I qualified as an electronic service engineer some 30+ years ago..... And I've NEVER seen such an elegantly simple demonstration of a variable resistor. EVER! Kudos to you.
I saw something like this in a free Wednesday children program The set was a bulb light whose light was dimmed or brightened with the position on the pencil. Title was msybe 1 2 4 something And the introduction video sequence had a mesmerizing drop falling into water and the bouncing wave and maybe a small round drop coming up in the air. There was all sort of science vulgarisation for kids and fun to see to invite to curiosity. French television from late 70's or early 80's. TF1 or Antenne 2 or FR3 by the time
@@bobedwards8896 im sure we are all pleased that you've seen it before, in fact i was about go give you a medal, but then revoked it due to the fact that an inquisitive mind of 20+ should have better grammar. 🤡
@@maelixdiogen1383 You are probably thinking of 3 2 1 Contact... I can't find the exact episode but here is an episode where they demostrate a generator: ruclips.net/video/gK6NnqGmb1o/видео.html if you look up episode 1 it shows them recording the theme song. I used a pencistor in a science far project around 3rd grade... we got a bit carried away with it and since we were homeschooled :D
Thanks Eric, I want people to comment here. I do read through them and overall am extremely happy with what I find but expect it to be appropriate to the channel. When needed I will remove sexual, political, religious, or offensive comments, there are plenty of other places for those types of comments and viewers may seek them out if they so desire.
@@YeanyScience My esteemed professor, I've learned a lot from you, and Keep your creations on my computer But Have you ever asked yourself these questions? "What is the purpose of LIFE?" "My life?" "Your Life?"
Now that was an excellent home science video. I'm doing my best to be that kind of dad who encourages his kid to try things and who experiments together with them.
I'm 25, but these videos really take me back to being a kid. Simple and effective explanations, fun practical experiments, safe and family friendly.. Move over Bill Nye!
I love this. Simple experimentation is a joy. I used to do experiments in the house with my young kids, using food coloring and water. Do something, observe result, change something, do the same thing, observe new result. Now there is only one small step to making it real science: add a hypothesis at the beginning and a conclusion at the end. Yay! The power of human thought.
Excellent video. I like the way your simplicity and the way you explain with a smile on your face. It reminds me of my late grandfather who sowed the seed of science in me :-). I subscribed to your channel.
6:27 - you don't get a change in frequency with this design, but you do get a slight change in timbre as you move around the disk. It sounds a lot like changing the pulse width on a synthesiser, where moving towards the outside edge of the disk sounds like a narrower pulse, and the centre sounds like a wider one. This must be to do with how quickly the hole moves past the air on the different edges. Also your 4 - 8 hole design sounds like the harmonic series, which is pretty cool!
@@GhostsniperAus no, the pulse width can vary, while each pulse occurs at the same regular interval. You're thinking of wave length, which does affect pitch.
I may have misinterpreted the design but it almost sounded like a flange effect. The same effect heard when two tone sounds play simultaneously with a slight variance.
I'd not say "slight"... it's a rather noticible change, most notable as the airflow begins to cross the edge; that adds another,non-harmonic, turbulent airflow, and an undertone.
Hi Bruce awesome video. My daughter, husband and myself the wife have done some of your projects especially the dancing static balls in a box. We love that one. Thank you for this video. We will be doing this one.
The speed that little motor can achieve is a long way from the failure point even with the holes added. One demonstration I have seen resulted in the cd shattering at 23,000RPM. Yes the holes do reduce the integrity some, but the 3,082.5RPM one of this video's cds rotated at to produce the note obtained is still well below the failure point of ones with holes.
Cool demonstration thanks. Interesting that the balloon pump in both sucking and blowing is a kind of alternating current, an air current in this case.
Around 6:00: I intuitively expect that past a certain size, the loudness will decrease again. I’d think the size of the holes influences the resistance that would have to be matched to the energy input regulated by disk speed and the air speed out of the tube. Some form of impedance matching. Louder = better match. Just a thought.
Thickness of the disk is a factor too. Too thin and it will not "chop" the air as much as a thicker disk. But too thick and it will hold too much of the sound back.
For that disc with the slots, and for the disc with 8 holes both at the center and at the edges, the pitch doesn't change, but the "shape" of the sound changes; it gets either buzzier or smoother. If you record the audio and look at the waveforms in eg. Audacity, you'll be able to see the difference; buzzier sounds will have sharper waves (closer to a sawtooth wave), and smoother sounds will have more rounded waves (closer to a sine wave). A similar effect happens when woodwind instruments change the shape of their mouth around the mouthpiece.
