dBA and Bels

[John H.]

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)

 

[Rod Speed]

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/accoustics/accoustics.html
http://www.atra.mod.uk/atra/rsabst/pdf/B-Maths/B05-Decibels.pdf

 

[Arno Wagner]

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

 

[John H.]

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

 

[John H.]

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.

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.

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.

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


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


http://www.silentmaxx.net/know_how/accoustics/accoustics.html
http://www.atra.mod.uk/atra/rsabst/pdf/B-Maths/B05-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/modul...s&file=index&req=viewarticle&artid=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.

 

[Rod Speed]

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.

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.

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.

Some more links:

http://www.silentpcreview.com/modul...s&file=index&req=viewarticle&artid=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.

 

[John H.]

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.

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.

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.

 

[Rod Speed]

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.

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.

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.

 

[John H.]

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.

 

[CWatters]

This web site...

www.silentmaxx.net/know_how/accoustics/accoustics.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.

 

[Rod Speed]

Oops, I guess I did overlook that little detail.
(Takes a while to sink in)
Correct.

Power values are NOT filtered as pressure values are using the A scale.

Not clear what you think that sentance means.

So converting bels to pressure would give a dB value, not dBA.
Correct.

But I see no reason why power couldn't be measured
using the same filter to give you a 'belA' rating.

That makes no sense. Its the distribution of sound with frequency
and intensity thats relevant to the ear's perception of sound. So
there cant be a simple factor that can be applied between the
two. As should be obvious from the different ration you saw
between bels and dBA with the hard drive and the fan.

Wonder why they don't do it that way?

Because it aint even possible.

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.

And here you are massively mangling in the basic metric scale units
into a MUCH more complicated concept. The difference between
dB and B is just the metric scale unit. Like between M and kM.

This seems to make a dBA rating a better indicator of
how loud a drive will appear than what a bel rating is,
Yes.

and yet most manufacturers don't give
you the dBA rating. Doesn't make sense.

Thats because even the dBA is pretty hopeless with
hard drive noises for the reasons I already pointed out.

OTOH, all the acoustic power generated
by a drive has to be dissipated somewhere,

Yes, but thats not relevant to how noisy the drive itself is.

much of it in the case frame and covers
which can resonate and make things worst,

And particularly the Barracudas can choose
to add sound damping to the drive itself too.

so I guess knowing the unfiltered power rating is good too.

Trouble is that that brings up yet another problem. Some of
the higher frequency sounds are rather easier to damp by
how the drive is mounted, and that resonance effect can never
be quantified with the drive itself, it depends on the case etc.
So cant be stated by a drive manufacturer on a datasheet.

What would really help with HD noise is switching
to 2.5" drives, even 10,000 RPM models.

Thats mad. It depends entirely on where the noise is coming from.
If the drive rotation system is very quiet at 7200, and the bulk of
the noise is from head activity, you wont get that effect necessarily.

3.5" drive storage capacity is actually getting too
big for most home systems unless used for video.

Maybe. But 2.5" drives of what you consider to be a
suitable size are much slower and much more expensive.

Makes a lot more sense to say buy a very quiet 60GB
single platter 3.5" drive like a Samsung P80 and revel in
the tons on space and forget about analy comparing pretty
useless dBA numbers and just revel in the quiet drive.

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.

Because that is completely pointless when clearly
its easy enough to make a very quiet 3.5" hard drive.

The modern reality is that its only something that a couple
of hard drive manufacturers care much about and one of
those has blown both feet right off on that by disabling
AAM which is an excellent way of making a drive quiet.

IBM/Hitachi has been stupid enough to have the deliberate
movement of the heads to avoid them staying on the same
track for too long when idle, irritatingly noisy for no good
reason at all. The fool responsible for that terminal insanity
should be taken out the back and shot.

 

[J.Clarke]

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.

Why would that help? What leads you to believe that a 2.5" drive with a
given capacity and performance level will be quieter than a 3.5" drive
with the same capacity and performance level?

3.5" drive storage capacity is actually getting
too big for most home systems unless used for video.

But many home systems _are_ used for video. And for that a 200 gig
drive is not all that large--I'm debating whether to upgrade my server
to a terabyte array or just wait for terabyte drives to drop out of the
bottom of the market at 50 bucks a pop.

