Geddes on Distortion perception

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#264
peufeu said:
Thanks 😉

Although common sense and intuition are invaluable sometimes you just need some numbers...

I had a project of building an instrument to measure this stuff, it will probably be resurrected when I finish the FPGA module for the DAC...
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I think that it would be fairly easy to track Re during a high level pulse using just a sound card and MathCAD as I do. Just measure the Re using the voltage and the current samples and the transfer function between them. This could be done every 2048 samples. The value of Re would simple be the fitted value since for a single FFT this value is uncertain at any one frequency, but very certain across the entire data set. This value could be plotted out and from that the thermal time constant calculated. I could do this is very short order, but I have so much else going on.
 
#266
Earl, from a perceptual standpoint, what are the practical implications of mildly non-pistonic cone behavior? Maybe that's an oxymoron, as a cone isn't shaped like a piston - but I'm talking about when the cone starts flexing a bit (before really severe break-up sets in).

Or, put another way, what are the practical perceptual benefits of a pistonic or non-flexing cone?

Thanks,

Duke
 
#267
audiokinesis said:
Earl, from a perceptual standpoint, what are the practical implications of mildly non-pistonic cone behavior? Maybe that's an oxymoron, as a cone isn't shaped like a piston - but I'm talking about when the cone starts flexing a bit (before really severe break-up sets in).

Or, put another way, what are the practical perceptual benefits of a pistonic or non-flexing cone?

Thanks,

Duke
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Hey Duke

I would put this at a mild level, but it could be seveer in some situations. The cone situation is fairly predictable. What happens is the edge of the cone begins to move in phase with the main body but its amplitude is increasing. This causes a slight rise in output and narrowing of the polar response. I use this effect in virtually all of my designs as it is quite useful when combined with the crossover roll off to create a sharp filter response.

But very quickly the cone goes into full resonance where the outside edge moves with large amplitude and out of phase with the main body. This will cause a sharp decrese in the axial response with a smaller decrease in the off-axis response. The crossover must be sharp enough to supress this effect or there will be problems ether on or off axis. How the cone is terminated (role or pleat, cloth or foam, etc.) and what kind of damping it has is crucial to this region. Usually right after the hole there is a sharp rise in output at the next resonance and then all hell breaks loose. The response has to be down by at least 15-20 dB by this point or there will be a serious effect on the tweeter response both axially and polar.

So a mildly flexing cone is not a problem at all, but once this goes into full resonance then for all practical purposes the driver is no longer useable.

I pay a lot of attention to this first breakup as it is the limiting factor on how high the crossover can be set. This region basically determines how well the crossover will work and it tends to seperate the good loudspeakers from the bad ones.
 
#269
Very interesting about the narrowing and then widening as the cone starts to flex; I was aware of the widening, and now looking at some of the data I have I can see the pattern that you describe. There's an off-axis notch, then it comes back up a bit, then all hell breaks loose. I had no idea what I was looking at before - now all of a sudden that data is much more valuable to me.

"Thank you" seems like such an understatment. I am amazed at how much knowledge you freely share here. I hope you're holding back some of your secrets!

Duke
 
#270
Dear Dr Geddes
can we discuss yet another kind of distortion?

the so called "time distortions", "loudspeaker noise", "transient noise"

I mean something about Linkwitz writes that:

I think a recent experience while attending a San Francisco Symphony performance gave me further insight into why we are able to tell a loudspeaker from a live instrument. Loudspeakers reproduced pre-recorded material, interspersed with the musicians' playing, during the performance of several modern pieces of music. It seemed, that coming out of the loudspeaker a sound carried a comet like trail of newly created sounds with it, that formed a continuum of background sounds, which was completely absent from the live instruments and made the speaker immediately recognizable as such. Live instruments had a space between tones, like a black background, and even en mass always remained articulate. I believe the observation had nothing to do with recorded ambience, which was present occasionally, or with hall reverberance. It reminded me of other incidences, where I had easily recognized live instruments, though there was no reflection free path between the source and my ears, and where I then struggled to describe to myself what would have been different, if a loudspeaker was playing instead. It seems to me that the ongoing-ness of sound is one of the major problems with speakers.
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best,
graaf
 
#271
audiokinesis said:
Very interesting about the narrowing and then widening as the cone starts to flex; I was aware of the widening, and now looking at some of the data I have I can see the pattern that you describe. There's an off-axis notch, then it comes back up a bit, then all hell breaks loose. I had no idea what I was looking at before - now all of a sudden that data is much more valuable to me.

"Thank you" seems like such an understatment. I am amazed at how much knowledge you freely share here. I hope you're holding back some of your secrets!

Duke
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Ted Jordan had more insight to cone flexure, and had published very inspiring knowledge. I think we should thank him for it.
 