7:00, sounds like a filter cutoff control. The outer bands get you brighter tone than the inner bands. Another thing you can try, is do 1 CD vs 3 stacked CDs.
Bingo. A couple times the OP said “sounds the same” & I disagreed. Same pitch, sure, but different timbre. I think the brass disc with slits is designed to be matched to another just like it as the air supply orifices. I expect you’d get a very loud result, with very fast rise/fall times, i.e. piercing.
About the slotted disc and the discs with the same number of holes at different radii: You are right that it doesn't change the pitch. But there is a slight change in timbre because the timings of flow/no-flow of air changes relative to each other. That is probably not the purpose of the slotted disc but it is an audible difference. Also a similar technique was heavily used on older sound chips of home computers but with e.g. high/low voltage level timings on square waves to vary the sound.
I think the brass disk with the slot was used for scanning light beams. The device used two disks, one for horizontal and one for vertical scanning. The light from an object is focussed on the disks and the resulting beam is a serial scan of the object. I've also experimented with a resistance made from pencil lead drawn in a heavy line on paper.
4:58 you can hear the timbre change ("ooo" and "ahhh" is how I hear it). is this because of the additional disk mass the air stream passes over in between holes? I'm also wondering what the air column "looks" like when traveling through one of these, specifically *after* moving through the disc.
Yes! So it's sort of like pulse width modulation. - When the holes are closer to the center, the distance of travel between two holes is similar to the distance across the hole itself. This means the "on" time and the "off" time are comparable, giving you something close(r) to a square wave (the roundness of the holes will round off the waveform somewhat too but let's ignore that for now). - When the holes are far apart, the "on" time is much smaller than the "off" time and so you get a narrow "pulse wave" which has more more high frequency (harmonic overtone) content. "Ooh" formants have less harmonic content than "aah" formants, so this is why you interpret the inside as "ooh" and the outside as "aah". However, this will only work when you compare them. On it's own, neither of them will sound like "ooh" or "aah".
@@RijuChatterjee This is exactly what I was thinking! I imagine the slotted disk does something similar since as you get further away from the center, the ratio of open to closed would change. While you're still getting the same number of pulses (hence pitch) the length of the pulses changes, giving you a change in timbre as the harmonic structure/distribution changes. Its pretty subtle, but you can almost hear a saw-wavy sound around 6:40 when he is near the outer edge, and less sharp (fewer higher harmonics?) when in the middle. With a cleaner air source you could probably run this through some spectral analysis and see all that. Idea for a follow up video?
@@CrumbleB33 I wouldn't say you need a cleaner air source. You could probably get informative results even from just a frequency-domain analysis of the audio in this video. Time-domain analysis might not work out as well because the digital codecs used for audio compression often mess up phase stuff. If you had a good .wav file you could do time-domain as well.
The slotted disc essentially is the disc you showed with 8 holes on each of 2 concentric circles. But instead of n discrete concentric circles, you have infinity. I don't know if that is the purpose of the disc or not, but the observed principle, I think, is the same as the demonstration at about 4:50.
The slotted disk did not chnage pitch because the number of pulses per revolution is the same at any distance from the center. Your other disks have a different number of holes depending on the position of the air stream.
So when you said that the number of holes on the cd effected the pitch, did the speed of the disc have anything as well? Because the disc was spinning faster towards the edge, if they had an equal number of holes for each concentric circle around the disc, would the pitch also change? Or not because the further distance between holes cancels out the moving faster..... idk
I was confused as well. But when the hole of the inner row is at the top, the corresponding hole of the outer row is at the top as well. When the inner hole is at the bottom, the outer hole is too. So they pass at the air stream in exactly the same intervals.
velocity = distance/time In the outer ring, distance, and therefore velocity get bigger, while time stays the same, and time=time interval is all that matters in this case
The slotted disk creates the same pitch, but the timbre of the tone is altered as you move in and out. For example, a male and female singing the exact same pitch of note will sound very different.
For the disk with slots as well as the ones with the same number of holes, you can notice a change in the timbre of the tone as you move from the inside to the outside. If you think of the sound wave like a pulse-width-modulated square wave, you can think of the sound as getting "thinner" as the pulses get thinner, and getting "thicker" as the pulses even out.
we have a change in the linear speed going on here, I wonder how the shape of the hole or slot might address this. Round hole towards the center compared to oval shaped or double holes towards the outside. I have some other projects going on but still want to explore this further
at 7 min, the purpose of that disc shape is to alter the pulse width of the sound wave while keeping the main frequency / pitch (fundamental frequency) unaltered.
I may have misinterpreted the design but it almost sounded like a flange effect. The same effect heard when two tone sounds play simultaneously with a slight variance.
