Any way to shield a non-sheilded center channel ?

You don't say, I guess I was misinformed! Learn something new every day, thanks Herman.
Tim

On first reading I missed the comment about the ground above. Connecting the metal plate to an electrical ground like an outlet cover screw will have no effect. Magnetic flux lines cannot be grounded, they must be guided away from the TV via some magnetic material.

The other option not mentioned is distance. The flux lines spread out and exert less influence as the speaker is moved away from the TV. However, the distance that it takes to achieve good results may not be acceptable in your setup.

Herman, i do not know about this specific aspect, but am throwing this out for you and others to comment on.

I've always thought that lead was a great magnetic shield. If this is true, some type of lead based material SHOULD re-direct or block the magnetic field away from the TV below it. While this might not solve the problem, it could minimize it.

What i'm basing my above statement on is the fact that lead is used as a diffusor / reflector / shield for radio waves and X-Ray's. Since RF signals and X-Rays are simply concentrated and controlled magnetic waves that "float" at high frequencies, i would "think" that the same principles would apply to low frequency magnetic fields. Granted, some devices have different efficiency curves as frequency changes but i doubt that lead becomes useless at these frequencies. I may be wrong though, so please correct me. I would rather be wrong and learn what is right than to continue on in ignorance.

As to installing a "bucking magnet" on the back of a driver that was not designed for it, i highly recommend NOT doing that. This changes almost every electrical characteristic of the driver. As such, it would / could alter the performance of the system to a very noticeable degree. Like anything else, taking all of the variables into account should be done BEFORE the project is completed and the design finalized.

I do agree that moving the speaker away from the TV is the easiest approach. Whether or not the sonic presentation is still acceptable is the question. Sean
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try turning it upside down. I use 5 Totem Mani-2's in my HT system, and one of them as a center under the TV. Initially, same problem, until I called Vince (head designer) at Totem- he suggested it- tweeter is now on top of woofer, but I have it angled up anyways. No more funky colours on the screen from the magnets, and sound is just fine...

Sean, continuing on in ignorance is not too bad. I've been doing it for years. I agree that installing an extra magnet in the your speakers is probably a bad idea. I just pointed out this design technique in the hope of clearing up some of the confusion about shielding.

As far as using lead to shield against RF, your defintion of "concentrated and controlled magnetic waves that "float" at high frequencies" leaves out the electric field that is also part of the wave. RF, x-rays and the like are electromagnetic waves of various frequencies. They are made of alternating electric and magnetic fields that vary in amplitude as they travel through space. Lead will block RF, as will copper and aluminum and any other metal that is a good electrical conductor.

This is a different animal than a magnetic field like that from a speaker magnet that is not varying. It has no frequency. It is a constant pull against the opposite pole unless you move the magnet. Kind of like gravity exerts a constant pull except magnets have two poles, north and south, and gravity is a monopole. This magnetic force is usually desribed in terms of lines of force (flux) that go from the north to south pole. Remember the metal shavings and magnet experiment and how the shavings line up. The flux lines cannot be blocked or broken, only redirected by placing a magnetic material in the field. The flux lines will follow the path of least resistance, which is the magnetic material. So placing a magnetic material between the speaker and the TV will concentrate the lines in the metal and they will be weaker on the other side.

BTW, lead is also an excellent shield against Superman's X-ray vision.