Planning to magnetically shield...

[stereophonicfan]

I have a pair of old speakers that I'd like to magnetically shield for pratical uses.

I've looked up some method but I'm not quite sure which is best;

---Using some foil like "MuMetal" to attache on the inside of the speakers (which I have access to, lucky me). I'd also like to know how that is done, with some kind of glue or more drastic? And how many layers for a proper performance, (minimal distortion)?

---Or the use of another magnet, illiminating the emitted field by the drivers? And how does one install that? How good is that?

---Or another method?

---Or should I forget all about it, because these installment will interfere with the proper functioning of the speakers and their resonance?

Won't somebody clarify this matter?

[Smokey]

Here are several options concerning shielding speakers:

1: Surround the magnet area (voice coil) of the speaker with plain sheet steel (ferrous metal). If you look inside the shielded speakers that come with computers you'll see a stamped sheet metal cover over the back side of the speaker. Non-ferrous metals such as aluminium, stainless steel, brass, copper, etc will not work.

2: A material known as "MU-Metal" can be used to shield the case or cabinet, you can purchase a lab kit of "mu-metal" from Magnetic Shielding Corp (630-766-7800) and attached a .025" thick of their version called Co-Netic to the appropriate side of the TV and/or speakers. MU-Metal is very efficient at reducing and/or blocking magnetic fields. MU-Metal is the method that has the best chance of success.

3: Magnetic shielding can also be accomplished with "bucking magnets" epoxied in reverse pole of the speaker magnet. It WILL NOT shield the front or the sides of the speaker, but it does well in the back (rear) facing direction.

4: Cover the magnet of a speaker with a tin can. Find a can slightly larger than the magnet and silicone it over the magnet and onto the basket of the speaker. Be sure to use enough silicone to keep the can from rattling. - DO NOT use a non-ferrous (aluminium) can, as this will not work.

Or, these fully charged ferrite donut magnets (below picture) have many uses. Can be used to add shielding to small woofers, midranges or tweeters, which allows speaker to be placed in close proximity of picture tubes and computer monitors.

Commonly referred to as bucking or cancellation magnets. Simply attach the magnet (in reverse polarity) to the speaker back plate using epoxy or cyanoacrylate (super glue). As a general rule, the bucking magnet should be approximately 1/2 to 2/3 the size of the driver magnet.

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=329-202

<img src="http://www.partsexpress.com/imageslarge/329-207i.jpg">

Good luck :)

[woodman]

Your question regarding the shielding of loudspeakers cannot help but generate a question back to you of ........ why? What are they going to be used with where shielding would be necessary?

If they will be placed anywhere near an RPTV set, shielding will NOT be needed at all. Rear projection sets do not use color CRTs but monochrome ones (that are NOT affected by magnetic fields). If they're gonna be placed close to a direct-view TV set where the speaker magnets could affect the screen purity, they need to be placed farther away from the screen if you plan on having any hope for a stereo soundstage from them. Thus, shielding again should not be necessary.

Hope this helps you

[stereophonicfan]

Your question regarding the shielding of loudspeakers cannot help but generate a question back to you of ........ why? What are they going to be used with where shielding would be necessary?

If they will be placed anywhere near an RPTV set, shielding will NOT be needed at all. Rear projection sets do not use color CRTs but monochrome ones (that are NOT affected by magnetic fields). If they're gonna be placed close to a direct-view TV set where the speaker magnets could affect the screen purity, they need to be placed farther away from the screen if you plan on having any hope for a stereo soundstage from them. Thus, shielding again should not be necessary.

Hope this helps you


I'd like to magnetically shield my speakers for all appliances near it. Mainly because my two sets of speakerboxes operate at close distance of eachother and secondly because they wouldn't interfere with my colour CRT TV set. I don't really have the luxury to put my speakers at a distance from eachother. Perhaps I might even have to place one speakerbox on top of the other (two sets of speakerboxes!).

I also thought the foil "Mu-metal" was the better solution for me, like Smokey suggested. I wasn't quite sure, but apparently the best results are obtained with the foil and preferably by using multiple layers.

Lack of room is my problem!