Intensity measurement and mapping are recognised as effective ways to determine the
location, quantify the absolute power and determine the relative contribution of individual sub-sources or ’hot-spots’ as observed on the surface of an object. However,
when it comes to identifying the internal root causes for the noise radiated, this method
only gives indirect indications, like the spectral content of the noise. These need to be
combined with extensive knowledge of the internal design to be really conclusive.
Selective intensity provides a direct way to measure whether an external ’hot-spot’ is
related to a specific internal root cause. Selective intensity calculates that part of the
full measured intensity that is coherent with a specific reference signal. If, for instance,
the vibration of a specific part is suspected to be the main cause of the noise radiated,
you can simply put an accelerometer on that part and use it as the reference for a
selective intensity calculation. If the suspicion is correct, the selective intensity will be
close to the full intensity observed.
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