Abstract: A pin type jack-and-plug coupling device is joined together by inserting the pin plug of a male connector into the pin jack of a female connector. The male connector has a captivated nut member and the female connector has an externally threaded member engageable with the nut member. After the pin plug has been inserted in the pin jack for electrical connection, the nut member is turned for threaded connection with the externally threaded member, whereupon the male and female connectors are lockingly joined together. The male connector also has a retainer nut for fastening the tightened nut member to prevent loosening.

Abstract: In stereo sound reproduction circuitry for use with a stereo signal source and stereo headphones, the improvement of dip filter means disposed between the stereo signal source and the stereo headphones, the dip filter means having a dip in the transmission characteristic thereof, the dip being in substantially the same frequency position as a dip which occurs in the sound pressure frequency response characteristic at the ear canal entrance when a sound source is disposed in front of a listener.

Abstract: A loudspeaker system has a cabinet in which a loudspeaker is mounted, the cabinet supporting therein a hollow duct which provides sound communication between the exterior and interior of the cabinet. A standing wave prevention member made of a sound absorbent material is disposed within the duct in spaced relation thereto, the member being smaller in volume than the duct.

Abstract: A speaker system comprising a speaker unit, a drone cone driven by the speaker unit; and a removable weight loaded on the front of the drone cone which can be exchanged from the front of the drone cone.

Abstract: In a bass-reflex type speaker system, in which sound signal waves radiating from the back of a speaker within a cabinet are emitted out through a hollow duct while the phase of the sound signal wave is reversed, the improvement comprising at least one dividing plate secured within the hollow duct and disposed parallel to the longitudinal direction of the duct or a hollow pipe with a diameter smaller than that of the duct, the hollow pipe being coaxially disposed within the hollow duct where the pipe may be made of sound absorbing material.

Abstract: An intermodulation antiinterference circuit for a superheterodyne receiver having a receiving antenna comprising a first high frequency amplifying circuit responsive to the receiving antenna; a local oscillating circuit; a first frequency conversion circuit responsive to the first high frequency amplifying circuit and the local oscillating circuit; a variable attenuation circuit disposed between the receiving antenna and the first frequency conversion circuit; a nonlinear circuit responsive to the receiving antenna having less linearity than the first high frequency amplifying circuit; a second frequency conversion circuit responsive to the local oscillating circuit and the nonlinear circuit; a comparison circuit responsive to the first and second frequency conversion circuits for generating an output when the output of the second frequency conversion circuit is greater than the output of the first frequency conversion circuit; and means for changing the attenuation of the attenuating circuit.

Abstract: A lock releasing mechanism for push button levers such as used in a tape recorder. The mechanism includes an electromechanical releasing system and a distinct mechanical releasing system commonly operable by a manual operator. The mechanical system functions for lock releasing only if the electromechanical system fails to provide lock releasing.

Abstract: A digital frequency display device for digitally displaying the operating frequency of a communication apparatus comprising a reference frequency oscillator, a first frequency mixer for mixing the output frequencies of a first oscillator of the communication apparatus and of the reference frequency oscillator, a second frequency mixer for mixing the output frequency of a second oscillator of the communication apparatus and the resultant frequency provided from the first frequency mixer to produce the display frequency shifted by the reference frequency, and a frequency counter for counting the output frequency from the second frequency mixer and for correcting the shifted frequency component to display the correct frequency.

Abstract: A cabinet for a record player comprising a cabinet body molded from hard resin concrete with large mass, a base of wood adhered to the bottom of the cabinet body and a plate adapted for attachment of a tone arm, the plate being composed of wood and adhered to the top of the cabinet body.

Abstract: A quartz crystal oscillation circuit comprising an active oscillation element; a quartz crystal resonant element connected to the active oscillation element; first and second variable capacity diodes respectively connected in series and in parallel with the quartz crystal resonant element; and means connected to the quartz crystal resonant element for varying the frequency of the oscillation circuit.

Abstract: A digital frequency display device includes a counter for counting a frequency to be displayed, a latch circuit for temporarily storing a plurality of digit signals from the counter and for outputting the digit signals in response to the latch pulses, a decoder for decoding the digit signals from the latch circuit into another coding system, a display section for visually displaying the digit signals decoded from the decoder, a gate for preventing the latch pulses from reaching the latch circuit at undesired times and a digit eraser for erasing any one of the digits of the numerals representing the frequency displayed when the latch pulses feeding to the latch circuit is blocked by the gate means.

Abstract: A pick-up cartridge has a plate-like first magnet magnetized thicknesswise and having a central through hole through which extends a cantilever having on one end a reproducing stylus and on the other end a disc-shaped armature of a highly permeable material, the first magnet being adjacent to the armature. The armature is supported by a damper so as to be vibratable with vibration of the cantilever. At least a pair of spaced coil-carrying pole pieces have their one ends located in the vicinity of and slightly spaced radially from the armature, the other ends of the pole pieces being connected to one polarity side of a second magnet magnetized thicknesswise. The first and second magnets have the same kind of polarity oriented in the same direction. A shield casing has its bottom connected to the other polarity side of the second magnet and disposed to cover the pole pieces and armature, the shield casing having its brim positioned adjacent to the first magnet in peripherally spaced relation.

Abstract: A stereo indicating circuit for use with an FM receiver having a multiplex demodulator, a stereo indicator and a stereo-monaural mode selector, the stereo indicating circuit comprising a smoothing circuit having a short time constant for changing the mode of the FM receiver from stereo to monaural and immediately turning off the stereo indicator after the power switch of the FM receiver is turned off by utilizing the sharp voltage drop of said smoothing circuit.

Abstract: In a stereo amplifier protective device having at least two relay circuits per channel where each circuit includes a pair of contact points, the improvement of the contact points in a first one of the channels being so disposed with respect to one another that the signal current flowing through a first pair of the contact points in the first channel is in a direction substantially opposite to that flowing through a second pair of the contact points in the first channel to thereby enhance channel separation in the stereo amplifier.

Abstract: An audio amplifier which processes mainly dynamic signals and which is provided with a plurality of amplifying systems each having a preamplifier and a main amplifier. A plurality of power sources are used to separately supply electric power to the respective amplifying systems, resulting in elimination of transient crosstalk.

Abstract: An input signal is converted into a dc voltage proportional to the frequency of the input signal in a frequency-voltage converter, while saw tooth waves are generated in a saw tooth wave generator triggered with the input signal. The dc voltage is applied to a variable resistance circuit where the resistance is changed corresponding to the dc voltage. The period of such saw tooth waves is controlled with the variable resistance circuit so that the saw tooth waves may follow the input signal frequency for automatically indicating at all times a desired number of waveforms on the screen of a cathode-ray tube. The variable resistance circuit may be controlled with means for free running operation of the saw tooth wave generator during the absence of the input signal.

Abstract: A speaker assembly comprising a dome shaped diaphragm, the cross section along the plane containing the base of the diaphragm having an oval contour; a voice coil connected to the diaphragm; magnetic means operatively associated with the voice coil; and support means for supporting the diaphragm, voice coil and magnetic means.