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Old 27th September 2008, 10:43 PM   #241
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by graaf
You mean AMBIOPHONICS? (www.ambiophonics.org)
I was inspired by ambiophonics when I tried something like this. I built rectangular box 23x23x23 cm with wide rangers of the size of JX92s on opposite sides.
What I was trying to achieve was an "ambiopole" i.e. "crosstalk-cancelled stereo array" without physical barrier or electronic cross-talk cancellation, which are normally required (alternatively).
I was relying just on the directivity of the drivers and of the cabinet.

And it worked! I positioned them diagonally close to the corner and into the room and also against the wall and in the middle of the room. And they worked in every position. It was amazing. This was the moment I finally departed from "standard stereo triangle" set up for good. In terms of recreation of natural space "standard stereo triangle" was pathetic in comparison. Unfortunately the thing didn't work well with some recordings and I finally postponed the project.
I'm interested in Ambiophonics and I tried it long time ago already
Try Ambiophonics with your speakers

But there are some practical barriers (pun intended) to tackle in cross talk cancelling.

I don't get it how the 'box' you describe could provide some cancelling? If you listen from distance, say, 2 meters from speaker the angle difference of the paths from the speaker to each of your ears is so small the directivity of the speaker do not change enough to provide any amplitude difference.

- Elias
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Old 28th September 2008, 10:02 AM   #242
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by gedlee
The need for directivty drops below 1 kHz for psychoacoustic reasons
Can you show any proof what is exactly the reason we wouldn't need directivity below 1kHz, say 200Hz-1kHz (that is above the modal region)?

- Elias
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Old 29th September 2008, 04:06 PM   #243
el`Ol is offline el`Ol  Germany
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Meanwhile I have found a very simple solution for my problem: Listen to such pop-style recordings mono. Not only do I get rid of this three-source stereo, but also of the psychedelic spaceousness I experienced with conventional setups. Now I also won´t speak any longer of a strange signature these digital reverbs produce. The problem seems to be not in the reverberation itself, but in the dirty tricks like crosstalk-cancelling or stereo-basis broadening. We must not forget that a very small minority listenes to pop music in a correct stereo triangle. Usually the situation is either a ghetto-blaster with a stereo-basis of ca. 50 cm or two speakers at places where they are least disturbing optically. Fortunately these recordings are produced mono-compatible to make them suitable for simple kitchen radios.

Elias,
since you seem to have my problem even with a conventional speaker setup, maybe mono is your solution, either with two speakers or with one. Nobody should be afraid of making himself laughable by choosing this way.
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Old 29th September 2008, 04:15 PM   #244
gedlee is offline gedlee  United States
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Quote:
Originally posted by MethMan


Gedlee,

DG recomend (or rely upon?) adding an uncorelated reverb in the left and right channel into the record for requencies below say 1000Hz to support "envelopment and externalization". What to do if it is not the case? Adding a reverbating device into the signal chain does not seem to me as a viable solution. Does the damped resonant walls adds the reverb? Or their duty is only to damp a pressure modes?
I would agree with adding decorrealetd reverb in the modal region because this helps to randomize the modes, its actually like adding modes in this modal weak frequency region. But above about 200 Hz. I don't see a technical reason to do this and I think that it might just be a personal preference of DG.

The damped walls do not add reverb, in fact they take it away, hence the desire to add back some reverb at the low end to compensate.
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Old 29th September 2008, 04:18 PM   #245
gedlee is offline gedlee  United States
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Quote:
Originally posted by Elias

Can you show any proof what is exactly the reason we wouldn't need directivity below 1kHz, say 200Hz-1kHz (that is above the modal region)?