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.

Where would be the market for it? What do you believe it would gain and
why?

 

[J.Clarke]

Would you have said the same thing back when only 5.25" drives were
available and someone mentioned 3.5" drives?

Yes. But why do you feel that that is relevant?

Lower mass should help a
lot

Why would this be? Why do you believe that reducing mass will reduce
noise?

and also allow higher performance.

Why do you believe that reducing mass will allow higher performance?

The only drawback compared to
a 3.5" drive would be storage capacity. But at the rate capacity is
increasing, that would not be a problem for long.


In that case the 2nd drive in your system could be 3.5" until 2.5"
drives got large enough for you.

And what do you believe that I would gain by such a combination over two
3.5" drives?

Even a terabyte is good for only
about 100 hours of HDTV - way less if you need to store uncompressed
data.

True--perhaps I should wait for exabyte drives to become available.

If it's faster, quieter, and consumes less power than any 3.5" drive,
the market would include just about everybody.

Even if it cost $20,000 each? If it's faster, quieter, consumes less
power, provides the same amount of storage, and costs the same, then it
has a market. Until then it would be a low-volume niche product that
wouldn't repay the development cost.

But you have yet to provide a convincing argument that it would be
faster, quieter, or consume less power.

I know I'd buy one

 

[J.Clarke]

I agree that a drive with a lower 'belA' rating could still have
higher sound pressure (dBA) in *some* directions (compared to the
drive with the higher 'belA' rating) even though the average of *many*
directions is lower. But the same is true for bel ratings. A drive
with a lower bel rating *might* still produce a higher sound pressure
at your ear. Sit at a different angle to the drives and just the
opposite could be true. So maybe what you really mean is that 'belA'
makes no more sense than bel.

The 12dBA, 3.5 bel fan I mentioned (a Papst 8412NGL,
http://www.papstplc.com/downloads/DC/8400n.pdf) would surely have very
differently shaped isobars (is that the right word here?) than what a
HD would, no doubt with a 'high gain' for the direction the fan is
blowing in and much lower in back. A hard drive would have pressure
variations too but I don't think anywhere near as much as a fan.

If all fans were rated in bels (or belA) only, would the ratings be
useful in comparing fans? I think so because the pattern for the
isobars for one fan shouldn't vary by any significant amount from
another fan. I suspect the same is true for hard drives of the same
type. But you can't compare bels for a fan to the bels for a HD to
determine which will appear louder (as my examples show very well).

The difficulty with all of this is that there is no established standard
for measuring the sound pressure or sound power levels of either drives
or fans. Therefore any differences in the reported measurements may be
the result of differences in the test procedures rather than in the
devices themselves.

I still think it's possible even if of no value. If the pressure
readings made for computing sound power were all "A" filtered, the bel
value would be "A" filtered too it seems to me.


I don't know what you're talking about here. Bel is used for acoustic
power, dB or dBA for acoustic pressure. I haven't used B anywhere.

That statement makes no sense. "dB" is the abbreviation for "decibel",
which is one tenth of a bel, just as "dm" is the abbreviation for
"decimeter", one tenth of a meter. "Bel" is "B" and "B" is "Bel" when
discussing acoustic measurements. B or Bel is used for acoustic
pressure and acoustic power and many other things. dB is used for
acoustic pressure and acoustic power and many other things. dB(A) is
normally used for acoustic pressure because that's the only area in
which weighting to provide a measurement comparable to the response
curve of the human ear has real relevance.

For some reason some disk manufacturers have been using B for acoustic
power and dB for acoustic pressure but that is not anything that they
are required to do by any standard or convention.

Still better than nothing. What I wish they'd do is provide an FFT of
a drive's noise so you could see the amplitude of all frequencies. A
sizable spike at some frequency (which would add practically nothing
to the bel rating) would be a clear sign to avoid the drive. HD
Reviewer's should do this. All they'd need is a PC with a sound
board, a good microphone and the right software.

Actually, that's not a bad idea.

They should provide everything, bels, dBA, sones, FFT plot and let
potential buyers go by whatever they want.

If you've got the FFT then you should be able to calculate the rest.

All else being equal, a smaller drive will be quieter. There's no
doubt about it in my mind.


