MK:427 Environmental Noise Microphone
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Appendix 3 The influence of the background noise level on calibration
and verification
High background noise levels can affect the calibration of any noise measurement system.
It is recommended that both the routine verification and reference calibration are carried out in
environments where the ambient noise level is more than 15dB below that of the calibration level.
The electrostatic actuation system will typically produce a level between 85dB and 95dB. To ensure
that the routine verification and reference calibration can be carried out successfully, it is
recommended that these are done in environments where the ambient noise level is less than
70dB(A)
As an example, if the electrostatic actuation system is generating a level of 90dB and the ambient
level is 85dB, the resulting level will be 91.1dB. It is also likely that the background noise level will
vary and so this will result in an unstable output level.
If the electrostatic actuation system is generating a level of 85dB and the background noise level is
75dB, the resulting level will be 85.4dB.
If the electrostatic actuation system is generating a level of 85dB and the background noise level is
70dB, the resulting level will be 85.1dB.
The chart below shows difference between two noise levels across the x axis and on the y axis the
level that should be added to the higher value. This shows the effect of the background noise upon
the calibration level. As the difference reaches 15dB, the effect becomes insignificant.
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