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Old 10th May 2008, 05:05 PM   #91
gedlee is offline gedlee  United States
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Quote:
Originally posted by graaf


yes, in such a set up what we perceive in the highs is mainly sound vertically reflected off the ceiling arriving at the ears with about 10 ms of delay
but this is not a problem because the hearing mechanism is processing what the ears receive in "stages" or "phases"
the first stage is sound source localization and it lasts <1 ms counting from first wave front arrival at the ear, the second is sound source size assessment and it lasts for the next 1<30 ms, the third is sound source identification which begins with pitch recognition occurring between 10<30 ms

thus all sound source localization is done completely before the delayed reflected sound reaches the ears, no problem at all

moreover, in case of sound localization in reverberant space like a room hearing relies mostly on time difference mechanism - the law of first wave front and the precedent effect (Haas effect) and additionally on phase difference mechanism and in that regard most important are the spatial cues around 1 kHz at which my speakers are not yet that much directional

Graaf

Your numbers here are not correct. The first 10 ms is the critical time for localization then out to 20 ms coloration (Tembre) is affected. Beyond 20 ms there is no effect at all on localization, but coloration can still be a factor if the loudspeakers don't have matching power and direct response curves. If they are CD then beyond 20 ms reflections are only a good thing - they create spaciousness - especially if they are lateral.

The rest of your commenst are too long to comment on at the moment. This is all a very complex subject.
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Old 10th May 2008, 06:34 PM   #92
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Quote:
Originally posted by graaf
[B] by saying "do the job" I meant "do the job" "of being much better than what we have now"
I certainly didn't mean "do the job" "of wavefield synthesis" in that sense surely it doesn't but in a sense "much better" it does

and what about ambiophonics? "transaural stereo"?
http://www.ambiophonics.org/
Unfortunately I havenít the occasion to listen such system. But I know well the website and can imagine the sonic impression: It should be the only realized loudspeaker approach until, which reach the stage to fault our brain for listen a genuine event.
Only disadvantage is the small working area. By my proposal that problem would be solved for the price of higher effort. The main ideas are very similar.


Quote:
Originally posted by graaf


Ö. ambiophonics or binaural playack are perfectly technically feasible. And would be much more commercially feasible. Well, this doesn't change anything in reality. From the perspective of the industry these are and most probably will remain only curiosities And "1296 speaker device" is even something more extreme, a real monstrosity

It would work also by 144 speakers, but it wouldnít be perfect


Quote:
Originally posted by graaf

well, psychoacoustically the loudspeakers are perceived in stereo as early reflections of a sound whose direct version we missed what is wrong with that? seems to me that nothing per se what is fundamentally wrong is rather the positioning of these early reflections in a room it is having these early reflections in a middle of the room what is higly unnatural and leading to lack of realism try damping of the wall in front of the listener and Beveridge positioning where the loudspeakers are acoustically integrated into the side walls

what do You think?

I am conform by Ralph Glasgal when he wrote on the site:
"Tonal accuracy is the best that can be hoped for in a traditional audio system; true spatial accuracy will never happen. Audio products should come bearing this disclaimer: WARNING: IMAGE PRESENTED IS LESS THAN LIFELIKE."

The fundamental problems of conventionally reproduction are indeed the early reflections. Its starting points are the mirror sources everywhere in the recording room. The attempt to reduce its spatial distribution upon a few channels must lead inevitably to utterly different perception.
The loudspeakers in the playback room generate an utterly different reflection pattern. That is shown in that small animation for the undirected radiation in main tone range:
http://www.syntheticwave.de/pictures/Stereo50.swf
It is revealing the utterly different impulse response. More adapted perception only is possible, if the recording room and the playback room vaguely similar. In all other cases only the suppression of the wrong playback room reflections remains. But by that way only the speakers remain as sound source. The reproduction becomes reduced only upon the few sources in the horizontal level of the speakers. Hardly IACC attractions arise, the sound becomes boring.

