Abstract
A combination multi-degree of freedom acoustic lining is designed. A given space volume (30 × 37 × 1000 cm3) is properly distributed in different levels. As a result 28-acoustic resonators of the Helmholtz type and two similar triangular chambers are obtained. These resonators are tuned to different frequencies, so that they cover a frequency range from 65 Hz to about 450 Hz.
The measured third octave band insertion loss showed a wide band attenuation in the frequency range from 80 Hz to about 600 Hz. When the triangular chambers are filled with loose fibre (jute) as absorbent material, the attenuation of the lining extends to higher frequencies, up to about 2000 Hz. An average insertion loss of more than 20 dB is measured in a wide frequency range.
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Shenoda, F.B. A multi-degree of freedom acoustic lining for noise suppression in broad air ducts. Sadhana 9, 271–280 (1986). https://doi.org/10.1007/BF02811969
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DOI: https://doi.org/10.1007/BF02811969