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PC CPU fan

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John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Terry Pinnell
It's just resting on the carpet and underlay at the side of my desk.
Then wood flooring and plasterboard lounge ceiling below.

That's not effective sound insulation. Your wood floor will love to
vibrate at 1 Hz, even if it's not tuned to that frequency. You need a
THICK pad -- no, thicker than that!
 
T

The Cheese Machine

Jan 1, 1970
0
FWIW - Maplin's sound dampening kit (A48AK) works quite well, though not
exactly cheap at 18ukp, especially against HD chassis-borne noise.
 
R

Rich Grise

Jan 1, 1970
0
I'm getting a sort of 'beat' effect from my PC. It seems to have been
triggered (or maybe just increased to a level at which I've become
aware of it) by adding a new (third) HD.

I'm at my desk, and the PC is on the carpet 3 feet away, at the side
of the desk. I can just hear this beat from here, behind the familiar
high frequency fan and HD spinning sound. Kneeling on the floor with
my ear by the PC case, I can hear the beat distinctly, at about 1
cycle per second. But my real gripe is that directly below, downstairs
in the lounge, it's surprisingly distinct. By no means deafening, but
it is intrusive. I'm aware of it even while watching TV. This is
through carpet, underlay and 2 layers of plasterboard.

It's the resonant frequency of the floor itself. I'm ass-u-me-ing that
you're talking about the beat frequency, which sounds like, wOwwwOwwwOwww...,
is that accurate? If it's just going thumpa-thumpa-thumpa, then you need
to fire your yard boy. ;-P

Go either to a scrap yard or a construction site, and get something
very massive, like a paving tile or slab of metal, put it on the floor
where the computer is now. Put some kind of acoustic insulation on top
of it, like get a discarded wet suit or some old inner tubes, and put
the computer on top of that pile. Don't use "acoustical tile", because
you want the opposite of rigidity here.

Good Luck!
Rich

(of course, you could overwhelm it by playing that tape of the barking
dog that seems to come up here periodically. ;-) )
 
R

Rich Grise

Jan 1, 1970
0
I read in sci.electronics.design that Terry Pinnell


That's not effective sound insulation. Your wood floor will love to
vibrate at 1 Hz, even if it's not tuned to that frequency. You need a
THICK pad -- no, thicker than that!

Apropos nothing, I once was renting a guy's basement. It was always
uncomfortably cold, but there was a gas space heater, but all of the
warm air, of course, floated up to the ceiling (which was the underside
of the floor of the upstairs), so my feet would freeze, while my head
would sweat. In lieu of walking around the apartment on my hands, I
took one of those little fans - you know, the shaded-pole motor, with
about a 3" (8 cm?) aluminum fan blade - and hung it from a joist to
blow warm air downwards toward my bed and stuff. It went "THRUMMMMM!!!!"
and my roommate/landlord didn't like the noise. Well, it turns out
that he also had an old turntable (remember record players?) that he
was going to toss, so he let me salvage it, and I took a couple of
the suspension springs from the turntable, and hung my little fan
from them. The silence was golden. :) :)

Floors make surprisingly good sounding boards. :)

Good Luck!
Rich
 
R

Rich, Under the Affluence

Jan 1, 1970
0
I'm getting a sort of 'beat' effect from my PC. It seems to have been
triggered (or maybe just increased to a level at which I've become
aware of it) by adding a new (third) HD.

I'm at my desk, and the PC is on the carpet 3 feet away, at the side
of the desk. I can just hear this beat from here, behind the familiar
high frequency fan and HD spinning sound. Kneeling on the floor with
my ear by the PC case, I can hear the beat distinctly, at about 1
cycle per second. But my real gripe is that directly below, downstairs
in the lounge, it's surprisingly distinct. By no means deafening, but
it is intrusive. I'm aware of it even while watching TV. This is
through carpet, underlay and 2 layers of plasterboard.

Get an office that adjoins a machine shop/fab shop. I guarantee, you
won't notice the noise from the computer! ;-P

Cheers!
Rich
 
P

Pig Bladder

Jan 1, 1970
0
FWIW - Maplin's sound dampening kit (A48AK) works quite well, though not
exactly cheap at 18ukp, especially against HD chassis-borne noise.

Yup! Can't let them sounds dry out!
 
R

Rich Grise

Jan 1, 1970
0
Not at all, you can do it too. The beat he's hearing is the same as
tuning a musical instrument. My question is: how accurate is the '7200'
RPM? Would different models be phase locked or are they just 'close'?
AND, is it a balance issue with the drives (or fans)?

Well, drives shouldn't whine so much that they beat against each other's
whine (there's gotta be a joke in that sentence somewhere - anyone?) -
take the noisy drive back to the store, and get one that isn't eating
its own bearings.

Good Luck!
Rich
 
J

James Sweet

Jan 1, 1970
0
Terry Pinnell said:
I'm getting a sort of 'beat' effect from my PC. It seems to have been
triggered (or maybe just increased to a level at which I've become
aware of it) by adding a new (third) HD.

I'm at my desk, and the PC is on the carpet 3 feet away, at the side
of the desk. I can just hear this beat from here, behind the familiar
high frequency fan and HD spinning sound. Kneeling on the floor with
my ear by the PC case, I can hear the beat distinctly, at about 1
cycle per second. But my real gripe is that directly below, downstairs
in the lounge, it's surprisingly distinct. By no means deafening, but
it is intrusive. I'm aware of it even while watching TV. This is
through carpet, underlay and 2 layers of plasterboard.

