## 3aEA6. Image-derived second-order differential microphone on a finite baffle.

### Session: Wednesday Morning, May 15

### Time: 10:20

**Author: Gary W. Elko**

**Location: Bell Labs., Lucent Technologies, 600 Mountain Ave., Murray Hill, NJ 07974**

**Abstract:**

A single first-order dipole microphone placed close to a reflecting plane
results in a unidirectional second-order differential microphone. In practice an
infinite reflecting plane is not attainable and it is therefore of interest to
examine the effects of using a finite reflecting surface on second-order
image-derived microphones. This talk will present results obtained in the
investigation of a finite reflecting surface size by using the solution to the
wave equation for scattering and diffraction from an oblate spheroid. The
particular solution that is investigated is for the case of an infinitesimally
thin oblate spheroid, the disk. Results show that the response of a first-order
bidirectional sensor over the disk is sensitive to sensor location as well as to
disk size relative to the acoustic wavelength. For a centrally located
image-derived second-order microphone, the differential sensor response
approaches a second-order response at a frequency where the reflecting baffle
size is at least one-half the acoustic wavelength. Experimental results for both
circular and rectangular baffle geometries will also be shown.

from ASA 131st Meeting, Indianapolis, May 1996