17 Jun
2011
17 Jun
'11
10:58 a.m.
Excerpts from Fons Adriaensen's message of 2011-06-16 22:35:10 +0200:
On Thu, Jun 16, 2011 at 10:11:25PM +0200, Philipp
wrote:
After a little off-list discussion with Gabriel and refreshing my basic
trigonometry a bit I understand your formula, but I still have no idea
what it tells us. The main problem might be that I have no idea how
velocity vectors relate to sound and what the decreasing magnitude tells
us.
Regards,
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?
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,