CD Horns

[eibei]

Do CD horns require a different type of crossover than sectorial horns.

Thank you in advance to anyone offering an answer.

Lynn

[Richard C.]

Lynn,

According to what I have read in two different papers, a CD horn has a natural reduction in output as the freq. rises, starting at about 3500Hz. Both papers mentioned that in order to be "flat", you would need a special EQ just for a CD horn. My new electronic crossover has this "CD EQ" setting and I am pretty sure that my Altec Model 14 crossovers have this slope built in. Since the HF driver is usually attenuated about 10dB anyway to match the sensitivity of the woofer, there is some room to boost the extreme highs. One paper mentioned that even though the HF driver can't take the power of the woofer, it can be driven harder at these higher frequencies because there is very little music power up there. A single sectorial horn doesn't need this EQ but a Multi-cellular horn might.

Richard C.

[Jim D]

Croosover differnt, no, but:

1. CD horns as they are conical in expansion take more acoustic length them exponentials (sectorals are exponentials interpolated onto a horn section)to get to the same lower frequency loading.
2. Sectoral's vertical beamwidth colapses (gets narrower) with frequency.
3. Horn drivers do not have flat response, the higher frequencies attenuate on a slope determined by the interior driver geometry and diaphragm perormance.
4. CD horns, in the upper registers, do not tend to beam like the sectorals. they distribute the HF uniformily along the horn wavefront, whatever that angle may be.
5. Therefore when you are on axis to a sectoral horn it appears that the HF is faily flat as the horn tends to beam on about the same ratio as the horn driver is rolling off. The good, and I do mean good, CD horns sound a bit dull as the whole HF power is not concentrated in one narrow beam.
6. Therefore many users of CD horn in music situations add H.F. Boost to get it to sound flat.

In PA uses the CD horns can be nicer as you can better define your coverage pattern. The ALTEC drivers, especially those with the radial phase plugs do not have near as much H.F. rolloff as others, especially those with 4" diaphragms. Most cases, when we use the Mantaray horns, we did not have to add boost as for voice it usually worked just fine without it.

This is one of the reasons the movie sound critics used to discredit multicells. They said the beaming in each cell made for an uneven pattern at the higher frequencies and they were therefore no good. Too bad, the CD horns do not have a constant acoustic center, and that the JBLs favored by them were sloppy at the edges and movies now sound worse than before. Funny how things change and how the older products hold up in critical listening..... Jim