz I think you would see a net response gain lower down. And most people don't listen to their stuff at 100% wattage all the time so it stands to reason you could sacrifice spl for flatter response and then just turn the sub setting on your reveice/atreo up one to adjust for the overall lower output.
I think that is exactly why people believe polyfill works. It makes the upper frequencies, the stuff from 60 up to 100 Hertz, quieter. So they compensate by turning up the volume and thus gives the impression of improved low frequency extension.
@@DIYAudioGuy so what I think your saying is that poly fill does not ADD low end, it dampens high end (relative to this specific application ofc) but in the world of cheap wattage the net effect for the user is that they can add a little more volume and the net response in their experience is in fact added low end correct? Because in the end whether it mutes the mid and high range of the driver or truly adds to the low end is kind of semantics. If you can simply bump your subwoofer output by one and get a flatter frequently response that allows the total system to play lower overall and less peaky you're getting exactly what you want out of the polyfill aren't you? You're getting a cheap addition to an enclosure you're stuck with that allows you to play lower in the frequency range!
Great video. You showed the polyfill results for one driver. I have drivers with different QTS and VAS values where polyfill really can make a change that matters. Remember some drivers operate better in a ported enclosure(lower VAS driver) vs. a sealed enclosure (higher VAS driver - usually a cheaper driver).
24 years ago we all ran sealed boxes and they definitely sounded louder then the portered boxes of today. We all ran Polly fill in them. I think the box has to be 2 cubes or larger to see a difference not this tiny box you are running. but that's just my 2 cents.
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Though the effect of adding poly fill can certainly be debated, I've never heard anyone that goes through the effort to build a subwoofer enclosure complain of how challenging or time consuming it is to put poly fill in a box before. Usually I've heard and even said the exact opposite. Poly fill is cheap and easy to try.
Polyfill is great for large speaker cabinets, but especially for 4th order bandpass subwoofers. It allows for precise tuning of the sub. Be careful not to have too much of it around the driver as this will kill output.
Where did you have that bag of poly fill during the tests? If it was in the testing room it could impact results
I use it in 12" Sica middbass woofer. I can hear 40hz shaking windows. Rrrrrr rrrrr.
But not too much, cause it can kill the bass. Half of the cabinet filled.
My current tube has foam all around the internal walls.
I did it due to I’ve heard it lowers the resonant frequency but I personally never noticed any difference. Wish I could have done some testing but taking the enclosure out once it’s in the car and the sub too is not an option. Lol
The microphone was not 3 feet away...
I have no test devices. But could tell audibly a difference. I built my own wedge shaped box to hold 3 DB Drive 10s for my regular cab S10. I built it only deep enough to give the sub maybe 4mm clearance from the back of the box. When I finished it, I wasn’t happy with the height. So I cut it down 6 inches, and added polyfill. The same higher bass note from a song played on the box when it was larger was now not as loud when played On the smaller box. I lost higher end but got the resonant frequency farther down in the lower end. Although, this modification did seem to narrow the loudest playable frequency range. I’d say the polyfill was worth the effort. And I didn’t use much of it either.
Great video! It would be more interesting to test it with pink noise. Just make a try! With certain speakers (speaker and cabinets) the difference can be interesting... Polyfill always used for reason. Resonancy control / shaping / tuning, in-box echo reduction, harmonic distortion reduction caused by box resonancy, etc... The difference can be more noticeable in ported boxes. For example, if I would remove the polyfil from my studio sub, it would make a plunky, "flat" knocking bass. With the originally installed polyfill it gives smooth, soft but deep and accurate bass. During the past so many years I found that the amount of fill really depends on the speaker, cabinet qualities. How they behave together. And, if something sounds good in an isolated environment might not sounding the same in another room. It is not as easy as 1 x 1.
