Abstract: A sound field correcting system for correcting for multipath frequency-characteristic distortion in an acoustic reproducing system. In one embodiment, the level and delay of an original signal are adjusted and superposed on the original signal so as to obtain a signal which, when reproduced by a loudspeaker, yields a sound pattern at a listening point having a flat frequency characteristic. The delay adjustment is effected in accordance with a difference between the travel distances of direct and reflected sound waves to the listening point.

Abstract: An automatic sound volume device which adjusts the volume of an audio signal in a vehicle to compensate for vehicle noise. A time constant circuit smooths the level output of a microphone to smooth the volume variations. However, the time constant is long for increases in noise but short for decreases in noise.

Abstract: A sound field correcting device for use in a stereophonic system intended for vehicular use. Speakers are installed on opposite sides of both the front and rear seats of the vehicle. The number of persons seated in the vehicle is determined and applied to a correcting unit. When plural persons are seated in the vehicle, the sound pressure levels in the high-frequency range of loudspeakers is increased. Also, the sound pressure levels of the speakers can be corrected in accordance with the positions at which persons are seated in the vehicle.

Abstract: An automatic gain control unit particularly adapted for vehicular use is disclosed. The ambient noise level inside the vehicle is detected, as is the level of the audio signal. A difference is formed between detection signals thus produced, and a frequency characteristic of a gain varying device, inserted in an audio signal path of the audio device, is varied according to this difference.

Abstract: A mobile sound field correcting system for correcting an acoustic characteristic in a vehicle sound field formed by direct waves radiated from loudspeakers and reflected waves thereof providing satisfactory acoustic characteristics for different vehicles and different listening points within a vehicle. A first correcting means corrects a power spectrum of each loudspeaker in a frequency range above a frequency at which a decrease of starts of the power spectrum in a high-frequency range of each loudspeaker. Second correcting means corrects for irregularities in the frequency characteristic of each loudspeaker caused by interference of the direct waves with the reflected waves in a frequency lower than the drop-off frequency of this power spectrum.