Stanley WSL141, Руководство по установке, эксплуатации и техническому обслуживанию

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7.2 Noise
Noise is any kind of sound which causes a disturbance, interferes with a person
’s work and causes
harm to health and well-being. Individuals can have different reactions to the same noise at different
occasions. The perception of sound also depends on the current mood of an individual.
Every device which operates with fluctuation is a source of sound. The spread of sound or noise is also
affected by walls and other obstacles in the vicinity of the device. This is why the correct choice of
location of the device is very important.
Sound emissions of the device into the surroundings are described by physical quantities such as sound
power and sound pressure. Both physical quantities are specified in the dimensionless unit decibel (dB).
Sound power level of (L)
Sound power level is the energy of sound which the device emits into the environment per second. It is
a quantity which is used for the basic comparison of various sound sources and for determining whether
the machine or device complies with the regulations and standards for noise radiation. Sound power
depends on the environment in which the source is located.
The reference sound power is 10
-12
W.
Example: The sound power of human breathing is 10
-11
W or 10 dB.
The sound power of whispering is 10
-10
W or 20 dB.
The sound pressure level (p)
The sound pressure level is the changing pressure of sound waves which a sound produces. Sound
pressure is detected or heard as volume. It depends on the environment where the source is located
and the distance of the listener to the source of the sound.
The standard reference sound pressure in the air is 20
m
Pa (10
-6
Pa). This is the sound auditory
threshold at the sound frequency of 1 kHz.
Example: The sound pressure of normal human speech at a distance of 1 m ranges from 2 to 20 mPa
(10
-3
Pa) or from 40 to 60 dB.
Decibel (dB, dB(A))
A decibel is the unit without dimension with which we express the ratio between the changing quantity
and the fixed reference. Among others it is also used for measuring the intensity of sound or sound
energy. It is calculated on a logarithmic scale which means that if the ratio increases by 3 dB, the sound
energy doubles, if it increases by 10 dB, the sound energy increases by a factor of 10 and if it increases
by 20 dB, the sound energy increases by a factor of 100, etc.