730/730-IS Dosimeter Manual
B-3
Decibel (dB)
A unit of measure commonly used to describe the ratio of one power level or field level value to another on a
logarithmic scale. The decibel is a simplified way of representing a large span of signal levels, and sometimes very
large numbers, as opposed to using the Pascal. For example:
To directly add or subtract physical quantities expressed in decibel form, you can use the following equation to
convert decibels to Pascals.
With regard to measuring noise exposure, remember the following rules when dB values are used for sound levels:
• Doubling of the Sound Pressure = 6 dB
• Doubling of the Sound Power = 3 dB
• Doubling of the Perceived Sound Level = (approx) 10 dB
Dose
Detector
The part of a sound level meter that converts the actual fluctuating sound or vibration signal from the microphone
to one that indicates its amplitude. It first squares the signal, then averages it in accordance with the time-
weighting characteristic, and then takes the square root. This results in an amplitude described as rms (root-mean-
square).
Equivalent-Continuous Sound Level (L
eq
)
The level of a constant sound, expressed in dB, which in a given time period (T = T
2
- T
1
) has the same energy as
does a time varying sound. For the dosimeters, a L
eq
value is recorded for 2 different intervals. The first interval
records a L
eq
for the entire record’s run time. The second records a L
eq
for each individual time history sample. The
L
eq
is annotated as L
Aeq
for an A frequency weighted L
eq
or as L
Ceq
for a C frequency weighted L
eq
. The equation is
FIGURE B-1
dB
Power Ratio
Amplitude Ratio
50
100 000
316.2
3
1.995
≈ 4
1.995
≈ 2
-50
0.000 01
0.003 162
(t) = instantaneous, frequency weighted (A or C), sound pressure in pascals
0
= reference sound pressure, 20 µPa
T = measurement period or Run Time (T = T
2
– T
1
)
