Larson Davis System 824, Reference Manual

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D-6 824 Reference Manual 11/3/00
pressure levels instead (usually denoted P in acoustics), the
equation will be the same, since the “two” in the squared
units will move from within the bracket and become a 20 log
instead of a 10 log and thus compensate for using linear or
quadratic units. Please note that it is not allowed to use 20
log for squared units, since that expression assumes that we
use linear units, like sound pressure in acoustics or voltage
in electrical engineering. This is illustrated in equation D-1
below:
Table 2 illustrates how a a tenfold increase of the sound
pressure will result in an increase in 20 dB steps, while
sound power increases in 10 dB steps. See the linear form
(Table 2) and compare with equation D-1. In conclusion, dB
values are always the same, independent of using sound
power or sound pressure as the base unit. A 6 dB increase
implies four times the sound power or two times the sound
pressure.
dB 10Log
10
P
2
P
0
2
--------
20Log
P
P
0
-----
= =
p ;
0
20
µ
Pa =
Table 2
Linear form, non-squared units
Level form
Ration of Value to Reference
Exponential Form of
Ratio
20•Exponent
1 10
0
0
10 10
1
20
100
10
2
40
200
10
2.3
46
1,000 10
3
60
10,000
10
4
80
100,000
10
5
100
1000,000 10
6
120
(eq. D-1)