Page 236 - Master Handbook of Acoustics

simplification, the door and a window will be neglected as having minor effect. Figure 11-21
2
shows the untreated condition. The concrete floor area of 373 ft and the gypsum board area of
2
1,159 ft are entered in the table. The appropriate absorption coefficients α are entered from the
table in the appendix for each material and for the six frequencies. Multiplying the concrete floor
2
area of S = 373 ft by the coefficient α = 0.01 gives a floor absorption of 3.7 sabins. This is entered
under Sα for 125 and 250 Hz. The absorption units (sabins) are then figured for both materials and
for each frequency. The total number of sabins at each frequency is obtained by adding that of the
concrete floor to that of the gypsum board. The reverberation time for each frequency is obtained by

dividing 0.049V = 182.7 by the total absorption for each frequency.

FIGURE 11-21 Room conditions and calculations for reverberation example 1.