Previously John H. wrote:
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?

dBA is actually deci Bel (A). So disregarding the (A) for the moment,
10 dB = 1 Bel. The (A) is a weighting curve that reflects the human
ear's sensitivity, so dB(A) is more honest than dB or Bel. The problem
is that the human ear's sensitivity is only loosely conectet to the human
mind's resulting anoument. For that you need a measurement in "Sone".
The german computer magazine c't regularly lists dB(A) and Sone in
its HDD tests and there are drives that have good dB(A) ratings but
only not so good Sone ratings. E.g. a high-pitched whine will cause
that.

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)

Depends. As I said above dB(A) is not a measurement for anoyment, just
for how lound you can hear it. dB is just pure sound energy.

Arno

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