Hello all, this is *really* offtopic but really you know more about
electrothings than the others so here is it..

I need/want to build a high directivity sound outdoors microphone, in a
fifty-fifty challenge/savemoney basis. I want to build it from two or three
electret mics (or four.. I really want to be able to pinpoint the noise
source), adding amplitudes on on-phase signals and rejecting out-of-phase
signals. The problem is.. where I could locate some info about op-amp
circuits and mechanical/lambda mic distance needed, or simply something
related to this subject?. I remember an elektor magazine issue of the last
year regarding this kind of device (where I picked the idea) but I do not
have that issue, and I do not have a easy way to get it.

As usual, thanks in advance and keep on PICing

Sebastian

PS: Only this time.. I think that analogic electronics are better. DSP's are
a bit far for me yet.