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PC CPU fan

T

Terry Pinnell

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.

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?
 
M

Michael Gray

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.

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?

It is usually the sides of the case behaving like a drum.
Try damping both sides with your hands, and see what happens.
 
T

Terry Pinnell

Jan 1, 1970
0
Michael Gray said:
It is usually the sides of the case behaving like a drum.
Try damping both sides with your hands, and see what happens.

That makes sense, but holding both sides doesn't diminish the beat. I
can now *feel* it as well as hear it (~ 1 Hz). Any other ideas on
stopping it? How about that rpm reduction I mentioned?
 
D

Dave D

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?

You'll need to isolate the cause of the sound. Try stopping the CPU fan
briefly either by putting your finger on the centre hub of the fan or
unplugging it. Don't worry about overheating, an idle CPU will be OK for
several minutes without a fan before it gets uncomfortably warm. If the
noise is still there, go through all the other spinning devices one by one.
Disconnect hard drives and case fans and see if you can isolate the
offending item. Still no luck? Disconnect the cpu fan, case fans and all the
hard drives and power up. The only rotating item should be the power supply
fan. If the noise is still there, that's the problem.

I've seen quite a few noisy PSU fans, and the way they are mounted means
they can transfer a lot of noise and vibration to the case so it acts like a
resonating chamber. To confirm a noisy PSU fan, you can temporarily disable
it safely by powering off, inserting a plastic rod carefully into the blades
and powering back on. I've even stopped moving blades with a plastic
implement without any damage, but it's unnecessary for your purposes. Never
insert anything metallic or conductive. Don't run the PC for longer than
absolutely necessary with a disabled PSU fan, they get very hot rather
quickly!

Dave
 
T

Terry Pinnell

Jan 1, 1970
0
You'll need to isolate the cause of the sound. Try stopping the CPU fan
briefly either by putting your finger on the centre hub of the fan or
unplugging it. Don't worry about overheating, an idle CPU will be OK for
several minutes without a fan before it gets uncomfortably warm. If the
noise is still there, go through all the other spinning devices one by one.
Disconnect hard drives and case fans and see if you can isolate the
offending item. Still no luck? Disconnect the cpu fan, case fans and all the
hard drives and power up. The only rotating item should be the power supply
fan. If the noise is still there, that's the problem.

I've seen quite a few noisy PSU fans, and the way they are mounted means
they can transfer a lot of noise and vibration to the case so it acts like a
resonating chamber. To confirm a noisy PSU fan, you can temporarily disable
it safely by powering off, inserting a plastic rod carefully into the blades
and powering back on. I've even stopped moving blades with a plastic
implement without any damage, but it's unnecessary for your purposes. Never
insert anything metallic or conductive. Don't run the PC for longer than
absolutely necessary with a disabled PSU fan, they get very hot rather
quickly!

Thanks, I'll schedule that for when I don't need the PC for a while!

But if this is a *beat*, presumably there are two components, not one?

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.

BTW, when it comes to disconnecting a HD to test its impact on the
noise, can I just close WinXP, remove the power plug from it and
reboot? On later reconnecting it, will WinXP have to go through any
hardware wizardry? My experience of that is mixed, so I like to avoid
it whenever possible!
 
J

John - kd5yi

Jan 1, 1970
0
Terry Pinnell said:
That makes sense, but holding both sides doesn't diminish the beat. I
can now *feel* it as well as hear it (~ 1 Hz). Any other ideas on
stopping it? How about that rpm reduction I mentioned?



You are an exceptional person to be able to hear 1 Hz!

John
 
D

Dave D

Jan 1, 1970
0
Thanks, I'll schedule that for when I don't need the PC for a while!

But if this is a *beat*, presumably there are two components, not one?

Not necessarily, it could be the natural resonance of the component/PC
casing.
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.

Could be the new hard drive isn't fantastically well balanced. For example,
I've had UW SCSI drives create quite a racket as they can vibrate a bit more
than slower devices.
BTW, when it comes to disconnecting a HD to test its impact on the
noise, can I just close WinXP, remove the power plug from it and
reboot?

Yes, but you don't have to let Windows boot to test for noise, just hit
pause at the POST screen, or hit F8 to stop Windows starting.
On later reconnecting it, will WinXP have to go through any
hardware wizardry?
No.

My experience of that is mixed, so I like to avoid
it whenever possible!

--

Best to not let Windows boot then. I've seen windows change drive letters
under these circumstances, which may or may not be a problem for you.

Dave
 
T

Terry Pinnell

Jan 1, 1970
0
Dave D said:
Not necessarily, it could be the natural resonance of the component/PC
casing.


