The speakers I’m using with my TV are nice but have not been properly shielded for stray magnetism so I’m getting the classic screwy picture unless I push the speakers way back in the entertainment center, which affects the audio. Can I alleviate this problem if I glue sheet steel to the cabinet wall between the speaker and the TV?
Just a WAG but I suspect if the speakers are physically seperate they are not meant to be placed next to the TV. They should ideally be as far away as is reasonably possible.
But if that is not an option I am sure someone has tips for shielding.
(trying not to whap Lobsang upside the head with my Giant Duh stick 
) Yeah, I figured that. But they sound shockingly good for what I paid for them (“And why do you think were they so cheap?” Lobsang asks, except he wouldn’t ask as much as make a patently obvious statement. 
) and I want to make them work.
If you’ve got a suitable piece of steel, go ahead and try it. My expectation is that it won’t be a 100% fix.
When speakers are described as “magnetically shielded” or “video” it’s usually not a matter of shielding or blocking magnetism with sheet metal or whatever, but of backing the magnet on the speaker itself with a “reverse” magnet so the net magnetism around the speaker is nil, but the effective magnetism inside the speaker is normal.
As you might guess, this is a bit tricky to set up on the fly at home since you don’t know the strength and polarity characteristics of the existing speaker magnets.
I don’t think the steel would do anything at all to help you. Objects can’t dampen magnetic fields. The only thing that will reduce a magnetic field is distance. Another magnet can be used to negate the net magnetic field, but without that type of setup, there’s nothing you can do to reduce the effect on your tv.
**90% sure that nothing I just said was bullshit.
Parental supervision?
Totally not knowing what I’m talking about, but… lead?
How old and pricey is your TV? I have had assorted TVs and speakers in close proximity for more than 20 years, and never had any problem whatsoever. My first suggestion is get a new TV if you heave really pricey speakers, or get new speakers if you have a really pricey TV. I currently have speakers above and to both sides of my TV, and no interference at all.
A Faraday cage should work, but it needs to be entirely around your TV, which really means you need to be inside it too to see the picture.
Try turning the speakers on their sides or upsode down. The characteristics of their fields will change slightly in relation to your TV, perhaps improving the pic, perhaps not.
Take some aluminum foil and just place it between the speaker and TV. I doubt it will make a difference, but if it does it will do just as good a job as sheet steel unless shrapnel is an issue.
If that doesn’t work, you might try relocating the tin foil. You pick where. 
This is not correct at all. A Faraday cage will not fix static magnetic field from messing up a TV screen.
Steel and other ferromagnetic materials can be used to shield against magnetic fields in the same way that any electrical conductor can be used to shield against electric fields, and for a similar reason. Ferromagnetic materials, like steel and mu metal, “conduct” magnetic fields much better than the air around them - the term is high permittivity. This is why transformers almost always have iron cores, rather than air cores.
Aluminum foil has about the same magnetic permittivity as air and free space, and would have zero effect on the magnetic field. You might as well use paper.
Ack. That’s high permeability, not permittivity. And I did it twice. :smack:
… damned high school science teachers.
Thanks for your cool-headed answer QED. The earlier poster’s [completely wrong] bald statement that “objects can’t dampen magnetic fields” really made me see red, and it’s been a rough evening. I might have been needlessly snide.
ESSENTIALLY ALL materials, including those we do not think of as “magnetic”, are inherently diamagnetic, meaning they will oppose and dampen any applied magnetic field. (You can think of the electrons orbiting the atoms as tiny current loops, which an applied field will tend to orient in an opposing direction. After all, we all know how magnetism loves opposites)
Didn’t we all do that experiment as a children in grade school: take a paperclip on a string; pull it with a magnet, so it “hangs” upward in the air; the n “cut” the field with a pair of steel or iron scissors?
Of course, static diamagnetic effects are the weakest of the magnetic effects, and are generally too weak to act as shielding. However, the diamagnetism of many conductive materials can surprisingly strong with rapidly changing magnetic fields, due to electric curents they induce. The extreme case, a superconductor, is a near-perfect diamagnet, due to its lack of internal resistance, and would be a perfect magnetic shield - if a bit impractical for this application. [Superconductor diamagnetism is also important in superconductor those magnetic levitation designs and demos we’ve all see ad nauseum in the past 20 years]
Unfortunately, audio frequencies are not considered very “rapidly changing” in the grand scheme of things. The thickness of non-ferromagnetic conductor shielding required would probably be prohibitive – but it wouldn’t be accurate to rule it out. The OP might have some heavy metal sculpture or something handy. Also, I also thought it was important to note that a static magnet is not necessarily a good test of audio magnetic shielding.
Okay, enough pedantry - let me see if I can give the OP some useful info.
