Introduction

Noise is often defined as “unwanted sound”, but this definition is subjective because of the fact that one man’s sound may be another man’s noise. Again the better definition of noise is: “wrong sound, in the wrong place, at the wrong time”.  Noise has become a very important “stress factor” in the present environment.

Noise has two important properties:

1. Loudness
2. Frequency: The human ear can hear frequencies from about 20-20,000 Hz, but can change according to the subject.

Sound levels of some noise
S.No.	Source of noise	Sound level (dB)
1	Whisper	10
2	Music on radio	85
3	Jet take-off	150
4	Speech on radio	80
5	Children shouting	79
6	Children crying	80
7	Speech, 2-3 people	73
8	Vacuum cleaner	76
9	Piano	86

Acceptable noise levels (dBA)
1	Residential	Bedroom	25
		Living room	40
2	Commercial	Office	35-45
		Restaurant	40-60
3	Industrial	Workshop	40-60
		Laboratory	40-50
4	Educational	Classroom	30-40
		Library	35-40
5	Hospitals	Wards	20-35

Park’s Textbook of Preventive and social medicine