I've been using Polyfill religiously for 30+ years which I was audibly sold on in the early 90's for sealed boxes. I've never noticed a tune difference on an RTA but I've been mesmerized my whole life on the audible differences in SQ. With that being said, I know it's sometimes hard to measure the psychoacoustics of what we hear especially with static frequency responses. Transient frequency testing is I believe where the differences could be measured. The "theory" is the Poly threads need to be able to absorb rear in-box sound waves, convert to kinetic energy and then dampen vibration as these fibers want to return to rest thus causing heat. Just know they can't absorb effectively if they are packed too tight, they need wiggle room per se. Probably why Kicker states "loosely half full". If this can be done most effectively in the sweet spot of compliance, we are essentially decreasing the pressure gradients (SPL) inside the box on a time scale. Testing should measure SPL inside a box over X amount of time. I think this is the effect of the psychoacoustic response we are hearing. If people want to call it bass in a small space, maybe that's the consensual audible perception? Audibly, I've felt the same way whether it can be measured effectively or not. Thanks for the video!!
Right, not much of a difference when measured but people tend to prefer the sound.
I have a single 18 in my car with a sealed box & polyfill in it. My builder couldn't make the box big enough for the room my car has. I think it sounds great & puts out some nice spl. According to my audiocontrol epicenter in dash, I've hit 157. I don't know how accurate the spl meter built into the epicenter is though.
I use it in my pa company, remember magnet cooling problems with vented pole, make box bigger and use damping around outside of box, not this pillow stuffing, it's helps with quality of sound and standing waves, the cone won't be interrupted as much with damper,, use it in vented boxes also,,
I was always under the impression that people used Poly-Fil to cut down on cabinet resonances. Also another video idea for you, get the SVS sound isolation feet and measure the subwoofer to see if it makes a difference in output, They are like $50 for 4 of them. I use them on my subs mostly because I use to live in a apartment and they'd keep the walls from shaking.
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To be honest what I thought would happen is that the higher bass would be attenuated and the lower bass also attenuated but more so, so it would sound "deeper" but you'd have to bump up the amp gain slightly to compensate. So I'm surprised at some gained efficiency on the lower bass notes, seeing as polyfill is taking up room in the box and making it smaller. The only thing I can think of is the polyfill simulating a longer coiled up tube in the box (as if you mounted the speaker in a funnel that went into an "intestine" with rigid walls with the other end closed off, or you made a long and skinny sealed box with a half wavelength at a low bass frequency), would it have some half wave resonance that boosted the output, even with the same total airspace?
Hey yeah if you want to do a spl comparison with polyfil that would be cool. Over the years I have bought loaded boxes from different manufacturers and many came with polyfil in them. I always thought it did make a difference, guess not. It'll be interesting to see if it is slightly louder.
I'll just have to wait and see if this video gets enough views to justify more testing. Give it a like and a share so that the algorithm will show it some love.
Thanks for linking me to this from your other video, and for taking the time to do all these tests.
I work in pro audio - the big stuff. I've seen pro manufacturers like Meyer, L'Acoustics, EAW, etc. use batting in their boxes for decades, so I have to think it must serve a purpose. Otherwise they would get rid of it and save the money in manufacturing.
One difference, is I've never seen polyfill. It's always fiberglass batting sheets. This leads me to wonder if the density of it would give you different results than poly.
Sadly, I don't have the test equipment to do my own experiments.
The key thing to remember about the test in this video I was focused on one very specific hypothesis, or rather I was attempting to verify or bust one very specific myth. I have been told for decades that if my box is too small I can add polyfill and make the box behave as if it were larger. My results indicate that this is 100% BS. If you build the box wrong there's no magic trick to fixing it.
How does the stuffing impact sound quality? I did not test that, I did not measure that.
The thing to remember is that polyfill, rockwool, fiberglass batting, jute, eggshell foam are all used for the same reason. You're trying to break up the standing waves and you're trying to keep reflections from coming back through the cone. I think that these things work for that purpose, and I will continue to believe that until I'm able to prove that they don't.
@@DIYAudioGuy the different materials absorb different frequencies though.
This I know from setting up a recording studio. 1.5" fiberglass is much more effective in taming mid frequencies than eggcrate foam.
For bass traps you need even thicker and denser materials.
I suspect the same is true in sub enclosures.
