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Discussion Starter · #1 ·
I've been doing some rewiring and rearranging of my various components, when it occurred to me I may have done something potentially harmful to one of my Replay TVs - I had the unit sitting directly in front of my center channel speaker. After a few days, a little alarm went off in my head when I realized the magnetic field from the speaker could pose a threat to my Replay TV's hard drive, so I have removed the speaker until I can figure this out.


My question is basically, am I overreacting, or should I indeed keep the Replay TVs at least two feet from all speakers?
 

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Well, first: putting the Replay in front of the center speaker would cause the sound from the speaker to get deflected/muffled by the Replay. Plus you have the fan sound mixing with the center speaker. :) So I wouldn't recommend this orientation for that reason.



But, I don't think putting a speaker behind the Replay would be a problem. On top of or in front of the replay might be problematic. I believe most of the magnetic fields of speakers are focused around and behind speakers, not in front (but I'm not an expert, so I could be wrong on this).
 

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Yes, that is potentially harmful. Two feet is probably overkill, but it can't hurt to have it too far away.


However, you have two things going for you:


1. If the hard drive was in front of the speaker, there was probably very little magnetic field reaching the hard drive. The magnetic field should radiate to the sides of the magnet, not in front of it. (BTW, how do you put something in front of your center speaker? Doesn't that kind of block the sound from the center speaker?)


2. Almost all center speakers are magnetically shielded. If they weren't, we couldn't put them on top of our CRT TVs without severe distortion and damage to the TV. As long as you have a purpose-built center channel speaker, it is shielded and you don't have any worries.


More good news is that you likely won't physically damage the hard drive with a magnet. Worst case is data loss and you have to spend time doing a low level format and us RTV Patch to load new software on it.
 

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no it won't damage it. many pc's, especially older ones, have a small 2 1/2 or 3 1/2 driver in the lower front portion of the faceplate, INCHES from the hard drive. magnetic fields decrease as a cube of the distance, so that little speaker is putting out WAY more then a larger driver located further away. not to mention most center channel drivers are shielded, and you have metal shielding between the hd and speaker anyway. (replay case)


same thing with credit cards. (if anyone has seen the mythbusters episode with CC's and magnetism...) they basically had a very hard time actually corrupting the data on the mag strip on the credit card, it took a VERY large electromagnet before anything worked...
 

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It is possible, but unlikely. If you bought a set of surround sound speakers that were designed for home theater use, they will be video shielded (aka Magnetically Shielded). Which means that the magnetic field of the speakers is reduced to an amount that shouldn't damage other electronic equipment.
 

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Discussion Starter · #7 ·
Thanks to everyone for their suggestions. Obviously placing my Replay TV in front of a speaker is not the ideal position, but I recently added a few components, things were getting a little crowded, and the speaker is about 15" high so it really didn't block the sound. I'm sure the speaker is not magnetically shielded, since if I hold it up close to the TV, you can see discoloration appear in the picture. So, I think I'm going to be safe rather than sorry and just find a new home for the Replay.
 

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FYI: I use magstripe keycards at work and keep it in my shirt pocket. Carrying a bare speaker chest high erased it. :(


DOH!


Greb
 

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The mechanical engineer in me is thinking about the acoustic energy and vibration going into the hard drive. If you like to blast your home theater sound like a movie theater, I would think twice about putting the 5400RPM drive near a vibration source. However, it should be fine at normal non-earsplitting sound levels.


I'm actually a rocket scientist and we used to pump high levels of acoustic energy to test our spacecraft and components to simulate the launch environment, which is very loud. Again, normal sound levels should not be a problem.
 

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just an FYI , i have used old hard drives to clean up screwes on my desk , the drives themselves have a strong mag feild on them to begin with , probly on par with a small computer speaker ( the internal one ) , but i wouldnt put a bare speaker on top of one , of course when the drive is running and reading/writing i deffenitly wouldnt put any magnets near them , but agin , they are well sheilded.
 

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Man this is fun to read...


I have to agree with all others that stat the center channel is most likely shielded. Like said before if not... it's going to kill your CRT.


That said I wouldn't put anything magentic next to a hard disk. Hard disks work off magentics and if you are going to do something to disturb what the disk has going on you are going to be doing something to the drive. most likely not to "damage" the drive itself. But you will be doing something to the data on the platters. And to me this is the bigger concern.


I can't understand why you'd want to put ANYTHING in front of any speaker. You ever notice what happens when some walks between you and the speaker? Same thing but all the time, maybe not to the full sound field, but you'll lose something.
 

