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RE: Do you find that

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Hi,

> your 15" driver exhibits the same directivity at say 500 hz
> (27 inch wavelength) as it does at 5 kHz (2.7 inch wavelength)?

No.

The SPECIFIC 15" Driver (JBL D130) referred to has a smoothly increasing directivity with frequency and it will have a good match in directivity at the top of it's range with the recommended (very narrow directivity) tweeter.

This has some interesting results.

First, the systems "on axis" response will be flat (depending on EQ and crossover of course).

Second, the off axis response will be significantly attenuated above a few 100Hz, ultimately forming in the midrange and up to ultrasonic frequencies a CONSTANT DIRECTIVITY system.

Arguably, the dispersion angle in the midrange and up will be very limited (around 40 degrees).

This has many distinct advantages for single seat "serious listening" (by significantly reducing the amount of room effects compared to wide dispersion systems, so room treatment needs to be MUCH LESS) and can provide significantly more of the original recordings acoustics than wide dispersion systems (I tend to refer to these as "reverb effects"), but is not very conductive to background music production that produces a diffuse sound-field all across a room (buy Bose 901 or Omni's if that is what you want).

So depending on specific personal requirements the D130 & 075 2-Way crossed over at several KHz may be the best speaker possible or a shut in and boring sounding antique.

The point I was making actually was that one needs to understand all aspects of a given acoustic system and consider them, plus the given target situation and then apply accordingly.

There are good reasons for both very narrow directivity systems, omnidirectional systems and even for speakers that produce eight times more reverb effects than they reproduce the actual recording.

Ciao T


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