Peter L. Madaffari

Computation of the performance of an electret microphone diaphragm

An attempt was made to simulate the performance of a tensioned‐diaphragm, electret‐based, microphone. Use of commercial finite‐element analysis programs were unsuccessful because of the computational system used. An alternate method was developed using a relaxation approach. A third‐order equation for the balance of forces appeared to give approximate solutions for both tensioned and multiply supported diaphragms. Contours of physical deformation and acoustic compliance were generated and mapped. From these computations, an improved electret backplate and diaphragm system were designed.

A comparison of directional microphone performance in free field and on a manikin

Four first‐order gradient microphones were constructed. These microphones differed principally in their internal time delay, which formed a geometric progression for successive members differing by the ratio 4∛. The square of this ratio coincides with the ratio that provides the classical cardioid, super‐cardioid, and hyper‐cardioid polar patterns. It is also approximately the ratio between time delay as measured in a free field and over the ear of the KEMAR (KEMAR is a trademark of Knowles Electronics Inc.) manikin. Each microphone was measured in a simulated hearing‐aid housing which was modified to provided a series of external port spacings varying by this same ratio. A 4×4 matrix of internal delay versus external port spacing resulted. The polar pattern of each entry of the matrix was measured in isolation and over the manikins right ear. The progressive pattern change measured on the manikin is similar to that found in the free field, but offset approximately one matrix element.