Mumbai university > FE > SEM 1 > Applied Physics 1

Marks: 5M

Year: May 2013

• Reverberation time is defined as the time interval between the initial direct note and the reflected note up to a minimum audibility level.

• More precisely, Reverberation time $(RT_{60})$ is defined as the time required, in seconds, for the average sound in a room to decrease by 60 dB after a source stops generating sound.

Sabine's Formula:-

$T = k \frac{V}{A}$

Where, k = Proportionality Constant = 0.161

Factors which determine the average absorption coefficient of a material:-

• Fiber Size: Sound absorption coefficient increases with a decrease in fiber diameter.

• Airflow Resistance: If the material is air-flow resistant, more of the sound energy will be converted to frictional heat causing decrease in the amplitude of sound waves and thus decreasing the intensity.

• Porosity: Porous materials cause more dampening of sound waves.

• Tortuosity: Tortuosity is a measure of the elongation of the passage way through the pores, compared to the thickness of the sample.

• Thickness: Low frequency sound absorption has direct relationship with thickness. However, at higher frequencies, the effect is insignificant.

• Density: Less dense absorbs sound of low frequencies; whereas, denser materials absorb sound waves of higher frequencies.