sound source localization - finding source vector This may sound a stupid question - but I am working on some simple microphone array beamforming sound source localization stuff.  I think I understand how to use beamforming to find the TOA of the sound source between 2 microphones (positioned, say on the x axis), and therefore how to find the angle, phi. If the source is positioned normal to the z axis then this makes theta (the azimuth) equal to pi/2. However how do I find the r coordinate of the source vector?  As I understand it , I cant localize the source without this coordinate.

Any help much appreciated, thanks in advance
In general, 2 microphones are not enough.  In 3 dimensions, you actually need 4 (non co-linear) for the 3 polar coordinates. 

There are cases where if you can bring more information to your problem, like knowing the signal of the source and the transmit and receive times of the signal, you can estimate the range for simple known geometries.  

A good reference is:

Strang, Gilbert, and Kai Borre. Linear algebra, geodesy, and GPS. Siam, 1997