@@PaulMillard1973yes, Pulse Width modulation can sound a bit like a phaser /flanger because also enhances or dampens certain frequencies in the harmonic spectrum while keeping the fundamental unaltered.
While the fundamental pitch remains the same regardless of the radius, (once the number of holes is the same, or with the slotted disc), it sounds to me like the harmonic content changes, with more upper harmonics present farther from the centre of the disc.
actually I believe the outer is higher pitch not cause more holes. but the outer rim spins faster then the inside holes so the speed is related to the pitch
@1:35 nope it’s not the number of holes but the tangential velocity that makes the pitch change. If you had the same number of holes the pitch would change anyway.
Typically, a British air raid siren rotates at 2850-2900 revolutions per minute, one end has 10 openings and 10 blades, the other has 12 of each. This creates two tones harmonically related to each other as a minor third. The tone in Hertz can be calculated by multiplying the rotation speed in R.P.M. by the number of openings and dividing by sixty. For example, at 2850 r.p.m. the two tones are 475 Hz and 570 Hz.
I believe the slotted disk is stationary and one with the holes rotates behind it…like De La Tours siren design, and similar in concept to the slots on the outside of a Federal Q design siren.
I would say that one could add multiple wind sources to the disk with the slots. Or one very wide air nozzle but with a narrow opening like a vacuum cleaner attachment might have.
Thomas Seebeck died in 1831. August Seebeck made the tone disk. It's interesting to notice that the design you used looks like fan blades captured by a camera's rolling shutter.
Your sirens reminded me of those colorful short tube siren whistles you can buy at the dollar stores. Taking one apart revealed a six hole slotted disc with beveled edges, like little ducted fans. They sound in either end of the tube you blow into. If you put two together in-line in the right way they sync up making an interesting jet engine like chorus effect, as they spin up so freely. If you flip one of the discs, or blow from the opposite end of the two in-line sirens they sound but not in phase. I put a 4 inch length of blue PEX tube on the end of the double siren which makes the effect more pronounced. I too thought of your spinning strings, and wondered what other variables could be introduced to confirm the reasoning behind the Mould Effect.
The sound from the foam was a lot more clear. I wonder if this is due to the thickness stabilizing the air stream as our flows through the holes? Reducing vortices And other turbulence? This could be tested by making a disc from a different material such as wood, metal,or acrylic sheet that is roughly the same thickness. Radiusing the holes both sides would also aid in reducing turbulence. Is also suspect the foam material may absorb and dampen some of these vibrations. I'm very curious about making some kind of organ that uses this principle. It looks like a lot of fun!
Run one of those with radial slits in front of one with holes. Slowing down the one with holes will produce a beat with the differential speed as frequency. Like the first on a half beat the second on fourth. What would this sound like?
One observation the material that was the worst conductor of sound was the best. Pretty sure because you heard the frequency of the air cut and compressing through the hole. Instead of the higher pitch vibrations of the material.
To my ear, for some of those experimental discs the pitch is staying the same but the tambre is changing. The effective fundamental tone is unchanged but there are other harmonics that are being added in. I find these experimental discs to be the more interesting and musically “usable” discs.
The slotted wheel seems to vary the harmonic content. While the fundamental pitch remains the same, the outer edge sounds "thinner" than the inner portion. I would guess the compressed wave over a larger area of solid material creates the distinction in harmonic content. Just a guess...
7:00 A flat disc version of a 'Zoetrope'? pre-film animation devices that produce the illusion of motion by displaying a sequence of drawings or photographs showing progressive phases of that motion.
While the fundamental pitch of the holes on the disc that has the same number of holes per ring doesn't change, the character of the sound does; the changes in linear velocity might be altering the way the air gets chopped and giving a different set of background noise and harmonics. Same effect on the slotted disc, too!
Thanks siberx4, I think that is quite noticeable, I'm curious about the idea of elongating the holes to make up for the change of linear velocity, I still have several old CDs around and will continue to experiment with it as time permits.
4:11 Thats actually the reason, why tires dont have evenly spaced bumps but rather "radom" ones. very even tires tend to be much louder. so to minimise sound emission, they are creating uneven tires.
A memory from my childhood -- My father once bought me a toy ambulance, about the size of an adult hand. It had a slotted flywheel and a matching stationary ring. The flywheel was geared be accelerated by pushing the ambulance on the floor repeatedly faster and faster, then releasing it to go by the flywheel energy. The flywheel slots were shaped to push air radially through the ring slots. My mother hated the sound right away and my father soon joined the haters chorus as well!
