May be I can give it a go:
Imagine two speakers with identical response placed in a stereo config in an anechoic chamber. If you produce a sound through both of them at the same time and it arrives at both the ears at the same time, there is no way for the brain to identify the distance between the ears and the source of the sound. The phantom image has to form between the ears. It would be the same if you placed the speakers at 20 feet from your ears or 10 feet from your ears.
Only when there are reflections can the distance between the phantom source and the ears/head be identified.
Imagine two speakers with identical response placed in a stereo config in an anechoic chamber. If you produce a sound through both of them at the same time and it arrives at both the ears at the same time, there is no way for the brain to identify the distance between the ears and the source of the sound. The phantom image has to form between the ears. It would be the same if you placed the speakers at 20 feet from your ears or 10 feet from your ears.
Only when there are reflections can the distance between the phantom source and the ears/head be identified.
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I've been in an anechoic chamber (chamber is bit of a misnomer here as it was only slightly smaller than a basketball court) but there were no stereo speakers set up.
On the other hand the explanation would imply that it should be difficult or impossible to judge the distance of a sound source and that is certainly not the case.
It would also imply that using stereo speakers outdoors should give a similar result and that is equally not true.
On the other hand the explanation would imply that it should be difficult or impossible to judge the distance of a sound source and that is certainly not the case.
It would also imply that using stereo speakers outdoors should give a similar result and that is equally not true.
The phenomenon of phantom images almost never happens in nature. Linkwitz gives the funny example of two lions roaring in front of you and your brain thinking there is only one lion in the center. It never happens. Even if there are two lions, their roar is going to be different.
But judging the distance of a source, a real source, is easy for the brain because there is only one source and two ears. By knowing the difference in arrival time between the ears, the brain can locate the source.
Outdoors there is always floor bounce. No reflections at all is really a hypothetical case and an anechoic chamber may get close. It really is not hard to imagine why a phantom image without reflections would form between the ears and not anywhere else. It would also probably require that the pinnae of your two ears are identically shaped. Although, I don't know if that is required or not.
Lotsa wild speculation here and I'll add a bit to it.
Your brain does no small amount of image processing in order to "sharpen" the sound image - you can view this as the familiar hifi experience of "learning the room" over a few minutes (or so) and that makes the speakers a whole lot clearer.
But you are learning the room (and how to hear the speakers), not learning the source. In fact, there is no way to "learn" the source which is cooked up by mysterious process (even when done under the illusion the engineer at Sheffield is using purist recording techniques).
The less the room reflections add to this confusion, the easier it is to make sense of the speakers and, hopefully, the source the engineer put on the recording.
Your brain does no small amount of image processing in order to "sharpen" the sound image - you can view this as the familiar hifi experience of "learning the room" over a few minutes (or so) and that makes the speakers a whole lot clearer.
But you are learning the room (and how to hear the speakers), not learning the source. In fact, there is no way to "learn" the source which is cooked up by mysterious process (even when done under the illusion the engineer at Sheffield is using purist recording techniques).
The less the room reflections add to this confusion, the easier it is to make sense of the speakers and, hopefully, the source the engineer put on the recording.
Yeah, the Greeks and Romans really new what there were doing with theater acoustics. Some amazing work going on in the classic era. Some real early audio design, there.
Off the south coast of Maui there is the little island of Molikini (see photo below). Shaped like an amphitheater it does a great job of focusing sound above and below the water. Get in the right spot under water and you can hear what sounds like every whale in the bay. 🙂
I would agree with you Dave. Having heard and even slept in that room. It's a good place for listening. The odd shape, the ample break-up and perhaps the generous number of "feline absorbers" all help. Gary Pimm also has a lot of hard surfaces in his living room, but the acoustics are quite good. JB Speakerman has managed to get good acoustics in his garage, mostly my filling it up with stuff. Being able to remove one of the walls (open garage door) is a neat trick, too.
My garage listening room started out with good acoustics, then I renovated and ruined them. Awful! But some big DIY acoustic panels are really helping now. Went from unlistenable to unleavable. A good change.
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Dan
Dan
ra7,
you need to listen more carefully 😉. SL was talking of tigers, not lions.😛
Same for the "reflections". SL was talking about a situation, when your head was totally fixed in front of two speakers and you were listening to a monaural phantom signal. No way to move or turn your head the slightest way. Yes, in such a situation you would not be able to determine the distance of the source. In fact, even an added "reflection" signal would not change that.
Probably you will want to listen to his BAF presentation once more.
Thanks Rudolf! Yes, I found that link too... was going to listen to it this evening. And yes, I was assuming all those things which I should've stated.
The point was reflections are healthy and natural and are needed in stereo, unlike, some of the opinions here that urge the complete removal of reflections.
The point was reflections are healthy and natural and are needed in stereo, unlike, some of the opinions here that urge the complete removal of reflections.
Why are you so pessimistic about what the brain can do? Did you never listen to an instrument (or orchestra or ...) and no longer realized the "machine" and it's "operator", but only the stream of music?