There are magnetic shielding foils (mostly nickel-iron), sold for scientific and audio use (often generically called “mu metals” because the Greek letter mu (µ) is the symbol for magnetic permeability) Do yourself a favor and price them at from a scientific supply or [better yet] metal-working sources; audio sources often charge $10/sq ft oreven much more, especially in small quantities. Everything gets more expensive when it approaches audiophiles. I’ve seen it be effective in thicknesses as low as .004" [There was a big roll of 0004" in a lab I ran once, but I don’t know how many layers the student used]
I’ve seen the stuff sold cheaply in thicker sheets (especially odd shapes, left over from the manufacture of military gear]. Shop creatively.
There is also “metglass”, a cobalt alloy which is used as a magnetic shield in thicknesses as low as 16 microns (0.00065"). It’s probably more expensive than mu-metal, and again, the number of layers needed will depend on factors like the frequency and field strength, but I think the existence ofmetglas the kind of thing that Dopers might find interesting – for building Evil HQs and the like.
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- Just get a piece of 1/16" or 1/8" thick steel (best is 4130 cro-mo, but mild steel will work too), maybe six inches wide and as tall as the TV, and hold it up against one side of the television, and see how much it helps by comparing the shielded and unshielded sides. You can try it either way (close to the TV or the speaker), but it should work best close to the television.
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- Or the counter-magnets work too. As noted, usually good speakers intended for this sort of use (surround system front speakers) have dual counteractive magnets built-in already, exactly so they don’t mess up the TV picture.
… - And I doubt you’d need actual mu-metal for this. It costs a lot more than regular steel and is generally only used when there is not enough physical space to use regular cheap steel, or the weight of regular pieces of (necessarily much thicker) steel would be prohibitive.
~
Just to point out the blindingly obvious - the advantage of stereo sound (in addition to the obvious advantage of higher sound quality than built-in TV speakers) is stereophonic reproduction, the effect of which is only adequately realized with sufficient source separation. This depends on the most common listening position. If you sit really close to the TV, short separation may be okay, but at a comfortable viewing distance (how large is your screen?) you will want to separate the speakers by a few meters in order to realize the sound field potential of the system. The only speaker that should be close to your TV is a dedicated center-channel of a surround sound system, if you are so equipped. Otherwise, try placing your speakers toward the edges of the room, angled slightly inward toward the listening position, at an elevation where the high frequency source (tweeter, whizzer cone, etc.) is roughly at the same height as ear level. You may find that positioning makes a significant difference in perceived sound quality.
I’d go to a place that makes steel ductwork for HVAC applications and buy some sheet-steel from them, drill some holes in the corners, and bolt them inside the cabinet close to the TV. They have nice flat panels of this stuff and will custom cut it to any size you want. It is also galvinized so it shouldn’t rust. One layer would probably work fine but you could stack as many as you needed.
[voice of sad experience] NEVER pick up more than two sheets in a stack. The middle layer in a 3-sheet stack will slide and cut hell out of you.[/voice of sad experience.]
Hope this helps.
Testy
A little experimentation with frying pans or cookie sheets might help you decide how big a piece of steel you need.
My apologies. Sorry to have frustrated you!! Seriously.
My AP Physics class in high school was 1st period, so I only actually went a handful of days the whole year. But I do remember on one of those days magnetism was covered.
I specifically remember the whole thing because I was set aback when the teacher said the only thing that can weaken a magnetic field is distance. I went up to him after class and asked him, how then are shielded speakers possible. And he got on the white board and explained the whole deal with using another magnet to even out the net magnetic field. I was satisfied with that answer (why shouldn’t I have been), and I’ve held it as fact for the last 8 years. I’ve held the idea of shielding with just a piece of steal as nothing but a misconception.
But if 5 years of Dopering has taught me anything, it’s that I WILL BE wrong if I post something without verifying it first. And ya know, I was about to get on google and make sure that I was not mistaken, but I was specifically told this by my teacher… so I figured I’d make everyone aware that I’m no Magno-field Guru, but I’m almost postive this is fact and leave it at that.
… anyway, sorry about that. I’ll be MORE careful in the future.
Metglas. Now there’s a blast from the past! I worked at metglas for a while between high school and college back when it was part of Allied Chemical (or Allied or Allied Bendix or Honeywell or whatever the hell it is now). I used to QC the stuff and run errands for the technicians. Watching that stuff get made was a hoot. I never knew about the Evil HQ application, though. They were building a frickin’ enormous whatchamacallit when I left so that must have been what it was for.
As to the OP - I had the same problem with my studio monitors and my computer monitor. I just spread the speakers out a little more and that did the trick. Is there no way you can put a few more inches of space between your speakers and your TV? All this sheet metal stuff sounds like overkill and ugly to boot.