Development of Sound Localization Control System for Car Stereo

In a two-loudspeaker stereophonic reproduction system of a passenger car, the geometrical configuration of the right and left loudspeakers has the disadvantage of being asymmetrical to the listener. For this system, we have made both theoretical and experimental verifications of the effects of strongly reflected sounds on the sound pressure level difference and phase difference between two ears which determine the location of sound image in a small compartment of a passenger car. On the basis of these verifications, we have developed a new sound localization control system. With this system, acoustical effects such as sound expansion and ambience have been greatly improved in a passenger car. In this system, input signals to the loudspeakers are controlled so that the sound image produced by the loudspeaker nearer to the listeners may acoustically move so as to position itself symmetrically with the other loudspeaker with regard to the listeners.

The corner-mounted loudspeaker and the sound localization control circuit constitute the distinctive features of this system. The corner-mounted loudspeaker suppresses strongly reflected sounds, which are characteristic of the sound fields in a passenger car, and improves the definiteness of acoustical sound localization. The corner-mounted loudspeakers are installed toward the corners of the intersections of the instrument-panel near the right and left doors so that the directivity axis of loudspeakers makes an equal angle of 45 degrees with the two vertical planes passing through the instrument-panel and each door. The sound localization control circuit consists of an inverter, a pre-amplifier and a delay circuit unit. This control circuit is connected to the power amplifier output stage of a conventional audio components. With this circuitry, acoustical effects such as sound expansion and ambience are greatly improved.