For years I use a trick that is to add some polyfill under the speaker cone, going around the speaker rim. You don't have to use much and you definitely have an extension on the lower frequencies and a better cone control. If you like that smooth bass go for this trick, specially on cheap subwoofers.
Great tip!
great test, i have been looking elsewhere for stuffing than polyfill for years.
its not dense enough.
i easily put 25 ounces in my 19 liter box with the stuff i use. even that i di not expect to much gain from it below 100hz, but 200hz and above you get nice absorption of the back wave frequencies.
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My guess is that polyfill is not dense enough for the low frequencies without serious amounts. So something like rock wool, sheep wool or some hefty synthetic stuff would be better. But then again there are many types of polyester stuffing so some probably work better than others with low frequencies. I haven't done any analytical tests, but I have had the impression that adding fill does usually make the sound a bit smoother and less boomy.
3:35 I have a hard time as I tend to hear differences of 0.2 dB, at least when talking about stereo image and finding a suitable balance between left and right. When EQ'ing, I normally want to use gear with 0.5 dB increments or less, as I've noticed the sometimes massive effect of a 1 dB. But of course I am talking about single sine wave frequencies and I certainly couldn't point them out without using a signal generator. Lately, I've become blatantly aware about the importance of room acoustics and the horrific effects of hard, untreated surfaces. I've spent way too much time with a mic (and ears) trying to find a nice EQ curve with multiple speakers. From now on I should really focus on room acoustics.
I've got the walls in my dual 12" ported enclosure covered with polyfill and I couldn't tell a difference. I'm sure it's doing something but worth laying on my side scrunched in the back of the car to Uninstall and install 2 85lb subs? Um no. Not even going to bother pulling it out lol. Thankyou for shining light on the theory
This is maths, not science.
Science establishes the cause of a natural phenomenon by formulation of hypothesis followed by systematic experimentation. Your tests were quantitive, science is qualitative.
The difference is subtle, “what caused that to happen?” (Looks at rain) this can be put through the scientific method, to do so you assume a cause of the effect, vary it, and see if it causes it. In doing so you either validate the hypothesis or validate the null.
Lastly science only deals with natural phenomenon, this is synthetic. Science seeks to illuminate the cause of an effect in nature, we know what the cause is when we measure how much…..with maths.
My understanding is that polyfill isn't necessary for subs but is useful for dampening higher frequencies. I don't use it in sub boxes but I do use it in bookshelf speakers.
I think you're probably right.
This should not be how insulation in speakers is used. People make this mistake all the time. Insulation should be used to address standing waves and to absorb energy which can cause reflections on the driver, as well as absorb the energy to prevent it from setting the enclosure into a resonating state, which can effect sound quality and have a constant frequency being put off that is not part of the music.
If you are doing it to make the enclosure "sound bigger," buy a different driver, one more suited to fit in the size that you intend to have the driver installed. That might mean saving up more. But you will be happier in the long run.
Now, for sub frequencies, constrained layer damping is one of the best ways to stop the energy in the enclosure, with 2# MLV being able to drop the dB of the sub frequency range by up to 19dB (varies over the range). That makes it an excellent candidate if trying to address cabinet resonances while not trying to increase the enclosure size.
If instead you want to go the insulation route, for subs, you MUST use 3.5" or thicker insulation, line the entire cabinet, and it should be denim, rockwool, or fiberglass. Polyfill, also called PET insulation, also called Dacron and Acousti-stuf (specific version with crimped polyester fibers that do inscrease its effects on frequencies) and other similar names, does practically nothing at the relevant FR for subs. As such, the use of poly outside of mids/woofers should stop. This can be seen in effectiveness charts in the loudspeaker design cookbook p.45 et seq.
Insulation helps to smooth the frequency response of the speaker. It should not be used to gain low end extension. Instead, if it is used properly, you can have smoother bass.
Look up Bobgolds website for absorption coefficient. This will show the only way to hit 125Hz or less is to use at least 4" insulation. With going deep, you may want 5.5" - 6". And there goes exploding the size of the enclosure.