I would describe 7:55 sounding like some pulse width modulation waveform where the duty cycle becomes smaller the further you move outwards from the disc.
working on it, I just got some software on my phone that can identify the frequency and notes to any tone. Another possible way is to use some free software on the computer, generate a specific note and adjust the wheel speed to match it.
You could make the disc into an optical encoder by having one radial section of the disc with only one hole on it. Then mount on either side of the disc a photosensor and a laser diode. You could count the pulses over an average time length fairly easily with a microcontroller like an Arduino or Raspberry Pi. I was also curious about this and was able to build a decent working prototype using fairly rigid cardstock and the components I mentioned above with an Arduino.
The easy high tech way is to get an audio spectrum analyzer app for your phone. You can also get a function generator app for your phone and match the frequency. If you have an older style fluorescent light that flickers at power line frequency, you can use that as a stroboscope that operates at twice the line frequency. North American 60 Hz power will produce a 120 Hz flicker. Most of the rest of the world is 50 Hz/100Hz. Paint a reference mark on the disk. Arduino users can make a stroboscope and/or frequency analyzer. Music people can use a tuning fork or any other tool for tuning instruments. If you have Lego Technic, you can use a gear train to divide the rotation rate down to something easy to measure with a stop watch. Some people can just tell by listening. There are many ways to measure frequency.
I think the slotted one is meant to be used as a shutter of some sort. Perhaps it will limit the extranious noises that are produced by the contraption so you can get a better measurement of the specific sound you're making.
I love that the variable resistor is made from a pencil.
I was going to comment the same thing. It brought back memories of my sparky youth.
I used a pencil resistor to control motor speed for a strobe light (combination of this post and one a couple of posts down).
That is pretty genius
@@EXwifeKILLER it's really not. It's fairly basic.
It's called a Pencistor.
I qualified as an electronic service engineer some 30+ years ago..... And I've NEVER seen such an elegantly simple demonstration of a variable resistor. EVER!
Kudos to you.
I saw something like this in a free Wednesday children program
The set was a bulb light whose light was dimmed or brightened with the position on the pencil.
Title was msybe 1 2 4 something
And the introduction video sequence had a mesmerizing drop falling into water and the bouncing wave and maybe a small round drop coming up in the air.
There was all sort of science vulgarisation for kids and fun to see to invite to curiosity.
French television from late 70's or early 80's.
TF1 or Antenne 2 or FR3 by the time
very cool indeed, but is an inquisitive person for 20+years , iv seen it for quite sometime.
@@bobedwards8896 im sure we are all pleased that you've seen it before, in fact i was about go give you a medal, but then revoked it due to the fact that an inquisitive mind of 20+ should have better grammar. 🤡
@@maelixdiogen1383 You are probably thinking of 3 2 1 Contact... I can't find the exact episode but here is an episode where they demostrate a generator: ruclips.net/video/gK6NnqGmb1o/видео.html if you look up episode 1 it shows them recording the theme song. I used a pencistor in a science far project around 3rd grade... we got a bit carried away with it and since we were homeschooled :D
Seeing a new Bruce Yeany video pop up in my notifications is the best feeling. I love your content! I always learn so much!
The disk with slots is an optical stroboscope. Spin it and look through it to stop motion like a regular strobe.
What I was thinking as well. Some searching didn't reveal one like it, but somewhat close.
@@1islam1 Sir, this is a Bruce Yeany video.
Thanks Eric, I want people to comment here. I do read through them and overall am extremely happy with what I find but expect it to be appropriate to the channel. When needed I will remove sexual, political, religious, or offensive comments, there are plenty of other places for those types of comments and viewers may seek them out if they so desire.
@@YeanyScience science is beyoond all
@@YeanyScience My esteemed professor, I've learned a lot from you, and Keep your creations on my computer
But Have you ever asked yourself these questions?
"What is the purpose of LIFE?"
"My life?"
"Your Life?"
Now that was an excellent home science video. I'm doing my best to be that kind of dad who encourages his kid to try things and who experiments together with them.
Finally a use for all of those old AOL CDs. Other than taking them to the range and shooting them.
Perfect drink coasters.
I remember taking a few every time I saw the stack in the grocery store as a kid just to use as a frisbee.
Still have some left with original Harry Potter promo 😄😄
What is a AOL?
@@ThatRollerCoasterNerd was/is an american internet provider, America Online
This is so cool I'm going to try building one with my son. I love how easy and informative your videos are. Thanks 😊
Every time i see one of your videos, i wish i had a teacher like you when i was young!!!
the world is built by men like this. creative, generous, passionate.
I'm 25, but these videos really take me back to being a kid. Simple and effective explanations, fun practical experiments, safe and family friendly.. Move over Bill Nye!
