Pioneer Electronic Corporation

Akio Tokumo

Takeshi Sato

Masayuki Kato

Yoshiro Kunugi

Toshikazu Yoshimi

Yoshio Sasaki

Shinjiro Kato

Makoto Odaka

Tatsuzo Hasegawa

Shuichi Mori

Shinichi Suzuki

Hideo Yamamoto

Kazunori Takagi

Shuuichi Mori

A power amplifier apparatus having an operational amplifier which works as a PWM (pulse width modulation) amplifier as well as an analog amplifier according to an input signal level to miniaturize the size of the apparatus and to maintain amplifying function thereof at the changeover of the function, which allows gain and frequency characteristic of the operational amplifier to have continuity before and after the changeover. The power amplifier apparatus according to the present invention comprising: an operational amplifier having two input terminals, an input signal being inputted to one of the input terminals; a triangular waveform generator for outputting voltage with triangular waveform; an input signal level detecting circuit for applying the voltage with triangular waveform from the triangular waveform generator to the other input terminal of the operational amplifier; a broadband power amplifier for amplifying an output of the operational amplifier; and a low-pass filter connected to an output terminal of the broadband power amplifier.

Power amplifier apparatus

In an ALC circuit for automatically performing an amplitude compression control operation according to the output level of a low frequency amplifier circuit, the output level of the amplifier circuit is subjected to amplitude compression according to the level of a control signal which is outputted in correspondence to the output level of the amplifier circuit. The differentiation time constant of a differentiating circuit (or cutoff frequency of a high pass filter) provided on the output side of the amplifier circuit is controlled according to the level of the control signal to control the cutoff frequency for the frequency band subjected to amplitude compression.

Automatic level control circuit

A pulse-width modulating amplifier circuit includes two bootstrap circuits for increasing the power voltage to drive circuits to prevent a drive voltage shortage. One bootstrap circuit is connected from the output of the a power amplifier to a drive circuit. The other bootstrap circuit is connected from the output of a filter demodulator to a drive circuit.

Pulse-width modulating amplifier circuit

A sound field correcting system for correcting for mulitpath 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.

Sound field correction system

A balanced transformer-less pulse width modulation amplifier circuit has two filter coils wound on the same core with the same polarity relative to the output. The arrangement reduces the possibility of magnetic saturation of the core and permits the cutoff frequency to be within the audio range.

Pulse width modulation amplifier circuit

A pulse width modulation amplifier circuit pulse modulates a triangular carrier wave with an analog input, and the pulse width modulated signal is amplified and demodulated. To reduce radiated interference, the carrier is first frequency modulated by a random signal.

A pulse width modulation amplifier circuit includes a comparator which receives an analog signal and generates first and second analog signals having a phase difference of 180 degrees. A phase shifting circuit produces first and second triangular wave carrier signals so as to establish therebetween a phase difference of approximately 90 degrees. First and second pulse width modulation amplifiers, having output terminals connected to a load, pulse width modulate the first and second triangular wave carrier signals with said first and second analog signals, respectively, and amplify resultant pulse width signals.

A limiter circuit divides the output of a low frequency amplifier into two parts which are respectively high pass filtered, and low frequency amplitude limited. The two parts may be recombined to form an audio output which is freed from clipping distortion at the low end, while the high end is increased. The invention is especially suited for environments such as automobiles, where the ambient noise level may be high.

Limiter circuit

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.

The acoustic transmission characteristics of a sound field, such as in the passenger compartment of a vehicle, are measured by placing microphones at the positions of ears of a dummy mannequin having a sound absorbing characteristic similar to that of a clothed adult human. The transmission characteristics are then corrected, such as with an automatic graphic equalizer, to provide optimized listening conditions inside the sound field for an actual listener. The use of the invention results in a listener's perception of completely natural sound.

Method and apparatus for measuring and correcting acoustic

A headrest-mounted acoustic device including at least a speaker mounted on the right or left side of a headrest provided on a seat, a cover mounted in the sound radiating direction of the speaker, and a sound radiating portion communicating with a chamber provided behind the cover and having an area much smaller than that which is defined by the diameter of the speaker, so that sounds from the speaker are radiated from the sound radiating part through the chamber.

Headrest-mounted acoustic device

An automatic sound field correcting system with graphic equalizer means to be provided in an audio signal supply line. A test signal such as a pink noise is radiated in the listening space and detected at a predetermined listening point to determine the detection frequency characteristic of the test signal, thereby to adjust the frequency characteristic of the graphic equalizer means. Thereafter, the frequency characteristic of the graphic equalized means is made equal to different band-pass filter characteristics, one after another, and each time the equalization is effected, the detected test signal is obtained through the grapic equalizer means for determination of the detected frequency characteristic of the test signal.

Automatic sound field correcting system

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.

Mobile sound field correcting device

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.

Automatic gain and frequency characteristic control unit in audio device

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.

Growing community of inventors

Saitama, Japan

Akio Tokumo