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Old 16th May 2008, 08:56 PM   #271
al2002 is offline al2002  India
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Quote:
Originally posted by Etienne88


Jean-Michel Le Cléac'h does think so. He is a very respectable man in the hifi world, he achieved great things like his horn design or his filter setup never having business in mind. Then he back up his saying as a real scientist. For these reasons I would tend to think like him. But if you prove me he is wrong with solid argument I will change my mind...
Given the masking effects in a real room with typical stereo speakers I would expect the audibility to be well above B-L thresholds. Unless you have access to quality data that shows otherwise, there is not much to dispute, is there?

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The truth is subjective, isn't it?
Strongly disagree in this case. However, I am not interested in getting involved in a philosophical discussion.

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Its original document is written in French, I will try to translate as good as I can: "People often refer to Blauert and Laws criteria has an argument tending to prove that phase distortion is inaudible. Blauert and Laws criteria is very little pertinent in hifi. The fact that two waves coming from 2 drivers seems to come from one source only does implies that the phase distortion is not audible."

In the original language:
On fait souvent référence au critère de Blauert et Laws comme un des arguments tendant à prouver que la distorsion de phase ne s'entend pas.
Remarque : le critère de Blauert et Laws est peu pertinent en haute-fidélité. Le fait que des trains d'ondes émis par deux hautparleurs semblent provenir d'une seule source ne signifie pas que la distorsion de phase n'est pas audible.

Now if you need further information, you would have to ask the author himself. He posts sometimes here.

Regards,
Etienne
I fear I do not speak French, but something seems to be lost in the translation. Your translation: ".... implies that the phase distortion is not audible" seems to suggest that he agrees. Can you please provide a reference with some measured data?
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Old 17th May 2008, 06:22 AM   #272
Etienne88 is offline Etienne88  Sweden
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Quote:
Originally posted by al2002

I am not interested in getting involved in a philosophical discussion.
Me neither!

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Originally posted by al2002

Can you please provide a reference with some measured data?
As I said: if you need further information, you would have to ask the author himself. He posts sometimes here.

Regards,
Etienne
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Old 17th May 2008, 06:39 PM   #273
al2002 is offline al2002  India
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It's not really all that important. This is more like a third order effect - there are more important things to worry about in speaker design.

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As I said: if you need further information, you would have to ask the author himself. He posts sometimes here.

Regards,
Etienne [/B]
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Old 20th May 2008, 02:02 PM   #274
john k... is offline john k...  United States
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Earl, if you are out there I have a question for you. In general can the in room response at low frequency, for arbitrary source and listening positions, be decomposed into a minimum phase compnent plus a linear phase component? That is, can it be reduced to minimum phase by removal of a time delay? I know this is possible in some cases but does it apply in general?
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Old 20th May 2008, 02:25 PM   #275
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...
Earl, if you are out there I have a question for you. In general can the in room response at low frequency, for arbitrary source and listening positions, be decomposed into a minimum phase compnent plus a linear phase component? That is, can it be reduced to minimum phase by removal of a time delay? I know this is possible in some cases but does it apply in general?
John, I have never viewed the problem in that light before so I am not sure. I do know that the concept of "minimum phase" is one that is derived for electrical circuits and one dimension problems, but in general such features of a system won't hold in three dimensional acoustic fields. In the geometical or statistical region of acoustics the direct field can obey such principles since there is no multi-path etc. and it is basically a one dimensional problem. The reverberation or steady state field would most definately not obey any minimum phase criteria. I have never been convinced that the free field sound radiation problem in 3 dimensions is minimum phase at all. In fact I believe that it isn't. The amplitude, phase and time of arrival of a wavefront can all change independently with angle about a complex source.

At LF in a room, it is kind of ridiculous to talk about a direct field since the time of propagation to a wall is on the same order as the period. Thus a single period cannot even have passed before there is multipath. How could such a situation be minimum phase except by coincidence.
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Old 20th May 2008, 03:18 PM   #276
Kilentra is offline Kilentra  United States
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John,

The way I see it, any linear system can be decomposed into a minimum-phase system and an all-pass system, including room acoustics for a particular speaker placement. Sometimes that all-pass component happens to be linear phase (i.e. constant delay), but I doubt that is the case here. You could extract the minimum-phase component from a long windowed FR measurement and divide it out to get the all-pass component. I bet its phase would be all over the place, but I haven't actually tried.
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Old 20th May 2008, 03:36 PM   #277
gedlee is offline gedlee  United States
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Originally posted by Kilentra
John,

The way I see it, any linear system can be decomposed into a minimum-phase system and an all-pass system, including room acoustics for a particular speaker placement. Sometimes that all-pass component happens to be linear phase (i.e. constant delay), but I doubt that is the case here. You could extract the minimum-phase component from a long windowed FR measurement and divide it out to get the all-pass component. I bet its phase would be all over the place, but I haven't actually tried.

Yes, of course this would be true - that you could seperate the two parts. I was thinking more along the lines of would the resulting seperation have any meaning as it does in the one dimensional case.

A long time window would basically be a steady state measurement - what meaning does "delay" have in such a context.

You could seperate a nonlinear system into minimum phase and all-pass components, but what would it mean?
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Old 20th May 2008, 03:37 PM   #278
john k... is offline john k...  United States
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I understand that all systems can be decomposed into and MP plus an all pass. That's text book stuff. I also know that the in room response can be MP plus delay in some cases. What I need to figure out is if at low frequency (modal range) it is MP plus delay always. At higher frequency, well above the modal region, it can definately deviate from MP depending on the relative strength of the direct and reflected sound.
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Old 20th May 2008, 03:47 PM   #279
Kilentra is offline Kilentra  United States
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Sorry about that John. Can you elaborate on which cases have minimum-phase plus delay responses?

I'll have to think about the significance of the decomposition. It doesn't really mean that much to me in the one dimensional case, either.

Thanks
Michael
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Old 20th May 2008, 04:02 PM   #280
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...
I understand that all systems can be decomposed into and MP plus an all pass. That's text book stuff. I also know that the in room response can be MP plus delay in some cases. What I need to figure out is if at low frequency (modal range) it is MP plus delay always. At higher frequency, well above the modal region, it can definately deviate from MP depending on the relative strength of the direct and reflected sound.

John if what you are asking is when seperated, is the non-MP part a pure delay independent of frequency? How could it be? And of course if you seperate off the MP part there will be a pure all-pass part and by taking the derivative of this phase you will get a delay, but in all liklihood it will be a complex function of frequency. What meaning could you subscribe to this?
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