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The art of PC noise reduction


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A lot of hardware review sites I know of, when discussing "noise", tend to focus on the obvious causes of noise: fans. The lower the decibels, the lower the noise generated by whatever the device. So if you have not-so-noisy hardware, you should end up with a not-so-noisy machine, right?

Well, things aren't so simple and I suppose this should have been more obvious given whom I work for. True story:

I recently upgraded my memory from 256MB to 512MB for a good cause: Tron 2.0. (Aside: that game rocks! It captures the spirit of the original movie perfectly and was just all around excellent -- but that's a topic for another thread...)

So I figured to get maximum airflow, I'd mount my existing 256MB stick closest to the CPU and the new one farthest, leaving one intervening and empty RAM slot open on my motherboard.

Well, after I buttoned up the case and restarted the system, I noticed things got noisier. I chalked this up to me nudging a cable or something into a fan or whatever. But I wasn't about to drag the PC out of the desk again just over a wire; I need a better excuse to go through that kind of pain than that.

Two months go by. I now have an excuse to attack the problem because I need to install an Ethernet card in preparation to getting broadband via cable. (Another aside: broadband rocks!) I put the card in, jiggle the wires around some, button it up and restart.

The machine is just as noisy. No, its worse. Much worse.

Fortunately my machine's front face removes allowing me access to the drive bays, which are on slide-out rails (kudos to whomever thought up that configuration). So, I get a drive out of the way and poke my hand inside and start tugging cables, with mixed results. Sometimes the noise gets better. Sometimes worse.

OK, I think: let's go back to the beginning. What causes the vibration? Obvious: the CPU fan. I touch it with my finger and its got the vibe pretty good. Maybe that means its off-balance or something, I don't know, but I have to live with that.

I follow the power wire from the fan to the knot of power cables. That small wire got the vibe but the cables aren't even vibrating in the least. So if it isn't the cables, what is it?

To make a long story short (too late?) I started feeling around the internals. And guess what? Remember that new RAM stick I put in? It is vibrating incredibly strongly. Suprised, I touch its mate closest to the CPU. No vibration. Touch the new one again and apply pressure -- the vibration stops.

In a moment of inspiration, I powered down, unplugged and moved that new stick closer to the CPU (the middle RAM slot). Power back up -- and the computer is much, much quieter. Actually, I think I do have a cable vibrating on something now, but I can do something about that.

So what was happening? I work for an engineering company, and although I don't know much about the finer points of mechanical engineering my theory is that the vibrations of the fan travel through the motherboard, and that RAM stick was at just the right location such that the frequency of vibration set off a harmonic reaction in the RAM stick causing it to vibrate in sync, amplifying the fan's vibrational frequency. Just like a tuning fork vibrating in reaction to a note being played. Moving the card changed the distance to the CPU fan, and/or moved it to a region of the board that may have been vibrating with a lesser amplitude or different frequency, thus dampening the noise.

I'm going to talk to one of our real engineers tomorrow and see how involved creating a model for analysis of this would be. It'd have to be simplified, but I figure a vibrating block attached to a thin plate with another plate jutting out should be sufficient. Of course, to be really accurate I'd need to know the exact dimensions of the mobo, the exact positions of the screw holes, etc. I just may create an arbitrary mock-up and experiment some.

Moral of story: having quiet parts is a good start, but never underestimate the havoc harmonic physics can wreak on you eardrums.

Another moral learned today: never wear earphones when you are blindly searching for the "headphone out" jack on a sound card while playing music and your software volume control is set to high volume. Not if you value your hearing, anyway.

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I have folded paper towers under the 2 front "feet" of the casing of my secondary pc, cos otherwise it would make an horribly loud noise. I also had to play with the cpu fan screws every night for about 2 weeks to remove the vibrations between the fan and the heatsink and its intermittent noise, but now both my systems are making as little noise as they could

quote:

Another moral learned today: never wear earphones when you are blindly searching for the "headphone out" jack on a sound card while playing music and your software volume control is set to high volume. Not if you value your hearing, anyway.

I have a VERY odd problem with my sound system ( an old but reliable and good one) - sometimes for reasons i can't determine i lose sound in one side. It's really not the computer, but it seems that unplugging and plugging back in the cable from the computer end works . I put my headphones offset to my ears so i don't temporarily lose hearing capability .. oh and turn off the speakers (if applicable)

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quote:

So what was happening? I work for an engineering company, and although I don't know much about the finer points of mechanical engineering my theory is that the vibrations of the fan travel through the motherboard, and that RAM stick was at just the right location such that the frequency of vibration set off a harmonic reaction in the RAM stick causing it to vibrate in sync, amplifying the fan's vibrational frequency. Just like a tuning fork vibrating in reaction to a note being played. Moving the card changed the distance to the CPU fan, and/or moved it to a region of the board that may have been vibrating with a lesser amplitude or different frequency, thus dampening the noise.

I'm going to talk to one of our real engineers tomorrow and see how involved creating a model for analysis of this would be. It'd have to be simplified, but I figure a vibrating block attached to a thin plate with another plate jutting out should be sufficient. Of course, to be really accurate I'd need to know the exact dimensions of the mobo, the exact positions of the screw holes, etc. I just may create an arbitrary mock-up and experiment some.


In the military, we start out by making sure the 2 cent plastic hinges used to mount the RAM aren't bent...

Save the wind tunnel and supercomputers for other stuff

Sorry, it was just too good to pass up

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quote:


Originally posted by Epsilon 5:

I have folded paper towers under the 2 front "feet" of the casing of my secondary pc, cos otherwise it would make an horribly loud noise. I also had to play with the cpu fan screws every night for about 2 weeks to remove the vibrations between the fan and the heatsink and its intermittent noise, but now both my systems are making as little noise as they could


Same here, only its a faux-rubber non-slip matting. That isn't such a bad idea, though, about the fan screws, except mine is held on by two spring-loaded metal clips. Maybe one day I'll mess with that some more, but I wasted enough time on it already as it is

quote:


Originally posted by Alacard:

In the military, we start out by making sure the 2 cent plastic hinges used to mount the RAM aren't bent...

Save the wind tunnel and supercomputers for other stuff


Heh -- I thought of that and they were rock solid; I just didn't mention it. The story was getting long enough as it was

Supercomputers? Nah, anyone can do this on a run-of-the-mill desktop PC; besides, with end-of-year slowdown I have some time on my hands.

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quote:

Originally posted by Epsilon 5:

I have a VERY odd problem with my sound system ( an old but reliable and good one) - sometimes for reasons i can't determine i lose sound in one side. It's really not the computer, but it seems that unplugging and plugging back in the cable from the computer end works . I put my headphones offset to my ears so i don't temporarily lose hearing capability .. oh and turn off the speakers (if applicable)

Sounds like your plug may be going bad, or you've got dust in the jack. When your computer is off, try to stick a clean and I mean clean pipe cleaner down the jack. If its not like sterile it could make your problems worse (Trust me, I learned that the hard way; sound crackled in the final performance of a show people were paying $100 bucks to go see. Boy, did my boss beat the shit out of me for that one.) cause it can just deposit more dust into the jack. If that doesn't help, you might look to buy a new sound system, or pm me and I might be able to help you further.

Oh, one last thing, if it isn't dust, try cleaning the plug with a little alcohol, then don't touch the tip before you plug it back in. Might just be hand oils on the plug causing it.

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