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Baffle Diffraction
Baffle Diffraction
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Old Yesterday, 11:04 PM   #391
mark100 is offline mark100  United States
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Hi all, a graph from this thread haunts me.....

I think it's all wrong...
I think for any waveform origination, phase alignment is when initial rise times are in sync....not peak energies.

And if that understanding is true, and IF our hearing is in sync with true waveform origination, graph must be back-asswards....????

Please straighten my thinking....
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Old Today, 05:44 AM   #392
gedlee is offline gedlee  United States
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I think that your definition of "phase alignment" and the graphs must be different. I didn't know exactly what was meant by the term when I read it, so IO just ignored that part of the plot.
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Old Today, 05:48 AM   #393
gedlee is offline gedlee  United States
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Quote:
Originally Posted by 33Polkhigh View Post
Afaik the brain makes sense of frequency response variations in both time and space ...
"and space"? How does the ear, which is fixed in space, do that exactly?
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Old Today, 07:05 AM   #394
RobWells is offline RobWells  United Kingdom
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Quote:
Originally Posted by mark100 View Post
Hi all, a graph from this thread haunts me.....

I think it's all wrong...
I think for any waveform origination, phase alignment is when initial rise times are in sync....not peak energies.

And if that understanding is true, and IF our hearing is in sync with true waveform origination, graph must be back-asswards....????

Please straighten my thinking....

I think you're talking about the difference between a minimum phase system and a linear phase system ?

I took these grabs from 'delay alignment a survey' pdf I found online.
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File Type: jpg linphase.jpg (104.2 KB, 75 views)
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Old Today, 07:12 AM   #395
PMA is offline PMA  Europe
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Quote:
Originally Posted by gedlee View Post
On the other hand, diffraction results from a boundary change and it too creates a virtual image source, but positioned exactly at the diffraction point (or line or whatever.).
Would it be possible to investigate these virtual image sources by a microphone placed near to baffle edge line as shown in the attached photo? If yes, what is the interpretation of the plot shown, measured this way. Thank you.
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File Type: png edge_diffraction.png (60.1 KB, 63 views)
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Old Today, 09:28 AM   #396
Bill Coltrane is offline Bill Coltrane  Netherlands
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Questions about diffraction audibility.

Localisation.
I just did an experiment where I was blindfolded and my kid was standing in random places in the room making a noise, and I was able to pinpoint his location very accurately even when standing right next to a corner, cabinet or couch. Shouldn't it be more difficult to pinpoint the location of a sound when close to a corner? This didn't seem to happen, but I'm not sure. Maybe others can do something similar and post their results.


When listening to square boxes, sounds seem all to have the same size. A small speaker, everything sounds small. A big speaker, everything sounds big. Is this due to diffraction?
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Old Today, 09:31 AM   #397
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by mark100 View Post
Hi all, a graph from this thread haunts me.....

I think it's all wrong...
I think for any waveform origination, phase alignment is when initial rise times are in sync....not peak energies.

And if that understanding is true, and IF our hearing is in sync with true waveform origination, graph must be back-asswards....????

Please straighten my thinking....
Hey Mark,

Create a Dirac pulse in RePhase and import it in REW, on the IR tab it will look like a single peak.
Baffle Diffraction-dirac-jpg

Next go to the filtered IR tab and choose some different filters, like 63 Hz, at 1/3th. Switch back each time to the IR tab to see the wave shape at that point, it will show the initial rise times are in sync.

Example from a filtered 63 Hz signal:
Baffle Diffraction-63onethird-jpg

Turn off all filters and create a wavelet and it will show this:
Baffle Diffraction-wavelet-jpg
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File Type: jpg 63onethird.jpg (80.0 KB, 54 views)
File Type: jpg wavelet.jpg (78.8 KB, 55 views)
File Type: jpg Dirac.jpg (63.0 KB, 54 views)
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Old Today, 02:58 PM   #398
gedlee is offline gedlee  United States
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Quote:
Originally Posted by PMA View Post
Would it be possible to investigate these virtual image sources by a microphone placed near to baffle edge line as shown in the attached photo? If yes, what is the interpretation of the plot shown, measured this way. Thank you.
I think that in principle it should work, but in practice it is going to be difficult. The reason is that what you are measuring is a composite of everything, some of which is the diffraction, but the diffraction is fairly low in level compared to the direct sound, and some are near field pressures which do not propagate. So sorting it out may be problematic.

This kind of reminds me of my attempts to measure sound radiated from the enclosure itself. Never could sort out anything of value.

There are techniques which fall under the general classification of Acoustic Holography, which again, can in principle do this problem. But they are know to be notoriously difficult at resolving secondary source locations better than 1/2 wavelength.

There are simple cases which are easy. Consider a circular piston centered in the end of a long circular tube. The difference in the radiation pattern from this configuration and that of a simple circular source in an infinite baffle is due to the edge diffraction. From this difference pattern we could work back to the source and find precisely what was being diffracted from the edge. But the general case is far more complicated.
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Old Today, 03:51 PM   #399
PMA is offline PMA  Europe
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Quote:
Originally Posted by gedlee View Post
I think that in principle it should work, but in practice it is going to be difficult. The reason is that what you are measuring is a composite of everything,
Thank you, this makes sense, of course. Would it be more revealing to measure aside and behind the baffle, so that bending of waves around the corner and diffraction should be more emphasized?
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