When I was auditioning the 2404 I noticed that it did not have the characteristic dip between 8-10K that the 2402s have (and do show up on the Behringer).



OK, I attributed this to the 2405 diaphram in the 2404 having a different characteristic resulting in a smoother response in this area.

So, I disassembled the 2404 to do some measurements and noted that it had had a 2402 diaphram installed in 1991 (marker note on the outter ring).

OK then...,

If it is not the diaphram, maybe it is a characteristic of the horn design.

If one examines the differences in the 075/077 diaphram pictures, it would appear that the "cone area" of the 075 is broader across the horizontal surface as the center mounting ring is smaller in diameter than the 077, and this additional space is composed of cone area on the 075. Furthermore, when one examines the phase plug of the 075, it would appear that this cental portion of the cone area is "shooting up" into the interior of the phase plug.

(It would also appear that the center mounting ring of the 077 being bigger in diameter is what interfers with its use with the 075 phase plug, and it could be a simple matter of shaving a hair off the inside diameter of the phase plug to use an 077 diaphram, but that's another story.)

The wavelength of a ~9,000 Hz tone is approximately 1-1/2", or about the length of the phase plug's interior. Could this be causing a cancellation back at the diaphram cone creating the dip? It would appear to be possible.

So has anyone tried to fill (partially or entirely) the phase plug and if so, what were your results?

Does anyone have one around (with the right equipment) that can perform this simple test?

Thanks