http://www.diyaudio.com/forums/showthread.php?s=7326aee582dd9ba9b634e8c19ade5347&threadid=1079&highlight=shielding
Go to diyaudio.com click on speakers, then click search, then type "shielding." You'll have to line your cabinets with sometype of metal (is one option). |
Any chance of experimenting with a simple metal plate (between the sony and the speaker) connected to an outlet cover screw? Plate might have to be somewhat larger than the speaker to be totally effective. |
The car audio company Dynamat makes a sound deading insulation that has a lead layer between the ply's, I think it even has adheasive on one side so it is super easy to install. |
The metal plate must be a material that can be magnetized. That way the magnetic lines of flux from the speaker are concentrated in the metal and they are directed away from the TV. Lead is nonmagnetic and will not work. As mentioned, mu metal is an excellent choice. Do an internet search for sources. Many (most?) "shielded" speakers are not shielded at all. They have another equal strength magnet behind the speaker magnet that concentrates the lines of flux inside the cabinet. |
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
> |
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. |
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
> |
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. |
