A small unidirectional microphone has been developed with the following features: maximum sensitivity along the axis of the microphone; a high ratio of electrical output to size; a sharper directivity pattern than a cardioid; a directivity pattern that is independent of the frequency; a blast proof vibrating system. The high discrimination which this microphone exhibits to sounds which originate from the sides and rear makes it particularly suitable for long distance sound pick-up in radio, television, sound motion pictures, and sound reinforcing systems.
A small unidirectional microphone has been develr oped with the following features: Maximum sensitivity along the axis of the microphone; a high ratio of electrical output to size; a sharper directivity pattern than a cardioid; a directivity pattern that is independent of the frequency; a blastproof vibrating system. The high discrimination which this microphone exhibits to sounds which' originate from the sides and rear makes it particularly suitable for long distance sound pickup in radio, television, sound motion pictures, and sound reinforcing systems.
The term personal radio receiver is used to designate a complete radio receiver with self-contained power supply, and of such physical dimensions that it can be easily carried by hand or in the pocket. The performance and compactness of personal radio receivers are limited by the efficiency with which electrical power is converted into sound power by the loudspeaker. Since the electrical power output is limited in the personal receiver, the efficiency of the loudspeaker is an important factor. A number of loudspeaker systems have been investigated, both theoretically and experimentally, as follows: direct radiator, combination direct radiator and phase inverter, horn, and combination horn and phase inverter. An efficiency of 25 percent has been obtained with the combination horn and phase inverter. This loudspeaker system has been incorporated in a complete four-tube radio receiver, having a content of 25 cubic inches.
A second-order unidirectional microphone has been developed consisting of two uniaxial microphones connected in series opposition. This system has been termed the bigradient uniaxial microphone. The directional efficiency, that is, the energy response to random sounds is one-ninth. The high discrimination which this microphone exhibits to sounds which originate from the sides and rear makes it particularly suitable for long distance sound pickup in radio, television, sound motion pictures, phonograph recording, and sound reinforcing systems.
The term personal microphone is used to designate a microphone worn by a speaker with the resultant sound pickup inherently limited to the person wearing the microphone. The operational characteristics of personal microphones will be described. Various types of microphones suitable for personal applications will be described.
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