Abstract: A sound reproducing apparatus is provided with a circuit comprising a first secondary phase shifter in a front stage of at least one of channels among a first power amplifier, a second power amplifier and a third power amplifier, and a second secondary phase shifter and an adder in at least one of remaining channels for providing an output by adding output signals of a music signal source and the second secondary phase shifter. The apparatus of this structure eliminates phase interferences between a center speaker and right and left speakers by controlling sound waves generated by the center speaker, thereby achieving excellent reproduction of music.

Abstract: A digital signal processing amplifier produces substantially no digital clipping. The amplifier includes an A/D converter provided with an overflow detecting function and a controller for communicating with external equipment and adapted such that an overflow of an input signal is detected and thereby an output level of a head unit serving as a source of the analog input signal is controlled.

Abstract: A loudspeaker device comprising a power amplifier (13) to which an input signal is delivered via a subtracter (6), a speaker unit (1) for reproducing output signals delivered from the power amplifier (13), an acoustic pipe (2) coupled in front of the speaker unit for guiding the sound waves, a microphone (4) for detecting an acoustic outputs radiated from the speaker unit, a microphone amplifier (5) for amplifying an acoustic output signals detected by the microphone, and a negative feedback circuit. Output signals of the microphone amplifier are delivered to the subtracter, at the same time the same output signal is connected to a high-pass filter (7) to be delivered to the subtracter. Thus the negative feedback circuit is formed to suppress peaks and dips for providing a flattened sound pressure frequency characteristic.

Abstract: The speaker disclosed in this invention comprises: (a) a central cap fixed on voice coil bobbin; (b) a shaft fixed in the center of the central cap; and (c) a bearing filled with lubricating fluid and fixed in a through-hole disposed in the center of a magnetic circuit. The speaker has excellent characteristics without sliding noise or harmful rolling phenomena but with reduced harmonic distortion due to the introduction of a magnetic fluid or a lubricant used as a lubricating fluid.

Abstract: In a sound reproducing apparatus, a target control value is determined automatically from a noise and a sound radiated from a loudspeaker unit, and a volume of a reproduced sound is naturally compensated according to an amount of the noise against a masking due to a noise at a listening point. A first microphone is located near a loudspeaker box, and a second microphone is located in the loudspeaker box. A gain of s variable gain amplifier is changed so that an integrated value of a signal obtained by filtering and adding the outputs of the microphone may be equal to an integrated value of the filtered signal of the output of the variable gain amplifier.

Abstract: A digital signal processing amplifier to produce substantially no digital clipping is disclosed, the amplifier including an A/D converter provided with an overflow detecting function and a controller for communicating with external equipment and adapted such that an overflow of an input signal is detected and thereby an output level of a head unit serving as a source of the analog input signal is controlled.

Abstract: In a sound reproducing apparatus, a target control value is determined automatically from a noise and a sound radiated from a loudspeaker unit, and a volume of a reproduced sound is naturally compensated according to an amount of the noise against a masking due to a noise at a listening point. A first microphone is located near a loudspeaker box, and a second microphone is located in the loudspeaker box. A gain of s variable gain amplifier is changed so that an integrated value of a signal obtained by filtering and adding the outputs of the microphone may be equal to an integrated value of the filtered signal of the output of the variable gain amplifier.

Abstract: The speaker disclosed in this invention comprises: (a) a central cap fixed on voice coil bobbin; (b) a shaft fixed in the center of the central cap; and (c) a bearing filled with lubricating fluid and fixed in a through-hole disposed in the center of a magnetic circuit. The speaker has excellent characteristics without sliding noise or harmful rolling phenomena but with reduced harmonic distortion due to the introduction of a magnetic fluid or a lubricant used as a lubricating fluid.

Abstract: A speaker having a voice coil bobbin wound around with the voice coil and a detection coil together. The detection coil is formed by a wire whose diameter is smaller than one fourth of that of the wire used for the voice coil, and wound in a space among the voice coil wires. In another example, the voice coil and the detection coil are formed using a flat type wire. In a speaker made in accordance with the present invention, the outer diameter of the whole coil structure containing a voice coil and a detection coil does not increase; as a result, decrement of the magnetic flux density in magnetic gap does not occur. Thus, the signals that proportionately represent the speaker vibration are made available without inviting deterioration in the efficiency of a speaker, nor an increased Q0.

