Actual sound levels VS. noise perception


The intensity of a sound can be measured by using a microphone to convert the sound into power and then interpreting the power obtained in terms of Decibels (dB). However, this physical sound level does not really correspond to the perception of the sound that we are having.


Measuring human noise perception

The human ear does not perceive all the sound frequencies in the same way: we are deaf to low-frequency sounds (below 20 Hz) and high-frequency sounds (above 20,000 Hz), and are most sensitive to sounds around 2000 Hz.

This is why there are different versions of the "dB" scale which are decibel readings that have been adjusted to take into account the varying sensitivity of the human ear to different frequencies of sound:

  • dBA (A-weighted sound levels) - measurement of common sound intensities, using a filter to account for the loudness as perceived by a human ear (everyday noises).
  • dBC (C-weighted sound levels) - measurement of higher sound intensities, specifying the effect of peak and high impact sounds on the human ear (extreme loudness such as a live concert).

It is not possible to reproduce the behavior of the "average" human ear with a single filter (and even less that of the ears of each particular individual), but in most situations our hearing can be measued with the the dBA scale. This scale is a good starting point from which to measure sound perception, but gives us only an idea of the perceived noise levels.


Factors impacting noise perception

In reality, the overall noise is composed by many different sound levels all across the frequency spectrum, which is why measuring the perception of sound is very complex and depends on a large number of factors:

1) Individual sensitivity (depending on age, culture, time of day...)
2) Spatial configuration (inside/outside, construction of the building, furniture in the room...)
3) Distance to the noise source (sensor position)
4) Sound frequency (low, medium, high)
5) Sound repeatability (continuous, intermittent, impulsive)
6) Temporal exposure (long-term, short-term)

These are the most common reasons that explain a difference between the actual sound and the perceived noise. The Decibel measurements can only give a limited representation of the perceived "reality", especially as the sensitivity to noise varies greatly from one individual to another. Some populations can be more vulnerable to noise exposure than others, such as students during an exam or people affected by hearing loss.


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