Low Frequency Design Considerations for Automotive Audio Systems

The automobile interior is a challenging environment for the audio system designer. Yet, the literature related to automotive acoustics is sparse compared to the amount of published information on the acoustics of rooms and performance spaces. This paper addresses three areas of importance to the design of high fidelity autosound systems. First, it is difficult to accurately predict the nature of the listening acoustics in a car at low frequencies because complex interior geometries make mode calculations almost impossible. At the same time, the cabin interior introduces acoustic gain in the first three octaves of musical reproduction. Secondly, the car environment is subject to constantly changing levels of so-called road noise that mask musical material at low frequencies. Finally, a simplified model is proposed for the characterization of the car door as a loudspeaker enclosure. Measurement data are presented to illustrate the nature of low frequency gain in automobile cabins and to evaluate the feasibility of the proposed enclosure model.