Path: utzoo!utgpu!attcan!uunet!lll-winken!ames!mailrus!uflorida!gatech!itm!brent
From: brent@itm.UUCP (Brent)
Newsgroups: comp.graphics
Subject: Re: Sound tracing
Summary: It's not that easy
Keywords: sound tracing, accoustics
Message-ID: <1256@itm.UUCP>
Date: 6 Jan 89 21:30:49 GMT
References: <241@raunvis.UUCP>
Reply-To: brent@itm.UUCP (Brent)
Organization: In Touch Ministries, Atlanta, GA
Lines: 38


    Ok, here's some starting points:  check out the work of
M. Schroeder at the Gottingen. (Barbarian keybord has no umlauts!)
Also see the recent design work on the Orange County Civic Auditorium
and the concert hall in New Zealand.  These should get you going in
the right direction.  Dr. Schroeder laid the theoretical work and
others ran with it.  As far as sound ray tracing and computer
acoustics being centuries behind, I doubt it.  Dr. S. has done things
like record music in stereo in concert halls, digitized it, set up
playback equipment in an anechoic chamber (bldg 15 at Murry Hill),
measured the path from the right speaker to the left ear, and from
the left speaker to the right ear, digitized the music and did FFTs
to take out the "crossover paths" he measured.  Then the music played
back sounded just like it did in the concert hall.  All this was done
over a decade ago.

    Also on acoustic ray tracing: sound is much "nastier" to figure
than pencil-rays of light.  One must also consider the phase of the
sound, and the specific acoustic impedence of the reflecting surfaces.
Thus each reflection introduces a phase shift as well as direction
and magnitude changes.  I haven't seen too many optical ray-tracers
worrying about interference and phase shift due to reflecting surfaces.
Plus you have to enter vast world of phychoacoustics, or how the
ear hears sound.  In designing auditoria one must consider "binaural
dissimilarity" (Orange County) and the much-debated "auditory backward
inhibition" (see the Lincoln Center re-designs).  Resonance?? how many
optical chambers resonate? (outside lasers?)  All in all, modern
acoustic simulations bear much more resemblance to Quantum Mechanic
"particle in the concert hall" type calculations than to simple
ray-traced optics.

    Postscript: eye-to-source optical ray tracing is a restatement
of Rayleigh's "reciprocity principle of sound" of about a century ago.
Acoustitions have been using it for at least that long.

        happy listening,

                brent laminack (gatech!itm!brent)