To do this experiment properly, it requires two boxes, both built to have the open space being the same volume in the end. That means the final open volume in the speaker enclosures must be the same, but one built with the extra thick insulation and one without it at all. Then, you are not trying to change the Q of the driver, instead you are trying to absorb the energy before it can effect the enclosure. Surely 4"-6" insulation is not practical as it greatly increases the size of the enclosure. But, it takes that to make insulation effective at smoothing at lower frequencies.
Lowe's carries (although out right now) 3.5" and 5.5" UltraTouch Denim insulation which is a decent price. For Rockwool, you can get 3x 2'x4'x4" insulation for $65. That would be the thinnest I would recommend to have an effect on sub frequencies. At 0.15 absorption coefficiant, or 15%, this is negligible on performance. As such, anything showing 50% at 125Hz will be less than that by the time you reach 40Hz, or even 20Hz. That means you will need something reading near or at a coefficient of 1 at 125Hz if you have any hope to damp low frequencies. Hence the 3.5" being the minimum to consider, and 5"+ preferred for very low frequency damping.
This was the second time I typed this, so lost some things, but I think this is enough to start with. I put no links because YT likes to delete my posts when I link things. So, hope you can find things I referenced.
15 in. x 47 in. R21 Thermafiber Fire and Sound Guard Plus Mineral Wool Insulation Batt is at home depot, 5.5" thick rock wool. $53.85 around here.
Right, it has its use, but making your box bigger might not be the best use.
As a previous owner of 3 Custom Audio Stores, I have to disagree. My main tools were LEAP and the LMS systems + Audio Control Spectrum (Former IASCA Judge). Dacron was the preferred fill back in the day. Filling is an artform to produce certain outputs. Especially in Sealed Enclosures . The use mostly reduces standing waves and other problematic issues within the Enclosure. Is much better for those who have limited space for Enclosure size as stuffing results in lowering the bottom end but also the SPL. Designing an Enclosure that geometrically cancels standing waves and internal issues is much more preferred, but a Dacron laced or filled enclosure will always produce a nicer tighter bottom end. If it doesn't , you're doing it wrong. my Bla bla bla... Previous Owner 'Audio Innovations inc, Sound Service inc, Mad Monster Customs inc.' drivers encluded, Dynaudio, Seas, Morel, Audax, Fostex, (many many others) and Drivers Custom made for me using my own Thiel Small Parameters, first batch copied Rockford Fosgate 12" Pro with tweeking.. A Simple Uncalibrated Spectrum Analysis always does not give you the true nature. You Have To Listen.
Reducing Internal Standing Waves Flattens out the Bottom End so there are no 'Notched' Losses or Gains.
I welcome disagreement. Thanks for sharing your experiences.
+1 for this! I have added fill to many small sealed boxes and it improves the sound greatly. Some boxes that have size limitations need the help. This analysis is very interesting, but it doesn't show what matters....how it sounds.
@@alejandronunez9796 Yes, the age old question. and the Survey says....... it's purely Subjective. My 60 year old ears do not hear what my 25 year old ears did. Everyone has their own 'Frequency Curve' . Some people hear better dynamic range... some higher frequencies.... and my Cat hates everything associated with my obnoxious Audio Systems.
The ear test says keep using poly fill
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Hope I'm not too late in posting this. I know the rule of thumb is content creators only read comments for the first hour. 🤷♂️
I'd like to point out a couple things you might try changing regarding how you're doing your testing. Though I will first admit I don't believe these will change your results but I've been proven wrong before so I figure it's worth pointing out.
The first is the mic placement is an odd choice. I get that you were going for a Near Field measurement, which technically you were still within the near field of the speaker. But on low frequency drivers the standard procedure is to place the mic centered with the dust cap and just beyond its linear excursion, or 0.11r where r is the radius of the driver, preferably in cm's. This results in a measurement devoid of reflections and even baffle defraction and resonance. By placing it a foot back you're still getting all of those added acoustical affects in the measurements. To add to this being on carpet and repeatedly moving and replacing the subwoofer is highly likely to result in slight differences in both distance and focus (directional aim). When your looking at 0.5 decimal references even a cpl millimeters can result in a change.