That's because they're made for laptops. So far, the primary design
goal for 2.5" drives has been low power consumption, not high
performance. A 2.5" drive's performance should be able to exceed that
of a 3.5" for the same reasons 3.5" exceeds 5.25": lower mass in every
part. Do you think 3.5" is some kind of magic number for hard drives,
that anything bigger or smaller must have poorer specs?


That may be ok for now, but what would you want in 5 or 10 years?
Wouldn't you prefer a 1TB+, 2.5" or less drive with much faster access
times, lower power consumption AND lower noise?

How about a one petabyte, .25" square solid state storage device with
nanosecond access, milliwatts of power consumption, and zero noise? How
long do you want to wait? How much do you want to pay?

You're probably one of those guys who said "64KB is enough memory for
anybody." I'm not as anti-progress as you seem to be.

Don't know if you've ever lived with Barracuda IVs. The ones I have are
inaudible--the first time I powered one up I thought it was broken
because I couldn't tell that it was doing anything. And when it started
seeking I could feel it if I touched the drive but could not hear it.
There is no real point in trying to make a drive quieter than that.

 

[Mark M]

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

From http://tinyurl.com/xis6 ...

========START 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.
======= END QUOTE

 

[John H.]

Why would that help? What leads you to believe that a 2.5" drive with a
given capacity and performance level will be quieter than a 3.5" drive
with the same capacity and performance level?

Would you have said the same thing back when only 5.25" drives were
available and someone mentioned 3.5" drives? Lower mass should help a
lot and also allow higher performance. The only drawback compared to a
3.5" drive would be storage capacity. But at the rate capacity is
increasing, that would not be a problem for long.

But many home systems _are_ used for video. And for that a 200 gig
drive is not all that large--I'm debating whether to upgrade my server
to a terabyte array or just wait for terabyte drives to drop out of the
bottom of the market at 50 bucks a pop.

In that case the 2nd drive in your system could be 3.5" until 2.5"
drives got large enough for you. Even a terabyte is good for only about
100 hours of HDTV - way less if you need to store uncompressed data.

Where would be the market for it? What do you believe it would gain and
why?

If it's faster, quieter, and consumes less power than any 3.5" drive,
the market would include just about everybody. I know I'd buy one
tomorrow if I could.

 

[John H.]

That makes no sense. Its the distribution of sound with frequency
and intensity thats relevant to the ear's perception of sound. So
there cant be a simple factor that can be applied between the
two. As should be obvious from the different ration you saw
between bels and dBA with the hard drive and the fan.

I agree that a drive with a lower 'belA' rating could still have higher
sound pressure (dBA) in *some* directions (compared to the drive with
the higher 'belA' rating) even though the average of *many* directions
is lower. But the same is true for bel ratings. A drive with a lower
bel rating *might* still produce a higher sound pressure at your ear.
Sit at a different angle to the drives and just the opposite could be
true. So maybe what you really mean is that 'belA' makes no more sense
than bel.

The 12dBA, 3.5 bel fan I mentioned (a Papst 8412NGL,
http://www.papstplc.com/downloads/DC/8400n.pdf) would surely have very
differently shaped isobars (is that the right word here?) than what a HD
would, no doubt with a 'high gain' for the direction the fan is blowing
in and much lower in back. A hard drive would have pressure variations
too but I don't think anywhere near as much as a fan.

If all fans were rated in bels (or belA) only, would the ratings be
useful in comparing fans? I think so because the pattern for the
isobars for one fan shouldn't vary by any significant amount from
another fan. I suspect the same is true for hard drives of the same
type. But you can't compare bels for a fan to the bels for a HD to
determine which will appear louder (as my examples show very well).

Because it aint even possible.

I still think it's possible even if of no value. If the pressure
readings made for computing sound power were all "A" filtered, the bel
value would be "A" filtered too it seems to me.

And here you are massively mangling in the basic metric scale units
into a MUCH more complicated concept. The difference between
dB and B is just the metric scale unit. Like between M and kM.

I don't know what you're talking about here. Bel is used for acoustic
power, dB or dBA for acoustic pressure. I haven't used B anywhere.

Thats because even the dBA is pretty hopeless with
hard drive noises for the reasons I already pointed out.