Only way for avoid that problem is changing the playback room acoustic dependent of the reproduced program. In that matter my idea is very less expensively as continually employee fife craftsmenís.
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Old 10th May 2008, 08:11 PM   #93
gedlee is offline gedlee  United States
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The problem with any of these multi source systems is the audio quality of each single source. The source problem will dwarf the image problem unless high quality sources are used, and then you are talking mega-bucks in sources alone. I have heard many of these "image field" enhancers and each one of them lack sound quality because of the poor sources. The images were where they were supposed to be, that much worked, but the sound quality was very poor and ruined the whole thing IMO.
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Old 10th May 2008, 10:11 PM   #94
graaf is offline graaf  Poland
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Quote:
Originally posted by gedlee

Graaf
Your numbers here are not correct. The first 10 ms is the critical time for localization then out to 20 ms coloration (Tembre) is affected. Beyond 20 ms there is no effect at all on localization, but coloration can still be a factor if the loudspeakers don't have matching power and direct response curves.
OK!
I accept those corrections, thank You

anyway, the numbers are all approximations
my approximations are taken from Josef Mangerís presentation "Acoustical reality", they are after Eberhard Zwicker and Hugo Fastl ("Psychoacoustics Ė facts and models" Springer Verlag Berlin 1999) I believe (though I am not sure)
anyway, the numbers You gave and the numbers I gave after Manger are not so much different, not significantly different

You say "first 10 ms are critical for imaging" - OK! I concur!
but the sense of the direction of sound is established sooner, isnít it? the precedence effect, it's <1 ms I believe

Quote:
if the two sounds arrive within 1 ms of each other, you will confuse the location of the sound source and think that it's somewhere between the direction of the direct sound and the reflection (a phenomenon known as summing localization) [Blauert, 1997]"
from "Introduction to Sound Recording"
see: http://www.tonmeister.ca/main/textbook/node339.html

even more scientifically put:
Quote:
"Summing localization" refers to a delay (0Ė1 ms) when the sounds from the lead and lag sources are perceptually fused and when both the lead and lag contribute to the perceived direction of the fused image (e.g., de Boer, 1940; Warncke, 1941; for review see Blauert, 1997, pp. 204Ė206). Note that the simplest case of summing localization, as illustrated in Fig. 2(B), assumes no temporal overlap between the direct and reflected signals and the perceived location is an average of the two directions. In cases where the stimuli overlap in time, perceived direction is mediated by more complex averaging that include the amplitudes and phases of the summed wave forms.
from "The precedence effect" ASA Paper
see: http://www.waisman.wisc.edu/~litovsky/papers/1999-3.pdf

You say "first 10<20 ms are critical for timbre" - OK! I second that as well

10<20 ms or 10<30 ms - whatís the practical difference? I believe none

best,
graaf
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Old 10th May 2008, 10:41 PM   #95
gedlee is offline gedlee  United States
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Quote:
Originally posted by graaf


OK!
I accept those corrections, thank You

anyway, the numbers are all approximations
my approximations are taken from Josef Mangerís presentation "Acoustical reality", they are after Eberhard Zwicker and Hugo Fastl ("Psychoacoustics Ė facts and models" Springer Verlag Berlin 1999) I believe (though I am not sure)
anyway, the numbers You gave and the numbers I gave after Manger are not so much different, not significantly different

You say "first 10 ms are critical for imaging" - OK! I concur!
but the sense of the direction of sound is established sooner, isnít it? the precedence effect, it's <1 ms I believe


from "Introduction to Sound Recording"
see: http://www.tonmeister.ca/main/textbook/node339.html

even more scientifically put:

from "The precedence effect" ASA Paper
see: http://www.waisman.wisc.edu/~litovsky/papers/1999-3.pdf

You say "first 10<20 ms are critical for timbre" - OK! I second that as well

10<20 ms or 10<30 ms - whatís the practical difference? I believe none

best,
graaf

In small rooms these small time differences make BIG perceptual differences because the time delays are always in this range.

