Room acoustics - Building Acoustics - page 136

R

W

Source S 1

Figure 4.15 Example on image source not being visible in receiver positions R.

We shall put a source midway between the floor and the ceiling, initially assuming
that the absorption factor α is the same for these boundary surfaces. The energy density
w at a receiver position may then be expressed by

n

⎡

( )

⎤

∞

1 −

α W 1

∑

w = ⎢ + 2 ⎥ , (4.63)

2 2

4

π

c

r r

⎢ ⎥

0

⎣

n

⎦

n = 1

where W is the source sound power, r and r n are the distances between the source and the
receiver and between the receiver and the image source with index n , respectively.

S 2

S 1

R

S

S 1

S 2

S n

Figure 4.16 Image sources in a “flat” room.