WWhat What you should know about noise

Definitions

decibels: A physical measure of the loudness or volume of a noise. The more decibels the greater is the noise and generally less acceptable.

Three decibel increase: is subjectively just detectable but represents a doubling of noise energy.

Ten decibel increase: subjectively is twice as loud but represents a ten fold increase in noise energy.

dBA (decibels measured on the A scale): is a method of measuring noise which relates to its subjective effects as far as causing annoyance. Tis holds true for most mid frequency noises (traffic, music, people etc) but is a poor indicator for noise which, predominantly, contains low frequencies or infrasound.

Frequncy of noise: It used to be considered the human ear could detect sounds in the frequency range (or number of vibrations per second) from 20Hz (low pitched ) to 20,000 Hz (high pitched sounds).Also most noises lie well within this range.

However it is well established that some noises have considerable energy below 20 Hz, jet aircraft, air-conditioning systems being just two sources. Also for sounds these low frequecnies are audible and can be particularly disturbing.

Low frequncy noise: the predominant audible sound energy is below 100Hz.

Infrasound: the predominant sound energy is below 20Hz.

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