Larson Davis 831 - Appendix D Glossary

Model 831 Manual Glossary D-1
APPENDIX
D
Glossary
This appendix contains technical definitions of key
acoustical and vibration terms commonly used with Larson
Davis instruments. The reader is referred to American
National Standards Institute document S1.1-1994 (R2004)
for additional definitions. 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,
Criterion 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, q 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
ave
= 95 then
This means that if a person is in this area for 2 hours and 31
minutes he will have accumulated a Noise Dose of 100%.
Standard: ANSI S12.19.
The table for Exchange Rate (Q), Exchange Rate Factor (q)
and Exposure Factor is shown in the section Exchange Rate
(Q), Exchange Rate Factor (q), Exposure Factor (k) on page
D-7.
Average Sound Level (L
avg
) It is the logarithmic average of the sound during a
Measurement 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 (unsteady) sound levels. If the Measurement Duration
is the same as the Criterion Duration, then L
avg
=L
TWA(LC)
where the Measurement Duration (specified time period) is
T=T
2
-T
1
and q is the Exchange Rate Factor. Only sound
T
i
T
c
L
avg
L
c
–Q
2
-----------------------------------------
T
c
L
avg
L
c
–q
10
-----------------------------------------
==
T
i
8
2
95 90–3
--------------------------
8
10
95 90–10
-------------------------------
2.52 = 2 hours and 31 minutes== =