Sound is caused by the vibration of an object, as clearly visible in the movements of a loudspeaker cone. The surrounding air is compressed at intervals, thus creating a sound wave.
The loudness of sound is related to the extent of that compression and the resulting degree of pressure of the sound wave. This is measured in decibels (dB). After correcting for the perception of the human ear, the level is given as dB(A).
The scale runs from the faintest sound the human ear can perceive: “0 dB(A)” up to 180 dB(A), the noise emanating from a launching pad when a rocket is launched. Decibels are a logarithmic number. This means that, if the dB number increases by 10, the intensity of the sound increases tenfold.
A sound’s pitch is determined by the number of changes in pressure per second and is expressed in hertz (Hz).
The human ear can perceive pitches between about 20 Hz (the lowest note on a large pipe organ) and about 20,000 Hz, like the sharp, high note of a dog whistle, which humans can hear but barely.
The ear is most sensitive to sound waves with frequencies between 1,000 and 6,000 Hz.
Noise causes hearing damage faster than you might think, as shown in the table below:
Noise level in dB(A)/Safe exposure time per 24 hours
80 dB(A) 8 hours
86 dB(A) 2 hours
92 dB(A) 30 minutes
98 dB(A) 7 minutes
People’s sensitivity to sound differs. In general, levels higher than 80 dB(A) can damage hearing. When people have to talk more loudly to make themselves heard, the surrounding level is 80 dB(A) or higher.
The higher the level, the greater the risk of hearing impairment. Very loud noises of short duration, such as those caused by an explosion or the firing of a gun can result in pain and an immediate serious or even permanent loss of hearing.
Exposure to noise levels between 80 and 120 dB can cause “imperceptible” damage — damage that people are unaware of at the time, but that they notice only after it has happened when it is too late. The longer the length of time one is exposed, the greater the damage that is caused.
Some people react to sound by becoming uneasy, fatigued or irritated. This can result in a raised heart rate, higher blood pressure or an excess of gastric acid. Noise can also affect performance when carrying out difficult assignments due to inability to concentrate.
The following locations and activities can cause hearing damage:
– Average factory noise +/- 90 dB(A)
– Circular saw +/- 105 dB(A)
– Aircraft cabin / 80 dB(A)
– Disco/rock concert +/- 110 dB(A)
– Noisy party / 85 dB(A)
– Motorcycling +/- 95 dB(A)
– Sports event +/- 100 dB(A)