Could be the new hard drive isn't fantastically well balanced. For example,
I've had UW SCSI drives create quite a racket as they can vibrate a bit more
than slower devices.


Yes, but you don't have to let Windows boot to test for noise, just hit
pause at the POST screen, or hit F8 to stop Windows starting.


Best to not let Windows boot then. I've seen windows change drive letters
under these circumstances, which may or may not be a problem for you.

Dave

Thanks a lot for the follow-up.
 
K

Keith Williams

Jan 1, 1970
0
Not necessarily, it could be the natural resonance of the component/PC
casing.


Could be the new hard drive isn't fantastically well balanced. For example,
I've had UW SCSI drives create quite a racket as they can vibrate a bit more
than slower devices.

At 1Hz? I doubt it, unless it is beating against something else (like another
drive ;). I'd suspect the fans before the drive(s). Disconnect one at a time
and listen for any change.

Best to not let Windows boot then. I've seen windows change drive letters
under these circumstances, which may or may not be a problem for you.

I've had Windows change drive letters for no apparent reason too. It's easy to
change 'em back though.
 
A

Anna Daptor

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?
How many HDD's have you? I had a similar problem when I added a second 7200
HDD to my system. It was a complete ba£T@rd to solve the problem, eventually
cured by moving the second drive into an external USB2 enclosure.
 
G

Glenn Gundlach

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

John

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)?
GG
 
T

Terry Pinnell

Jan 1, 1970
0
How many HDD's have you? I had a similar problem when I added a second 7200
HDD to my system. It was a complete ba£T@rd to solve the problem, eventually
cured by moving the second drive into an external USB2 enclosure.

This new one is the third. I had to buy a 5.25" tray for it, to
install it below my DVD & CD drives. All 3 are 7200 rpm.
 
T

Terry Pinnell

Jan 1, 1970
0
Glenn Gundlach said:
John - kd5yi wrote:

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)?
GG

Thanks Glenn. All 3 of my HDs are Maxtors (2 x 60GB, and this latest
200GB), and all are 7200 rpm. Are you speculating that one might be
spinning at 432.000 kHz, and the other at 432.001 kHz?!
 
J

John Woodgate

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

Yes, with my old DIY computer with two hard drives.

What is your computer standing on? If it's rigidly connected to the
building structure, the beating frequencies will get into the structure
and appear, amplified, in all sorts of strange places, as you found.

Try standing the computer on a THICK (think 75 mm) of none-too-soft PU
foam, that doesn't collapse under the weight.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Terry Pinnell
Thanks Glenn. All 3 of my HDs are Maxtors (2 x 60GB, and this latest
200GB), and all are 7200 rpm. Are you speculating that one might be
spinning at 432.000 kHz, and the other at 432.001 kHz?!

I think you multiplied by 60. 7200 RPM is 120 Hz.
 
J

John Woodgate

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

Try loosening its fixing screws. If that stops the beat, tighten
slightly at random until the beat comes back. Reverse last step. Relax.
 
T

Terry Pinnell

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Terry Pinnell


I think you multiplied by 60. 7200 RPM is 120 Hz.

Oops! That makes a lot more sense, thanks <g>.

So is it plausible that a HD1 could be spinning at 120 Hz and HD2 at
121 Hz (7260 rpm) to cause such a 'beat'?
 
T

Terry Pinnell

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Terry Pinnell


Try loosening its fixing screws. If that stops the beat, tighten
slightly at random until the beat comes back. Reverse last step. Relax.

OK, will try that, thanks. As the tray has to be removed to get at the
screws, that potentially implies means a lot of rebooting though.

It's too soon to be sure, but I think I've made an improvement by not
using the 'locking knob' after attaching the side panel of this MESH
UK Athlon 1800 PC. The LF hum is still there, but it sounds almost
steady now, rather than beating.

I may also try some self-adhesive insulation of some sort on that side
panel.
 
T

Terry Pinnell

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Terry Pinnell


Yes, with my old DIY computer with two hard drives.

What is your computer standing on? If it's rigidly connected to the
building structure, the beating frequencies will get into the structure
and appear, amplified, in all sorts of strange places, as you found.

Try standing the computer on a THICK (think 75 mm) of none-too-soft PU
foam, that doesn't collapse under the weight.

It's just resting on the carpet and underlay at the side of my desk.
Then wood flooring and plasterboard lounge ceiling below.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Terry Pinnell
So is it plausible that a HD1 could be spinning at 120 Hz and HD2 at
121 Hz (7260 rpm) to cause such a 'beat'?

Maybe, but you don't need to know. I've given you two ways to tackle it.
Try them.
 
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