I love this. Simple experimentation is a joy. I used to do experiments in the house with my young kids, using food coloring and water. Do something, observe result, change something, do the same thing, observe new result. Now there is only one small step to making it real science: add a hypothesis at the beginning and a conclusion at the end. Yay! The power of human thought.
These videos are amazing. Your ideas are definitely a huge source of inspiration for other science youtubers.
I can see a synth patch being created in honor of this called "table saw".
why youtube keeps recommending me videos like this after midnight? this is why i get up late
Thank you so much, your wonderful video saved my life from my physics teacher.
you're welcome, seriously hope it's not as bad as that sounds
wow bruce laural is a great teacher
Excellent video. I like the way your simplicity and the way you explain with a smile on your face. It reminds me of my late grandfather who sowed the seed of science in me :-). I subscribed to your channel.
thank you
Thanks Bruce, always a pleasure watching your videos!
This seems like a channel that is just right up my alley!
Cool stuff Mr Yeany, thanks for the video!
Gracias hermano. Disfruto mucho sus videos. No concibo que alguien teniendo acceso a RUclips, diga que se siente aburrido😀👌
6:27 - you don't get a change in frequency with this design, but you do get a slight change in timbre as you move around the disk. It sounds a lot like changing the pulse width on a synthesiser, where moving towards the outside edge of the disk sounds like a narrower pulse, and the centre sounds like a wider one. This must be to do with how quickly the hole moves past the air on the different edges.
Also your 4 - 8 hole design sounds like the harmonic series, which is pretty cool!
I was expecting him to lose an eye at that point.
Changing the pulse width IS changing the frequency , it’s the same thing
@@GhostsniperAus no, the pulse width can vary, while each pulse occurs at the same regular interval. You're thinking of wave length, which does affect pitch.
I may have misinterpreted the design but it almost sounded like a flange effect. The same effect heard when two tone sounds play simultaneously with a slight variance.
I'd not say "slight"... it's a rather noticible change, most notable as the airflow begins to cross the edge; that adds another,non-harmonic, turbulent airflow, and an undertone.
Using the pencil as a potentiometer is honestly so creative! Awesome!
Two thumbs up! Excellent demonstration.
Hi Bruce awesome video. My daughter, husband and myself the wife have done some of your projects especially the dancing static balls in a box. We love that one. Thank you for this video. We will be doing this one.
You should really wear some sort of safety goggles when rapidly spinning cds with holes drilled in them
I knew there would be one of you.
I was thinking the same thing!
holy moley that was actually kinda scary
The speed that little motor can achieve is a long way from the failure point even with the holes added. One demonstration I have seen resulted in the cd shattering at 23,000RPM. Yes the holes do reduce the integrity some, but the 3,082.5RPM one of this video's cds rotated at to produce the note obtained is still well below the failure point of ones with holes.
Famous last words
@@TheAchaicus Holes is one thing, what about slots like at 6:30?
Learned lots in this video! Thanks for sharing your knowledge!
SIr you are awesome.. thanks for your cool educational videos.
Cool demonstration thanks. Interesting that the balloon pump in both sucking and blowing is a kind of alternating current, an air current in this case.
For sending signals to neighbors.
Fun way to send a message.
You could send ASCII as FSK encoded binary
This is so cool! Thank you for the information.
Heyyyy! I had forgotten this channel existed, glad this was recommended
6:33 made me wince, imagine that deathtrap shattering and blasting you in the face with shrapnel
Around 6:00:
I intuitively expect that past a certain size, the loudness will decrease again.
I’d think the size of the holes influences the resistance that would have to be matched to the energy input regulated by disk speed and the air speed out of the tube. Some form of impedance matching. Louder = better match.
Just a thought.
Thickness of the disk is a factor too. Too thin and it will not "chop" the air as much as a thicker disk. But too thick and it will hold too much of the sound back.
wow using graphite to change speed is something new for me, i didnt knew that
Never knew I needed something I didn’t existed until 5mins ago.
Know^ existed.
For that disc with the slots, and for the disc with 8 holes both at the center and at the edges, the pitch doesn't change, but the "shape" of the sound changes; it gets either buzzier or smoother. If you record the audio and look at the waveforms in eg. Audacity, you'll be able to see the difference; buzzier sounds will have sharper waves (closer to a sawtooth wave), and smoother sounds will have more rounded waves (closer to a sine wave).
A similar effect happens when woodwind instruments change the shape of their mouth around the mouthpiece.
That's a pretty cool trick of using the graphite of the pencil to act like a variable resister.
It's a crude slide pot (potentiometer)
@@blindleader42 yes that's what I meant.
