730/730-IS Dosimeter Manual
B-9
Sound Pressure Level (SPL, Lp)
The logarithmic form of sound pressure. It is also expressed by attachment of the word decibel to the number. The
logarithm is taken of the ratio of the actual sound pressure to a reference sound pressure which is 20 Micro-pascals
(
Pa). The fundamental relationship between sound pressure level and sound pressure is shown in the equations
below, where p
0
is the reference sound pressure of 20 µPa.
Threshold Level
The threshold level is applied in hearing damage risk assessment. According to the ANSI S1.25 standard, it refers to
the A-weighted sound level below which the dosimeter produces little or no dose accumulation. For that reason,
measured sound below this level may be disregarded. The threshold should be selected to be within the
measurement range of the instrument which is between 70 dB and 140 dB for the dosimeter. The current OSHA
threshold is 80 dB.
Time-Weighted Average Sound Level (TWA, LTWA(TC))
The Time-Weighted Average Sound Level is used for hearing damage risk assessment. It is the level of a constant
sound over the Criterion Duration (8 hours), which would expose a person to the same Noise Dose as the actual
(unsteady) sound over the same period. If the Exchange Rate is 3 dB, then the TWA is equal to the Leq. The equation
shown here applies where TC = T
2
-T
1
(the measurement time), and q is the Exchange Rate Factor.
Standard: ANSI S12.19
Windscreen
Air (wind) blowing across the microphone generates pressure fluctuation and vibration on the microphone
diaphragm. Thus, your noise exposure reading would include wind noise, an undesirable component. To achieve
the best result with the Spartan 730 dosimeter, we recommended using the provided WS012 windscreen.
