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APPENDIX
C
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 for additional definitions. Specific use of the terms defined are in the main body of the
text.
Allowed Exposure Time (Ti)
It is the allowed time of exposure to sound of a constant Aweighted sound level given a chosen Criterion Level, Criterion
Duration, and Exchange Rate. The equation for it is
Tc
Tc
T i = ----------------------------------------- = ----------------------------------------(L
– Lc ) ⁄ Q
(L
– Lc ) ⁄ q
2 avg
10 avg
where Lc is the Criterion Level, Tc is the Criterion Duration, Q is
the Exchange Rate, K is the Exchange Rate Factor and Lavg is the
Average Sound Level.
Example: If Lc = 90, Tc = 8, Q = 3 and Li = 95 then
8
8
T i = ------------------------------= ------------------------- = 5.656 = 5 hours and 39 minutes
( 95 – 90 ) ⁄ 10
( 95 – 90 ) ⁄ 3
2
10
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 (Lavg)
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
Model 820 Technical Reference Manual
Glossary
C-1