7:00, sounds like a filter cutoff control. The outer bands get you brighter tone than the inner bands.
Another thing you can try, is do 1 CD vs 3 stacked CDs.
Bingo. A couple times the OP said “sounds the same” & I disagreed. Same pitch, sure, but different timbre.
I think the brass disc with slits is designed to be matched to another just like it as the air supply orifices. I expect you’d get a very loud result, with very fast rise/fall times, i.e. piercing.
Yes, the experiment should have included varying disk thickness just to complete the possible variables.
@@kelvin0mql I wouldn't say timbre but harmonics, it is not a pure tone. But you are still right.
@@theeastsensation5295 I have my moments… rare though they may be.
Thank you for making this video.
About the slotted disc and the discs with the same number of holes at different radii: You are right that it doesn't change the pitch. But there is a slight change in timbre because the timings of flow/no-flow of air changes relative to each other. That is probably not the purpose of the slotted disc but it is an audible difference. Also a similar technique was heavily used on older sound chips of home computers but with e.g. high/low voltage level timings on square waves to vary the sound.
I saw some dogs doing this in my front yard the other day. I thought they would never stop.
Volume change for the radially cut designs. Closer to center, cut portion becomes proportionally smaller relative to circumfrence.
I think the brass disk with the slot was used for scanning light beams. The device used two disks, one for horizontal and one for vertical scanning. The light from an object is focussed on the disks and the resulting beam is a serial scan of the object.
I've also experimented with a resistance made from pencil lead drawn in a heavy line on paper.
4:58 you can hear the timbre change ("ooo" and "ahhh" is how I hear it). is this because of the additional disk mass the air stream passes over in between holes? I'm also wondering what the air column "looks" like when traveling through one of these, specifically *after* moving through the disc.
Yes!
So it's sort of like pulse width modulation.
- When the holes are closer to the center, the distance of travel between two holes is similar to the distance across the hole itself. This means the "on" time and the "off" time are comparable, giving you something close(r) to a square wave (the roundness of the holes will round off the waveform somewhat too but let's ignore that for now).
- When the holes are far apart, the "on" time is much smaller than the "off" time and so you get a narrow "pulse wave" which has more more high frequency (harmonic overtone) content.
"Ooh" formants have less harmonic content than "aah" formants, so this is why you interpret the inside as "ooh" and the outside as "aah". However, this will only work when you compare them. On it's own, neither of them will sound like "ooh" or "aah".
@@RijuChatterjee This is exactly what I was thinking! I imagine the slotted disk does something similar since as you get further away from the center, the ratio of open to closed would change. While you're still getting the same number of pulses (hence pitch) the length of the pulses changes, giving you a change in timbre as the harmonic structure/distribution changes.
Its pretty subtle, but you can almost hear a saw-wavy sound around 6:40 when he is near the outer edge, and less sharp (fewer higher harmonics?) when in the middle.
With a cleaner air source you could probably run this through some spectral analysis and see all that. Idea for a follow up video?
@@CrumbleB33 I wouldn't say you need a cleaner air source. You could probably get informative results even from just a frequency-domain analysis of the audio in this video. Time-domain analysis might not work out as well because the digital codecs used for audio compression often mess up phase stuff. If you had a good .wav file you could do time-domain as well.
The slotted disc essentially is the disc you showed with 8 holes on each of 2 concentric circles. But instead of n discrete concentric circles, you have infinity.
I don't know if that is the purpose of the disc or not, but the observed principle, I think, is the same as the demonstration at about 4:50.
The slotted disk did not chnage pitch because the number of pulses per revolution is the same at any distance from the center. Your other disks have a different number of holes depending on the position of the air stream.
So when you said that the number of holes on the cd effected the pitch, did the speed of the disc have anything as well? Because the disc was spinning faster towards the edge, if they had an equal number of holes for each concentric circle around the disc, would the pitch also change? Or not because the further distance between holes cancels out the moving faster..... idk
I was confused as well. But when the hole of the inner row is at the top, the corresponding hole of the outer row is at the top as well. When the inner hole is at the bottom, the outer hole is too. So they pass at the air stream in exactly the same intervals.
velocity = distance/time
In the outer ring, distance, and therefore velocity get bigger, while time stays the same, and time=time interval is all that matters in this case
The slotted disk creates the same pitch, but the timbre of the tone is altered as you move in and out. For example, a male and female singing the exact same pitch of note will sound very different.
