Sound transmission in buildings. Flanking sound transmission - Building Acoustics - page 346

The flanking sound reduction index R f , involving the flanking element of area S i in the
sending (source) room and the corresponding one in the receiver room of surface area S j ,
we shall define as

⎛⎞ ⎛ ⎞ ⎛ ⎞

1 W I ⋅

S
S

()

S i

RR ==⋅ 10 lg =⋅ 10 lg =⋅ 10 lg .

(9.24)

⎜⎟ ⎜ ⎟ ⎜ ⎟

f ij

⎜⎟ ⎜ ⎟ ⎜ ⎟

ij

τ W I ⋅

⎝⎠ ⎝ ⎠ ⎝ ⎠

ij ij j j

The quantity W S is the sound power incident on the partition, and W ij is the radiated
power from element j in the receiving room caused by vibration transmission from the
element i in the sending room. The sound intensity I i is the intensity at the walls, assumed
to be the same at all surfaces in the sending room. The intensity I j , however, is the one
radiated from the element j .

S i D ij ( K ij ) S j

R i R j

W ij

W s

R d

S s

Figure 9.17 Sound transmission between two rooms, direct and flanking transmission paths.

Another choice, may be a more natural one, could be to use the actual area S i in the
definition given by Equation (9.24) in place of the area S S of the partition. The advantage
of using the latter, as pointed out in section 9.2.3 , is that having a common reference area
for all transmission paths one may directly sum up the accompanying transmission
factors. The sound powers W S and W ij may as before be expressed as

2

2

p

p R

S

ij

W = ⋅ S and W = ⋅

A

,

(9.25)

S S ij

4 ρ c 4 ρ c

00 00

where the sound pressure in the receiving room, having the total absorbing area A R , is
caused by flanking transmission only. The brackets indicate, as usual, a space averaging.
Inserting into Equation (9.24) , we get

S

()

S

RL L =− +⋅ 10 lg .

(9.26)

ij S R

ij

A

R