Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 228

Fig. 9.5 Example of
variation of dB according to
the difference in sound
intensity level. For instance,
doubling the power of the
sound signal corresponds to
a gain of +3 dB

The logarithmic scale has been adopted also because a doubling of acoustic
power does not correspond to a doubling of hearing perception. For instance, the
difference in decibels between a signal with a power of 1 W and another of 2 W is
10 log (2/1)

¼

3 dB. If the difference in signal between 1 and 2 V, 20 log

(2/1) 6 dB. Figure 9.5 indicates how the decibel scale varies according the values

of sound pressure.
Doubling a power gives a rise of 3 dB and doubling a voltage produce a rise of
6 dB. In Table 9.2 are reported the dB level and the amount of acoustic pressure of
some common sounds and the noise level caused by anthropogenic causes.
A value in decibels has no meaning if there is no reference measure. In some
cases the reference measure is implicit; for example, the sound pressure level (SPL)
has a reference level defined worldwide as 2

¼

10 5 N/m 2 Pa). Often a

symbol is added after dB (V, u, v, m, A) that means a reference level:

(20 μ

dBV: 1 V
dBu: 0.775 V (Europe)
dBv: 0.775 V (USA)
dBm: 1 milliwatt
dbA: dB SPL, A-weighted response

The decibel is used also to describe the voltage gain of a device. For example,
when a microphone amplifier has a gain of 50 dB, this means that the input voltage
has been multiplied by a factor 317 because 20 log 317/1 ¼ 50 dB.