Mikrofonverhalten in kleinen Räumen am Beispiel eines Freisprechmikrofones im PKW

The diploma thesis is locked till march 2015.

The characteristics of hands-free microphones, mounted in the interior of a car, are investigated in cooperation with the company AKG ACOUSTICS.

Besides the continuous development of more efficient power train engineering, motor vehicle manufacturers put great effort in the design of entertainment electronics inside the Car-Cabin. These In-Car entertainment systems are often combined with hands-free microphones, which are used for hands-free telephony as well as voice control of the electronic systems. For both applications, good speech intelligibility by the suppression of any ambient noise is eligible.

The critical issue for this task is the directivity of such hands-free microphones. In general, the directivity is determined by the measurement of a polar diagram under free-field like conditions in an anechoic room. However, due to sound reflecting planes like windows, there is good reason to doubt that such free-field conditions can be expected inside a car cabin.

In this work, it will be shown how the application in the car-cabin affects the directivity of a microphone. The examination will be made for different types of microphones and different alignments. If any distortion of the free-field measured directivity occurs, it will be due to reflections at sonically hard planes. For that reason, effort will be made to classify those reflexions – by acoustic measurements as well as a simple simulation.

Besides the observations regarding the microphones, the ambient noise in a car-cabin is examined, too. Good knowledge of its nature can be helpful for a proper rejection.