Computer near large speaker - bad idea?

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WCES Ryan

Gawd
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What are people's opinions on placing a PC near a large speaker (or enclosed subwoofer)? My apartment is fairly cramped, and with 2 PC's in the living room, I am having a hard time finding a way of keeping them distanced from my home theater speakers. Is this common sense that I don't seem to have? What harm could potentially come from this?
 
I'm not going to say its' a horrible idea, but it isn't a good idea either.
 
It's fine. Your PC is shielded, unless you have a plastic case. Just don't run cables over the speaker cables. You'll be able to hear if they are too close, your speaker will start humming or making clicking noises.
 
zoobaby said:
It's fine. Your PC is shielded, unless you have a plastic case. Just don't run cables over the speaker cables. You'll be able to hear if they are too close, your speaker will start humming or making clicking noises.
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I'm going to have to disagree with you big time on this one.

Some individual components have some shielding but not much. (Such as the actual tuner part of a TV-tuner card.) Point me towards some PC cases that have shielding please. I've never seen any that came with EM shielding. I know that Macintosh machines did in the past but even they ditched that when they put out their larger G5 boxes. Metal alone doesn't constitute shielding.
 
Dan_D said:
I'm going to have to disagree with you big time on this one.

Some individual components have some shielding but not much. (Such as the actual tuner part of a TV-tuner card.) Point me towards some PC cases that have shielding please. I've never seen any that came with EM shielding. I know that Macintosh machines did in the past but even they ditched that when they put out their larger G5 boxes. Metal alone doesn't constitute shielding.
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The PC box is itself a shield. Most PC cases are steel or aluminum boxes. Last time I put a shield on a board, it was made from cheap steel. Aluminum will stop noise too. The components inside are all noisy as hell, most do not have extra shielding. That is why I said don't route cables over the speaker wire.

Last time I looked premade PC models had to meet FCC regulations. The only way they do is because the case prevents the noise from leaking out.

EDIT: And as I stated above, if there is interference he should be able to hear it and make changes accordingly.

EDIT2: Any noise coming out will likely be common mode noise that is coupled onto the cables.
 
zoobaby said:
Most PC cases are steel or aluminum boxes. Last time I put a shield on a board, it was made from cheap steel. Aluminum will stop noise too. The components inside are all noisy as hell, most do not have extra shielding. The PC box is itself a shield. That is why I said don't route cables over the speaker wire.

Last time I looked premade PC models had to meet FCC regulations. The only way they do is because the case prevents the noise from leaking out.
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Steel and aluminum can stop some noises, sure, however EM shielding is generally made from a shiny tin-like material. I am not sure what differences this makes on a technical level. Pre-made PC's from companies like Dell, HP and Gateway need to meet FCC regulations but those regulations only specifically state that the PC isn't allowed to generate harmful interfearance or that any interfearance it does generate may only be within certain predetermined limits. However PC's and any other consumer level device have no restrictions on what interfearance they can receive. Meaning that if your TV or computer do not work while your microwave is on that's just too bad for you. Or something to that effect.

That is how I understood things at least. I could be wrong, I don't know. I don't work for the FCC nor do I pretend to understand all the legal jargon.
 
Dan, you are right about them receiving other interference. But they must pass the spec in regards to generating noise. That level is pretty low too. PC cases are very good at trapping noise in and keeping noise out. That means the only way for them to radiate or have noise injected into them, is via the external cables.

While I am not an expert in the EMC world, I do get to play in anechoic chambers from time to time in order to get products to meet FCC regulations.

Also that shinny tin like material used for shielding, it is typically cheap steel sheets.
 
zoobaby said:
Dan, you are right about them receiving other interference. But they must pass the spec in regards to generating noise. That level is pretty low too. PC cases are very good at trapping noise in and keeping noise out. That means the only way for them to radiate or have noise injected into them, is via the external cables.

While I am not an expert in the EMC world, I do get to play in anechoic chambers from time to time in order to get products to meet FCC regulations.

Also that shinny tin like material used for shielding, it is typically cheap steel sheets.
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Well good to know.
 
I had another thought on this as I was working today. If your case is plastic or if your case has a window in it, you do not want the speaker near that side of it. Interference could come through it. But you would hear the interference over the speakers. Kind of like when you place your cell phone on them and have someone call you, your speaker often catches the signal and hums along.

Also wanted to correct/qualify my statement on the cables, the noise itself is most likely to be generated by the boards inside the case, then couple onto the cable via the connector. That is why some cables have ferrites on them.

Sorry that Dan and I derailed you a bit, but it was all on topic. ;)

Let us know how it goes.
 
I know from experience that placing a CRT monitor next to speakers can cause unwanted discoloration over time. Moving the speaker and degaussing the monitor eliminates the problem though. The computer's case is better protected then a CRT though.

A computer's case will act to a certain extent as a faraday cage. An ideal faraday cage blocks RF (think cell phone in an elevator), but doesn't block all magnetic fields. The faraday cage effect from the case would block a fast changing magnetic field from the speakers, which, without the case, would induce current as it crosses the conductors in the PCBs traces. But the static magenetic field from your speakers when powered off could pose a problem that your case wouldn't protect against. Even in a worst case scenario though, I speculate the static field would do no more than flip some bits on your hard disk.

From Wikipedia's Faraday Cage article:
A Faraday cage will not shield its contents from static magnetic fields. However, rapidly-changing magnetic fields create electric fields in accordance with Maxwell's equations. The conductors cancel the electric fields and therefore the changing magnetic fields as well. The wall materials' thickness and skin depth set the frequency at which the cage suppresses electromagnetic fields. Static or slowly-changing magnetic fields penetrate the cage; rapidly-changing ones do not
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Thin metal stops EMI, but not a magnetic field - but don't worry, your sub-woofer doesn't produce nearly the magnetic field gradients needed to cause bit errors in a hard disk. Everything else in a modern PC is immune, unless you still use floppy disks lol
 
very good answers and an interesting read. i've always kept my subwoofer on the far side away from my pc ;)
 
Regular magnets won't affect your HDD, confirmed.

From PCWorld.com
The only magnets powerful enough to scrub data from a drive platter are laboratory degaussers or those used by government agencies to wipe bits off media. "In the real world, people are not losing data from magnets," says Bill Rudock, a tech-support engineer with hard-drive maker Seagate. "In every disk," notes Rudock, "there's one heck of a magnet that swings the head.
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