Sensor CE (European) Installation (ESR) Rack Fan Noise Information and Sensor Sound Suppression 'SSSh' Hoods & Skirts 'SSSs' 'SPL' or 'DB'

Sound (not noise) may be defined as any pressure variation that the human ear can detect. The number of pressure variations per second is called the frequency of the sound. This is measured in Hertz(Hz). The frequency of a sound creates its distinctive tone. Combinations of these tones make up the everyday sounds we hear, be it traffic noise or music. There are low frequencies such as thunder or high frequencies such as a whistle. The normal hearing range for a healthy young person is about 20 Hz (low tone) to 20,000 Hz (high tone).

Another main quantity used to describe sound is the size of the sound pressure level (SPL) fluctuation on the human ear. It is the increase or decrease of sound pressure that allow us to hear things as getting louder or softer in volume. Sound pressure is measured in decibels (dB). This is a scale used to measure how much sound pressure there is at given time and place. Because the dB scale is logarithmic, an increase of 6 dB represents a doubling of the sound pressure level. However, an increase of 10 dB is required before the perceived sound appears to be twice as loud.

In terms of sound pressure level, audible sounds range from 0 dB (silence) to 130 dB (pain). Some examples of dB measurements are: a library / 35 dB, a business office / 65 dB, boulevard traffic / 90 dB, and a jet take-off / 125 dB.

Sound is recorded and measured through a weighting network. There are three different internationally standardized weightings: "A", "B" and "C". The following dB test data was collected using "A" weighting (dBA). Weightings "B" and "C" were not used because they do not correlate well with subjective tests.  
Noise may be defined as any unwanted sound, regardless of decibels (dB) or frequency of the sound.