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Old 26th July 2013, 09:08 PM   #91
gedlee is online now gedlee  United States
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Well we fundamentally disagree here and you have offered no rational for not using a resonant filter for response shaping except to say that it does not track changes in the driver which I thought that we both agreed were minimal for a compression driver. I don't think that your objections have any merit.
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Old 26th July 2013, 09:20 PM   #92
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Earl,
It seems that Wayne is saying that he will only use a compression driver with no anomalies in the pass band and perfect waveguide or horn that has zero ripple anywhere from the crossover point up. I would like to know what combination that is as I have never seen a perfect combination that can do that?
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Old 26th July 2013, 09:32 PM   #93
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I don't mind 2dB ripple, and find that is a reasonable expectation. There are plenty of horn profiles that are capable of reaching that goal.

What I find unacceptable is using notch filters to knock off the peaks of a resonant horn, one that has large peaks and dips in its passband. Lots of constant directivity horns are like that, and no amount of response shaping makes them sound good, in my opinion.
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Last edited by Wayne Parham; 26th July 2013 at 09:56 PM.
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Old 26th July 2013, 10:28 PM   #94
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Originally Posted by Wayne Parham View Post
What I find unacceptable is using notch filters to knock off the peaks of a resonant horn, one that has large peaks and dips in its passband.
This is a change in what you said. You discounted resonant filters, period. Not just "to knock off the peaks of a resonant horn". I stated that there were resonances in the driver itself and that resonant filters were the only way to smooth out these resonances. My waveguides have no resonances, but ALL compression drivers have at least two and at least one of those virtually always needs to be smoothed and ONLY a resonant filter can do that.

Its kind of hard keeping track of what it is you are saying - it seems to change.
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Old 26th July 2013, 10:53 PM   #95
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My position hasn't changed in years. In fact, I wrote the same things in the PDF files I linked earlier in this thread, and I wrote those documents over a decade ago.

I think you may be confusing a filter used for impedance compensation with a filter used for response shaping. Those two impedace peaks you're talking about will modify the transfer function of a passive crossover if they are in the passband, especially if padding is used.
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Old 27th July 2013, 05:30 AM   #96
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Default Argumentum Ad Hominem ...

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Just like a religious extremist you go to the extremes to make a point. Of course anyone can create "certain conditions" for which nonlinearity is audible. My point is that one can also create a system for which it is not audible (within non-extreme conditions). I choose to do the latter, so naturally that's what I use as a basis for my claim. If all you design is junk then I guess I would worry about nonlinearity as well.
simply does damage to its author's credibility only. Religious parallels have been drawn, yet again, to somehow mask the issues of acoustics as well as psychoacoustics. While classic measures of distortion do not track the perception of it well, that fact is certainly not a new discovery. Thanks to the work of Klippel, Voishvillo and you as well, a regimin can now be tailored that gets us closer to an optimum design, were a prescribed level of acoustic performance can be delivered at an obtainable minimum cost and expenditure of time.
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Old 27th July 2013, 06:40 PM   #97
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Quote:
Originally Posted by Wayne Parham View Post
I think you may be confusing a filter used for impedance compensation with a filter used for response shaping. Those two impedace peaks you're talking about will modify the transfer function of a passive crossover if they are in the passband, especially if padding is used.
I am not confused, I am pretty sure I know what I am doing.

I don't distinguish "a filter used for impedance compensation" from "a filter used for response shaping". As far as I am concerned there is only one goal and that is delivering a desired acoustic response. There is a filter, period. This filter must work with the driver/waveguide combination to achieve the goal. Resonant legs can be part of this filter with no ensuing problems, but acoustic resonances in the horn should be avoided because they, unlike the two principle driver related ones, cannot be dealt with in an effective manner with a simple electrical circuit.
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Old 28th July 2013, 03:45 PM   #98
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There is a fundamental difference between a filter used for impedance compensation and another used for response shaping. You've alluded to the difference in your last statement, saying "acoustic resonances in the horn should be avoided because they, unlike the two principle driver related ones, cannot be dealt with in an effective manner with a simple electrical circuit."

