[LAU] Where do the 60 degrees for stereo come from?

[Fons Adriaensen]

On Thu, Jun 16, 2011 at 10:11:25PM +0200, Philipp wrote:
> Hi there,
> in a discussion today someone asked me where those 60 degrees necessary
> for the production of phantom images come from and I couldn't deliver a
> satisfactory answer. Someone tried to explain to me that it has
> something to do with wavelengths or whatever but couldn't explain it in
> a way that anyone would understand.
> 
> My best guess is that with a larger angle the head gets in the way and
> the ears have an easier time telling the signals apart. Also, I guess 60
> degrees is a rough estimate and chosen because this leads to a nice
> Equilateral triangle.
> 
> So, what's the real reason behind those 60 degrees?

Just what you suggest: it leads to an equilateral triangle and
that *suggests* there is something fundamental about it. But as
far as I know there isn't. Another reason may be that +/- 30
degrees corresponds to the perspective of an average listener
in a concert hall - probably more than say +/- 45 degrees.

OTOH, a recording technique like e.g. Blumlein (two fig-8 mics
at 90 degrees) would suggest a speaker angle of 90 degrees
instead.

A wider angle will make near-center sources less stable. The
number that matters here is the magnitude of the velocity
vector which is cos(1/2 the angle): 0.866 for 60 degrees,
0.707 for 90 degrees, while for a 'real' source it would be 1.

Ciao,

-- 
FA