Quote:
Originally posted by Kevin C Brown:
I noodled this some more, and it still makes no sense. Even with dual rears, except for THX Ultra2 and Logic 7 sound fields, all you're doing is replicating a mono signal into 2 speakers. OK. In that case, where does the "image" appear? 1/2 in between the 2 rears, or directly behind you.
The image doesn't appear directly at the back of your head, but you get a sense of it being behind you. Our hearing is not as acute behind us as it is in front of us; that is why there's no problem with a single centre speaker in the front. Using two rear speakers is a good idea, whether they're both playing the same (mono) signal or not.

The problem, really, is that we judge direction horizontal direction based mostly on inter aural time delays; the time it takes a sound to reach one ear vs the opposite ear. When we hear the same sound in both ears (at the same time with the same intensity) we know that the sound is somewhere along our centre line. We can usually tell if it's coming from in front of us or behind us; but not always. This has been demonstrated plenty of times by acoustic researchers.

I've heard this phenomenon myself a couple of times. The last time, ironically, was on a THX Ultra 2 system. A test tone was being played that circled the room; as it went from the side speaker to the rear speakers, the sound momentarily jumped to the front before recovering to the rear. When I looked behind me, I was surprised to see the rear speakers sitting a mere six inches apart (I wasn't aware of Ultra 2 at the time). Spreading the speakers out a few feet really did help get rid of the problem.
Quote:
Originally posted by charlie:
First I have to say I don't completely buy into this front/rear confusion thing.
Fair enough; no need to take my word for it. And keep in mind, I'm not telling anyone not to have a single rear speaker; just informing them of possible problems with that configuration. Meanwhile, here are links to some published information that discuss this phenomenon. While some of these technical papers aren't really all that "technical", they're still a chore to read. Instead, when you're on the page, use the search function to look for the word "reversal". This will allow you to read the relevant passages and skip the boring stuff.

http://www.cyberus.ca/~karen/spatial/readme.txt

http://www.alumni.caltech.edu/~franko/thesis/Chapter4.html

http://www.hitl.washington.edu/publications/hollander/7.html

http://www.auditory.org/postings/2000/20.html

http://216.239.51.100/search?q=cache:tZjU5lJJVMwC:www.khri.med.umich.edu/research/middlebrooks_lab/ewan/icad94/macp_icad.pdf+front-back+reversals&hl=en&ie=UTF-8

Best,
Sanjay
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Sanjay