Larson Davis System 824, Reference Manual

Page: 505 / 536

11/3/00 D-1
C H A P T E R
D
Glossary
This appendix contains technical definitions of key acousti-
cal and vibration terms commonly used with Larson Davis
instruments. The reader is referred to American National
Standards Institute document S1.1-1994 for additional defi-
nitions. Specific use of the terms defined are in the main
body of the text.
Allowed Exposure Time (T
i
)
It is the allowed time of exposure to sound of a constant A-
weighted sound level given a chosen Criterion Level, Crite-
rion Duration, and Exchange Rate. The equation for it is
where L
c
is the Criterion Level, T
c
is the Criterion Duration,
Q is the Exchange Rate, K is the Exchange Rate Factor and
L
avg
is the Average Sound Level.
Example: If L
c
= 90, T
c
= 8, Q = 3 and L
i
= 95 then
This means that if a person is in this area for 5 hours and 39
minutes he will have accumulated a Noise Dose of 100%.
Standard: ANSI S12.19
Average Sound Level (L
avg
)
It is the logarithmic average of the sound during a Measure-
ment Duration (specific time period), using the chosen
Exchange Rate Factor. Exposure to this sound level over the
period would result in the same noise dose and the actual
T
i
T
c
L
avg
L
c
–
( )
Q
⁄
2
-----------------------------------------
T
c
L
avg
L
c
–
( )
q
⁄
10
-----------------------------------------
= =
T
i
8
10
95 90 –
( )
10
⁄
-------------------------------
8
2
95 90 –
( )
3
⁄
--------------------------
5.656 = 5 hours and 39 minutes = = =