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Chapter 2
Hardware Setup
2.1 Measuring at Low Static Pressure
The frequency response of the microphone depends on the static pressure. Using a Sound Level Calibrator
to adjust the sensitivity of a sound level meter at the calibration check frequency provides no information
on the influence of static pressure on frequency response. Conformance to the specified standards
ensures that the system measures within the standards’ tolerances, in the range of 85 kPa to 108 kPa.
Data for the frequency response as a function of static pressure for Microphone Type 4188 can be
found in Microphone Handbook BA 5105.
At the calibration check frequency, both the microphones and the recommended Brüel & Kjær Sound
Level Calibrator Type 4231 are rather insensitive to static pressure variations below 0.001 dB/kPa.
2.2 Frequency Weightings
The A and C frequency weightings conform to requirements in IEC 60651 and IEC 61672 – 1 standards.
Table 2.1 states the design-goal frequency responses for the frequency weightings according to
IEC 61672 – 1. They are stated for the complete instrument including the microphone. For the A and C
frequency weightings, these design goals are equivalent to the ones specified in IEC 60651. The
corresponding tolerance limits can be found in the standards.
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