Electronic Sound Absorber

Abstract

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.

Active diffusers: some prototypes and 2D measurements

“…The first description of actively controlled impedance was made by Olson and May 4 in the context of a sound absorber, but practical systems were not in general feasible until advances in digital computers from the 1980s onwards. Much subsequent research centred on the active minimisation of a sound field, with many papers originating from Nelson and Elliot 5 .…”

An Active Technology for Improving the Sound Transmission Loss of Glazed Facades

“…The approaches by Leug's patent in 1936 and (Olson & May, 1953) are the first examples of ANC feed-forward control, when prior knowledge of the noise is obtained with an upstream microphone, and ANC feedback arrangement, where the detection microphone is close to the active secondary source respectively. Both approaches relate to the main concept of ANC, and hold its drawbacks: when applied to buildings' glazed facades, they need an external microphone for disturbance monitoring, and internal error sensors and loudspeakers for control purposes.…”

“…According to the patent, the sound field is detected using a microphone, whose signal is passed through an electronic controller, such that it adjusts the loudspeaker to produce a cancelling wave in a duct, resulting in destructive interference of the primary or noise source wave. A feed-back arrangement was produced by Olson and May (Olson et al, 1953), who developed an active noise control system that is based upon detecting the offending sound with a microphone and feeding the signal back through a controller to a control loudspeaker located close to the microphone. They also demonstrated good local reduction at the microphone over a range of frequencies from 20 to 300 Hz.…”

Active control of a sound field with a state feedback electro-acoustic transducer

“…In the previous section, R 1 was formulated so that the performance index was related to the sound pressure on the diaphragm of the control system. Thus, the design parameters in the computer simulation are r 2 , and the assumed vibration frequency f a (= ω a /(2π)) of the diaphragm used in Eq.…”

“…Olson and May's "electronic sound absorber" [1,2] is one of the most efficient methods of applying feedback control to active sound field control. In their system, the sound pressure at a microphone collocated with a loudspeaker is fed back through an electro-acoustic transducer.…”