CESVA DC112 - Alternative Free-Field Method

DC112d/DC112
User’s manual
43
8.2 Alternative free-field method
For alternative free-field verification, suggests the use of the B&K 4226 multi-
frequency calibrator, using the following procedure:
a) Switch on the multifunction acoustic calibrator and select:
Function
Æ Calibration
Sound field
Æ Pressure
Sound Level dB
Æ Lin. 94
b) Insert the microphone of the DC112 into the acoustic coupler of the multi-function
acoustic calibrator
c) On the multi-function acoustic calibrator select:
Frequency Hz
Æ 63
Wait until the corresponding LED stops flashing.
Note the measured value of function L
A1”
.
d) Repeat with the frequencies 125, 250, 500, 1k, 2k, 4k and 8k.
e) Remove the microphone from the acoustic coupler and repeat points
b) to d).
f) Calculate la arithmetic mean of the two values measured at each frequency.
g) With the values from point
f), calculate the free-field response relative to 1 kHz.
Lclr
f
= Lm
f
– Lc
f
+ Cpcl
f
– Lm
1kHz
+ Lc
1kHz
– Cpcl
1kHz
where:
Lclr
f
- Free-field response, at frequency f, relative to 1 kHz
Lm
f
- Arithmetic mean of the measured values at frequency f
Lc
f
- Level of calibrator at frequency f
Cpcl
f
- Correction of sound field generated by B&K multi-function
acoustic calibrator model 4226 in free-field at frequency f
Lm
1kHz
- Arithmetic mean of the values measured at 1 kHz
Lc
1kHz
- Level of calibrator at 1 kHz
Cpcl
1kHz
- Correction of sound field generated by B&K multi-function
acoustic calibrator model 4226 in free-field at 1 kHz