Decibel A, B and C - Engineering ToolBox
www.engineeringtoolbox.com/decibel-d_59.html
Knowledge about the human ear is important in acoustic design and sound measurement. To compensate for the human hearing sound meters are normally fitted with filters that adapts the measured sound response to the human sense of sound. Common filters are
dB(A)
dB(B)
dB(C)

dB(A)
The decibel A filter is widely used. dB(A) roughly corresponds to the inverse of the 40 dB (at 1 kHz) equal-loudness curve for the human ear.
With the dB(A) filter the sound level meter is less sensitive to very high and very low frequencies. Measurements made with this scale are expressed as dB(A).
Note! The abbreviation dBA or db(A) is not recognized by SI. According to SI - use
"the A weighted sound pressure level is x dB"
or
"LA is x dB"
where
x = the weighted sound pressure level (dB)
Anyway - dBA (or dB(A)) is commonly used.

With the dB(A) filter the sound level meter is less sensitive to very high and very low ... The resulting sound pressure level can therefore be estimated to approximately 57 dB(A) ... Suburban areas with some commerce or industry, 10.

Sound level meter - Wikipedia
https://en.wikipedia.org/wiki/Sound_level_meter
A sound level meter is used for acoustic measurements. It is commonly a hand-held instrument .... Sound exposure level—in decibels—is not much used in industrial noise ... is 10 times the base 10 logarithm of the ratio of a root-mean-square A-weighted sound .....

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Note added at 6 days (2016-11-27 12:35:08 GMT) Post-grading
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Tack så mycket :)