Question

The volume and surface area of a room are $800{\text{m}}^3$ and $34{\text{m}}^2$ . The reverberation times with and without material on the walls are $1.6\text{sec}$ and $2\text{seconds.}$ The absorption coefficient of the material on the wall is (neglect absorption coefficient of the walls)

• A. 0.8
• B. 0.4
• C. 0.5
• D. 0.6

Answer 1

The correct option is C 0.5

reverberation time is $T_r=0.161\frac{V}{\alpha A}$

time without material

$T_o=0.161\frac{V}{\alpha A_o}$
$2=0.161\times \frac{800}{34{\alpha }_o}$
${\alpha }_o=1.89$

$T_r=0.161\frac{V}{\alpha A}$

$1.6=0.161\frac{800}{34({\alpha }_r+{\alpha }_o)}$

${\alpha }_r+{\alpha }_o=2.38$

${\alpha }_r=0.47$