Every horn will have peaks in its electrical impededance curve at the low end of its passband. However, a horn with good acoustic loading will not have corresponding peaks in its response curve when provided a drive signal from a voltage source, e.g. one that has nearly zero ohms output impedance. So the behavior of a horn with good acoustic loading is fairly different than one with poor acoustic loading.

This is germane to the discussion about impedance compensation versus response shaping. A horn with good acoustic loading generally needs no response shaping to deal with ripple, but probably needs impedance compensation if used with a passive crossover. However, a horn with poor acoustic loading may have excessive ripple, and impedance compensation won't help it. This is also true if the mouth isn't sized right, or if the flare profile or any number of other attributes cause it to have ripple. If a horn creates ripple in its passband even when driven by a voltage source, no amount of impedance compensation will help because that's not the problem. Such a horn is a resonant device, and the only way to smooth its response is with some form of equalization.

But even a horn that presents a good acoustic load will still have peaks in its electrical impedance curve. They are usually lower and of different shape than a horn that presents a poor acoustic load, but all horns create these impedance peaks at some level. These peaks are large enough to be reflected in the response curve when driven with a current source. But when a horn is driven by a voltage source, then the horn/driver's impedance peaks are not reflected into the response curve.

So impedance compensation must be used on a horn that has impedance peaks in the passband, esepcially if there is resistance in tweeter circuit, like what is used for padding. This impedance compensation is provided by some form of damping, and can be integral to the padding network or can be an additional shunt leg, used specifically for impedance compnesation.

Impedance compensation will modify the transfer function, but what sets it apart from a network used for response shaping is the damper circuit is really only needed to keep the load right for the filters. Again, it is to make the transfer function more like what it would be if the source impedance were zero.

On the other hand, a horn that has ripple in its response curve even when connected to a voltage source cannot be corrected solely with impedance compensation. Impedance compensation may be also required, but by itself, that's not all that is needed. A horn that produces peaks even when driven directly by an amplifier requires response modification, some form of equalization. This is a different matter entirely. You could connect such a horn directly to an amplifier, where no impedance modification is needed, but it would still be peaky and would still need equalization.

As for the two peaks at low frequency, not all horns exhibit this in their response curve. Exponential horns, for example, provide enough acoustic loading to provide smooth response even at low frequencies. Conical horns and waveguides provide much poorer acoustic loading, so they tend to have peaks at low frequency, but some are better than others.

I think it is good to say this again for emphasis: Not all horns create response peaks at low frequency. So to say it is a trait of the compression driver is somewhat misleading. It is a trait of the system, but not purely the compression driver. Just like the resonant peak of a direct radiator is modified by the box it is installed in, so is the resonant peak of a compression driver. The behavior is set by the system, not just one of its parts.

Some horns generate a nearly flat response curve, from their lower cutoff point all the way up to their upper cutoff. Some horns have a single peak at cutoff, followed by a relatively flat response. Others have more peaks, and some of the worst have periodic ripple all the way through the passband. So but my point is that not all horns create peaks at the lower end of their response curves. I would argue that the amount of ripple is one of the quality factors of the horn.
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Old 28th July 2013, 05:35 PM   #99
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Wayne - the issue is your criticizing Bill Waslo for using notch filters.

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The thing is, I've never been a fan of notch filters for response shaping.
He and I both use them and there is nothing wrong with that. If I didn't need to use them, I wouldn't (why do something that is unnecessary?) You seem to be implying that you can get an ideal response without them and I don't see how. All of this "response shaping" versus "impedance shaping" is just talking around the issue.
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Old 28th July 2013, 05:39 PM   #100
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Quote:
Originally Posted by Wayne Parham View Post
I think it is good to say this again for emphasis: Not all horns create response peaks at low frequency. So to say it is a trait of the compression driver is somewhat misleading. It is a trait of the system, but not purely the compression driver.
Maybe I need to reemphasis that all horn/driver combinations as a "system" will have peaks at low frequencies - even if the "horn" does not.
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