Building Acoustics

Room acoustics 113

10 20 50 100 200 500 1000

Frequency (Hz)

-50

-40

-30

-20

-10

0

p/(Q

ω)

dB

Figure 4.3 Transfer function between sound pressure and monopole source volume acceleration in a room of
dimensions 6.2 x 4.1 x 2.5 metres and reverberation time 1.0 seconds. Source position (1.7, 1.0, 1.5), receiver
position (3.5, 2.5, 1.5). Thick solid curve – analysis in one-third-octave bands. Dashed line – diffuse-field
model. The points show calculated resonance frequencies.

The response is also shown resulting from an analysis in one-third-octave bands, a
normal procedure when performing measurements in buildings. It is then of interest to
calculate the result if one is using a simple diffuse field model for this case (see section
4.5.1 below). Assuming that the pressure at the receiver position is not affected by the
direct field from the source, we may use the simple relationship between the source
power W and the average sound pressure in the room stating that

22

00 00 0

55.3

,

44

pp

WA

ρρccc

V

T

⋅

=⋅=⋅



(4.19)

where A is the total absorbing area in the room. A monopole source freely suspended in
the room will radiate a power

22

00

monopole 4.

ck Q

W

ρ

π

=



(4.20)

Equating these powers, we obtain

0 0.

55.3

p cT

QV

ρ

ωπ

=



 (4.21)