730/730-IS Dosimeter Manual
B-1
Appendix B
Glossary
This glossary contains technical definitions of key acoustical and vibration terms commonly used with Larson
Davis instruments. If you need additional information, please refer to the American National Standards Insti
-
tute document S1.1-1994 (R2004) for additional definitions. Specific use of the terms defined are in the main
body of this manual.
A-weight
One of 4 defined frequency weighting scales that measures the impact of sound in dB. The A scale is used to
simulate the response of the human ear for noise—generally for very loud sounds in the same frequency range as
human speech, and for very loud noise (when used a band-limiting filter that diminishes above 20kHz to account
for ultrasonic noise). Mandated by all noise and occupational health agencies, the A-scale can help you identify the
risks of deafness or decreased speech recognition in a noisy work environment.
Allowed Exposure Time (T
i
)
The allowed time of exposure to sound for a constant A-weighted sound level in a chosen Criterion Level, Criterion
Duration (8 hours for Model 730), and Exchange Rate. T
i
is calculated using the following equation.
Average Sound Level
(
L
avg
)
The level of a constant sound, expressed in dB, which in a given time period (T = T
2
– T
1
) would expose a person to
the same noise dose as the actual (unsteady) sound over the same period. ANSI S1.25-1991 defines L
avg
or average
sound level.
C–A
This measurement is an L
avg
that enhances the low-frequency components of the sound signal. It’s the result of
subtracting the A-weighted L
avg
from the C-weighted L
AVG
for the same measured signal.
C-weight
One of 4 defined frequency weighting scales that measures the impact of sound in dB. The C-weighted standard
simulates the response of the human ear when exposed to high amplitude noise.
L
c
= Criterion Level
Tc = Criterion Duration
Q = the Exchange Rate
q = the Exchange Rate Factor
L
avg
= Average Sound Level
L
AS
= A-weighting frequency and slow-exponential
weighting time sound level in dB (in the formula
above, if the sound level is less than the user
specified threshold level, then L
AS
= -∞)
T = measurement period or Run Time (T = T
2
– T
1
)
T
S
= work shift duration, or Shift Time
q = exchange rate constant
• if exchange rate = 3, q = 10
• If exchange rate = 4, q = 4 / log
10
(2) ≈ 13.29
• If exchange rate = 5, q = 5 / log
10
(2) ≈ 16.61
• If exchange rate = 6, q = 20
B
