2440 vs. 2441

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Originally Posted by Earl K

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- FWIW ; I believe that most magnetic measurements are more commonly referenced into the metric system.

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Yeah, I thought so. It's just that I couldn't find my little precision metric ruler but I could find the blade from my Starrett combination square with one scale graduated in 64ths, so I used that and translated.

I think that for building a two-way WM/TW beryllium is where it's at.

David

Maybe this helps ?

Mr Widget,

Any news regarding the possibility to make a batch for us forum members, and whether or not the dias fits the 2441?

I'm really interested to know more about the guy that can make something like that.

regards: Jakob

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Originally Posted by Jakob

Any news regarding the possibility to make a batch for us forum members...

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I am going to have to lean on him... he has been otherwise engaged and I can't seem to pin him down.

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Originally Posted by Jakob

...and whether or not the dias fits the 2441?

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I think Steve's post covers it.

http://www.audioheritage.org/vbullet...62&postcount=5


Widget

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Originally Posted by edgewound

Gap depths have to be the same for diaphragm interchangeability. The gaps are deeper in the 2482 & 2485 that came with phenolic diaphragms. My 1976 JBL Professional catalog with 2440 & 2482 says 20,500 gauss for all the large format drivers, my 1980 catalog says 18,000 gauss for both 2441 & 2482....both catalogs state 118dB sensitivity for these same drivers. I can't explain the difference in gauss....you're theory sounds good.

I haven't measured them,though...for the diaphragms to be truly, usefully interchangeable, the top plate gap depths must be the same for the voice coils to be symmetrical from either end of the gap...or they'd be terribly distorted.

Thanks,

Edgewound

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Hope nobody minds if i post to a 10-yr old thread, i stumbled over this today and do know the following from the 2440, 2441 and 2482 cores that i have tried to measure. When re-magging, i noticed that the probe of my cheap HT-20 Teslameter (the black, not brown probe) would just fit into the gaps of 2441 & 2482, but not into the 2440 gap => the reason for the stated higher flux density is maybe gap width.

After re-magging at a friend's, we got the following (hope i remember it correctly) on his pro-quality meter
2440 : below 2T (around 19.800 Gauss, we did quite a few. Why not 2.05T => Widget mentioned a meas accuracy issue in early JBL specs)
2441 : exactly 1.8T (on four samples)
2482 : just below 1.7T (16.700 to 16.950 on 4 samples)

Assuming the gap width of 2482 and 2441 is the same, info in this thread that 2482 has slightly more (inside) pole plate thickness may account for the flux density difference to 2441. My Apr.'84 data sheet of 2482 states 1.7T, earlier specs 1.8T (see above).

As to the difference between 2441 and 2440, i have read elsewhere on this site that JBL was forced to do it because the higher power delivered by transistor amps would mean that heat would make coils expand more in the gap, giving rise to reliability issues with customers. Which JBL apparently reacted to by making the gap wider on 2441. The simultaneous fram change meant unchanged mid output.

I am sure most of this info is elsewhere on this site, hope someone finds it useful here. Btw, all these cores are sold, i'm into D502's currently. I believe TAD's reworked TD4003/2002 plug, Yamaha's JA6681 and JBL "Coherent" all borrowed from it.

Talking of which: who can borrow/sell me my 2nd 476Be to finally try that baby with Be fram, silver-on-pole and "coherent" plug in stereo ?

Enjoy the Sunday,
Ralph



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[QUOTE=gibber;378217]Hope nobody minds if i post to a 10-yr old thread, ....

I am sure most of this info is elsewhere on this site, hope someone finds it useful here. QUOTE]

I believe this is one of the best reasons for keeping all these old threads preserved. The occasional addition of new information makes and keeps them valuable.

Thank you,
Barry.