For the disk with slots as well as the ones with the same number of holes, you can notice a change in the timbre of the tone as you move from the inside to the outside. If you think of the sound wave like a pulse-width-modulated square wave, you can think of the sound as getting "thinner" as the pulses get thinner, and getting "thicker" as the pulses even out.
we have a change in the linear speed going on here, I wonder how the shape of the hole or slot might address this. Round hole towards the center compared to oval shaped or double holes towards the outside. I have some other projects going on but still want to explore this further
On the one with strait lines there was a audible change, further in was more deep and while further out was more high pitch
at 7 min, the purpose of that disc shape is to alter the pulse width of the sound wave while keeping the main frequency / pitch (fundamental frequency) unaltered.
I may have misinterpreted the design but it almost sounded like a flange effect. The same effect heard when two tone sounds play simultaneously with a slight variance.
@@PaulMillard1973yes, Pulse Width modulation can sound a bit like a phaser /flanger because also enhances or dampens certain frequencies in the harmonic spectrum while keeping the fundamental unaltered.
While the fundamental pitch remains the same regardless of the radius, (once the number of holes is the same, or with the slotted disc), it sounds to me like the harmonic content changes, with more upper harmonics present farther from the centre of the disc.
actually I believe the outer is higher pitch not cause more holes. but the outer rim spins faster then the inside holes so the speed is related to the pitch
I love your videos
Thanks Bruce very cool
@1:35 nope it’s not the number of holes but the tangential velocity that makes the pitch change. If you had the same number of holes the pitch would change anyway.
The design with slots is the one which I once found on a loud siren - sounded like air raid siren.
I was thinking something similar. One of the disks sounded like an old Police siren.
Typically, a British air raid siren rotates at 2850-2900 revolutions per minute, one end has 10 openings and 10 blades, the other has 12 of each. This creates two tones harmonically related to each other as a minor third. The tone in Hertz can be calculated by multiplying the rotation speed in R.P.M. by the number of openings and dividing by sixty.
For example, at 2850 r.p.m. the two tones are 475 Hz and 570 Hz.
What happens if you vary the size of the holes on the same row?
A volume based vibrato would be my guess
I believe the slotted disk is stationary and one with the holes rotates behind it…like De La Tours siren design, and similar in concept to the slots on the outside of a Federal Q design siren.
I love how we heard nothing about harmonic series in this, yet I heart harmonic series.
Nice man! Love it👊
5:13 the placement of the holes did make a difference; not in frequency (obviously) but in the timbre of the tone produced.
I think that the disighn with the lines is meant to demonstrate the softnes and hardnes of sound.
I would say that one could add multiple wind sources to the disk with the slots. Or one very wide air nozzle but with a narrow opening like a vacuum cleaner attachment might have.
Thomas Seebeck died in 1831. August Seebeck made the tone disk. It's interesting to notice that the design you used looks like fan blades captured by a camera's rolling shutter.
thank you for the correction, most of the information I would find only listed the last name.
Maybe you had to have been there
Your sirens reminded me of those colorful short tube siren whistles you can buy at the dollar stores. Taking one apart revealed a six hole slotted disc with beveled edges, like little ducted fans. They sound in either end of the tube you blow into. If you put two together in-line in the right way they sync up making an interesting jet engine like chorus effect, as they spin up so freely. If you flip one of the discs, or blow from the opposite end of the two in-line sirens they sound but not in phase. I put a 4 inch length of blue PEX tube on the end of the double siren which makes the effect more pronounced.
I too thought of your spinning strings, and wondered what other variables could be introduced to confirm the reasoning behind the Mould Effect.
The sound from the foam was a lot more clear. I wonder if this is due to the thickness stabilizing the air stream as our flows through the holes? Reducing vortices And other turbulence? This could be tested by making a disc from a different material such as wood, metal,or acrylic sheet that is roughly the same thickness. Radiusing the holes both sides would also aid in reducing turbulence. Is also suspect the foam material may absorb and dampen some of these vibrations.
I'm very curious about making some kind of organ that uses this principle. It looks like a lot of fun!
Pretty neat. With all those holes drilled into those CDs, maybe a face shield is a good idea lol!
Nah - the holes are circular, so no cracks or stress concentration, and it would take a lot more speed too.
@@stereoroid There could be cracks, the way drill bits like to grab plastic when you break through.
@@rong4189 haha someone that actually knows what there talking about, love it.
5:00 Those pitches are different. Near as I can tell the ones closer to the center make a flatter note. The edge set definitely sounds "brighter"
Great job, as usual.
👍
I believe the disc model with the continuous slots is meant to be used with a variable speed motor.
Not sure why, but I LIKE it... subscribed 😁
Nice, I wonder what sounds you would get tracing out patterns generated from the Chladni plate .
great idea
I recommend that your next video be on how to build a safety enclosure for your spinning disc
I'm wondering if that slotted brass wheel was originally used in a kinetoscope.
