CD Horn EQ

[cclark65]

I am hoping to tap some of the brilliant audio people on this board about the CD HORN EQ settings.

I am running a 4-way active PA system, and my crossover doesn't have CD HORN EQ on it. Can I use a 31band eq to manually set the eq curve for the horns? I am using the MRII594A horns, and will be putting 299 drivers on them (when I can fund a couple more anyway!).
I plan on crossing them over from 1200 on up.

Thanks for ANY advice and comments!

[Todd W. White]

The CD Horn EQ craze was originally propagated by people who used inferior CD horns - they found the horns they were using didn't perform as well, sonically, as they should, so they came up with EQ schems to "fix" the problem.

It didn't, but it sure sounds hi-tech!

The Altec MANTARAY horns didn't really need all of the extra, or "special" EQ, but Altec offered modules for it because many acoustical consultants, who were used to using ordinary CD horns, wouldn't accept the Altec models without some sort of special EQ capability.

[David Yost]

Hello all:

Todd, I don't understand how this could be because, by definition, a CD horn's output will follow the compression driver's frequency response, and if it in turn adheres to the Newman criteria, the driver will have an aprox 6 dB/ octave drop above roughly 2-3000 Hz that will need to be equalized. As far as I know, all compression drivers are subject to this phenomenon, joining the Newman curve at some point, depending on the driver's designed bandwidth. If Altec engineers were able to achieve flat on and off axis frequency response from the Mantaray horns within their specified coverage angles, then they deserve a Nobel for exploiting/discovering new laws of physics.

[Todd W. White]

Well.....the manufacturers of ordinary CD horns were actually EQ'ing quite a bit more than that...

The Altec drivers are so well behaved that any anomalies in their performance characteristics could easily be adjusted using traditional equalization methods....no need for special black boxes...

[cclark65]

ok, so they do need adjusted, and can be done easily with a standard EQ, which is what I am doing. I was just looking for the specifications needed to get a good start on the frequencies I need boosted and cut to make it "flat". I know that basically I need to EQ to what I think sounds right.
Another source I have read from suggests the following:
around 16k, gain of +7, around 2.2k a gain of around +3, and for 3.35 they suggest a gain of -2. I will try this next time, but I am sure it will need a fairly smooth curve between these settings. (If I only had an analyser to play with!)

[joyspring]

Happy New Year everyone!

Dave's absolutely correct on this one - just plain physics, folks.

A true constant-directivity horn will yield a frequency response curve equivalent to its plane wave tube response. That is, the CD horn response will mirror the true acoustic output of the compression driver.

Hence, an Altec Mantaray requires the same type of rising input power vs. frequency that every other CD horn requires to compensate for the compression driver's falling acoustical output vs. frequency (the Newman curve).

The special `black boxes' are simple +6db/octave filters that generally have an adjustable turnover point. These will nearly always be preferable to using standard EQ (particularly graphic EQ) to compensate for the CD horn.

BobR

[joyspring]

Charles,

The Altec 299 datasheet ought to have a plane wave response curve; this will be the best starting point for determining the turnover point for your filter.

BobR

[joyspring]

And you'll find the datasheet at Todd's site:

http://alteclansingunofficial.nlenet...99A-Driver.pdf

BobR

[cclark65]

hmm, maybe I need to learn how to build this little filter, or get a decent parametric EQ and find somebody with an analyser and set it for the particular driver/horn combo, and leave it there, using a graphic for minor changes in different rooms.