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)

John H <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...

> 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).

The other problem is that some noises hard drives make
can be MUCH more irritating than others, even when they
are identical as far as the measurement is concerned.

> 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).

And that last is an illustration of the problem. Most
find that the Barra is significantly quieter than that
Maxtor drive. And the Samsung P80 is much quieter
than the Maxtor, even tho its listed at 2.7 bel.

> How do you compare apples and oranges?

Obviously you cant.

> Which is better to know, bels or dBA?

The only thing you can really say is that bels are
most commonly cited but clearly have a problem.

> I'm thinking that (for HDs anyway) 2.5 bels is less than
> 25dBA SPL, which makes the WD very noisy by comparison.

And in practice thats bullshit, particularly
when compared with the Maxtor.

> (I have a cooling fan that's 3.5 bels and 12dBA)

http://www.silentmaxx.net/know_how/a...ccoustics.html
http://www.atra.mod.uk/atra/rsabst/p...5-Decibels.pdf

Previously John H. <(E-Mail Removed)> 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

--
For email address: lastname AT tik DOT ee DOT ethz DOT ch
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"The more corrupt the state, the more numerous the laws" - Tacitus

On 1 Dec 2003 20:56:06 GMT, Arno Wagner <(E-Mail Removed)> wrote:

> Previously John H. <(E-Mail Removed)> 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.

If I read this article right, sones can directly be converted to phons, and
there's not much difference between phons and dBA for low to moderate sound
levels (which hopefully includes the HD).

http://www.phys.unsw.edu.au/~jw/dB.html


> > 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.

On Tue, 2 Dec 2003 06:14:35 +1100, "Rod Speed" <(E-Mail Removed)> wrote:

>
> John H <(E-Mail Removed)> wrote in message
> news(E-Mail Removed)...
>
> > 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).
>
> The other problem is that some noises hard drives make
> can be MUCH more irritating than others, even when they
> are identical as far as the measurement is concerned.

That's usually ball bearing noise which should soon be history once WD
switches over.

> > 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).
>
> And that last is an illustration of the problem. Most
> find that the Barra is significantly quieter than that
> Maxtor drive. And the Samsung P80 is much quieter
> than the Maxtor, even tho its listed at 2.7 bel.

Then somebody's lying in their specs. You wouldn't think that that could
last long. If say Samsung is put at a competitive disadvantage by telling
the truth, they should complain to the FTC.

> > How do you compare apples and oranges?
>
> Obviously you cant.

Then all manufacturers should give both ratings, dBA AND bels. Adding a dBA
rating (one reading) is easy compared to taking many readings to calculate
bels. Maybe that's why WD provides dBA only - it's quick and easy.

A spec sheet I have for an old Quantum HD shows the noise rating as being
3.6 bels and 32 dBA. So how about saying dBA equals ~10*bel-0.4 for a HD.
Would that be close? That would make a Maxtor only 21 dBA compared to
WD's 34.

> > Which is better to know, bels or dBA?
>
> The only thing you can really say is that bels are
> most commonly cited but clearly have a problem.


> > I'm thinking that (for HDs anyway) 2.5 bels is less than
> > 25dBA SPL, which makes the WD very noisy by comparison.
>
> And in practice thats bullshit, particularly
> when compared with the Maxtor.
>
> > (I have a cooling fan that's 3.5 bels and 12dBA)


> http://www.silentmaxx.net/know_how/a...ccoustics.html
> http://www.atra.mod.uk/atra/rsabst/p...5-Decibels.pdf

Some more links:

http://www.phys.unsw.edu.au/~jw/dB.html
http://ccrma-www.stanford.edu/courses/150/SPL.html

http://www.silentpcreview.com/module...tid=121&page=1

If any of them answer my original question, how to convert bels to dBA, I
missed it.

Your first link says "[it is] not possible to convert between sound power
level and sound pressure level." I think that would be true only if the
sound source isn't emitting power equally in all directions. If it is, I
bet 10dBA/bel at 1 meter will be close. I'm just guessing though.

John H <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Rod Speed <(E-Mail Removed)> wrote
>> John H <(E-Mail Removed)> 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).

>> The other problem is that some noises hard drives make
>> can be MUCH more irritating than others, even when they
>> are identical as far as the measurement is concerned.

> That's usually ball bearing noise

Nope, because that at least is constant.

> which should soon be history once WD switches over.

Sure. Doesnt explain the significant differences in
the irritation levels seen with fluid bearing drives tho.

And the other variable is whether AAM has been enabled,
and whether fools like Seagate have disabled that completely.

>>> 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).

>> And that last is an illustration of the problem. Most
>> find that the Barra is significantly quieter than that
>> Maxtor drive. And the Samsung P80 is much quieter
>> than the Maxtor, even tho its listed at 2.7 bel.

> Then somebody's lying in their specs.

