Why is there no SI unit for sound?

[Ralphonsicus]

The deciBel is probably the most commonly used unit for sound, but why isn't there an SI unit? Also, what is a logarithmic unit? Thanks.

 

[torquil]

Sound are waves of pressure fluctuations, and this is an SI unit for pressure

http://en.wikipedia.org/wiki/Pascal_(unit)

This explains the logarithwic dB unit:

http://en.wikipedia.org/wiki/Decibel