Apple Impulse Response Utility - Manual (Page 26)

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The Virtual Echo Chamber Approach
A good alternative to the auralization approach is placement of your speakers and
microphones in a way that creates a virtual space which resembles a physical echo
chamber. To create this kind of impulse response, face the loudspeakers towards the
corners, and the microphones towards the opposite corners. This is how microphones
in a physical echo chamber would be placed. This eliminates a direct path from the
speaker to the microphone, and captures more reflections. The image below illustrates
how you could set up two speakers and two microphones to create a stereo impulse
response, using this virtual echo chamber approach.
This way you can mix the reverb into the dry signal, without any phase cancellation
issues caused by early reflections or direct signals. This approach works particularly well
if you want to keep your signal mostly dry, without any alteration or coloration from
the reverb, but still want to add a high fidelity reverb tail to your audio.
You can also use this method for surround or multi-channel reverbs. The main concept
to remember is that the speakers should be pointing at the wall, to eliminate direct
paths between microphones and speakers. The illustration below offers a possible
layout for a five channel reverb chamber. The loudspeakers, placed in a circle, are
directed at the walls, and the microphone array is in the center of the circle.
L R
Surround
microphone
tree
C
R L
Rs Ls