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Old 12th April 2012, 08:24 PM   #1
Frosteh is offline Frosteh  United States
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Default How to know distortion?

Is there a way to know the distortion of a speaker without actually owning it and testing it? Many of the drivers at PE only have response and impedance curves, but that doesn't tell the entire performance of a speaker. I'm designing a new 3 way system and would like to know the drivers I'll be buying will actually perform as well as I'd like.
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Old 12th April 2012, 08:31 PM   #2
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Originally Posted by Frosteh View Post
Is there a way to know the distortion of a speaker without actually owning it and testing it? Many of the drivers at PE only have response and impedance curves, but that doesn't tell the entire performance of a speaker. I'm designing a new 3 way system and would like to know the drivers I'll be buying will actually perform as well as I'd like.
No, more complete specs such as distortion and large signal behavior are not typically reported by driver manufacturers. This is why sites like Zaph Audio and audioheuristics.org are very valuable (there are a couple more that I can't think of at the moment), since these people report tests on actual drivers themselves.

The one exception that I have seem from SOME manufacturers is for pro drivers where they report 2nd and 3rd order distortion along with frequency response.

-Charlie
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Old 12th April 2012, 08:54 PM   #3
Frosteh is offline Frosteh  United States
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Well that's lame. No wonder the ridiculously expensive drivers all have distortion graphs on PE.
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Old 13th April 2012, 01:04 AM   #4
gedlee is offline gedlee  United States
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Don't worry too much about THD and/or 2nd and 3rd harmonics, they just don;t correlate very well with sound quality. If you are trying to do a 3-way system then matching sensitivity and frequiency response will be the bigger challenge, unless you are using an active crossover. If you do use active then get the drivers with the most copper in the voice coil. This can usually be assesed by voice coil diameter, etc. but not always. Higher efficiency is usually a good indicator of quality. It implies a lot of things that are expensive and desirable. And even if the manufacturer does post data, its usually not very accurate and sometimes just plane wrong.
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Old 13th April 2012, 01:42 AM   #5
Bazukaz is offline Bazukaz  Lithuania
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I know two German magazines that do tests on speakers :
"hobby hifi" and "klang+ton".
There are plenty of them floating on the net in .pdf format.
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Old 13th April 2012, 01:54 AM   #6
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Originally Posted by gedlee View Post
Don't worry too much about THD and/or 2nd and 3rd harmonics, they just don;t correlate very well with sound quality. If you are trying to do a 3-way system then matching sensitivity and frequiency response will be the bigger challenge, unless you are using an active crossover. If you do use active then get the drivers with the most copper in the voice coil. This can usually be assesed by voice coil diameter, etc. but not always. Higher efficiency is usually a good indicator of quality. It implies a lot of things that are expensive and desirable. And even if the manufacturer does post data, its usually not very accurate and sometimes just plane wrong.
Earl, what about the various resonances highlighted via "impedance glitches"?

For example, the JA8008 is pretty efficient (91.5db/w/m), but its impedance trace:

Click the image to open in full size.

seems more questionable than the impedance trade of this less efficient scanspeak (85.5db/w/m):

Click the image to open in full size.

Are those apparent resonances really a worthwhile tradeoff for better power compression behaviour?

It seems to be a theme with higher sensitivity drivers. See also, this B&C (89.5db/w/m):

Click the image to open in full size.

compared to this Usher (85.5db/w/m)

Click the image to open in full size.

I'm all for more efficient speakers, but it seems to me that you have to be willing to accept various resonances to get it. As far as I can tell, preference aside, mechanical resonances are not a desirable trait in a reproduction system at any SPL. Are these things simply not audible once equalized?

Last edited by RockLeeEV; 13th April 2012 at 02:17 AM.
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Old 13th April 2012, 12:09 PM   #7
gedlee is offline gedlee  United States
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To me resonances are not "distrortion". Distortion is a nonlinear thing, resonaces are a linear one. I was only talking about nonlinear effects, not frequency response (per the threads title.) But I don't know of any connection between efficiency and resonances. Why would there be? There are low resonance high efficiency drivers just as there are for low efficiency ones. You just have the wrong examples. But remember that a high efficiency driver will show a larger impedance aberation for a given resonance than a low efficiency one will, so there is not a direct one to one comparison possible when looking at just the impedance curve.

And its not thermal compression that I worry about but thermal modulation - i.e. "dynamics". High efficiency drivers have it and low efficiency ones don't. Some of each kind have resonances and some don't. Generalizations are always dangerous, but I would not put too much stock in distortion curves for a loudspeaker. Frequency response yes - if it can be trusted. Most can't.
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Old 13th April 2012, 12:45 PM   #8
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Originally Posted by gedlee View Post
But I don't know of any connection between efficiency and resonances. Why would there be?
High efficiency must mean low moving mass, which in turn means a thin membrane. Surely this would mean more resonances in the higher frequency response (as there's not much material to actually damp the resonances) - guitar speakers are a good example here, with efficiencies of sometimes over 100dB@1w, very light cones, and cone break-up abound.

Perhaps I'm missing something?

Chris
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Old 13th April 2012, 12:53 PM   #9
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But I don't know of any connection between efficiency and resonances. Why would there be?
Maybe the lighter, high-efficiency cones have less damping and are more prone to resonance. Alot of the lower efficiency drivers have well damped cones, coating etc but sound less "dynamic".

How does a typical resonance (if there is such a thing) appear off-axis? I wonder if it possible to EQ resonance without other issues arising. Would seem like a better solution than layer upon layer of coating.

Edit: Beat me to it, Chris

Last edited by samadhi; 13th April 2012 at 12:54 PM. Reason: Beat me to it, Chris
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Old 13th April 2012, 01:30 PM   #10
gedlee is offline gedlee  United States
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Chris

Guitar speakers are designed to break-up so thats a bad example. Efficiency is usually obtained through larger voice coils and bigger magnets - more force. The mass is usually not what is changed, but in general it tends to be heavier cones, not lighter ones.

The key is to not have any "significant" resonances within the passband that you are looking for, outside of that band resonances are not siuch a big issue unless they are very pronounced. In almost all drivers the first resonance is usually the worst and the most difficult to control. It is caused by the rim or surround going into resonance. Hence, more so than the cone is the way the surround is done that determines how high up in frequency one can take any given driver. Once a cone starts to "loose it" that driver is done.

In most loudspeakers the greatest damping comes from the electromotiove damping of the voice coil. This is greatest for a higher efficiency driver.

There are a lot of variables in the problem, but from what I have found the best compromises come from more efficient drivers. I am talking here, of course, about drivers intended for limited bandwidth, not full range. Full range drivers are a completly different animal. I don't deal with those at all for the obvious reasons.
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