Decibels (abbreviated dB) are easy-to-manage logarithmic comparative representations of the very large range of sound intensities we are capable of hearing, from the threshold of hearing expressed as 0 dB to the threshold of pain at 130 dB.
"A-weighting" (expressed as dBA) is an adjustment that is made to the sound measurement equipment to take into account our decreased sensitivity to low frequency sounds.
Some typical sound levels measured close to the source:
Doubling the power of a sound raises the intensity by only 3 decibels (e.g. two working jack hammers would measure 103 dBA). A 10 fold (10 dB) increase of sound power is required before a perceived doubling of intensity or loudness occurs (e.g. it would take four hair dryers to sound almost twice as loud as one). Likewise, a 10 dB decrease in sound intensity results in a halving of the loudness.
The "natural quiet" or ambient sound in national parks and wilderness areas is so low, it approaches the threshold of hearing. Assuming this low ambient noise level is 10 dB, a jet flying over increasing the ambient noise level by 60 dB, results in a 64 fold increase in perceived sound. This results from an increase in the power of the sound by a factor of 1,000,000!
The decibel unit helps us to manage the very large numbers involved with sound measurement, but it can be misleading as the numbers sometimes appear quite small for what they actually represent.
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