Her: so what do you play?
Me: it's complicated
Run one of those with radial slits in front of one with holes. Slowing down the one with holes will produce a beat with the differential speed as frequency.
Like the first on a half beat the second on fourth.
What would this sound like?
I think an air raid siren uses similar slots in a cylinder and tube to make the sound. The spinning also draws in the air thru the siren.
Wonderful as always. I think the foam disc sounds nicest.
i think the one with slots cut in is for light experiments. i think that's how early television prototypes were designed?
One observation the material that was the worst conductor of sound was the best. Pretty sure because you heard the frequency of the air cut and compressing through the hole. Instead of the higher pitch vibrations of the material.
To my ear, for some of those experimental discs the pitch is staying the same but the tambre is changing. The effective fundamental tone is unchanged but there are other harmonics that are being added in. I find these experimental discs to be the more interesting and musically “usable” discs.
Listen for the “brightness” or “darkness” of the note changing while the pitch remains relatively constant.
It's spelled _timbre,_ but you pronounced it right. ☺️
@@blindleader42 That's really funny. I know that's how it's spelled and for whatever reason spelled it differently. Ugh. hah
The slotted wheel seems to vary the harmonic content. While the fundamental pitch remains the same, the outer edge sounds "thinner" than the inner portion. I would guess the compressed wave over a larger area of solid material creates the distinction in harmonic content. Just a guess...
It's pulse width modulation :)
i dont know how i got here, but i enjoyed the whole video
That pencil trick is such a macgyver i love it
Thanks for the video
7:00 A flat disc version of a 'Zoetrope'?
pre-film animation devices that produce the illusion of motion by displaying a sequence of drawings or photographs showing progressive phases of that motion.
While the fundamental pitch of the holes on the disc that has the same number of holes per ring doesn't change, the character of the sound does; the changes in linear velocity might be altering the way the air gets chopped and giving a different set of background noise and harmonics. Same effect on the slotted disc, too!
Thanks siberx4, I think that is quite noticeable, I'm curious about the idea of elongating the holes to make up for the change of linear velocity, I still have several old CDs around and will continue to experiment with it as time permits.
4:11 Thats actually the reason, why tires dont have evenly spaced bumps but rather "radom" ones. very even tires tend to be much louder. so to minimise sound emission, they are creating uneven tires.
That is amazing!
Love the channel! I subbed!!
Very interesting!!
A memory from my childhood -- My father once bought me a toy ambulance, about the size of an adult hand. It had a slotted flywheel and a matching stationary ring. The flywheel was geared be accelerated by pushing the ambulance on the floor repeatedly faster and faster, then releasing it to go by the flywheel energy. The flywheel slots were shaped to push air radially through the ring slots. My mother hated the sound right away and my father soon joined the haters chorus as well!
good one, I had a siren whistle ring that I drove everybody mad with, fun times!
I would describe 7:55 sounding like some pulse width modulation waveform where the duty cycle becomes smaller the further you move outwards from the disc.
Is there a simple way of figuring out the speed of the disk spinning so perfect notes could be made?
working on it, I just got some software on my phone that can identify the frequency and notes to any tone. Another possible way is to use some free software on the computer, generate a specific note and adjust the wheel speed to match it.
@@YeanyScience hand held laser tachometer gun?
You could make the disc into an optical encoder by having one radial section of the disc with only one hole on it. Then mount on either side of the disc a photosensor and a laser diode. You could count the pulses over an average time length fairly easily with a microcontroller like an Arduino or Raspberry Pi.
I was also curious about this and was able to build a decent working prototype using fairly rigid cardstock and the components I mentioned above with an Arduino.
The easy high tech way is to get an audio spectrum analyzer app for your phone.
You can also get a function generator app for your phone and match the frequency.
If you have an older style fluorescent light that flickers at power line frequency, you can use that as a stroboscope that operates at twice the line frequency. North American 60 Hz power will produce a 120 Hz flicker. Most of the rest of the world is 50 Hz/100Hz. Paint a reference mark on the disk.
Arduino users can make a stroboscope and/or frequency analyzer.
Music people can use a tuning fork or any other tool for tuning instruments.
If you have Lego Technic, you can use a gear train to divide the rotation rate down to something easy to measure with a stop watch.
Some people can just tell by listening.
There are many ways to measure frequency.
Wow that's a really neat design. Simpler than a typical squirrel cage blower style siren. I wonder how loud this can get if it's scaled up.
I think the slotted one is meant to be used as a shutter of some sort. Perhaps it will limit the extranious noises that are produced by the contraption so you can get a better measurement of the specific sound you're making.