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Appendix A
Corrections and Adjustments
A.1 The Sound Level in the Coupler – Using the Internal Signal Generator
The following describes the corrections automatically applied to the calibration sound levels
generated in the coupler and applies only when the
Function
switch on Type 4226 is set to
Calibration.
The sound levels generated in the coupler when loaded by a Type 4180 microphone are adjusted
to account for the responses of microphones listed under “a”, “b” and “c” categories when used
with a
Sound Field
= Free-field setting. This does not apply when the
Sound Field
= Pressure,
therefore, no such adjustments are made.
Furthermore, in the case when
Sound Level
= 94 Inv. A, an additional correction simulates a
constant A-weighted sound level of 94 dB at each discrete frequency.
Table A.1 shows the corrections for 94 Inv. A, and Table A.2 shows the Free-field corrections for
microphones listed under a, b and c categories.
Table A.1 Inverted A-weighting corrections automatically applied to the Sound Level in the coupler to simulate a constant
A-weighted level of 94 dB at each discrete frequency. Valid when coupler is loaded by a Type 4180 Microphone
Frequency
(Hz)
31.5 63 125 250 500 1 k 2 k 4 k 8 k 12.5 k 16 k
Inv. A 39.4 26.2 16.1 8.6 3.2 0.0 –1.2 –1.0 1.1 4.3 6.6
Table A.2 Free-field corrections (dB) automatically applied to coupler sound levels for microphones listed. These figures are
measured with a Type 4180 pressure microphone
Microphone
Setting
Frequency (Hz)
Microphone Type
31.5 – 500 1k 2k 4k 8k 12.5k 16k
Traditional
a 0.00 0.15 0.50 1.35 4.50 7.35 – 4129, 4130, 4176
b 0.00 0.20 0.45 1.05 2.80 5.60 7.85 4155, 4165
c
0.00 0.10 0.35 0.95 2.60 5.05 6.75
4133, 4134, 4147,
4149
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