RPTV's and magnetically shielded speakers? [Archive] - Audio & Video Forums


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12-05-2005, 07:47 AM
What's the deal here? If you google enough for info you'll get all kinds of contradictory claims. I've always been under the impression that your basic RPTV's are immune to magnetic interference from unshielded drivers? I've stumbled across some contradictory claims over the past few weeks, not sure what to believe.

Anyone know for certain? Maybe Ed? In my case, I have a 15" woofer right beside my 51" television with no problems at all. I'm looking to build some speakers for my nephew, but I can't get shielded versions of the driver I want, and bucking magnets are just cost inefficient.

If RPTV's are (or aren't) immune to the interference, why?

12-05-2005, 08:38 AM

CRTs need shielded speakers because magnets can bend the path of the electron streams in the tubes, creating a weird northern-lights effect. Shielding is definitely in order for direct views, partly because the screens are small enough to mean that the speakers will be nearby. On that reasoning RP CRTs are a little less susceptible, except maybe for certain center channels, but magnetic interference is still possible. The reason for the controversy is that many people simply don't have a problem with it, and you might not either. Most TVs nowadays can correct themselves fairly quickly if the colors start to run. In the old days, we'd have to de-gauss the screen. In fact, I think my de-gausser is still in the closet. Anyway, if it ain't broke--you know the rest.

So far as your nephew's speakers are concerned, have you considered covering the voice coils with ferrous metal? I don't know anything about it, but apparently something called MU-Metal is very good at protecting against magnetic fields. I have no idea where you get it. Maybe another google, huh?


12-05-2005, 08:50 AM
Thanks for the info Ed,

If I were to test this, is it just as simple as moving a speaker close to the set? Or does the speaker need electric current (EMF) running through it?

12-05-2005, 10:36 AM
I believe that audio speakers have permanent magnets in them, and that the electromagnetic field that the current produces is meant to interact with them. So I'd say that speaker magnets could have an effect on a screen with or without current. But your speaker might have to be close to the set under any conditions to find out. Second opinions?

12-09-2005, 12:17 PM
The speakers will effect the tv on or off. They are always magnetized. I have to keep a walI of books between my speakers and my TV now. I was interested in the Hitachi 42" HDTV (42V710). The problem is it will most definitely butt right up to my speakers. Now in theory, the picture should not be effected by the magnets like a tube would be, as it is being projected onto the screen from the rear of the TV. However....if the electronics are close enough, it might effect them. Has any one in here tested this? I cannot afford to buy a whole new surround system and the TV.

12-09-2005, 12:22 PM
Although I have a set picked out! ; p

12-09-2005, 02:10 PM
Unlike CRTs, LCDs have no electron streams for a magnetic field to bend. I don't see how you can have a problem.

12-10-2005, 05:57 AM
Thanks for the info!