I would recommend placing the sub and mic on a wood panel and mounting stop blocks on the front and side of the sub (just short blocks obviously) allowing you to press the sub back in the exact same position every time. This would allow you to move the mic further up to a true near field low frequency testing position. I'm guessing that's a 10in Sub so that would roughly be 2.8 centimeters, assuming the driver truly measures at 10in.
The other thought I had, and not knowing the model of the driver used I could be completely wrong on this, but just visually that 0.4 cubic ft box looked way too small for the driver you were using. I know the idea is that polyfill can make a smaller box function more like a correctly tuned box. But I've always heard that was only to a small extent, and again just going visually that box seemed excessively too small for that driver. Perhaps a better test would be to use a box sized closely to the reference tuning for the driver, and then test the effects of polyfill on that setup.
Lastly, and this would really push the limits of your time so I wouldn't expect you to try this more than once, is the idea that the polyfill will shift and settle over time and use. So you could try doing a burn in on perhaps the recommended polyfill amount by running the sub for a while playing a constant square wave at first then perhaps some music for dynamics. This would give the polyfill time to shift and compress then run the measurement again and see if there's any difference.
I'm definitely intrigued by this proof of concept. I think more investigating under different parameters is warranted and I hope you give this another go!! I wish I had the resources to try this myself but alas at this time I don't have any way to do that.
The main thing is to maintain a consistent test environment.
@@DIYAudioGuy I agree. I'm mainly just offering ideas on ways to improve that consistency. Either way, thx for taking the time to read my post!
I jammed a small cloth bag of thermal foam in a really cheap ported subwoofer cab to stop it from distorting on very low notes. Not only did it eliminate the distortion, but I think it extended the low end a bit via slowing the air down to the port. The bass also sounds less boomy without significant output loss. Better all around for $15.
You created an Aperiodic enclosure. Its a cross between ported and sealed. An Aperiodic enclosure is one in which the woofer breathes through a resistive membrane to control it's cone characteristics. In laymen's terms, it makes a woofer in a tiny enclosure act as if it were in a large, sealed enclosure. Since you had ported stuffing made it more sealed lowering SPL slightly, tightening up the bass, and extending the low end.
Currently planning out a 3.75 cuft box for some 12s and decided on poly fill after lots of research, would be curious to see some tests with a larger volume setup. Great video.
Fun video! Great info! One suggestion: part of your charm is your gesticulation, just don't block your face. Keep your hands away from the lens itself. It's distracting and feels like I need to duck! lol Thanks for the content about speaker fill. Looks like I have some testing to do.
as a kid I would use coushom foam in speaker boxes to get the bass response. muck denser that poly fill and easy to salvage from discarded couches and chairs. LOL salvagd speakers from discarded stereo consoles that needed a fuse or a solder joint fixed maybe a broken wire. or one part of the whole console broke and others were fine but they wanted a new one. LOL literal "Trash to Treasure in stereo equipment and speakers. salvagd kitchen cabints for enclosures too... lol talk about cheap audio guy or rather kid.that was me at 10yo thru my teens
I like the video. You do some initial scientific testing, which you already say can be improved by using statistical techniques and doing the test dozens of times, etc. But you also mentioned another limitation which I always bring up in these kinds of videos: how does it sound to YOUR ears? It's one thing to use scientific measurements, but at the end of the day all that matters is how the sound is perceived by the human ear. One serious limitation is that your ear is different from mine, but I'd still lend that kind of analysis a lot of authority, especially if you consistently use parameters like the CheapAudioMan. Another, major limitation is the room. What you hear (or measure) in your room could be vastly different from my living room. This is a very good start, nevertheless.
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Some years ago (15-25?), wool was the “preferred” stuffing for speakers enclosures. Curious if it is better than what everyone uses today since wool is not man made.
That's a good question.
Fiberglass batting was also popular. I have pulled apart a few 70's era home speakers and found the walls lined with yellow fiberglass, the itchy stuff.
@@chrishuyler3580 Ahh yes I forgot about that itchy fiberglass! I’ve been in a few of those (regretted it for awhile! Lol)
fiberglass filled speakers too 🔊 😬
My worry about this test is that the Polyfill will be mucho squashed - made much denser - so that would skew the results.
