Civil Engineering Reference
In-Depth Information
Noise and sound insulation
Chapter 1.9
Sound insulation
Noise descriptors
Noises differ in their level (loudness),
frequency content (pitch), and they
may vary with time. Consequently
different units have been developed to
describe different types of noise.
Noise level
Noise level is described on a
logarithmic scale in terms of
decibels (dB). If the power of a noise
source is doubled (eg two
compressors instead of one) the
level will increase by 3 dB.
Subjectively, this increase is
noticeable but not large.
Frequency content
The ear can respond to sounds over a
wide frequency range (roughly
20 Hz to 20 kHz), but most
environmental noises lie between
20 Hz and 5 kHz. The ear is more
sensitive to sounds of some
frequencies than others, and is
particularly sensitive between
about 500 Hz and 5 kHz. The 'A
weighting' is an electronic circuit
built into a sound level meter to make
its sensitivity approximate to that of
the ear. Measurements made using
this weighting are expressed as
dB(A). Noises with tonal
components (such as fan noise) are
particularly annoying, and
sometimes this is recognised by
adding 5 dB(A) onto a measured
level. An increase of 10 dB(A)
doubles the perceived loudness of
a sound.
Figure 1.57
'Eight ways to annoy your neighbour'
Buildings may be required to protect
their occupants from noise and
vibration from a wide variety of
fixed and mobile sources, and
sometimes buildings will be
required to protect both the rest of the
inside and also the outside
environment from noisy activities
taking place within the building
(Figure 1.57).
When a building has to contain
noise it is common practice to set a
maximum noise level at the boundary
of the building plot. Where the
building has to protect the occupants
from external noise, often a
requirement is put on the insulation
of the building envelope. The
purpose of this section is to explain
common noise descriptors, and to set
the scene against which the
performance of individual
components can be assessed.
