Industrial Noise & Vibration Centre

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Tonal noise (hum) evaluations. Why the abysmal failures?

All environmental noise projects require 3 types of feature evaluation:-

stack and fan noise control
  1. Broadband noise (dB(A)): the simple default - quite often used inappropriately
  2. Low-frequency tonal noise that does not contribute significantly to the dB(A) value
  3. Intermittency/variability: impulsive sound, sources switching on and off

Despite tonal noise issues being very common causes of complaints, objective identification of the tones using narrow-band frequency analysis is incredibly rare in consultant reports. They present, at best, octaves and 1/3 octaves. Octaves are totally inadequate and 1/3 octaves are not much more useful. As there are very capable free smartphone narrow-band frequency analysis apps, there is simply no excuse for this lack.

This is rank incompetence that wastes time, money and resources

Including objective tonal analysis in assessments and reports is best practice. It not only accurately reflects the subjective effect of the noise, but it is also an invaluable diagnostic resource to determine the cause - and hence the optimum mitigation options.

How to use narrow-band analysis to evaluate and eliminate tonal noise problems >