The porous material with continuous pore is useful for the sound absorbing material. In this research work, rice straw, rice husks, and buckwheat husks were dealt as a porous sound absorbing material that applied the biomass. About rice straw, geometrical condition of that was reproduced in the narrow tube of the simple structure, and the effect of absorbing sound of the tubule in the composite structure was verified. In the experiment, for the various thickness and the back air space were tested by using two microphone impedance tube, and the normal incidence sound absorption coefficient was measured. Moreover, the absorption coefficient was calculated from the acoustical constant obtained from the result of a measurement in a specific condition. And, these calculation values were compared with experiment values. As a result, it was shown to be able to estimate the absorption coefficient of the condition of the unmeasurement. As for rice straw, rice husks, and buckwheat husks, it has been understood it has a useful characteristic of absorbing sound. It leads to the fixation of the carbon, and even if the incineration processing is done, it is a carbon neutral.
2011 by The Japan Society of Mechanical Engineers