16
Reference
Output sound pressure level compensation
The output sound pressure level generated by the pistonphone depends on a certain extent
on the static (atmospheric) pressure and on the effective load volume that is applied due
to the mounting of the microphone (this will differ according to the microphone type).
When performing calibration, compensation for these two quantities must be provided to
determine the exact output sound pressure level.
Change of output sound pressure level according to static
(atmospheric) pressure
The sound pressure
p
(N/m
2
) produced by the pistonphone changes at a rate proportional
to the static (atmospheric) pressure. To determine the exact output sound pressure level,
the static pressure at the time of use should be measured, and compensation according to
the specifi ed sound pressure level data given in the calibration chart should be applied.
p
= ×
P
×
2 ×
A
p
×
S
V
× √2
............................................................................. Equation 1
: Specifi c heat ratio of air 1.402
P
: Static
pressure
Pa
S
:
Piston cross section
m
2
A
p
: Cam
stroke
m
V
: Coupler
volume
m
3