G.R.A.S. Sound & Vibration
Pistonphone Types 42AA/42AA-S1 - Page 8
2.3 Static-pressure Corrections
The Pistonphone is factory adjusted to give a nominal sound pressure level of 114 dB re.
20 µPa. This nominal value is valid for the following ambient reference conditions:
• Temperature 23º C
• Static pressure 1013 hPa
• Relative humidity 50 %
For other static pressures, the nominal Pistonphone level will have to be corrected. The correc-
tion ∆ P, in decibels, is given by the following equation:
∆ P = 20 ⋅ Log ⋅ ( )
P
a
P
r
(3)
Where:
P
a
= measured static ambient pressure (hPa)
P
r
= reference static pressure (1013 hPa)
The corrections for ambient static pressure are shown in Fig. 2.2 (see also Appendix A.1 for an
extended pressure range). These values should be applied to the nominal Pistonphone level.
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