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Not to nit pick over semantics, but I don't think damage to the HDD will occur from the speaker magnets. However, you may lose some data if the field were strong enough. Even still, I do not believe that a center channel shielded speaker would generate enough magnetic interference to cause the HDD much trouble. Of course, I haven't made any measurements to know for sure. Regardless of the HDD, I don't think your setup sounds too attractive.


Cheers
 

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I have to agree with Jeff D that some of this is amusing. Hard drives are very well protected from magnetic fields and shock and vibration. The spindle motor generates a magnetic field. The read/write head actuator generates a magnetic field and vibration. Hard drives are installed in environments that frequently contain magnetic fields. They are intentionally designed to withstand magnetic fields and considerable mechanical shock, even while operating (although they can handle much more shock while not operating). Here's something you can try for fun. Take out a hard disk (especially a high-capacity hard disk manufactured in the last couple of years), run a real ribbon cable to it (not one of those aesthetic but noisy round cables, etc.). Run some disk diagnostic software on it to make sure that it is working properly. Then place it directly on top of a subwoofer, and run the diagnostic while the 1812 Overture is playing at full volume. I'll bet that there isn't a single (uncorrected) error. I could make enough money off of you guys to retire, except that in my state vices like gambling are only legal when they are sponsored by the state. Speaker magnets and acoustic energy aren't going to affect a hard drive. High-quality drives will run maintenance tasks on themselves when they are idle, refreshing data and remapping bad areas, without the OS's knowledge.
 

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Discussion Starter · #15 ·
Amazingly Smooth - yeah, data loss is what I actually meant.


This thread has inspired me to start a new Ebay business of "magnetic-field absorbing" drop cloths you place over your speakers which allow sound to pass through while protecting your monitor, hard drives, and any old VHS tapes lying around from stuff like the 1812 Overture played at high volumes. I'm sure I'll find some gullible - er - I mean grateful buyers. :D


And Grebbler - I knew a lady whose husband supposedly kept getting his credit card declined because he kept placing his wallet on the TV whenever he came home, and the TV erased the magnetic strip. Or so she said - maybe he just had a lousy pay history.
 

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There was a lady at my work that just about every week had to come in and get a new ID badge. We use the ones with magnetic stripes on them.


Turned out that whenever she was in her car she would place her purse next to the car speakers, which was erasing the ID badge. The stuff in her wallet was not effected because it was in a wallet in the center pockets of her purse. She kept her ID badge loose in the outer pocket of her purse.
 

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I think the term "erase" is a bit of a misnomer. More likely the data would be corrupted. It doesn't take many wrong bits to mess up a system--typically one will do it. Some systems do employ error correction, but some do not.


Cheers
 

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Quote:
Originally posted by rkramer
no it won't damage it. many pc's, especially older ones, have a small 2 1/2 or 3 1/2 driver in the lower front portion of the faceplate, INCHES from the hard drive. magnetic fields decrease as a cube of the distance, so that little speaker is putting out WAY more then a larger driver located further away. not to mention most center channel drivers are shielded, and you have metal shielding between the hd and speaker anyway. (replay case)


same thing with credit cards. (if anyone has seen the mythbusters episode with CC's and magnetism...) they basically had a very hard time actually corrupting the data on the mag strip on the credit card, it took a VERY large electromagnet before anything worked...
I love the concept of Mythbusters, but they often go about proving/disproving based upon a preconceived belief, rather than trying to do exactly what the "myth" said happened.


That said, I had an ATM card corrupted in college by placing my wallet on a classmate's tower speaker while visting his dorm room. DOH! Speakers can, and will, corrupt magnetic data. Shielded AV speakers are specifically designed to NOT cause such severe magnetic effects. RF/magnetic shielding is not expensive or difficult to accomplish. You can bet that any good HDD engineer would make sure to have a certain amount of shielding from stray and self-produced EM. (including preventing "broadcast" of self-produced EM, which would violate consumer electronics laws)


Ever wonder if the EZ-bake oven inside Replay was more than just a feeble attempt to overheat the drive? Hmmmmm....
 

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Quote:
I'm actually a rocket scientist and we used to pump high levels of acoustic energy to test our spacecraft and components to simulate the launch environment, which is very loud. Again, normal sound levels should not be a problem.
I used to run a 40 gig drive in a custom computer I built in my car, for mp3 use. the hard drive lasted about 6 months, but I think it was more due to the road vibration and cold (-10 to -20 F) then the 145 db my car is capable of... :D
 

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HDDs actually have one of the strongest types of magnets (rare earth) right between the heads, there are two at the base.


Take an old HDD apart. They are great fun. Don't get your fingers between the two magnets when you remove them from the head assy. They will pinch your fingertip hard enough to make a blood blister. Ya, I did do that.


I like the above advise abouting keeping external magnetic fields seperate from your drive. If nothing else - just to keep the HDD gnomes happy.
 
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