The "Summing localization" and "precedence" effects are widely overstated in these discussion because they indicate - as you said - the principle direction of the sound perception. They do not indicate whether there is an increase in image blur or coloration, both of which exist for these small delays. SO yes the "principle" direction is set very early 1-2 ms, but the stability and coloration of that image is strongly influenced by the next 8-10 ms. I want a stable and uncolored image, not just a "good idea" of which direction its in. Blauert admiots such in his "Spatial Hearing" book.
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Old 10th May 2008, 11:56 PM   #96
graaf is offline graaf  Poland
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Quote:
Originally posted by gedlee

In small rooms these small time differences make BIG perceptual differences because the time delays are always in this range.
The "Summing localization" and "precedence" effects are widely overstated in these discussion because they indicate - as you said - the principle direction of the sound perception. They do not indicate whether there is an increase in image blur or coloration, both of which exist for these small delays. SO yes the "principle" direction is set very early 1-2 ms, but the stability and coloration of that image is strongly influenced by the next 8-10 ms. I want a stable and uncolored image, not just a "good idea" of which direction its in. Blauert admiots such in his "Spatial Hearing" book.
well, in small rooms, in most listening rooms, with standard loudspeaker positioning the time delays are typically <10 ms

this is why I say 10<20 ms or 10<30 ms is no difference in practice
only from that perspective

Iíve demonstrated in my first post in this thread that by means of special positioning of special loudspeakers in a room we can achieve a delay of around 10 ms for every reflection, floor and ceiling included, in bigger room perhaps even up to 20 ms but with very high ceiling, a really big room
and 30 ms of delay is not realistically achievable at all

I understand that with CD speakers like Summa or AI-Audio something different is achieved - the level of reflected sound is lowered, reflections are as if they were filtered with a low pass filter
and with the positioning I proposed the reflections are not filtered nor lowered in level but delayed by around 10 ms or more

are the effects comparable? can this two approaches be regarded as equivalent alternatives? like in time/intensity trading?

can we just choose a solution best suited to our rooms acoustics or dťcor?

who knows?
I donít know
but why not? it makes sense

best,
graaf
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Old 11th May 2008, 12:10 AM   #97
gedlee is offline gedlee  United States
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Graaf

I tried to go back and read your first post. It is not clear enough to me to agree or disagree, only that with omni-directional loudspeakers in a small room like that I would expect a whole lot of VER (< 10 ms.) coming from all over the place. You seem to "assume" otherwise. In my rooms I measure the impulse response so I KNOW that my VERs are very low. I think if you measure the rooms impulse response for your setup you will find that its not what you think it is.
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Old 11th May 2008, 08:31 AM   #98
graaf is offline graaf  Poland
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Quote:
Originally posted by gedlee
Graaf

I tried to go back and read your first post. It is not clear enough to me to agree or disagree, only that with omni-directional loudspeakers in a small room like that I would expect a whole lot of VER (< 10 ms.) coming from all over the place. You seem to "assume" otherwise.
I donít "assume" otherwise
I just did some simple calculations, perhaps to simple, I donít know
I drew the sound path lines, calculated them and then I calculated the delays. The only assumptions I made is that "the speed of sound = 344m/s"
and also that "angle of incidence = angle of reflection"
two assumptions
I have found similar way of reasoning and same assumptions in Harold Beveridge brochure (see image attached):

Quote:
Now let's look carefully at figures 20 & 21. The direct path of energy from speaker to listener is obvious and there are no near images.
Three important points need to be made. First, these full frequency range reflections are identical in form to the direct path sound. Second, they are nearly as intense as the direct path. Third, the delay in these paths is easily made large enough to avoid confusion and the ear accepts them as normal room reflection. This adds spaciousness and depth to the sound.
In stereo, an exact and precise "image" of the orchestra is desired: violins on the left, cello and bass on the right, and so on. Such an image is best produced when at least 10 milliseconds of the first-arrival energy is delivered to the listener with no overlap of sound from image speakers to produce confusion.
180 degree cylindrical wave speakers meet this criterion. No near reflection paths are present and no near image speakers appear. All four image speakers are far enough away from the primary speakers for a clear and unencumbered packet of first-arrival energy to be perceived. A precise stereo image is formed.
see: http://www.bevaudio.com/White_Paper.htm

is anything wrong with that reasonig? the law of reflection does not apply in this case? I don't know - I assume that it applies
Is this assumption wrong?

