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Low frequency sound propagation in activated carbon

Bechwati, F, Avis, MR, Bull, DJ, Cox, TJ, Hargreaves, JA, Moser, D, Ross, DK, Umnova, O and Venegas, RG 2012, 'Low frequency sound propagation in activated carbon' , The Journal of the Acoustical Society of America, 132 (1) , p. 239.

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Abstract

Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining the resonant frequencies of Helmholtz resonators with different backing materials. It was found that the addition of activated carbon increased the compliance of the backing volume. The effect was observed up to the highest frequency measured (500 Hz), but was most significant at lower frequencies (at higher frequencies another phenomenon can explain the behavior). An apparatus was constructed to measure the effective porosity of the activated carbon as well as the number of moles adsorbed at sound pressures between 104 and 118 dB and low frequencies between 20 and 55 Hz. Whilst the results were consistent with adsorption affecting sound propagation, other phenomena cannot be ruled out. Measurements of sorption isotherms showed that additional energy losses can be caused by water vapor condensing onto and then evaporating from the surface of the material. However, the excess absorption measured for low frequency sound waves is primarily caused by decreases in surface reactance rather than changes in surface resistance.

Item Type: Article
Themes: Subjects outside of the University Themes
Schools: Colleges and Schools > College of Science & Technology > School of Computing, Science and Engineering > Acoustics Research Centre
Journal or Publication Title: The Journal of the Acoustical Society of America
Publisher: Acoustical Society of America
Refereed: Yes
ISSN: 00014966
Depositing User: Users 29196 not found.
Date Deposited: 25 Jul 2012 10:33
Last Modified: 03 Jul 2014 09:49
URI: http://usir.salford.ac.uk/id/eprint/23061

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