Nope, the problem is that the sound pressure levels
have **** all to do with the percieved noisiness of a
drive. Essentially because some noises are MUCH more
irritating than others at the same sound pressure level.

> You wouldn't think that that could last long.

Yep, so it cant be the problem.

> If say Samsung is put at a competitive disadvantage
> by telling the truth, they should complain to the FTC.

The FTC has no say whatever on the problem
of quantifying how irritating a noise level is.

>>> How do you compare apples and oranges?

>> Obviously you cant.

> Then all manufacturers should give both ratings, dBA AND bels.

The problem is that even when both are quoted, and the dBa which
purports to make some allowance for the difference between the
percieved noise level and the sound pressure level, it was developed
WAY before the problem with the irritation some hard drive noises have.

> Adding a dBA rating (one reading) is easy compared
> to taking many readings to calculate bels. Maybe
> that's why WD provides dBA only - it's quick and easy.

Or they recognise bels are useless and dont bother with them.

> A spec sheet I have for an old Quantum HD shows the noise
> rating as being 3.6 bels and 32 dBA. So how about saying
> dBA equals ~10*bel-0.4 for a HD. Would that be close?
> That would make a Maxtor only 21 dBA compared to WD's 34.

And most consider the Maxtor to be a noiser drive.

>>> Which is better to know, bels or dBA?

>> The only thing you can really say is that bels are
>> most commonly cited but clearly have a problem.

>>> I'm thinking that (for HDs anyway) 2.5 bels is less than
>>> 25dBA SPL, which makes the WD very noisy by comparison.

>> And in practice thats bullshit, particularly
>> when compared with the Maxtor.

>>> (I have a cooling fan that's 3.5 bels and 12dBA)

>> http://www.silentmaxx.net/know_how/a...ccoustics.html
>> http://www.atra.mod.uk/atra/rsabst/p...5-Decibels.pdf

> Some more links:

> http://www.phys.unsw.edu.au/~jw/dB.html
> http://ccrma-www.stanford.edu/courses/150/SPL.html

> http://www.silentpcreview.com/module...tid=121&page=1

None of which do a damned thing about the fundamental
problem, that some hard drive noises are MUCH more
irritating that others, at the same sound pressure level.

Very occasional head exercising movements designed
to ensure that the heads dont stay over the same tracks
for too long when the drive is inactive are completely
immeasurable in terms of sound pressure level and
are damned irritating to the user.

Some of the older drives produced a sound very
close to the sound of a cricket trapped in a small
cardboard box when moving the heads energetically.
Bugger all sound pressure level but very irritating.

> If any of them answer my original question,
> how to convert bels to dBA, I missed it.

There cant be a simple factor. Read the pdf, it spells out why.

> Your first link says "[it is] not possible to convert
> between sound power level and sound pressure level."

Precisely.

> I think that would be true only if the sound source
> isn't emitting power equally in all directions.

You're wrong. There is MUCH more involved than just that.

> If it is, I bet 10dBA/bel at 1 meter will be close.

You've just lost your bet.

> I'm just guessing though.

And havent managed to understand the basics.

On Tue, 2 Dec 2003 10:46:24 +1100, "Rod Speed" <(E-Mail Removed)> wrote:

> > If any of them answer my original question,
> > how to convert bels to dBA, I missed it.
>
> There cant be a simple factor. Read the pdf, it spells out why.

I read it and still don't know why. What did I miss this time?

> > Your first link says "[it is] not possible to convert
> > between sound power level and sound pressure level."
>
> Precisely.
>
> > I think that would be true only if the sound source
> > isn't emitting power equally in all directions.
>
> You're wrong. There is MUCH more involved than just that.

Wrong how? Sound pressure readings are used to calculate sound power, are
they not? If it's known that the sound source is emitting power equally in
all directions, only ONE reading from any direction is needed because
readings from all other directions would be the same. If one pressure
reading at distance x is enough to calculate power, it follows that knowing
the power is enough to calculate pressure at any distance. Of course you
need to know the air pressure (assume sea level) and not have any
reflections (acoustic test chamber). So what is the "MUCH more" you
mention? Kindly give me the DETAILS if you know them.

> > If it is, I bet 10dBA/bel at 1 meter will be close.
>
> You've just lost your bet.

The Quantum I mentioned was close to 10dBA per bel, 3.6 bels and 32 dBA.
Why would another drive be much different? I'd guess that the SPL "gain"
(any deviation from what equal power in all directions would be) for a drive
mounted 1 meter in front of a SPL meter would be similar for all drives. In
other words if one drive has x dBA/bel, they probably all have about the
same.

> > I'm just guessing though.
>
> And havent managed to understand the basics.

Some noises are much more irritating than others at the same sound pressure
level. I understand that. But what I was asking about is how to figure out
what that sound pressure _IS_ when only the sound power is given.

John H <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Rod Speed <(E-Mail Removed)> wrote

>> John H <(E-Mail Removed)> wrote

>>> If any of them answer my original question,
>>> how to convert bels to dBA, I missed it.

