Performance Study of an Automotive Fresh Air Subwoofer

Abstract

Today’s automotive audio systems have to meet high quality expectations with ever-decreasing development costs. Methods to predict the performance of sound systems in view of the optimal locations of loudspeakers, loudspeaker enclosure volume dimension and tuning to get the best audio in a car can help to overcome this challenge. Automotive audio system involves subwoofers to produce low frequency sound waves,and that possesses space constraints and the ability to produce sound wave of frequency below 50Hz. To increase the lower frequency sound production range and to reduce the space requirements, fresh air subwoofer concept has been introduced.
A fresh airsubwoofer enclosure is exposed to outside atmosphere through port the reby giving almost an infinite volume. The enclosure and the port acts as a Helmholtz Resonator.This article describes performance study of a fresh air subwoofer in an automotive sound system. It involves study of Thiele and small parameters of loudspeaker and other parameters affecting the fresh air subwoofer (FAS) fitted to the car body structure. The work involves development of response equations for performance parameters of FAS by circuit analysis of FAS analogous circuit and also developing a MATLAB® Graphic User interface (GUI) for calculating Thiele and small parameters of FAS. COMSOL Multiphysics ®software is further used to predict the Sound Pressure Level (SPL), Loudspeaker Impedance and Diaphragm Excursion of fresh air subwoofer attached to a car cabin. The results from the MATLAB® GUI are then compared with the FEM simulation results wherein the enclosure and port of a FAS are modeledin detail.