# car pc and sub magnets



## robbyho (Oct 21, 2005)

I'm redoing the amp rack in the kit car and am thinking about putting some big ole subs back there. The problem is that I have a carpc and would like to build a new rack mount one to install below the subs. I'd like to do a pair of dyma 12"s (if I can get another one) inverted with the amps and car pc below it. I know the dyma's have some pretty intense magnetic fields, and am concerned about my hard drive. I placed a sub on my buddy's old server and his hard drive never worked again.

Anyone experience issues with pc's and sub magnets? How far apart is enough? 

Rob


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## Tempe (Jun 3, 2005)

The FUNNY thing about your topic is that I did a few moves in a short amount of time. Each time my desktop tower was not far from my RE HC 15 as I have an extended cab truck. There simply is not much room back there especially with a 4 cube net enclosure. IIRC the HC motor has three .75" by 8" slugs. I know my SE has three slugs that are 6" and the HC's motor is much wider, so I'm guessing on 8" slugs. Bottom line is I never even thought about damage to the hard drive, and I was lucky enough for no data loss! My most recent move was from IN to AZ over three days.

T


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## azngotskills (Feb 24, 2006)

What about implementing some sort of shielding case to the cpu of your carpc?


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## khail19 (Oct 27, 2006)

I think you would either have to shield the HD somehow as well. You can't do the carPC under a seat up front?


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## demon2091tb (May 30, 2005)

Simple, don't put it near the subs 

put it upfront under a seat, modify the glove compartment to access the cpu, stash it behind the dash.

Get an extra long cable and just move the HD upfront somewhere 

I used to keep my tempest in my dorm room a good 3-4ft from my desktop, no problems then, and thats running for over 6months.


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## jeffrey (Jan 3, 2007)

What about those anti-static bags. They are Faraday cages. Will that provide an electromagnetic shield? Obviously sealing the HDD in a bag is not the ideal thermal solution.


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## cvjoint (Mar 10, 2006)

do all your guys' reccomendations hold for a sub magnet near an amplifier? My IB subs are 1/4 inch above by amps, if the screws are not held down properly they get pulled on the magnet!


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## khail19 (Oct 27, 2006)

cvjoint said:


> do all your guys' reccomendations hold for a sub magnet near an amplifier? My IB subs are 1/4 inch above by amps, if the screws are not held down properly they get pulled on the magnet!


Amps aren't affected by magnetic fields, as far as I know.


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## Spasticteapot (Mar 5, 2007)

Strictly speaking, the subwoofers should not cause any damage to a carputer - however, you're much better safe than sorry. Moving your carputer to a location where it won't be near massive electromagnetic fields is probbably worth it.


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## khail19 (Oct 27, 2006)

Spasticteapot said:


> Strictly speaking, the subwoofers should not cause any damage to a carputer - however, you're much better safe than sorry. Moving your carputer to a location where it won't be near massive electromagnetic fields is probbably worth it.


So a huge magnet won't damage a nearby hard drive?


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## Spasticteapot (Mar 5, 2007)

khail19 said:


> So a huge magnet won't damage a nearby hard drive?


Nope. Those suckers are shielded like no tomorrow - unless it's literally stuck to the bottom of the subwoofer magnet, it should be fine. 

I'd worry more about your motherboard - while metal cases provide shielding, those long copper traces can work like antennas. And you do NOT want the bassline from your new favorite song being fed to your processor.


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## robbyho (Oct 21, 2005)

Spasticteapot said:


> Nope. Those suckers are shielded like no tomorrow - unless it's literally stuck to the bottom of the subwoofer magnet, it should be fine.
> 
> I'd worry more about your motherboard - while metal cases provide shielding, those long copper traces can work like antennas. And you do NOT want the bassline from your new favorite song being fed to your processor.


hmm...common consensus speaks otherwise. Although the consensus could be wrong.

My kit car is a small 2 seater. I have a spot for the carpc now that is hidden away. I'd like to display it more, alongside the amps and subs. 

Can we get a 2nd for magnet won't damage the HDD?

Rob


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## shinjohn (Feb 8, 2006)

In general, it's quite difficult to erase a HDD from the outside using a magnet. I used to work in the industry, and haven't seen anything like this happen myself. Note that the VCM inside most drives have stronger magnets (neodymium) than what you would find in a typical loudspeaker. (even large subs)

I remember years ago trying to use HDD VCM magnets on the outside of a drive to see if I could actually erase data, and it never happened. I placed the magnets directly on the top cover, as close as possible to the platters, and no problem.

Although the stray flux of many subs can be quite high, it would have to penetrate the sheet metal PC case, plastic, air gaps, etc.. and then the HDD case in order to get to the sensitive media. Pretty unlikely IMHO. Also note that the majority of HDDs use stainless steel (400 series, IIRC) top covers, which actually are very effective at magentically shielding. This is done partly to keep the stray flux from the HDD VCM from getting out of the drive.

This is not to say it can't happen; I haven't tested this assumption with a massive sub in close proximity to a drive.... I just think it's really, really unlikely. You have a much greater change of damaging the computer (or HDD) through ESD discharge than anything else!


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## shinjohn (Feb 8, 2006)

jeffrey said:


> What about those anti-static bags. They are Faraday cages. Will that provide an electromagnetic shield? Obviously sealing the HDD in a bag is not the ideal thermal solution.


The antistatic bags may help for ESD, but won't do anything to block a magnetic field.

I can tell you for certain you don't want to run a drive in one of these bags. That's probably the very best way to make it overheat as quickly as possible.


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## Whiterabbit (May 26, 2006)

If you are really that worried about it, put a steel plate between the magnet and the PC. doesnt have to be encased or anything, every little bit helps.

the less carbon in the steel the better. Nothing that'll hold a magnetic field. Fortunately, this requirement usually means cheaper steel. 

1/4 inch thick is way more than enough.

I took a gauss meter and measured an IDMAX magnet and measured 1000 gauss at 0 inches. then add an inch between the magnet and the box, add .75 inches for box thickness, then tilt the subwoofer 30-45 degrees for the angled baffle and I measured 175 gauss (this is about 2 inches away and at an angle). This is where I wanted to place my laptop.

I looked up the manufacturerspecs for the harddrive I was running and it was rated for a max field of 6 gauss. After reading this thread, this must be the max rating outside the casing. No way these drives would be so robust as described here if that was a requirement inside its casing.

I installed a 1/4 inch plate of (I believe) A36 construction low carbon steel right on top of the box and remeasured the field. Dropped from 175 gauss to 12 gauss. I figured it would be enough. I see now based on this thread it would have been WAY more than enough. Absolutely above and beyond real world requirements. My steel plate was about half the size of my laptop footprint.

You can get some steelplate from onlinemetals for probably $14 plus shipping, or can easily scrounge pieces anywhere for free (which is what I did)

Sounds overkill, but if you are really that worried about it and motivated to do something about it, feel free to have at it. If my laptop ever goes out the the car these days, I've long since stopped caring about stray magnetic fields.

our local carPC enthusiast has way more problems with thermal cycling than with stray magnetic fields (from two 18" eD o series subwoofers)


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## robbyho (Oct 21, 2005)

awesome, I'm real glad I made this thread. I really didn't have a clue about this.

Thanks guys.


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