Question

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

Answer 1

See below.

Explanation:

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`.