microphone placement question

[Chris Clark <>]

Dear Bioacoustics-l,

I'm designing an experimental setup to measure sounds from feathers placed in a wind tunnel.  In my searches of the aeroacoustic / acoustic engineering / bioacoustics literature so far, I have not been able to find a discussion on the placement of a microphone relative to the sound source, with respect to near field and far-field effects.  In particular, my setup has high levels of background sound, and I'm constrained to place the microphone <30 cm from the source, which I think for low frequency sounds (<1kHz), means it will be in the near-field.  As a part of this, I'm trying to find a reference that (quantitatively) discusses the near-field far-field "boundary", along with how this might vary with different types of sound sources (point sources, extended sources, etc).  My hope is to compare SPL from different feathers, with the hope that these measurements being hopelessly confounded by differences in frequency.

Many thanks in advance for suggestions or suggested reading.  

Regards,
-- 
Christopher J. Clark, Ph.D.
Gaylord Donnelley Environmental Postdoctoral Associate, Prum Lab
Yale Institute of Biospheric Studies (YIBS)
Department of Ecology and Evolutionary Biology
P.O. Box 208106
165 Prospect Street
New Haven, Connecticut 06520-8106  



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