The design of a modular sound absorber for very low frequencies.
Studios and sound control rooms usually have their walls acoustically treated to control the reverberation time. in the BBC, this treatment often takes the form of modular absorbers of which there are a number of BBC designed types for sound absorption in different frequency bands. This report describes an investigation of the feasibility of a modular absorber for the 50-100 Hz frequency range. A method of measuring absorption coefficient over a continuous frequency range using a standard wave duct is described. This allows a single modular absorber to be tested instead of requiring a batch of prototypes to be constructed for a reverberation room test. This technique was used to test a variety of absorbers, including porous, Helmholtz and membrane types. These tests led to a design of membrane absorber, and a small batch of prototypes was constructed and tested in a reverberation room. This test verified that the prototype module had useful absorption in the frequency range of interest.
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