Re: [LAU] ambisonics and number of speakers

On Sun, Feb 28, 2010 at 02:21:08PM +0100, Jörn Nettingsmeier wrote: Have a look at the Bessel functions (either spherical or cylindrical, they are different but similar). The degree N Bessel function determines how much an order N component contributes to the pressure field, in function of distance from the reference point (= the sweet spot). The argument is 2 * pi * distance / wavelenght. With some imagination you'll see that for each distance their is a set of orders that dominate the reconstruction. If these harmonics are missing then field reconstruction at that distance will be impaired. As an extreme case, just imagine that all harmonics except the zero and first order ones are absent, as would be the case for first order reproduction with a very large number of speakers. So the field is reconstructed according to the J0 and J1 functions only, and it decays rapidly as you move away from the reference point. In fact this would be some form of focussing on the sweet spot. The 'area of reconstruction' is the one were field reconstruction is dominated by those harmonics that are reproduced exactly rather than aliased. Its radius is expressed in wavelengths, so for all except LF, at least one of your ears it out of it. At real HF this doesn't matter so much, at least not if you have the usual random distance errors. But there is a mid frequency range where the effect of incorrect field reconstruction can be very marked. Ciao, -- FA O tu, che porte, correndo si ? E guerra e morte !