- Elias

Our difficulty in localizing frequencies below about 500 Hz is well know and by 100 Hz it is virtually impossible. So clearly the localization capacity is falling starting somewhere below 1 kHz. There is no exact transition point, its a gradual thing. Thus, if the directivity gradually decreases (widens) below say 500 Hz. then this could not be a problem for imaging.
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Old 29th September 2008, 09:08 PM   #246
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by gedlee
Our difficulty in localizing frequencies below about 500 Hz is well know and by 100 Hz it is virtually impossible. So clearly the localization capacity is falling starting somewhere below 1 kHz. There is no exact transition point, its a gradual thing. Thus, if the directivity gradually decreases (widens) below say 500 Hz. then this could not be a problem for imaging.
Your claim is simple not true. There is nothing correct in your statements. Localisation accuracy does not decrease at lower frequencies despite common believe that some may have. See the pic from Blauert Spatial Hearing, it shows that localisation blur is getting smaller at lower freqs making localisation actually _improving_, not getting more difficult as you claim! Having localisation blur of only ONE degree at 500Hz hardly makes these freqs 'virtually impossible' to localise.

I think you need to revise your understanding of sound localisation and spatial hearing.

- Elias
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Old 29th September 2008, 09:12 PM   #247
graaf is offline graaf  Poland
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Quote:
Originally posted by Elias
Hello,
I'm interested in Ambiophonics and I tried it long time ago already
Try Ambiophonics with your speakers

But there are some practical barriers (pun intended) to tackle in cross talk cancelling.

I don't get it how the 'box' you describe could provide some cancelling?
well - frankly speaking I don't get it either
therefore I have nowhere never said that there is crosstalk cancelling
rather I have said that": "crosstalk is diminished" or perhaps even more precisely: "negative effect of crosstalk is diminished"

BUT this is of course just a hypothesis

in fact my aim was to create an ambiopole that would require minimal physical barier according to the formulas given by Ralph Glasgal

BUT to my surprise I discovered that in case of such "ambiopole" adding theoretically required physical barier leads to no perceptually significant change!

I was surprised but that was what I had found then

so frankly speaking I have no certainty as to the principle operating here
I supposed that it has to have something to do with directivity of box speaker, of a dynamic driver on a baffle (see picture attached)

best!
graaf
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Old 30th September 2008, 02:06 AM   #248
gedlee is offline gedlee  United States
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Quote:
Originally posted by Elias
Your claim is simple not true. There is nothing correct in your statements. Localisation accuracy does not decrease at lower frequencies despite common believe that some may have. See the pic from Blauert Spatial Hearing, it shows that localisation blur is getting smaller at lower freqs making localisation actually _improving_, not getting more difficult as you claim! Having localisation blur of only ONE degree at 500Hz hardly makes these freqs 'virtually impossible' to localise.

- Elias

I will have to look that up in Blauert as something doesn't seem right.

Clearly localization at LF has to get worse because ALL theories of localization depend on interaural differences which have to go to zero at LF. There is no significant phase difference at the ears at LFs nor a level difference - hence there cannot be localization in that situation.
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Old 30th September 2008, 08:38 AM   #249
graaf is offline graaf  Poland
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interesting PhD dissertation:
http://ses.library.usyd.edu.au/bits...524302whole.pdf

"Spatial Hearing with Simultaneous Sound Sources: A Psychophysical Investigation"

best!
graaf
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Old 30th September 2008, 12:54 PM   #250
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Quote:
Originally posted by gedlee



I will have to look that up in Blauert as something doesn't seem right.

Clearly localization at LF has to get worse because ALL theories of localization depend on interaural differences which have to go to zero at LF. There is no significant phase difference at the ears at LFs nor a level difference - hence there cannot be localization in that situation.
This confusion comes up freqeuntly about sensitivity to time vs phase. It is best to think in units of time.

The general statement is that we are sensitive to interaural time rather than phase. One rule of thumb is that we are sensitive to about 25usec, or so, which would be a smaller interaural phase difference at 500 Hz than at 800 Hz (of course).

I am not sure where this notion of spatial acuity being so poor below 1000Hz comes from. That is simply not true.
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