## 3aEA4. Static pressure and temperature coefficients of laboratory standard microphones.

### Session: Wednesday Morning, December 4

### Time: 8:50

**Author: Knud Rasmussen**

**Location: Dept. of Acoust. Technol., Tech. Univ. of Denmark, DK 2800 Lyngby, Denmark**

**Abstract:**

The sensitivity of condenser measurement microphones depends on the
environmental conditions due to the changes in the acoustic properties of the
enclosed air between diaphragm and backelectrode and in the cavity behind the
backelectrode. A theoretical investigation has been performed based on an
extended lumped parameter representation of the mechanical and acoustical
elements of the microphone, assuming the velocity distribution of the diaphragm
to follow the zero-order Bessel function. The extension involves the frequency
dependency of the dynamic diaphragm mass and stiffness as well as a first-order
approximation of resonances in the back cavity. It was found that each of the
coefficients, for a given type of microphone, can be expressed by a single
function when the coefficients are normalized by their low-frequency value and
the frequency axis normalized by the individual resonance frequency of the
microphone. The static pressure and temperature coefficients were determined
experimentally for about 20 samples of type BK 4160 and BK 4180 microphones. The
results agree almost perfectly with the predictions for BK 4160, while some
modifications of the lumped parameter values are called for to make the results
for BK 4180 fit the predicted values.

ASA 132nd meeting - Hawaii, December 1996