We all know that sounds can be pleasant to listen at such as sounds of nature, music or high nuisance like noise from a highway or loud neighbour that prevents you from sleeping.
To quantify noise there are several terms used, in the blog the basic ones. We perceive hearing through an amazing and versatile organ, our ears. Together with the ‘processing’ of the sound waves we can hear.
The human ear has an astonishing range of sound power levels that it can determine or hear.
The human ear is not a linear device. For example, we can hear the difference between 1 or 2 cars passing but we cannot determine the difference in sound between 100 and 101 cars.
To make it easier to talk about noise quantities, we are using the decibel, this is a logarithmic scale. The threshold is set at 0 decibels (0 dB). A sound 100 times as strong will be 20 dB, calculate with logarithms, 10 * log (100) = 20 dB. Means that a sound 1000 times stronger is 30 dB higher (10 * log (1000) = 30 dB.
In a scientific formula, it’s written like this: The Decibel (sound pressure level) for sound in air is relative to 20 micro pascals (μPa) = 2×10−5 Pa, the quietest sound a human can hear.
This also implicates that if you have 2 sound sources of 80 dB, together they don’t produce 160 dB but only 83 dB !
As our ear is not linear for different frequencies (low tones, high tones) a scale has been introduced called ‘A’, written like dB(A). This means that the sound with frequencies are weighted as to how a human will perceive them. We perceive low-frequency noise as less intruding than high-frequency noise.
We see that there are 2 important factors in how we perceive sounds, frequency (high/low) and intensity (high/low).
Some examples of typical decibel levels:
0 dB would be the lowest level that a young, healthy person can ‘hear’ or perceive. 120 dB is the pain threshold.
The WHO (World Health Organisation) recommends keeping exposure to sound to be less than 80 dB(A) during the daytime to prevent the risk of hearing loss.
Follow me:
Comment on “Basic Noise units and formulas”