I store my data CDs in plastic boxes in stacks on top of and beside one of my stereo’s speakers. (Music CDs live in racks above and near the other one.) Last night a guest noticed my CD boxes and warned me that the CDs were at risk of being erased/scambled/damaged somehow.
He couldn’t say exactly what the cause of the potential damage was, it was just something ‘everyone knew.’
Well, if so, ‘everyone’ didn’t include me. And, on the empirical level, I’ve kept music CDs near speakers for dozens of years and none of them have stopped playing yet.
Okay, back when home computer were new, newbies were warned to keep their floppies well away from magnets. In particular, special mention was made of things that you might not realize contained magnets or created magnetic fields while operating such as speakers and telephones.
But CDs aren’t magnetic media, are they? Aren’t they written by laser? I’ve got to figure that if speakers gave off light at laser intensity, I’d have noticed it before now…
OTOH…maybe the source of the damage is some other aspect I’m not thinking of? Please fight my ignorance.
Also, most speaker magnets are shielded. The speakers to my stereo sit on top of the TV to no ill effect. For future reference. YMMV, read the manual to your equipment.
It’s completely absurd; there’s no need for any sort of citation or reference in order to demonstrate the falsehood of this claim. However, if you hang out with a diverse enough group of audiophiles for any length of time, you’ll see that far stranger claims are made routinely.
There exist magneto-optical disks which have various forms of combination mechanisms, but I don’t think that any of these are in common use any more, and in any case they’re very different from a CD or DVD.
What WILL destroy CD’s and DVDs is long-term exposure to sunlight, or short-term exposure to any significant heat source. This is probably the one that gets most folks; they leave a CD on a desk or window sill for a few weeks, or a car trunk during the summer.
The only possible concern is heat. It’s conceivable that when the speakers are in use, they might warm up a little. I doubt they get hot enough for it to be even a remote concern, though.
Most speaker magnets are NOT shielded. Magnetic shielding costs money and since most speakers, particulary large ones, are not intended for use near CRT devices like TVs and computer monitors, they don’t have any shielding.
Huh??? The minidisks (audio minidisks are CDs and video minidisks are DVDs) are nothing more than half-sized CDs/DVDs, and they use optical storage techniques like any other CD or DVD.
For the record: CDs and DVDs record data through the means of microscopic dots that are embedded in the data surface.
For ROM disks (like the ones that have software or movies already on them, and whose data you cannot change): The data is usually stored on the disk label. If the label becomes scratched or otherwise damaged (like heat warp), that data can no longer be “read” by the computer, so the disk becomes worthless. Many early-generation CDs have also suffered to some extent from having the label flake off for no apparent reason. Early music CDs seem to be most susceptible to this, but that may be only because software CDs didn’t become popular until the media itself was more stable.
For Recordable disks (which can be recorded, but not erased and re-recorded): The data is literally “burned” to the disk by the recording drive, but the recording media itself is normally buried between two separate layers of plastic. As far as we can determine at this point, only excessive heat or excessive scratching/abuse can make these disks completely unreadable, although very early CD devices may not be able to read them regardless of their condition.
For ReWritable disks (which can be recorded, erased, then re-recorded), the risks are pretty much the same as for Recordable disks. For Recordable disks, extreme heat temperature is used to write the data to the disk. For ReWritable disks, even higher temperatures are needed to erase the existing data prior to replacing the data with new data, and you must have a relatively new CD/DVD drive to read them at all.
None of these are susceptible to magnetic fields in any way. However, both floppies and hard drives ARE susceptible to magnetic fields. This is why speakers that are created specifically for computer use can be assumed to be shielded.
No, Minidisk is a magneto-optical format which resides on a small disk in a permanent casing. They are recordable and can be re-recorded upon many times, which is why they are still used for audio recording.
This isn’t really accurate either. A CD is basically three layers, the transparent polycarbonate plastic (about 1.2mm thick) a super-thin layer of aluminum (or sometimes gold) and a laquer on the top. The label is applied on top of the laquer, usually by silkscreening. The data on the disc is encoded on the top of the polycarbonate layer, underneath the lacquer. So if you scratch the label side deep enough, you can damage the data. But the laquer is much harder to scratch than the bottom of the polycarbonate, so the format is pretty robust.
friedo is quite right about the layer stacks, but the data layer in a CD is damaged more easily than you might think. Hold a CD up in front of a light source (silvery side towards you) and see how many pinpricks of light you can see shining through. DVDs are better protected, having layers of plastic protecting both sides of the recording layer.
I worked for a number of years on optical recording development (CD, DVD and Blu-Ray), and I could bore you senseless with stories behind technical quirks and the wonderfully arbitrary parameters of the original specification. But here’s the lowdown on the projected lifespan of a CD-R: Unfortunately not very long. A good quality branded CD-R should last about 10 years or so if kept at 20 degrees Celcius and shielded from ultra-violet. Keep them in an airtight box in the fridge or in a cool wine cellar or old church crypt, and you might get 20 years out of them. Leave a CD-R outside in the sun, wind and rain and it will last just a few weeks, if that. The recording layer and the protective lacquer will both just slough off*. I don’t have a lifetime figure for CD-RWs, but it will be significantly less than for CD-Rs as they’re much more delicate with respect to recording integrity.
Don’t use cheap, no-name CDs, they’re rubbish. Don’t use cheap, quality brand CDs from a dodgy source, they’re undoubtably pirates and rubbish too. Use a good quality recordable drive, a good quality disc (as recommended by the drive manufacturer if possible - these will work best) and record your CD-R at half the rated drive top speed. Record your CD-RWs at half the rated speed of the range shown on the disc itself.
All optical discs contain errors in the data, and to get around this there is a lot of redundant data that is encoded onto the disc too that enables lost data to be reconstructed. Sometimes too much data is lost, and an unrecoverable error is produced. An audio CD player may try and ‘fudge’ over this, but for a data CD you’re in trouble.
If anyone’s interested I can give more hints and tips on getting the best possible quality recording to an optical disc. There are quirks and features that the marketing monkeys don’t admit to.
*Be warned that the recording layers of recordable CDs and DVDs contain exotic and brain-damaging heavy metals. Don’t let them get into the soil or water supply.
Oops, forgot the original point of the OP: Yes, I agree with everone else in that domestic magnetic fields won’t damage any optical disc. You could damage them with a strong enough field, but not of the sort that’s found outside a big physics lab.
Speakers for TVs and PC monitors are always screened, otherwise they’d be pulling your CRT electrons off to one side, giving a glorious rainbow effect. Put a hi-fi speaker next to your PC and you’ll notice this effect. You’ll also notice the colours remaining once you’ve removed the offending speaker! This is because the speaker magnet has magnetised your screen. Fortunately CRTs contain a degaussing coil that puts out a demagnetising field every time the TV/monitor is turned on, so any smeared colours should eventually self-correct.
It will throw it against the wall to smash into pieces, and/or induce a large electrical current in the Al layer sufficient to melt it.
Electricity and magnetism are two sides of the same coin. Any electrical conductor will have magnetic properties, even if a permanent magnet doesn’t stick fast. The (mechanical) speedometer in your car is nothing more than a rotating magnet acting on an aluminium disc that’s tensioned by a small spring. Mouse-click here for more magnetic oddities that aren’t intuitively obvious.