Still better than nothing. What I wish they'd do is provide an FFT of a
drive's noise so you could see the amplitude of all frequencies. A
sizable spike at some frequency (which would add practically nothing to
the bel rating) would be a clear sign to avoid the drive. HD Reviewer's
should do this. All they'd need is a PC with a sound board, a good
microphone and the right software.

Yes, but thats not relevant to how noisy the drive itself is.


And particularly the Barracudas can choose
to add sound damping to the drive itself too.


Trouble is that that brings up yet another problem. Some of
the higher frequency sounds are rather easier to damp by
how the drive is mounted, and that resonance effect can never
be quantified with the drive itself, it depends on the case etc.
So cant be stated by a drive manufacturer on a datasheet.

They should provide everything, bels, dBA, sones, FFT plot and let
potential buyers go by whatever they want.

Thats mad. It depends entirely on where the noise is coming from.
If the drive rotation system is very quiet at 7200, and the bulk of
the noise is from head activity, you wont get that effect necessarily.

All else being equal, a smaller drive will be quieter. There's no doubt
about it in my mind.

Maybe. But 2.5" drives of what you consider to be a
suitable size are much slower and much more expensive.

That's because they're made for laptops. So far, the primary design goal
for 2.5" drives has been low power consumption, not high performance. A
2.5" drive's performance should be able to exceed that of a 3.5" for the
same reasons 3.5" exceeds 5.25": lower mass in every part. Do you think
3.5" is some kind of magic number for hard drives, that anything bigger
or smaller must have poorer specs?

Makes a lot more sense to say buy a very quiet 60GB
single platter 3.5" drive like a Samsung P80 and revel in
the tons on space and forget about analy comparing pretty
useless dBA numbers and just revel in the quiet drive.

That may be ok for now, but what would you want in 5 or 10 years?
Wouldn't you prefer a 1TB+, 2.5" or less drive with much faster access
times, lower power consumption AND lower noise?

Because that is completely pointless when clearly
its easy enough to make a very quiet 3.5" hard drive.

You're probably one of those guys who said "64KB is enough memory for
anybody." I'm not as anti-progress as you seem to be.

The modern reality is that its only something that a couple
of hard drive manufacturers care much about and one of
those has blown both feet right off on that by disabling
AAM which is an excellent way of making a drive quiet.

I wonder how long Seagate will continue to do that if other
manufacturers never follow suit and get away with it? If they're
worried about a patent then they should just pay for it - probably
wouldn't be over $0.25 or so per drive.

IBM/Hitachi has been stupid enough to have the deliberate
movement of the heads to avoid them staying on the same
track for too long when idle, irritatingly noisy for no good
reason at all. The fool responsible for that terminal insanity
should be taken out the back and shot.

How do other manufacturers avoid the problem of heat buildup? They don't
move the heads too?

BTW, how S.M.A.R.T. is your Samsung? Can it do temperature? How about
the error rate attributes? For some reason reviewers never talk about
S.M.A.R.T. capabilities or lack thereof.

 

[Folkert Rienstra]

From http://tinyurl.com/xis6 ...

========START 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.
======= END QUOTE

Aha, now I get it. You and CWatters are one and the same person,
It just takes you a day to switch from one to the other.

 

[Rod Speed]

I agree that a drive with a lower 'belA' rating could still have
higher sound pressure (dBA) in *some* directions (compared
to the drive with the higher 'belA' rating) even though the average
of *many* directions is lower. But the same is true for bel ratings.

You're mangling the entire story utterly. The only difference
between bels and decibels, B and dB is the usual metric
scale factor. Just like between M and KM etc.

The A signifys a quite different application of the A law to the
sound being measured to allow for the ear's frequency response.

Thats all an entirely separate issue to whether the sound
is being radiated uniformly in all directions. Thats hardly
ever the case with real world sound sources and certainly
isnt whats seen with hard drives or fans.

A drive with a lower bel rating *might* still produce a
higher sound pressure at your ear. Sit at a different
angle to the drives and just the opposite could be true.

Correct. BUT thats an entirely separate issue to the A
law compensation for the frequency response of the ear.

So maybe what you really mean is that
'belA' makes no more sense than bel.