The squashing would get more pronounced the more fill is inserted.
Plus, there will be differences in the mechanical link between the driver and the bottom panel... and thus, the top panel... and thus, the frequency response/excursions of the driver at different frequencies. So altering the measurements.
Hope this makes sense!
Guy
Line the inside of your box with speaker carpet I do it to all my sub boxes yes I think it helps a lot
You mean like the same stuff that you put on the outside of most car subwoofer enclosures? I've never heard of trying that.
I have been building speakers since the late 1970s. Point blank, Polyfil is crap. I line my DIY made cabinets and ammo can speaker builds with "BoomMat" carpeting (similar to old school automotive jute) and/or DynoMat (Mat66). The bass is deeper, richer, reduces cabinet resonances, and maintains internal cabinet volume space. For big wood subwoofers...I start with stapling in BoomMat on the back behind the sub and adding more to the sides to find the "sweet spot" by ear using a tone generator. Bass output can be tricky to master...it takes a good ear and proper placement to find what works for the listening environment.
I should give that a try.
I like to cram as many subs into a specified enclosure size as I can. Why? Because cone area is king. Also, you can kind of overcome the smallish enclosure size by not just adding in poly fill but also by increasing the power input
Cone area is king.
there is a lot of talk about poly fill used to make a small box seem bigger. but this test was the same box? i've always used poly fill but for the Dampening effect. not enclosure size, because i make my sealed enclosure to the recommended spec of my speaker. great test but didn't compare with different sized boxes.
Good video.! Geez this RUclips rabbit hole was deep. I'm voting for another video with different materials and a test for sound quality if that's possible?
Fiberglass, Rock wool, ect.
Testing the harmonics everything I've seen saying polyfill is useless but other materials make slight improvements on sound quality maybe even try some closed cell insulation.
I'm going to be pulling my speakers and trying something but just going for highest sound quality possible not for spl or trying to help a small space
That's the problem with these kind of rabbit holes, a lot of people want more detailed tests, but when you start making the more detailed test people stop watching. I think I said toward the end of the video that if this video got a quarter million views that I would do more testing. So I'm sticking to that.
The output transistorsb are close to it's limit, they get hot. Oh the poly fill, I thought it may help offset the space taken up by the driver. I don't really know if the pillow stuffing helped extend the bottom end.
Poly fill or damping material has been used for ever i have built only 2 subs a 12 inch and 15 inch both ported both loaded with old fill from a pillow both sound perfect used measure from comercially sold subs using there size and put in port never tested with equiptment but to my ear sound good .i think stiffening box helps seal leaks
As far as the hearing of frequency. I can hear frequencies most can’t. I don’t know how that is! But I can and I’ve had expert I’ve proven wrong and they changed the tuning of their speaker box designs
I would be interested in the same test with a woofer that has a much higher QTS. At 0.49, while not terribly low, that is low enough that the Ultimax 10 is going to be fairly tolerant of varying box volume / fill. One of the ways around too small an enclosure is to use a woofer that will work well in a wider range of enclosures. Not arguing the results, just postulating.
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Great video, It would be nice to see acoustic foam glued on the inside of the speaker housing as an experiment.
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The proper way is to line the inner walls especially the back inner wall with fiberglass and then stuff polyfill in the box. It can lower tuning up to 7hz.
Interesting! Yeah, I was wondering if I should do anything such as polyfill to the NVX 1.3 cu ft sealed enclosure that's coming with my new sub...tomorrow
***I am super happy with my new system. With the amp it sounds like I have a low power subwoofer already.
***Really enjoying it! ...and researching upgrading my other vehicles as well. I have confidence and more knowledge now. Gotta have it in all my cars!! 🤣
The polyfill is for damping internal reflections and standing waves, especially in a cubic box
@DIY Audio Guy
I heard the point of polly fill is to dampen standing waves and produce a cleaner sound. Could you test that? Also, did you listen to music at each fill just to see how it effects more than just a sweep?
Reminds me of suspension systems with a spring and damper whereas poly fill could be the helper spring or the twin tube gas that smooths out the ride.
