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The Decibel
Experience has shown that having to do with
levels and comparative values is not easy at first.
The term level means the logarithmic relationship
to two sizes, characterized by adding dB to the
numerical value. The dB must not be understood
as a unit of a quantity. In case of absolute levels,
the reference value must always be indicated,
provided that it is not supposed to be known.
By using the decibel, one takes the experience
into account that the sensation strength of man is
not proportional to the stimulus intensity. According
to the Weber-Fechner law, only a tenfold stimulus
intensity R leads to a doubling of the sensation
strength E.
∆E
=
Issue 04 | 2010
R
lg(
R
2
1
)
The airborne sound reaching the human ear is audible,
if the threshold of audibility will be exceeded. The human
ears are frequency- and amplitude-selective, and it should
be added that frequency and amplitude are in context with
each other, as can be seen from the diagram. The human
ears are able to register frequencies lying between 16Hz
and 20kHz. The lower threshold of audibility of a 1kHz-tone
is at a pressure of 0,00002 Pa.
Another strong argument in
favour of using levels is the large
bandwidth when it comes to
sound pressure levels reaching
from 2 μPa to more than 1kPa.
TRANSFER OF TECHNOLOGY
Fig. 4:
Threshold of audibility and curves of equal loudness
Table 3:
Examples of sound pressure levels
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