3M DL, SE PTWA , Peak C , Preferred Noise Criterion (PNC) Curves , Projected time (Prt) , Reference pressure

Appendix B
143
Models SE and DL
TW A L
avg
ER log
2
Prt
CT
---------
 
  dB+=
PTWA
This is a projected TWA determined for a projected tim e (Prt) in relation to the Criterion Time
(CT) as follows.
Peak –C
The following chart illustrates the range of Sound Level with C-weighted Peak.
Level Range (dB)
Peak C Level Range (dB)
Level Range (dB)
Peak C Level Range
(dB)
-20 to 70
42.2 to 73
20 to 110
42.7 to 113
-10 to 80
42.6 to 83
30 to 120
46.7 to 123
0 to 90
41.6 to 93
40 to 130
55.4 to 132
10 to 100
43.4 to 103
50 to 140
66.3 to 142
Preferred Noise Criterion (PNC) Curves
The Preferred Noise Criterion Curves, a type of tangency method, was an update to
Beranek’s original NC curves that accounted for the lower frequency side of the criterion
curves (1971). The PNC curves extended the range t o 32 Hz instead of 63 Hz used in NC
curves.
Projected time (Prt)
A time interval used in some calculations, usuall y different from the actual run time of a study
or session.
Reference pressure
The sound pressure at the threshold of human hear ing, as measured under standard
conditions. This generally accepted magnitude of this pressure is 2 × 10-5 Pascals (Pa).