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

[Philipp]

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?

Regards,
Philipp