#272
Hi graaf,

You quoted Linkwitz -

>> It seemed, that coming out of the loudspeaker a sound carried a comet like trail of newly created sounds with it, that formed a continuum of background sounds, which was completely absent from the live instruments and made the speaker immediately recognizable as such. Live instruments had a space between tones, like a black background, and even en mass always remained articulate. <<

Amplifiers do this - especially SS NFB class-AB types.

Such amplifiers can have impressive steady sine measured THD specifications, yet have this lack of 'blackness' behind the music.
They generate noise as they attempt to control voltage waveform irrespectively of resultant LS system current flow which is modified by reactively induced crossover and driver back-EMFs which have not settled from music waveforms which passed momentarily before. Energy becomes trapped in the cable+crossover+LS system with respect to the ultra low SS amplifier output impedance.
Non-NFB tube amps cannot, hence do not cause this effect to arise.

As we do not know what kind of sound reinforcement amplification was used where Linkwitz heard the San Francisco Symphony performance, maybe their loudspeaker systems were not causing the 'energy tails'.

Cheers .......... Graham.

(This was why I developed my own SS class-A//AB amplifier - two separate output stages working simultaneously - 'A' for accuracy - 'AB' for power - in a design which is notably 'black' behind the notes. My website is long overdue being re-written, but it must do for now as I use 'quality time' to achieve other things;-
http://www.gmweb2.net/
http://www.gmweb2.net/Documentation/GEM document authored by Graham Stephen Maynard.htm )
 
#273
graaf said:
Dear Dr Geddes
can we discuss yet another kind of distortion?

the so called "time distortions", "loudspeaker noise", "transient noise"

I mean something about Linkwitz writes that:



best,
graaf
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Linkwitz's comments were purely a subjective impression which cannot really be commented on because it offers nothing objective on which to comment. I guess that all I would say is that they must have been poorly designed loudspeakers.
 
#274
gedlee said:

Linkwitz's comments were purely a subjective impression which cannot really be commented on because it offers nothing objective on which to comment. I guess that all I would say is that they must have been poorly designed loudspeakers.
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Linkwitz comment refers generally to all (almost all?) loudspeakers He listened to throughout His career,
description of the specific event is only an illustration, serves as an evocative example

of course I don't ask You to comment on His subjective impression 🙂

my question is whether His subjective impression can have its cause in any objective problem with loudspeakers 🙂

the problem of "the music stops but the speaker plays its own song " - the loudspeaker noise

best regards,
graaf

ps.
image attached - typical, not particularly bad, example
 

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#276
Graham Maynard said:

Amplifiers do this - especially SS NFB class-AB types.
(...)
They generate noise as they attempt to control voltage waveform irrespectively of resultant LS system current flow which is modified by reactively induced crossover and driver back-EMFs which have not settled from music waveforms which passed momentarily before. Energy becomes trapped in the cable+crossover+LS system with respect to the ultra low SS amplifier output impedance.
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I see
but how high (below the music signal) is this NFB noise? is its level comparable to the loudspeaker noise?

Graham Maynard said:

As we do not know what kind of sound reinforcement amplification was used where Linkwitz heard the San Francisco Symphony performance, maybe their loudspeaker systems were not causing the 'energy tails'.
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absolutely ALL loudspeakers are causing 'energy tails' - only to a greater or to a smaller degree
aren't the tails clearly visible on every CSD plot?

perhaps I misinterpret the measurement? I don't know
please explain 🙂

best regards,
graaf
 
#277
Hi graaf,

Of course loudspeakers contribute audibly recognisable signal induced resonances, but amplifiers can have significance too.

It is just that Linkwitz's descriptions of 'comet trail' and loss of 'black background' are akin to what I have heard quite separately via loudspeakers with their individual resonances, where the amplifier and not the LS was the source or cause of the 'ongoing-ness of sound'.

Cheers .......... Graham.
 
#278
graaf,
the most significant "distortion" in any non-nearfield-recording and in any non-nearfield-reproduction of recorded music is coming from the room and the intrinsic faultiness of stereo reproduction. So I simply don´t buy Linkwitz´s "I believe the observation had nothing to do with recorded ambience, which was present occasionally, or with hall reverberance." His own observation "... the ongoing-ness of sound ... shows less with recordings of a single voice with small accompaniment, so often favored by audiophiles, but in complex passages of classical orchestral music and choral works" strongly supports my opinion, that he indeed is observing a distance related phenomenon.
 
#280
Rudolf said:
graaf,
the most significant "distortion" in any non-nearfield-recording and in any non-nearfield-reproduction of recorded music is coming from the room and the intrinsic faultiness of stereo reproduction.
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can You elaborate on these questions - of "room distortions" and of "intrinsic faultiness of stereo reproduction"?
perhaps in the "loudspeaker and room as a system" thread 🙂

anyway - there are still "time distortions" in loudspeakers apart from any distortion resulting from the room interaction and/or "intrinsic faultiness of stereo"

or not? what is Your opinion? Do those things visible on CSD plots indicate real audible problems?

best regards,
graaf

ps.
 
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