Audibility of distortion in horns!

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#241
gedlee said:
You just need to figure out how to deal with all that information and how to simplify it down to something usable - like a single number - that can be shown to be correlated to perception. Sounds simple enough.
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LOL. Yes, simple enough. 🙂

Back in the 1970s (I think) there was work done in Japan on amplifier distortion in which different amps were subjectively rated, then the distortion spectra of those amps studied. Alas I have never found the original work, just some mentions of it and a few graphs of harmonics.

Don't know if anything like that has been done for loudspeakers.
 
#243
weltersys said:
My experience does lead me to agree with Earl Geddes that diffraction, HOMs, and other forms of linear distortion certainly can have an undesirable effect on the sound quality of horns or waveguides.
His claims that non linear distortions have no undesirable effect on sound quality (until they suddenly do) simply don't match what I can still hear after 41 adult years in the sound reinforcement and recording industry.

Art
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thats the same for me.(although my tenure is not as long as yours)


i was pretty happy with a 2482 on a 90x60 (can't remember the horn number) and a 2470 driver on the 2345 horn modded by simply dropping in a 2420 diaphragm(behaved like a super tweeter)that combo on top a Martin "Philishave" gave me a wide stable coverage pattern.
 
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#244
turk 182 said:
thats the same for me.(although my tenure is not as long as yours)


i was pretty happy with a 2482 on a 90x60 (can't remember the horn number) and a 2470 driver on the 2345 horn modded by simply dropping in a 2420 diaphragm(behaved like a super tweeter)that combo on top a Martin "Philishave" gave me a wide stable coverage pattern.
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Turk,

Glad to see you corrected your model numbers :^). I used the bi-radial 2370 horns for a while in my home stereo in the mid 1980s, my recollection is I preferred the 2345 radial horn's sound, though never actually compared the two at once.

The 2345 was more sensitive on axis than the 2370, reducing the drive level (and distortion) for a given SPL.

By the time the 2370 was introduced, the JBL diaphragms went from aluminum to titanium which improved longevity by an incredible margin, though had little sonic benefit.

Art
 
#245
yeah had to correct the model #'s my organic harddrive is developing "stiction"(and some bad sectors)

i was never happy with with the flat faced bi-radials regardless of what driver was on them (so much for newer is better)

i'm one of those guys that still pines for phenolic diaphragms they could take a beating and keep working unlike titanium's that shatter or split and don't get me started on the price...
 
#246
turk 182 said:
yeah had to correct the model #'s my organic harddrive is developing "stiction"(and some bad sectors)

i was never happy with with the flat faced bi-radials regardless of what driver was on them (so much for newer is better)

i'm one of those guys that still pines for phenolic diaphragms they could take a beating and keep working unlike titanium's that shatter or split and don't get me started on the price...
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Phenolic is a good material for longevity, but not for high frequencies other than with very small diameter diaphragms.

With over 140 titanium diaphragms (about an even mix of JBL 2445 and 2425) in use from 1983 to 1992 we did not have a single failure due to shattered or split diaphragms. The dozen EV DH1AMT (also using titanium diaphragms) I purchased in 1992 are all still going strong, only lost one due to a split surround (and burnt coil) when it was accidentally plugged in to the LF output.

The current trend of lots of complicated figures embossed into titanium diaphragms to extend HF response (HF breakup...) seems to be responsible for the fractures now commonly experienced. The extended HF response comes at the expense of both longevity and increased distortion.

Again, so much for "newer is better".

Art
 
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#248
turk 182 said:
Adamson mh225 used the EV dh1 and that was long before the patterned diaphragm i guess touring where husky's don't dare go takes it's tole with repeated heat/cool cycles!
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I don't think the heating cooling cycles are responsible for diaphragm failure in the frozen north.

When pulled out of a -30 degree truck, and brought in to a warm venue, water can condense and freeze the diaphragm to the phase plug. If (high) power is applied before the diaphragm is unfrozen, the voice coil could tear the surround as it moves and the diaphragm does not.

Normally, the time between set up and testing the system is long enough for the ice to melt, but with a fast crew that may not be the case, as we found on one Minnesota winter gig around 1981. None of the JBL 2420s would make a sound initially, though they read normal impedance. Pulled the cover on one, the inside was covered in frost. We waited for them to thaw, they all worked fine, though over several years eventually had to replace every cracked aluminum diaphragm with titanium.

Art
 
#250
gedlee said:
Regarding DDF post, it reminds me of the situation that I found when I started to study NLD. There were lots of hypothesis about the thresholds of perception of THD, etc. for sine tones and they seemed all over the map. And pure tones are such an idealistic test signal - not very close to reality - that I had my doubts about its validity. What was clear is that there is a threshold below which no NLD could be heard, but there was no metric that could be used to say that "A is better than B" regarding NLD. One might be able to say that both had inaudible NLD but one could not say that if they were both above that level which one is preferred. To study the perceptual effects of NLD one had to have a valid metric of the underlying problem.