I did also have mechanical noise from the fan (which itself may have
been due to multiple causes, such as bearings, dust and one loose
screw). But I've fixed that, and am left with this pesky beat. It
doesn't appear to be anything I can stop by touching any PC panels, or
even holding the fan itself. So I assume it's some sort of beat in the
air itself, caused by the rpm speeds of various components being very
close together? Rather like 'heterodyning' in radio terms?

I'm not sure what the best approach is. Presumably I can take the beat
frequency out of this apparently sensitive LF region by lowering the
CPU fan speed rpm a bit? I could wire a couple of series diodes in the
supply. Maybe as an initial step I should buy a new 60mm CPU fan,
which is surely unlikely to be similar in rpm speed to the present
one.

Any advice would be appreciated please. Anyone else had similar
behaviour?

I've had things like this happen when the hard drive bracket wasn't screwed
down tightly, or the case just poorly designed so it's not as rigid as it
should be. Sometimes if the floor is a little uneven and you set it a
certain way, some metal part of the case will resonate, sometimes moving it,
tightening screws, or sticking a piece of tape between whatever's vibrating
and whatever it's attached to will help.
 
F

Franc Zabkar

Jan 1, 1970
0
It may be coincidence, but I've only become aware of this since
installing a third HD - a 200GB Maxtor Diamond, 7200 rpm, in addition
to my two 60GB Maxtors.

I would think it unlikely that your two identical drives would spin at
a speed that is different enough to produce a 1Hz beat. That's a
difference of 1:120, or 1:360 if you consider a possible harmonic
effect of the motor's three windings. AFAIK, the speed is crystal
locked. Your observation in respect of the 200GB drive sounds more
plausible since it could involve different crystal frequencies.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.
 
F

Franc Zabkar

Jan 1, 1970
0
You are an exceptional person to be able to hear 1 Hz!

John

The 1Hz is the amplitude modulated envelope (cos b) of a higher
audible frequency (sin a). In other words, you are hearing a higher
frequency signal whose volume fluctuates at 1Hz.

sin (a + b) + sin (a - b) = 2 . sin a . cos b

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.
 
R

René

Jan 1, 1970
0
I would think it unlikely that your two identical drives would spin at
a speed that is different enough to produce a 1Hz beat. That's a
difference of 1:120, or 1:360 if you consider a possible harmonic
effect of the motor's three windings. AFAIK, the speed is crystal
locked. Your observation in respect of the 200GB drive sounds more
plausible since it could involve different crystal frequencies.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Obviously, the near empty new drive is filled with a minimal amount of
data, located on one side of the platter. This causes a considerable
unbalance, causing vibration.
Just put more stuff on that drive.

And now I will go on with my design of a battery charger that cuts off
the charging process based on weight increase of a charged pack.
 
P

Paul Burke

Jan 1, 1970
0
René said:
And now I will go on with my design of a battery charger that cuts off
the charging process based on weight increase of a charged pack.

Take a 12V, 100AH battery. That's 12*100*3600J = 4.32MJ. e=mc^2, so the
mass gain from flat to full is e/c^2 = 5e-11N, or about 5e-12Kg. Piece
of piss, but works better with bigger batteries.

Paul Burke
 
T

Terry Pinnell

Jan 1, 1970
0
The Cheese Machine said:
FWIW - Maplin's sound dampening kit (A48AK) works quite well, though not
exactly cheap at 18ukp, especially against HD chassis-borne noise.

Thanks, I'll take a look at it.

But I must say that I'm now into the 2nd day of *relative quiet* ! As
described earlier, this significant change has come about simply by
not using the 'locking lever' on the back corner of the PC case. In
fact, I have to conclude that I must have had it in that unlocked
state before installing my new HD.

I can still hear *some* LF noise, but only downstairs in the lounge,
not sitting here at the PC!
 
T

Terry Pinnell

Jan 1, 1970
0
Franc Zabkar said:
I would think it unlikely that your two identical drives would spin at
a speed that is different enough to produce a 1Hz beat. That's a
difference of 1:120, or 1:360 if you consider a possible harmonic
effect of the motor's three windings. AFAIK, the speed is crystal
locked. Your observation in respect of the 200GB drive sounds more
plausible since it could involve different crystal frequencies.

Thanks, makes sense. Just under 1% is probably acceptable tolerance
for an advertised speed of '7200 rpm'. Mind you, given that this new
one is Maxtor too, and broadly same 'Diamond' range, I'd have expected
the same crystal to be used.
 
T

Terry Pinnell

Jan 1, 1970
0
James Sweet said:
I've had things like this happen when the hard drive bracket wasn't screwed
down tightly, or the case just poorly designed so it's not as rigid as it
should be. Sometimes if the floor is a little uneven and you set it a
certain way, some metal part of the case will resonate, sometimes moving it,
tightening screws, or sticking a piece of tape between whatever's vibrating
and whatever it's attached to will help.

Thanks for all the follow-ups. As per my earlier post, situation is
now much improved.
 
J

John Woodgate

Jan 1, 1970
0
And now I will go on with my design of a battery charger that cuts off
the charging process based on weight increase of a charged pack.

Don't forget to correct for the buoyancy of the evolved hydrogen.
 
J

John Woodgate

Jan 1, 1970
0
(in said:
Take a 12V, 100AH battery. That's 12*100*3600J = 4.32MJ. e=mc^2, so the
mass gain from flat to full is e/c^2 = 5e-11N, or about 5e-12Kg. Piece
of piss, but works better with bigger batteries.
5 nanograms? I'm sure Win could measure that in a force 8 gale.
 
I

Ian

Jan 1, 1970
0
John Woodgate said:
Don't forget to correct for the buoyancy of the evolved hydrogen.

Once it has evolved, does it turn into Helium? Have to be careful about
fusing.

Regards
Ian
 
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