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Old 28th July 2013, 06:17 PM   #101
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Originally Posted by gedlee View Post
Maybe I need to reemphasize that all horn/driver combinations as a "system" will have peaks at low frequencies - even if the "horn" does not.
That's not true. A horn that provides reasonably good acoustic loading will not have peaks its response curve when driven with a compatible driver. There are numerous examples of horn/driver combinations that provide smooth, ripple-free response.

I don't know if yours is capable of that, but from your objections, I would guess not. The SEOS horns have peaks at 1kHz, 2kHz, 4kHz and 7kHz. Where are the peaks in yours?

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All of this "response shaping" versus "impedance shaping" is just talking around the issue.
That also is not true. Using filters for impedance compensation is well-understood. Otto Zobel is the first I know to describe them, back in the 1920s or so. Response shaping is completely different, and may be employed even where impedance compensation is not.
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Last edited by Wayne Parham; 28th July 2013 at 06:24 PM.
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Old 28th July 2013, 07:11 PM   #102
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Wayne,
While I agree that an impedance correction circuit can flatten the impedance rise or a peak in the impedance curve that is only a part of the picture. Typically as Earl has stated you have a single impedance rise in the bottom of the band due to the device resonance which is often ignored and taken care of by a suitably high crossover point, though this is not a perfect solution as Earl has pointed out as you will still have some in-band ripple and the second source would just be the typical rising rate of most devices impedance curve. This second rate increase can be countered by a conjugate matched tank circuit that will flatten this impedance rise though actually making it perfectly flat doesn't often happen. But neither of these two impedance correction circuits is going to do anything about the normal mass roll-off of a compression driver. This would require a filter with either a shelf or a matching slope to bring up the top end. What would bother you about doing this either passively, difficult to do well, or actively and flattening the FR of the pass-band? I have not brought into the discussion of any resonant behavior in the pass-band due to a mechanical problem with the compression driver as this I have a problem with myself and do not think that an electrical circuit is truly capable of successfully correcting without causing phase and program problems while still leaving the simple mechanical resonance problems that can be excited with or without an electrical signal.
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Old 28th July 2013, 07:23 PM   #103
gedlee is offline gedlee  United States
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There are numerous examples of horn/driver combinations that provide smooth, ripple-free response.
Wayne

Show me an example of a horn/compression driver system that has no peaks when there is no electrical modification.
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Old 28th July 2013, 09:16 PM   #104
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Originally Posted by Kindhornman View Post
...neither of these two impedance correction circuits is going to do anything about the normal mass roll-off of a compression driver. This would require a filter with either a shelf or a matching slope to bring up the top end. What would bother you about doing this either passively, difficult to do well, or actively and flattening the FR of the pass-band?
Using filters to conjugate mass-rolloff doesn't bother me. You pretty much have to do that for any horn that provides constant directivity but it's a pretty simple first-order slope. There's a little more to it than that, because the response below mass rolloff is generally flat, so the conjugate filter needs a flat region followed by a second region with rising response, to counter where mass-rolloff begins.

What bothers me is using horns that have a lot of ripple, and then smoothing them with response-shaping notch filters. I have never found that approach to be satisfactory.

As for impedance compensation, there are a myriad ways to do it, but sometimes I like having the complex impedance of the horn/driver in the circuit to modify the transfer function in a favorable way. The changing impedance can be expoited to one's advantage. In those cases, I do not try to set load impedance flat, but instead use changing impedance of the load to modify the transfer function. This approach uses fewer parts, and sometimes allows really useful filter functions to be formed, with more complex shape than one would expect from the parts count. But the point still remains, that there is a filter function type that specifically requires a flat "resistive" load. This would be an impedance modification filter, like what was described by Zobel so long ago.
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Old 28th July 2013, 09:42 PM   #105
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Originally Posted by gedlee View Post
Show me an example of a horn/compression driver system that has no peaks when there is no electrical modification.
Below you'll find a pretty good example. It's a TAD compression driver on one of their radial horns of a decade ago.

You can find lots of other examples like this. I myself used a radial horn for quite some time that was really smooth on-axis and had pretty good horizontals too.
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Old 28th July 2013, 10:11 PM   #106
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Wayne,
The top octave on that horn is why I used the TAD ET-703 from 10khz on up.
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Old 28th July 2013, 11:07 PM   #107
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Yes, it doesn't do the top octave but is a good example of a horn that is ripple-free down low and midband. With decent acoustic loading, the amplitude response is smooth. Plenty of other examples like that out there too.
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Old 28th July 2013, 11:09 PM   #108
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While I might question the details of that system, I'll give you that it might be possible, but it is the exception, not the norm. Most systems will not be over-damped with extremely low cutoffs like that one and those will always exhibit a peak. A peak which is easily and effectively flattened with a LRC circuit.
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Old 29th July 2013, 12:02 AM   #109
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I think this is where we meet in the middle. I tend to agree that, especially for conical horns and waveguides, it is often useful to damp the lowest peak with the crossover. Conical horns and waveguides tend to have poor acoustic loading at low frequencies so you have to live with that to get their inherent benefits in other areas, i.e. directivity, wavefront propogation, etc.

But just like I said in the Uniform Directivity thread, I wouldn't throw the baby out with the bathwater. I'm not willing to trade smooth response and accept a lot of ripple. I'm ok with one resonant mode, down in the crosover region where I can damp it naturally. But I'm not ok with three or four of them, all the way up the band. That's the way some of the old prosound CD horns act, and they sound nasty even when equalized flat.
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Old 29th July 2013, 12:54 AM   #110
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I still am not in agreement, but I am tired of arguing with you.

"where I can damp it naturally" whatever that means.
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