Wrong. The frequency response of the ear is still a very
important factor in the perception of how noisy a drive is.

The problem is that its only part of the story and the other
real problem with quantifying how noisy a drive is is the MINDS
perception of noises. Some sounds produce very little sound
pressure but are very irritating to the MIND. And the reason
that isnt quantified is because its essentially unquantifiable.
Unlike the frequency response of the ear.

The 12dBA, 3.5 bel fan I mentioned (a Papst 8412NGL,
http://www.papstplc.com/downloads/DC/8400n.pdf) would surely
have very differently shaped isobars (is that the right word here?)

Nope. Presumably you mean the spacial contours of equal SPL.

than what a HD would,

Yes, but the much more important factor is the different
frequencys of the sounds produced, and the effect of the
A law filter on those. THATS the main factor in the different
ratio between the dBA and bel values with the two devices.

no doubt with a 'high gain'

There is no 'gain'. Certainly the sound isnt uniformly
radiated in all directions with both types of device.

for the direction the fan is blowing in and much lower in back.

You dont get that effect either with quiet fans.

A hard drive would have pressure variations too
but I don't think anywhere near as much as a fan.

Thats just plain wrong too, particularly with the drives that
have acoustic damping designed in like the Barracudas.
Clearly there wont be as much sound getting thru the thick
rubber mat in some directions. Thats the whole point of it.

If all fans were rated in bels (or belA) only,
would the ratings be useful in comparing fans?

To some extent, particularly because fans are much
more uniform noise sources, particularly if they are
constant speed fans. Uniform in the sense of the frequency
distribution of the noise they make. So dBA is more useful
when comparing fans than it is with hard drives which produce
different noises depending on what they are doing etc.

And its the dBA that matters because that allows for the
frequency response of the ears. But you STILL cant have
a simple ratio between dBA and bels even with just fans,
because some fans produce a lot more high frequency
noise than others, particularly high speed small fans
produce a lot more air turbulence noise than much
slower rotating large fans moving the same volume of air.

I think so because the pattern for the isobars for one fan
shouldn't vary by any significant amount from another fan.

Thats just plain wrong too. The spacial distribution of
the noise will vary significantly between a high speed
very small fan and a big slow rotating fan both moving
the same volume of air. And then you have the other
massive difference between the types of fans, radial
bladed fans and turbines/blowers, cylindrical fans etc.

At the extremes you get quite different effects when
the tip speeds are approaching the speed of sound too.

I suspect the same is true for hard drives of the same type.

You're wrong. Most obviously because the design of the body
of the drive has a big effect on the spacial distribution of sound.

AND when the frequency of the sounds vary from drive
to drive, there cant be a simple conversion between
dBA and bels either, just because of the A law curve.

But you can't compare bels for a fan to the bels for a HD to
determine which will appear louder (as my examples show very well).

You cant with hard drives either as I pointed
out in your original list of particular drives.

I still think it's possible

You're wrong. It aint. While ever the frequency of the
noise produced by drives vary from drive to drive, there
cant ever be a simple ratio between dBA and bels.

even if of no value. If the pressure readings made
for computing sound power were all "A" filtered, the
bel value would be "A" filtered too it seems to me.

You're wrong again. The is NO filter applied the bel reading.
Thats the whole point of the A letter in dBA, it signifys that
THAT value has the A law filter applied.

I don't know what you're talking about here. Bel is used for acoustic
power, dB or dBA for acoustic pressure. I haven't used B anywhere.

B is just Bel. dB is decibel. dB aint the same as dBA.

Still better than nothing.

Sure, and thats why its quoted.

What I wish they'd do is provide an FFT of a drive's
noise so you could see the amplitude of all frequencies.

That would be useless as far as how irritating it is TO THE MIND.

A sizable spike at some frequency (which would add practically
nothing to the bel rating) would be a clear sign to avoid the drive.

Nope. Some frequencys are barely audible. True in spades of
TVs where the line frequency isnt even audible for most people.

HD Reviewer's should do this. All they'd
need is a > PC with a sound board, a
good microphone and the right software.

And that would be completely useless when the main
problem today is how irritating the sound is TO THE MIND.

You dont even get general agreement on that. Some find
that white noise is quite soothing and produce it deliberately.
Some find that the residual whistle you end up with with
very quiet systems not objectionable at all, others hate it.