Our brain WANTS to buy the stereo illusion. It will happily listen "through" the speakers as it listens "through" the room. But it will do that only, if it can "understand" the loudspeakers as part of the room.
We can help the brain in "understanding" by achieving three goals. Linkwitz has listed them in his BAF presentation:
- On-axis: Flat response
- Off-axis:Frequency independant at every angle
•acoustically small
•point source
- Room: Flat reverberation
Whereby "flat" is not meant as a ruler on a diagram, but "for the ear as true to the source as possible".
The room reflections will be confusing to the brain, if they are
- missing, where the brain would expect them (too much "deadening")
- distorted, because of not constant directivity, frequency dependant absorption or time-smearing diffusion.
Rudolf
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For a full reproduction of a recording, I would think that one would want the minimum amount of secondary contributions.
Frankly, I believe the most perfect reproduction of music, etc., is with Binaural recordings played back through enclosed headphones. While I may get reflections inside my head, you won't and I believe that you may agree that the HP's don't have much, if any, reflection patterns associated with them.
Best Regards,
TerryO
I thought the big problem with headphone sound (inside the head) was that you can't turn your head and resolve whether the source is in front of or behind you. It seems like there wouldn't be a problem with that in an anechoic chamber. I certainly remember that you can easily tell where sound comes from in a chamber. when people talk you have a strange sense of "sound coming from a hole in their face" meaning a very tight sound source.
If you can localize a left speaker in a chamber, and a right speaker, I don't know why a virtual source wouldn't come from between the two real sources.
That said, as much time as I've spent in anechoic chambers I never sat and listened to stereo in one.
David S.
SpeakerDave
If you get the chance to listen to Stereo in an Anechoic chamber you should see if you can bring in a few diffusers to add some ambiance. Wonder what a fully treated room + good diffusing would sound like (Heavenly I assume).
Jr,
If you get the chance to listen to Stereo in an Anechoic chamber you should see if you can bring in a few diffusers to add some ambiance. Wonder what a fully treated room + good diffusing would sound like (Heavenly I assume).
Jr,
TerryO,
I am not into "the most perfect reproduction of music". My goal is more sinister.
Headphones don't cut it for me in that respect. 😛
Do headphones give you the dopa?
Rudolf
I haven't done that but I've kind of done the opposite.
I was listening to stereo in a normal room and had a helper, standing behind, raise and lower two rather large sections of fiberglass absorption about a foot or two either side of my head. (the pieces were about 2 ft by 3 ft) When lowered the absorbers would by no means block any of the direct sound from the speakers, but would pretty well absorb any of the side wall reflections.
Although side wall reflections hadn't been obvious, there was a distinct difference in sound quality when they were blocked. Sound took on a more dead, artificial or headphone (but narrower) quality. The stereo image shrank somewhat.
Very interesting.
David S
Dave,
When a mono sound is played through two speakers in a normal room, left and right speakers disappear. Same way, in the anechoic chamber the left and right speaker would disappear. Without reflections and by fixing the head in one position, the phantom image of a mono signal should form in the head.
I agree that if you shake your head, the image should fall back between the speakers.
One source for the SL quote might be here:
http://www.linkwitzlab.com/Recording/precis-reproduction-c.doc
"...For a loudspeaker the most important parameters are its on-axis frequency response and output volume capability. Usually overlooked is the polar response, yet it defines how the loudspeaker interacts with the room. The solo female voice halfway between two loudspeakers is an auditory illusion where little sound actually arrives from the central direction. But when played back in an anechoic chamber or over headphones the same voice is likely to be located between the ears and inside the head..."
I've heard the SVS Realizer which "reproduces" loudspeaker&room in headphones with personal HRTF and head angle tracking
SVS Technology
quite convincing on a short listen in the demo room with 5.1 source material - and you do need loudspeakers and room to do the "personalization" - but only for ~1/2 hr - some people have mastering studio "personal calibrations"
SVS Technology
quite convincing on a short listen in the demo room with 5.1 source material - and you do need loudspeakers and room to do the "personalization" - but only for ~1/2 hr - some people have mastering studio "personal calibrations"
Thanks for finding that bolserst.
I was sitting in the front row at BAF and was listening intently to SL's every word. Good to know that I wasn't halucinating. 🙂
This argument is silly.
There was some older literature, that indicated that under some very constrained conditions (in an anechoic chamber) the sense of externalization was reduced with 1) very narrow band signals, 2) short durations and 3) no head movements.
I would not place too much weight on those demonstrations. At some point, you may want to get a better understanding about what is meant by "phantom image" at a more technical level. One place to start is a pair of papers in JASA by Ben Bauer (1960s-1970s IIRC). The other is by Plenge (which is the source of the demos I mentioned above & I forget the references).
BTW, the issue of "externalization" of a sound image is a bit difficult to describe and measure when you get into these funny configurations.
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