A dB explaination...

M

Mickj83

New member
I have tried reading what exactly a decible is. But everyting I read was rather confusing. Is there a more simple answer to what a decible is? If so what is it?
 
I always thought it was just the unit of measure for how loud something is. Like Ohms, inches, Kelvin or whatever other unit of measure.

Someone that really knows correct me if I am wrong.
 
A decibel is one tenth of a "Bel", a unit named after A.G. Bell. It's a measure of sound pressure level. Which is different than loudness per se, because humans have hearing that is sensitive to the frequency of the sound being heard.
 
I think I see where your getting with that. Can it be simplified more? An analogy might help. But thanks none the less.
 
OK. The scale is actually an exponential comparison (ratio) between sound pressure levels (in watts/sq. meter for example). The choice of the sound pressure level that is 0 dB is one that roughly corresponds to the smallest noise that can/can't be heard by someone with very good hearing. In other words the crossover point between the two. Or in power terms, 1 picowatt/ square meter. I know I can't hear that at any frequency! I don't know what frequency is used as a standard here; probably ~1KHz. But sound pressure also decreases sharply with the distance from the source, in addition to the variation caused by the listener's ability to hear particular frequencies. The reason for having an exponential scale as opposed to a linear scale is that the range of hearable sound pressure levels is so darned wide. Between 0 dB and 73 dB is a factor of ~20 million times the sound pressure level! As to the use of this scale as seen and used on so many V/U meters, your best bet is to listen and watch and try to correlate the results. This is where a good V/U meter (digital or analog) can be distinguished from a crappy one. Reproducibility is everything here.
 
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