Some find soft sounds produced by a drive seeking
quite acceptible and the sound like a cricket in a small
cardboard box very irritating indeed in comparison.

They should provide everything, bels, dBA, sones, FFT
plot and let potential buyers go by whatever they want.

Might as well cut to the chase and include a wav
file measured under standard conditions, say the
drive running bare, outside any housing at all and
captured at the maximum SPL direction.

But even that would be pretty useless because some
sounds would be muffled much better by the typical case
than others. Non fluid bearing whine is particularly bad there.

And that opens up a whole nother can of worms, the
variation in bearing noise over time, and from copy to copy.

Its a lot simpler to quote the dBA and accept that that is
only useful for the most gross differences between drives.

All else being equal, a smaller drive will be quieter.
Bullshit.

There's no doubt about it in my mind.

Your problem.

That's because they're made for laptops.

Nope, thats the inevitable result of having to be smaller.

So far, the primary design goal for 2.5" drives has
been low power consumption, not high performance.

The primary goal for 2.5" drives is the physical form factor.

A 2.5" drive's performance should be able to exceed that of a 3.5"
Bullshit.

for the same reasons 3.5" exceeds 5.25": lower mass in every part.

More bullshit. And when the drive is essentially
silent when its idle, just rotating, reducing the size
of the platters cant make it any quieter than that.

Do you think 3.5" is some kind of magic
number for hard drives, that anything bigger
or smaller must have poorer specs?

Obviously not. But like I said, if the 3.5" drive is already
essentially silent when its idle, just rotating, reducing the
platter size wont have any effect on that noise, and you
are just wasting your money on the higher cost of the
smaller platters. Particularly when a single platter 3.5"
drive has already got ample space for all except video
with desktop systems.

That may be ok for now, but what would you want in 5 or 10 years?

Likely a much bigger drive to replace my current collection of video
tapes. They're a pain in the arse physically, just excellent value
per GB. And I only use those for time shifting, not for archival.

Wouldn't you prefer a 1TB+,
Yes.

2.5" or less drive

I dont care about the physical size.

with much faster access times,

Nope, that has no effect on what I do now.

lower power consumption

Dont care about that either except that a little less
would be easier as far as being able to stack drives
adjacent and ignore the drive temp is concerned.

AND lower noise?

Already got that. Its already so low that I cant detect
it being powered down or not. Already lower than ALL
the laptop drives I use. Amd thats with the 3.5" drive in
a case with never useing the case covers for convenience.

You're probably one of those guys who said
"64KB is enough memory for anybody."

Nope, never did.

I'm not as anti-progress as you seem to be.

I'm not anti progress at all. I've got the sense to have noticed
that the drive is ALREADY completely silent in the sense that
I cant detect when its been turned off and the sense to realise
that it would be stupid to use a 2.5" drive that wont perform
as well and which will cost significantly more in that situation.

I would welcome that drive available in multi TB
size at as low a cost as the video tapes per TB,
but that wont be happening any time soon.

When it does, I'll bin the video tapes as quickly as I have floppys.

I wonder how long Seagate will continue to do that if other
manufacturers never follow suit and get away with it?

I doubt too many of the mug punters who buy the
absolute vast bulk of hard drives would even know
what AAM was if it bit them on their lard arses.

If they're worried about a patent then they should just pay
for it - probably wouldn't be over $0.25 or so per drive.

Yep, thats what I meant.

How do other manufacturers avoid the problem of heat buildup?

Basically move the heads silently.

They don't move the heads too?
Yep.

BTW, how S.M.A.R.T. is your Samsung? Can it do temperature?
Yep.

How about the error rate attributes?

Its fine, as complete a set as with any.

For some reason reviewers never talk about
S.M.A.R.T. capabilities or lack thereof.

Yeah, most of them wouldnt know what
SMART was if it bit them on their lard arses.

I dont recall any of them actually citing the SMART
temperature rise seen in active use in their reviews.
Tho admittedly I dont bother with reviews much.

 

[Peter Martin]

Aha, now I get it. You and CWatters are one and the same
person, It just takes you a day to switch from one to the other.

Or thats what turns up using google, cretin wanker.