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With conventional automotive systems overall music sound quality depends on whether car is running or not. It is so because the low frequency component of the sound is masked by the road noise when running. To develop a system in which the sound is not easily masked by the road noise, we have paid attention to the difference between the speaker velocity changes (acceleration characteristics) due to the road noise and those of the music signal, and to the attack transient which is important to identify the timbre. The rise time response of the loudspeaker is a key factor for improvement, and conventional speakers have limitations in this regard. In 1995 the authors presented the New-AFB System1) in the SAE convention, which explained the technology and advantages of acoustic feedback in achieving flat sound pressure vs. frequency and enabling substantial improvement in response time of the speaker. Since then we have applied this to develop an optimum system for automobile use.

The acoustic feedback (AFB) system is to detect the acoustic signals radiated from a loudspeaker with a microphone, and feed them back to the previous stage of the amplifier. However, there were many problems to put it into practical use. A new AFB system has been developed, where the above problems are solved by setting the microphone at the optimum position and adopting a new feedback method. This was achieved by reviewing the loudspeaker performance from a new point of view. Thus, a wide-range feedback and the improvement in the speaker response have been obtained. Also, the problems of oscillation have been solved.