Any way to shield a non-sheilded center channel ?


Hello! I just purchased a Totem Mite-T center channel speaker here on Audiogon. Much to my dismay, I just discovered that it was un-shielded after setting it on top of the Sony XBR TV. It is a shame to discover this, since it has a good tonal match to my front speakers, and even the wife says it is attractive! The seller has already agreed to take it back minus the shipping cost, which was very kind of him to offer. Is there anything that can be done inside the cabinet that can cure this problem, or should I just ship it back to him? Thanks for your help!
bigshutterbug
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.
I want to thank each of you for your thoughts on the matter at hand! I wish I could move the speaker just a few feet away, but in the rack that things are in, we have no choice but to put it right on top of the speaker.
I will try some of the ideas that you all have mentioned, and see what happens tomorrow evening. If they do not work out well, I will just have to return it and try to find another shielded center to take the place of the Totem. Any suggestions for one that would be either dark cherry or mahogany finish, not too large, and $300 or under to match sonically with front Triangle speakers? Let me know...THANKS!
Herman thanks for all that valuable information especially the Superman stuff. I had completely forgot about that.
HAHAHAH.. I agree Glen : )

Thanks for clarifying that Herman. Your analogy about metal shavings and magnet trick brought back old memories. Thanks for knocking some ( at least a small amount ) of sense back into me.

Shutterbug, have you done the obvious yet ? Try contacting Vince at Totem and see what he can do for you. He might be able to suggest something that will take care of the problem. This would probably be better and easier for you than to have to look for a replacement that will physically fit, look good and blend with the other speakers. Sean
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I stumbled across this one on the net too. Its from URL: http://www.unik.no/~robert/hifi/faq/faq-9.html so you can get to the source. Its more or less correct. The next to last sentence in the first paragraph is correct; however, that doesn't mean shielding lining the internal walls with metal can't be done as an after thought. That being said, the last sentence in the first paragraph is the one I'm uncertain of. Hopefully the first link to links I provided helped some.

9.15 Can I magnetically shield my speakers for use near a TV?
You probably will need to buy speakers that are made with an integral magnetic shield. Magnetic shielding is usually done by either shielding the speaker magnet or by cancellation of the magnetic field very close to the magnet, or by both. Shielded speakers are NOT built by lining the enclosure with metal. While it sounds like a good idea, it doesn't work.

A common magnet shield is a mild steel cup around the magnet. This is the cheapest shield, and is usually fairly ineffective. It also will interfere with the speaker's critical magnet gap, so this type of shield can hurt speaker performance by shorting the magnetic field and reducing the magnetic flux density in the gap, which can reduce efficiency and affect the speaker's low frequency performance.

Cancellation is done using a reverse-polarized magnet glued to the back of the main magnet. If done right, it can almost completely cancel the rear stray field. In some cases it can also increase the magnetic flux density in the gap, which may or may not be desirable.