Building Acoustics

18 Building acoustics

have a bandwidth Δf ≈ 0.71⋅ f 0 and a one-third-octave band a bandwidth Δf ≈ 0.23⋅ f 0. As
mentioned above, specifications for such filters are given in IEC 61260.

-3 0 0.01 0.02 0.03 0.04 0.05

-2

-1

0

1

2

3

-3 0 0.01 0.02 0.03 0.04 0.05

-2

-1

0

1

2

3

p(t) p(t,f 0 ,Δf)

t t

f 0

Δf

f 0 f

Lp

Equation (1.24)

Figure 1.12 Frequency analysis of a sound pressure signal using fixed filters of bandwidth Δf. A filter having a
centre frequency f 0 is indicated.

We shall also give a specific example of such analysis using these two types of
band pass filter. Figure 1.13 shows the result of the analysis on a signal which could
represent the sound pressure measured at a certain distance from a given source. In
addition to the sound pressure levels using these filters, analysis is performed using a
discrete Fourier transform as described in section 1.4.4.

60 100 200 500 1000 2000 5000

Frequency(Hz)

40

50

60

70

80

90

100

Relative sound pressure level

(dB)

1/1

1/3

DFT

Figure 1.13 Stochastic noise signal with added pure tone components. Analysis in octave bands (1/1) and one-
third-octave bands (1/3) together with discrete Fourier transform analysis (DFT).