JBL 4333B Studio Monitors Upgraded with No-Rot 2236H.

JBL 4333B Studio Monitors. 2231H woofers reconed with what I will call my 2236H recone kit. Cloth surround hybrid cone assembly. Never to rot like foam. 2420 midrange drivers cleaned up with felt dampening pads. 2405 tweeters cleaned up. These will make you quiver, quake, and shake. What?!
Some are curious about measurements, since listening to them on a couple videos apparently doesn't translate. Other so-called "purists" will question my motives of "re-inventing the wheel"...after all...I'm just a lowly reconer...apparently. How could I possibly improve upon a classic JBL design that won't rot in ten years? Here's an email from an audio professional in academia that requested I build him a pair. He made some Theil/Small measurements and sent me the preliminary results. The measurements were taken after a 7 volt sinewave signal at 20Hz for about 8 hours to break-in a bit. I've redacted his name for privacy. And...No...I didn't make this up:
"hi yet again Ken,
These are preliminary as I still haven't done a run with the driver entirely vertical (though final ought to be well within 10%):
fs = 22.83 hz
Re = 6.3 ohm
Qts = 0.37
Qes = 0.39
Qms = 8.63
Vas = 316.47 l (11.18 ft^3)
Sd = 890 cm^3 (I used JBL's 2235H specs)
Bl = 19.695 Tesla*meter
ETA = 0.94%
Lp = 93.01 db (2.83 V / 1 M)
Mms = 171.03 g
Rms = 2.9194 kg / sec
Cms = 0.2842 mm / N
Thoughts:
fs is perfect.
Vas / Cms is also very good, and lowers input power for my application.
Qts is somewhat higher than expected but I'll check later tonight whether the range is OK. As the spider is the same as 2235H and Mms is close, I'm wondering whether that's the surround as it's obviously stiffer than foam. Vas is ~32% lower than 2235H so that's a pretty good indicator.
However, the 2235H total Q is 0.25 which is still far lower than 0.37... this is baffling. I did note that the free air impedance peak is very high, nearly 140 ohms.
Fwiw, for your customers that use standard bass reflex enclosures in QB3 alignment, Qts = 0.37 is nearly perfect (Qts = 0.38 is perfect).
Motor strength is lower than 2235H, equivalent to 2226H. Strange as it's the same 0.75" coil in the same motor though the difference is not quite so large as the total Q.
Ref efficiency and sensitivity are excellent, equivalent to 2235H. I was a bit apprehensive about this and the results are reassuring.
Once I have the test jig set up, then I can use the measurement mic and obtain large signal distortion and guesstimate Xmax with a strobe light and ruler. Hoping for 7.5 mm+ at less than 10% THD... achieving this would be epic.
I'll run the calcs for the enclosures and biquad filters over the next couple of days though I am willing to make some accommodations for these drivers.
Thanks again,"
Thanks for watching. Please like and subscribe.
Upland Loudspeaker Service
www.repairspeakers.com
www.uplandloudspeaker.com
[e-mail]
909-946-5944
Should you like to support my channel and ongoing shared research...
www.paypal.me/...

[@oturgator]

Good idea with the 2236H selection but aren’t they 8ohms? I thought the cross-overs for these are tuned for 16ohm components.

[@edgewound]

Yes, they are 8 ohms. The JBL 4333B system crossovers are designed for 8 ohm. Thanks for your question!

[@angelsanchezferia9705]

Do you know the size of the reflex? Thanks

[@edgewound]

4" diameter x 4 1/2" long