Self Adaptive Speaker System for Automotive Sound 2000-01-0074
The sound quality of current automobile audio systems differs under static and dynamic conditions. Under dynamic conditions, road noise imparts a masking effect on the low frequency range of the sounds being reproduced. In “The New-AFB system”  and “the NEW-AFB Automotive sound system”  reported to the SAE in 1995 and 1996 respectively, the Acoustic Feedback (AFB) system was discussed as a new playback system capable of correcting the transient characteristics of the speaker and overcoming the masking effect.
The AFB system has been improved and a new playback system developed that uses vehicle road noise as a sound control signal.
In this new system, an additional external microphone is added, which in conjunction with the normal AFB microphone allows the low frequency road noise component of the monitored sound to be extracted. The output level of the audio system is adjusted in response to the level of the degradation of the signal to noise (S/N) ratio caused by this low frequency road noise. The resulting adjustment in response to S/N degradation and road noise levels is made to be equivalent at the listener’s head position. This signal is then compared to the input signal without any road noise, and the system compensates for the shortage of low frequency content based on this differential.
The application of this system allows the low frequency masking effect to be eliminated, making ideal sound reproduction possible under dynamic vehicle conditions.