The electronic sound absorber is so named because it absorbs sound or reduces the sound level by means of an electronic transducing system, as contrasted to conventional sound absorption by direct conversion from acoustical to heat energy. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected so that, for an incident sound, wave and sound pressure at the microphone is reduced. Thus it will be seen that the electronic sound absorber is a feedback system which operates to reduce the sound pressure in the vicinity of the microphone. The sound pressure in the neighborhood of the microphone can be reduced 10 to 25 decibels over a frequency range of three octaves in the low-frequency portion of the audio-range. The electronic sound absorber may be used to reduce the noise over a small volume, that is, spot type noise reducer or it may be used with an acoustical resistance to obtain a high order of sound absorption in the low-frequency range.

The electronic sound absorber is so named because it absorbs sound or reduces the sound level by means of an electronic transducing system as contrasted to conventional sound absorption by direct conversion from acoustical to heat energy. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected so that for an incident sound wave the sound pressure at the microphone is reduced. Thus it will be seen that electronic sound absorber is a feedback system which operates to reduce the sound pressure in the vicinity of the microphone. The sound pressure in the neighborhood of the microphone can be reduced 10 to 25 decibels over a frequency range of three octaves in the low frequency portion of the audiorange. The electronic sound absorber may be used to reduce the noise over a small volume, that is, spot type noise reducer, or it may be used with an acoustical resistance to obtain a high order of sound absorption in the low frequency range.

A 200-syllable communication system has been built and tested that automatically analyzes, recognizes, and encodes speech at the transmitter. At the receiver, the digital code is used to synthesize speech from prerecorded speech elements. The result is highly intelligible speech transmitted at the extremely low bit rate of 8 bits/sec. This system is the result of several years of research on speech processing directed toward discovering the useful, invariant information-bearing portions of the acoustic signal. The analyzer processes speech spoken one syllable at a time and transmits an eight-bit code for each syllable. The features used to derive the code include intrasyllabic pauses, voiced-to-unvoiced sound transitions, rate of growth and decay, duration, and relative spectral information. The entire communication system has been completed and the memories have been charged to store the codes for 200 syllables. An overall performance evaluation has been made using four speakers over a ten-day period with a 24 000-voicing-test sample. The system responded to 91% of the voicings with an accuracy of 80%.

The closed cabinet, with or without a port, has become the standard mounting arrangement for a direct radiator loudspeaker mechanism for high fidelity sound reproducing systems. One of the objections to the cabinet for these systems is the large size required to obtain adequate low frequency response. The effective volume of a small cabinet may be increased by the use of an auxiliary loudspeaker mechanism which drives the radiating loudspeaker mechanism. This system has been termed a compound direct radiator loudspeaker. The use of the compound direct radiator loudspeaker makes it possible to obtain low frequency response comparable to that of the conventional wide range system but in a cabinet having only a fraction of the volume of the cabinet in the conventional system.

This paper presents two small experimental loudspeakers of the same general design, suitable for use in personal radio receivers. The design of the magnetic structure is unconventional in that the loudspeaker cone housing and the magnet occupy the same space, and the over-all loudspeaker depth is thereby reduced. The vibrating system of the loudspeaker is conventional so that the directional characteristics, distortion, and frequency response are, in general, similar to a completely conventional loudspeaker of the same diameter. Some general design considerations applicable to this type loudspeaker are discussed, together with a chart summarizing these design considerations.