Reduction of Comb-Filter Effects by Alternating Measurement Orientations in Automotive Environments

Loudspeakers in car cabins often are installed in positions primarily regarding design aspects. Acoustical aspects are mostly subordinate. For this reason loudspeakers frequently radiate against a window, the dashboard or the rear shelf, also a radiation to the floor room is common. Acoustical reflections at short distances causing interferences of direct and reflected sounds are the main reason for comb-filter effects at the listening position. For the measurements in this work two stimuli were used: a pseudorandom pink noise, recursively averaged over 15 seconds, when the measurement position was changed, and a sine sweep when the position was fixed during the measurement process. Both, microphone movements and head movements, lead to a robust averaging of the measured magnitude response, reducing significantly both the variations in the response and the comb-filter effects in the car cabin. Frequency responses measured by the process described here require less filtering effort to equalize the loudspeakers in the car cabin.