Pfannenberg Catalogue

ELECTRO-TECHNOLOGY FOR INDUSTRY
Technology
Frequency range and sound pressure level
The range of human hearing is from 20 to 20,000 Hz.
Deeper sounds (infrasound) and higher sounds (ultrasound)
cannot be heard. The human ear is most sensitive to sound
between 500 Hz and 3 kHz. With regard to volume, a sound
pressure of 2/10,000 = 0.0002 μbar is just barely audible.
This limit value is called ‘hearing threshold pressure’.
A sound pressure of 200 μbar and above causes pain.
This is known as the pain threshold.
In order to make the hearing range more manageable in
terms of numbers, the ratio of the actual measured sound
pressure to the hearing threshold pressure is converted to
a logarithm. This logarithmic relationship is known as the
sound pressure level and is expressed in decibels (dB).
The equation is:
Lp= 20 x log
measured sound pressure in μbar dB
hearing threshold pressure in μbar
100 000 000 μPa
10 000 000 μPa
1 000 000 μPa
100 000 μPa
10 000 μPa
1 000 μPa
100 μPa
140 dB (A)
130 dB (A)
120 dB (A)
110 dB (A)
100 dB (A)
90 dB (A)
80 dB (A)
70 dB (A)
60 dB (A)
50 dB (A)
40 dB (A)
30 dB (A)
20 dB (A)
10 dB (A)
20 μPa
0 dB (A)
Basic principles of acoustic audibility
The loudness of a sounder is expressed in dB (A) and measured
at a distance of 1 metre (USA 10 feet). The smallest
increase in the sound level that the human ear can detect is
3 dB. An increase of 6 dB is equivalent to a doubling of the
sound pressure. An increase of around 10 dB is perceived
as being twice as loud.
Reduction in the sound pressure level in
relation to the distance between the sounder
and the listener’s ear
0
Lower frequencies (at the same sound level) are perceived
to be quieter. This is all the more pronounced at lower sound
levels.
Alarm signals can be better heard when the difference
between the frequency of the ambient noise and that of
the sounder is greater. Interfering factors are, for example,
damping, fog, obstructions, wind speed and direction, rain
and air humidity.
Sound pressure reduction (dB)
-10
-20
-30
-35
-40
-50
Example
A doubling of the distance to the source of the sound is
equivalent to a reduction in the sound level of around 6 dB,
e.g. there is a sound pressure level reduction of 35 dB at a
distance of 58 m.
1 2 4 8 16 32 64 128 256
58
Distance (m)
27