Spartan 821/721 Manual
Glossary
C-4
• Doubling of the Sound Power = 3 dB
• Doubling of the Perceived Sound Level = (approx.) 10 dB
Detector
The detector converts the actual fluctuating sound from the microphone into a signal
that indicates its amplitude. Your choice for the Detector setting (Slow, Fast, or Impulse)
determines the amplitude change rate. The detector first squares the sound 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).
The Slow and Fast detector responses were originally developed to slow down the
movement of the needle on an electro-mechanical meter, so that the amplitude could
be determined. Slow and Fast detector settings are still useful in modern sound
measurement instruments. Slow has a time constant of 1 second. Fast has a time
constant of 1/8th second. The Impulse setting is a non-linear detector with the rise
controlled by a 35 ms time constant followed by a peak hold that has a decay rate of 2.9
dB/second.
Dose
See
.
Eight-Hour Time-Weighted Average Sound Level (L.TWA(8))
It is the constant sound level that would expose a person to the same Noise Dose as the
actual (unsteady) sound levels. The equation for this, according to the ANSI S12.19
standard, is shown below:
NOTE: This definition applies only for a Criterion Duration of 8 hours.
L
TWA 8
L
c
q L
og
10
D
100
---------
+
=
