Are W/m^2 and dB both units of sound intensity? What is the difference between them?

1 Answer
Mar 21, 2017


See below.


Human perception of loudness (aka sound intensity) is observed to be proportional to log of the scientifically measured intensity.

So a scientific machine will measure sound intensity as it is defined - as sound power per unit area whose units are #(Wat\ts)/m^2#.

But if the measurements are for human consumption, say the volume switch on a TV, it is better to use a log scale.

So, if we have measured # I_o# as being the standard threshold of hearing intensity, ie what you can just about hear, in #(Wat\ts)/m^2#, we get a more user-friendly metric #I_(dB)# if we say that:

#I_(dB) = 10 log_(10) (I/(I_o)) **decibels** #

This means, for example, if #I = I_o# then #I_(dB) = 0#.