Noise

Noise may be defined as an unpleasant or undesired sound. Perception of noise is an individual thing, and there are a number of subjective factors which determine our response. These include our mood, time of day, background noise levels and our expectations.

The Effects of Noise

Noise can have a range of effects on health and wellbeing, particularly when sleep is interrupted. Some effects of noise include stress, annoyance and tiredness. The experience of noise is individual, making it important to consider your own perception of sounds that annoy or disturb you.

Understanding Noise

The strength of sound, or sound pressure level, is measured in decibels (dB(A)). Variations of the dB(A) measurement are used to analyse noise and set prescribed levels for noise from commercial sites.

The “A” weighting is used to represent how humans hear sound. Generally speaking:

● A 10 dB(A) increase in sound level is perceived as about twice as loud.
● A 10 dB(A) reduction in sound level is perceived as about half as loud.
● A 3–4 dB(A) change in sound level is usually just noticeable.

Factors other than sound level are important. Even at low volume, a sound may be annoying due to the characteristic of the noise such as pitch, duration, impulsiveness or how frequently it occurs.

Some typical noise sources and their respective noise levels:

Noise Level (dB(A))	Source	Subjective Description
120	Rock concert	Intolerable
110	Accelerating motorcycle (at 5m)	Intolerable
100	Pneumatic hammer (at 2m)	Very noisy
90	Loud factory	Very noisy
80	Kerbside of busy street, shouting	Noisy
70	Busy traffic	Noisy
60	Department store, speech level	Noisy
50	Quiet restaurant	Noisy
40	Residential area at night	Quiet
30	Theatre	Quiet
20	Rustling of leaves	Very quiet
10	Human breathing (at 3m)	Very quiet
0	Threshold of hearing for normal young people	Very quiet

Source: Bies D.A and Hansen C.H, Engineering Noise Control: Theory and Practice.