A Study in non-linear seat shaker processors for enhanced integration with full range audio systems

Abstract

This MSc Thesis studies the integration of non-linear seat shaker processors in a full-range audio system, applied in the car environment. The thesis is conducted on behalf of the Research and Development Department of Premium Sound Solutions. The loudspeaker company wants to know more about the scientific implementation and research behind seat shaker processors in cars. Studies have been done on the subjective and objective influence of low-frequency sources, namely subwoofers, on persons. Fewer studies have been done on the haptics and body reaction of lowfrequency vibrational sound sources in a car environment. The transmission of low frequencies in a car has a different modal directivity. The signal affects both the auditory parts with the ear drums as the sensed parts in the rest of the body. It is found that the auditory spectrum has an influence on the perceived vibrations. Therefore a first experiment is done to retrieve subjective data for the influence of the low-frequency sound source on the body. The data is used to define the shaker positioning with the corresponding threshold of feeling. Secondly, the vibration acceleration levels are measured using accelerometers to retrieve the objective data. Using that objective data, the excited acceleration levels are matched with those of the subwoofer. A second listening experiment is done in the form of an A/B listening test. The interviewees are asked to quantify the difference of the perceived acceleration between the subwoofer setup and the shaker implementation. The subwoofer experiment showed that the threshold of sensing the vibrations in the body is frequency-dependent. It is also found that vibrations are sensed in different body parts. The excited body parts are also frequency dependent. The results of the A/B experiment, where both sound pressure levels and acceleration levels are matched, show that objective measurements and level matching have the potential to be used as a tuning method. However the quality and implementation of the used method can be improved