This is where things started to come apart because it was clear very early on that THD and IMD did not meet the requirements, because they lacked any correlation to perception. One could not say if a system had audible or inaudible NLD and if it did was it only a "little bad" or "terrible"? Basically a situation where no one could really say much of anything about the audibility of NLD with any certainty.

We showed that metrics could be developed that were accurate, but alas, that was a lot of work and no one wanted to go through all that. "We all know that THD is not accurate, but it is what we have always used." It amazes me how even today people will report THD numbers as if they had some meaning.
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I think there's broad agreement that THD is of no use, but specifying max % allowed distortion per component is highly useful.

This is independent of deriving a single number metric, which is a laudable goal, but focus should first be on setting thresholds for detection with confidence limits, component by component.

Its a valid argument that sine wave derived thresholds over headphones are most sensitive case, but all this takes is time and money to understand how different maskers or signals affect audibility. We used to do it all the time. It would be trivial to test this double blind and arrive at applicable thresholds.

To my knowledge no one has done this, and there is no financial incentive for anyone to bother, so I'm sticking with the sine based thresholds available. As opposed to being all over the map, these results have been relatively consistent.
 
#251
An RCF N480 phenolic diaphragm has more HF output than a JBL phenolic, and may be used in a JBL 1" driver (it's less money too).

I have seen 2445 diaphragms that developed pin-holes in the diamond suspension (they were run hard).
 
#252
interesting i guess i have to look at other drivers.
i have always felt the change in material type for diaphragms introduced changes (i'm afraid to call them NLD cause i'm mostly wrong about the nature and classification of distortion) that where not an audible improvement(with the exception high freq extension) and brought with it durability issues.
 
#253
turk 182 said:
interesting i guess i have to look at other drivers.
i have always felt the change in material type for diaphragms introduced changes (i'm afraid to call them NLD cause i'm mostly wrong about the nature and classification of distortion) that where not an audible improvement(with the exception high freq extension) and brought with it durability issues.
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Don't be afriad, speaker membranes, cones and domes often have nonlinearities easily measured and heard as distortion.

Also in contrast to what some people think or claim it's not always a question of a predictable and insignificant gradual increase. Sudden jumps from relatively low distortion to high can be seen as the structure of a flexing material collapses. This typically goes with high order distortion products.
 
#254
People are hanging their hats on one unique situation where THD is useful. That is when the nature of the nonlinearity does not change, then the THD level is valid as a judgement of perception. So take the same speaker and same problem - like the Klippel tests - and raise and lower just the level, not changing the type of nonlinearity, and you have a valid test. But you cannot now take those results to a different speaker or a different form of non-linearty and make a comparison using the THD numbers. That doesn't work.

THD can be used to judge a speakers if it has changed or does not meet a spec such as on the assembly line where every speaker is supposed to be identical. What you cannot do is to say that because speaker A has a lower THD level than speaker B it will sound better. You also cannot specify a THD number below which NLD will not be audible or above which it will.

It works sometimes, but not always, and for what one really wants to know, how two different speakers compare, it doesn't work at all.
 
#255
gedlee said:
People are hanging their hats on one unique situation where THD is useful. That is when the nature of the nonlinearity does not change, then the THD level is valid as a judgement of perception. So take the same speaker and same problem - like the Klippel tests - and raise and lower just the level, not changing the type of nonlinearity, and you have a valid test.
But you cannot now take those results to a different speaker or a different form of non-linearty and make a comparison using the THD numbers. That doesn't work.
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Not sure I follow completely on first part, but agree with the bold (by me) part.

THD can be used to judge a speakers if it has changed or does not meet a spec such as on the assembly line where every speaker is supposed to be identical. What you cannot do is to say that because speaker A has a lower THD level than speaker B it will sound better. You also cannot specify a THD number below which NLD will not be audible or above which it will.

It works sometimes, but not always, and for what one really wants to know, how two different speakers compare, it doesn't work at all.
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Agree 100%.

I seldom use or talk about THD and much less about THD+N. While a super low THD+N number of course is in general is good, it's harder to get something useful out of it at moderate or higher levels. For me it's basically useless.

I tend to look at noise (static or signal modulated) separately and the harmonic series and how they change with frequency and level.

Also, my interest is in budget gear as well as top notch high performance gear (I try to avoid the term "hi end" which to me really is above 10kHz..) so my approach naturally depends on the actual project.
 
#256
well i thought that this thread had moved on from navel gazing about distortion definitions and failed attempts at assigning significance to data that doesn't correlate properly.

maybe i'm to much of a pragmatist but rather than dwell on minutiae can we perhaps agree that audible distortion in horns exists and explore potential solutions rather then continue a diatribe that tries to discount it's existence or significance.
 
#257
right carry on then...

with respect to horn diaphragms could they benefit from Planet10's EnAble treatment (as in 3d printing/depositing fine film at specific area's) could this perhaps help control break up modes even maybe audible distortion?
 
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