Abstract: A signal produced by a speaker is removed from a totaled sound of noise around the speaker and the signal from the speaker, thereby extracting correctly the noise around. This structure allows an audio reproducing apparatus of the present invention to masking compensation more naturally. This audio reproducing apparatus includes a detecting coil (17) disposed on a bobbin (16) of the speaker (13), and a microphone (15) disposed around the speaker (13). An output signal from the detecting coil (17) and an output signal from the microphone (15) are respectively filtered, and then undergo an adding process. An input signal is adjusted its magnitude based on these processed signals.

Abstract: An audio reproducing apparatus is utilized in noisy environment in which noise level greatly varies. The apparatus includes first and second microphones placed respectively inside and outside a speaker box. Outputs of respective microphones are filtered, and then added with each other so that signals proportional to outside noise can be extracted. A gain of variable gain circuit can be changed with these extracted signals, whereby sound can be reproduced in noisy environments.

Abstract: A power amplifier system is used for numerous types of audio equipment, and prevents output distortion of the amplifier from deteriorating, under any condition, by controlling a voltage-controlled amplifier in response to fluctuation of an input signal and a power supply voltage. The power amplifier system includes a limiter that extracts a signal at a point of connection between a voltage amplifier and a power amplifier, converts the signal into a d.c. voltage with an integrating circuit after passing it through a voltage comparator, and varies the degree of amplification of a voltage control amplifier, so as to maintain an output voltage at a constant distortion ratio by application of a voltage limited according to an output level of the power amplifier.

Abstract: The object of the present invention is to offer an sound reproduction apparatus equipped with a speaker having a drastically improved acoustic characteristics securing a stable and high S/N ratio over a wide frequency range. In order to accomplish these objects, the inputted audio signal is amplified by a power amplifier and is reproduced in an acoustic output by driving a speaker, and the reproduced acoustic output is detected by a microphone disposed in a closed cabinet together with said speaker and the detected signal is amplified by a microphone amplifier and is processed by a filter. Then, the output signal from said filter and the input signal to said power amplifier are added and processed, and the difference signal between the added signal and said inputted audio signal is used as an input signal to said power amplifier constituting a negative feedback circuit accomplishing the objects of this invention.

Abstract: The invention is a volume and tone control circuit for audio sets which will not distort a signal when the volume is adjusted to maximum regardless of the tone. The circuit has a volume control in the form of a variable resistor with an intermediate fixed terminal, one end connected to an input terminal, the other end grounded, and a movable contact connected to an output terminal; an attenuation circuit connected to said input terminal; and, a tone control circuit connected between the output of said attenuation circuit and the intermediate fixed terminal. The degree of attenuation of the attenuation circuit is set so that the maximum gain of the attenuation circuit and the tone control circuit does not exceed 1. The position of the intermediate fixed terminal is determined so that amplitude-versus-frequency characteristics of the output signal become flat when the movable contact of volume control is set to maximum.

Abstract: In a pulse width modulation amplifier use for audio devices, an input side of an operational amplifier of a pulse width modulation amplifier is used as an alternating current amplifier by grounding its negative terminal through a series circuit formed with a resistor and a capacitor. The direct current gain of the operational amplifier becomes 1, and the offset voltage decreases to the inherent offset voltage of the operational amplifier. The operational amplifier has no direct current coupling with next amplifying stage and hence, the offset voltage is not increased after leaving the operational amplifier.

Abstract: A bass compensation circuit for use in a sound reproduction device is provided with a second-order positive feedback type high-pass filter. The filter has an operational amplifier and a first positive feedback resistor, a first variable resistor connected to an input terminal for receiving an input signal, coupled with a second variable resistor for volume control, and a second resistor for determining a Q-value and a cut-off frequency of a second-order positive feedback type high-pass filter. The first variable resistor and the second resistor are inserted in series between the first resistor and the ground. Thus, the bass compensation circuit can amplify only low frequency signals which do not serve as a masking sound used in masking middle and high frequency signals and has a low level when the sound volume is low. Moreover, the Q-value and the cut-off frequency of the second-order positive feedback type high-pass filter can continuously be changed by using the second variable resistor.

Abstract: A sound reproduction system suitable for automobile, the reproduction system having a band-pass filter, a phase-shifter for shifting the output of the band-pass filter and a mixer which mixes the output of the phase-shifter with the original audio signal at a suitable mixing ratio, whereby a low frequency standing wave which is generally produced in the small automobile room may be eliminated, thereby providing a desirable frequency response characteristic.