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Reply to Misc. Questions

Posted by djk (M) on June 28, 2007 at 01:13:53

In Reply to: RE: how on earth could that be time aligned? posted by angeloitacare on June 27, 2007 at 13:29:04:

"From the absence of large compression ratio a larger dispacement of the diaphragm results and then a quite high level of distortion (compared to a driver like the JBL245x by example) and a bell shaped frequency response curve."

Funny the data sheets don't show either. The JBL2445 on the 2380A has a higher peak/trough from 500hz~4Khz (about 8dB) than the Community does (about 6.5dB), and the Community has much less distortion too (JBL over 10% at 10W at 3.5Khz vs the Community hitting about the same 10%, but with 75W in! Even adjusted for dB down from actual output (the JBL has a peak where the Community has a dip) the Community has less distortion.

http://www.jblpro.com/pages/pub/components/2380a.pdf

http://www.community.chester.pa.us/files/specs/new/m200a.pdf

"If you use a bit of equalization between 500Hz and 3000Hz then the efficiency fall to 105 or less. "

The JBL is only 105dB at 500hz, the Community is 110dB. In the 1Khz region the JBL is 108dB, the Community is 112dB.

"IMHO the rear cavity is also too small."
"rear cavity of what"

Under the diaphragm. Make it bigger if you wish, it is designed for 500hz, but you can open it up and do anything you like.

"and this would be a positive effect."

Yes less distortion and more effortless sound at any volume level.

"as it is used this way, probably would it not beam ?"

It acts like a 2" point source, which is capable of over 90* dispersion to beyond the recommended 4Khz crossover point. Being a dedicated midrange driver dictates a different design than a wide-band unit.

"don't understand this"

The Community is nominally 112dB/2.83V in the 2Khz region where it is about 10 ohms. The Avantgard need it to be only about 107dB/2.83V/1M. Rather than add a bunch or resistors (and many audiphiles don't like resistors when used to attenuate horns), they raise the impedance so the driver draws less power. I am told the version they have made is around 30 ohms (if it was about 20 ohms it would be about 109dB, 40 ohms would be about 106dB).

A few years back I sold these with a money back policy. Most of the buyers already had JBL 2" drivers. No one ever returned a set, they sold their JBLs instead. The Community looks OK on paper, and I think it sounds even better than it looks.

Best results with the Community will be had on a horn without a narrow diffraction slot (ie: a JBL 2380 has a narrow slot, a 2350 or 2397 does not). Those $250 a pair black Tractrix horns on eBay look like they might sound good.

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