>> There cant be a simple factor. Read the pdf, it spells out why.

> I read it and still don't know why. What did I miss this time?

Basically dBAs allow for the ear's perception of sound, so
there can never be a simple factor between bels and dBA.

>>> Your first link says "[it is] not possible to convert
>>> between sound power level and sound pressure level."

>> Precisely.

>>> I think that would be true only if the sound source
>>> isn't emitting power equally in all directions.

>> You're wrong. There is MUCH more involved than just that.

> Wrong how?

Because dBA allows for the ear's perception of sound.

> Sound pressure readings are used to
> calculate sound power, are they not?

Thats only PART of whats involved.

> If it's known that the sound source is
> emitting power equally in all directions,

Which no real world device like a hard drive ever does.

> only ONE reading from any direction is needed because
> readings from all other directions would be the same.

And they aint with real world devices like a hard drive.

> If one pressure reading at distance x is enough to
> calculate power, it follows that knowing the power
> is enough to calculate pressure at any distance.

Only with a theoretical device that behaves
different to real world devices like hard drives.

> Of course you need to know the air pressure (assume sea
> level) and not have any reflections (acoustic test chamber).

All irrelevant with a real world device like a hard drive that
doesnt even radiate the sound equally in all directions.

You must have noticed the acoustic damping on the Barra drives.

> So what is the "MUCH more" you mention?

The A in dbA indicates that it ALSO allows for the ear's perception
of sound, AND thats an entirely separate issue to the MIND'S
perception of noises which may well not even be measurable in
terms of sound pressure levels, particularly with very intermittent
sounds, but which are what the user objects to with a particular drive.

> Kindly give me the DETAILS if you know them.

Already did. You just ignored them. Just like
you did with what is spelt out in that pdf too.

>>> If it is, I bet 10dBA/bel at 1 meter will be close.

>> You've just lost your bet.

> The Quantum I mentioned was close to 10dBA per bel, 3.6 bels and 32 dBA.

And those ratios are entirely a result of the PARTICULAR
noises that particular drive happens to emit and arent
useful for a different drive which is different on that detail.

That should be obvious from the different
ratio you get with that fan you cited.

> Why would another drive be much different?

Because the noises produced vary quite significantly.

In spades when comparing say a hard drive and a fan.

> I'd guess that the SPL "gain" (any deviation from what equal
> power in all directions would be) for a drive mounted 1 meter
> in front of a SPL meter would be similar for all drives.

Guess again. And thats an entirely separate issue to the A part of dBA.

> In other words if one drive has x dBA/bel,
> they probably all have about the same.

Fraid not. Most obvious when comparing that hard drive with that fan.

>>> I'm just guessing though.

>> And havent managed to understand the basics.

> Some noises are much more irritating than others at
> the same sound pressure level. I understand that.

You claim you do, but when you still want a simple ratio between
bels and dBAs, you clearly havent managed to grasp the problem.

> But what I was asking about is how to figure out what that
> sound pressure _IS_ when only the sound power is given.

Not even possible, as should be obvious from the very
different ratios you get with that hard drive and that fan.

And that still leaves the entirely separate problem that
stuff like occasional deliberate head moves wont even
be measurable in SPL terms, but are what the user
considers makes a particular drive particularly noisy.

On Tue, 2 Dec 2003 15:58:25 +1100, "Rod Speed" <(E-Mail Removed)> wrote:

> >>> If any of them answer my original question,
> >>> how to convert bels to dBA, I missed it.
>
> >> There cant be a simple factor. Read the pdf, it spells out why.
>
> > I read it and still don't know why. What did I miss this time?
>
> Basically dBAs allow for the ear's perception of sound, so
> there can never be a simple factor between bels and dBA.

Oops, I guess I did overlook that little detail. :-) (Takes a while to sink
in) Power values are NOT filtered as pressure values are using the A scale.
So converting bels to pressure would give a dB value, not dBA. But I see no
reason why power couldn't be measured using the same filter to give you a
'belA' rating. Wonder why they don't do it that way? Going by what the A
filter looks like in the link I gave (attenuated highs and lows), a 'belA'
value would be a lower number and therefore look better to some people.

This seems to make a dBA rating a better indicator of how loud a drive will
appear than what a bel rating is, and yet most manufacturers don't give you
the dBA rating. Doesn't make sense.

OTOH, all the acoustic power generated by a drive has to be dissipated
somewhere, much of it in the case frame and covers which can resonate and
make things worst, so I guess knowing the unfiltered power rating is good
too.

What would really help with HD noise is switching to 2.5" drives, even
10,000 RPM models. 3.5" drive storage capacity is actually getting too big
for most home systems unless used for video. I'm a little surprised that
somebody isn't making a high performance 2.5" drive (better than any 3.5"
drive) for desktops yet.

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." <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...
> 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)
>