This web site...

http://www.silentmaxx.net/know_how/a...ccoustics.html

says...

Quote:
Values in bel should be reserved for when talking on sound power level,
while values in decibels should be used for when talking on sound pressure
level. Values in bels can also be written followed by a capital B, but
should be written in all small letters when stated as bels. The abbreviation
for decibel is dB (always spelled with a small d and a capital B). A decibel
is a tenth of a bel: 1 B = 10 dB. While possible to convert between bel and
decibel, is it not possible to convert between sound power level and sound
pressure level.




"John H." wrote in message
news
I need a physics lesson. Assuming sea level, how do you convert between
sound power (bels) and sound pressure (dBA)? I think you'd have to assume
that the acoustic power is being emitted equally in all directions (which
may not be true for HDs).

WD tells you only the pressure (34 dBA for the 250 GB Caviar SE) while
most
other manufacturers tell you only the power (2.5 bel for the DiamondMax
Plus
9 and Barracuda V). How do you compare apples and oranges? Which is
better
to know, bels or dBA?

I'm thinking that (for HDs anyway) 2.5 bels is less than 25dBA SPL, which
makes the WD very noisy by comparison. (I have a cooling fan that's 3.5
bels and 12dBA)