best,
graaf
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Old 11th May 2008, 09:08 AM   #99
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Thank you Graaf for your answer and thank you Earl for completing

I have been listening to some music with my LS lying along the side walls of my living room. There are things I do like and things I like less with this set up. (My LS are FE167E Fostexes in a double BR box)
1) the WAF is bigger! my girlfriend said it was much better looking since the LS almost disappeared instead of being in the "middle" of the room.
2) the bass output is much stronger. This is due to the fact that the LS is much closer to 2 surfaces: the floor and the side wall. Nevertheless I can now locate where the bass is coming from what I couldn't do before. It is not pin point localisation but still!
3) I am not sure if the room disappeared but I can say that there is a feeling of space that I did not have before. For example, with a recording made in a church, the church has become much bigger than before.
4) I will tend to say that I have a more 3D feeling but I lost some depth, that for sure! the 3D feeling might come from the LS positioning but as well from the fact that I don't see the drivers any more (they are hidden from my view by two couches that are facing each other along the side walls).
5) this one seems a bit contradictory to me and it is kind of hard to explain: I have deeper silences between the notes but it doesn't sound as clear as with the drivers facing me. The "deeper silences" thing comes from the fact that I can now hear some noises from the CD player while listening to music! About the clear sound: I have the feeling that I am much far away from the musicians than before. This is maybe linked to the lake of treble I feel with this set up...
6) The sweet spot has grown for a tiny little spot to an area!

Conclusion: I like it very much so far and I will keep it like that for a while to see what it does to me in the long run. It makes me realise how much the reverberations pollute, distort the music. Bass speaker in a corner is very good as well (as long as it is not dipole bass!) I will certainly take all these experiences into account for the building of my next pair of speakers.

It also makes me realise that I am missing quite some knowledge about psychoacoustics. Any good book you recommend there? I checked Earl 's book but I wish something covering the topic in some more depths.

I am very interested by the question you lifted up whether the early reflexions should be delayed over 10ms or if they should be lowered in intensity (by means of absorption and/or diffusion).

Regards,
Etienne
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Old 11th May 2008, 09:45 AM   #100
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Quote:
Originally posted by graaf

...
The only assumptions I made is that "the speed of sound = 344m/s"
and also that "angle of incidence = angle of reflection"
...
best,
graaf
344m/s is OK for the speed of sound in the air at 20ļC at see level!
click this link if you need to discuss that in details.

More seriously: your second assumption is not always true. It is not true for the lower frequencies were ray theory can not be applied any more, wave theory has to be applied.
Where does this transition take place is the obvious next question!
First this transition does not take place at one unique frequency below which wave theory applies and above which ray theory applies. The transition takes place over 2 octaves during which both ray and wave theories rule.
The frequency where it starts (= the frequency below which wave theory can be applied without doubt) depends on the volume of your room and the absorption properties of the room. It follows the following formula:
F2=11250*SQRT(RT60/V) RT60 being the reverberation time in seconds and V being the volume of the room in cubic feet.
This formula yields F2=180Hz for a room of 63 m3 (25 m2 by 2,5 m which is more or less you room, if i remember well...) with a RT60 of 0,5 seconds.
The other frequency (the one above which ray acoustics can be applied without doubt) is 4 times the previous one.
This yields F3=720Hz for the same room as before.
All this comes from the Master Handbook of Acoustics by Alton Everest, page 324.

From that I can say that the assumption "angle of incidence = angle of reflection" is true from the highest frequencies down to F3, is less and less true from F3 to F2 and is unappropriated below F2.

Regards,
Etienne
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