  We propose a straightforward and cost-effective method to perform diffuse
soundfield measurements for calibrating the magnitude response of a microphone
array. Typically, such calibration is performed in a diffuse soundfield created
in reverberation chambers, an expensive and time-consuming process. A method is
proposed for obtaining diffuse field measurements in untreated environments.
First, a closed-form expression for the spatial correlation of a wideband
signal in a diffuse field is derived. Next, we describe a practical procedure
for obtaining the diffuse field response of a microphone array in the presence
of a non-diffuse soundfield by the introduction of random perturbations in the
microphone location. Experimental spatial correlation data obtained is compared
with the theoretical model, confirming that it is possible to obtain diffuse
field measurements in untreated environments with relatively few loudspeakers.
A 30 second test signal played from 4-8 loudspeakers is shown to be sufficient
in obtaining a diffuse field measurement using the proposed method. An
Eigenmike is then successfully calibrated at two different geographical
locations.