I've never thought about like that before.
Nice video, lots of good info, I do prefer the lower tones over the +70 hz range. Another measurement process is to do slower sweeps to get more data at frequencies at a slower rate. Another thought I've always wondered about using the "egg crate foam" that have peaks and valleys to break up the standing waves, similar to movie theater setups. Can you test that to see if it makes a difference?
Anything you put in the box to break up standing waves and cut down reflections will improve sound quality. The only thing this test shows is that you don't actually improve low end extension by adding polyfill to a box that is to small to begin with.
Poly fill works better in a full range speaker than a Subwoofer box. It helps resolve standing waves from the rear of the cone which can come thru the cone and muddy the sound.
You put so much Poly fill inside that small box that it acted as a dampener against the back of the cone. (It doesn't have to touch to effect) Which made your results look the way they did. It's NEVER placed directly behind the cone that close as it affects the Qms (which is what happened to you)
Right. Hopefully people will stop doing it!
Many years back I burned out a woofer. When I replaced it I replaced the scrawny internal crossover to woofer wire with a foot of 12 gauge. When I fired it up, oh, man, I blew the other woofer! No, not really. The other woofer worked as well as it ever had, but the woofer with one foot of 12 gauge was phenomenal.
Try replacing that 18 gauge in the housing with 12 gauge. Then run 12 gauge all the way back to the amp, on one channel. You will think the other channel is dead.
It all goes back to damping factor.
Great video and test. You did a nice job explaining everything as well. Is there any way I can talk you into comparing these results with a sealed box coated with expanding foam on the inside? Just squirt the expanding foam on a cheapo paintbrush then brush it on the inside surface of the box. When it cures it leaves a hard, not very thick, very bumpy surface. It's great for sound deadening and I'd love to see what would happen inside the box.
You mean this stuff: amzn.to/3jzFtor
@@DIYAudioGuy yes exactly!
I've always torn up shirts and used them, seems to work way better than stuffing
Would using sound deadening in the speaker box make a difference?
Why don't show us the actual sounds
I've used pollyfill before and it worked! I didn't over stuff the box though! I lined the inside of the enclosure with a couple sheets but never stuffed a whole bag or two inside?
The standard recommendation is 1 lb per cuft. As you can see form the video when you weigh it out 1 lb per cuft means cramming a ton of polyfill in the box.
I made an FRFR cabinet for celestions 2 way FRFR speaker. They recommend stapling some sort of wadding to a wall but aren't very specific. I have tons of Roxul safe n sound, I don't know if I should mess with it...sounds like a studio monitor already, I can';t really imagine it any better
If the goal is to break up standing waves and dampen second and third order harmonics then I think maybe some stuffing might be okay.
@@DIYAudioGuy I need to play with it some more. Its the closest I've ever had my live guitar rig sounding like it sounds in my studio control room, so I'm pretty happy. Maybe I'll hear something I don't like and need to fix it, but so far, loving it. If I build another, I'd like to make it slanted so its more aimed at where it matters, but not sure how to calculate the new dimensions, so I'll stick it on a speaker stand to tilt it.
Oh, and next time I will build ONE! Not the insane dual I have now, its way more than loud enough if I unplug one of the speakers
I added to my 10 inch kicker. The sub knocked a little harder. It's a different sound in the cab of truck.
also wouldnt running the sub repeatedly in the same box cause the air to heat up in the box regardless of the fill. how do you know its not the affect of the voice coil dumping heat.
perhaps the effect of cutting the higher frequencies a bit makes the subwoofer sound as though it is producing more of the lower frequencies?
That's exactly what I think is going on.
DIY Guy.......Interesting test. of course you are just testing for SPL, there might be other issues the Poly fill improves? It might be interesting to test Fiberglass, Acousti-Stuff and the recycled blue jean information Lowes sells?
There are an infinite number of tests that can be done.
Great video 😅👍
I always fill my speakers with polifill lol.
Do you have a DIY video on building that small subwoofer
Here is the video where I built the boxes. ruclips.net/video/BicefelesIA/видео.html