Sound is caused by the vibration of an object – as is 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 making a correction 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)” to a maximum of 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”.
What is frequency?
A sound’s pitch is determined by the number of changes in pressure per second, and is expressed in Hertz [Hz]. The human ear is able to 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 only just hear.
The ear is most sensitive to sound waves with a frequency of between 1,000 and 6,000 Hz.
When does sound become dangerous?
People’s sensitivity to sound differs. In general, it can be said that a level of more than 80 dB(A) can damage hearing.
When people have to talk more loudly to make themselves heard, the surrounding level will be 80 dB(A) or higher. The higher the level, the greater the risk of hearing impairment. Very loud noises of a 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 a noise level between 80 and 120 dB can cause “imperceptible” damage – damage that people are unaware of at the time, but that they notice only when it has happened and it is too late.
The longer the length of time one is exposed, the greater the damage that is caused.
Does noise affect more than just hearing?
Some people react to sound by becoming uneasy, fatigued, 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 an inability to concentrate.
Which sound sources can be harmful?
The following locations and activities can cause hearing damage:
Disco / Rock concert 110 dB(A)
Circular saw / 105 dB(A)
Sports event / 100 dB(A)
Motorcycling / 95 dB(A)
Average factory noise / 90 dB(A)
Noisy party / 85 dB(A)
Aircraft cabin / 80 dB(A)
How long does it take before noise becomes harmful?
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