I have a bookshelf speaker that is well matched to the rest of my
surround system, but the problem is that it is not shielded, so
putting it on top of the TV causes distortions in the picture.

I've found a few methods described online to add shielding to a
speaker:
- bucking magnets (example:
http://www.partsexpress.com/pe/showd...duct_ID=122474) which
are placed on the back of the driver in reverse polarity to cancel out
the field. I have concerns about the effect this will have on sound
quality.
- wrapping the driver in magnetic shielding foil
(http://www.lessemf.com/faq-shie.html#speakers) which can get pretty
expensive but should have less effect on the sound character of the
speaker.
- surrounding the speaker magnet with some off-the-shelf metal can(s).
I found a webpage previously that described using some sort of duct
fittings for this but can't find the link again.

I'd like any comments or experiences, particularly on the
effectiveness of various methods and whether they had any effect on
sound quality.

Thanks,
Collin

Collin Ong:
You might be better off to give it up and replace the speaker with a
shielded design or get it away from the television..... say several feet
below or above..... hang it on the wall above the television ? ? ?
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Collin Ong" wrote in message it on top of the TV causes
distortions in the picture.
I've found a few methods described online to add shielding to a
speaker:
Collin

"Collin Ong" wrote in message
om...
I have a bookshelf speaker that is well matched to the rest of
my
surround system, but the problem is that it is not shielded, so
putting it on top of the TV causes distortions in the picture.

I'd like any comments or experiences, particularly on the
effectiveness of various methods and whether they had any
effect on
sound quality.

I'd move the speaker farther away or buy a shielded one.

Getting the right sized bucking magnet can be difficult. Too
small and the cancellation is insufficient. Too large and you
have the same problem only reversed in polarity and a more
complex field distribution. If you have a toolbox of magnets you
might try various ones. The one with the LEAST attractive or
replusive force one is the one you want. Beware that the reverse
magnet can and often does change the driver parameters.

The cup method is usually used to redirect the residual field
AFTER you already added the bucking magnet. The cup alone
probably won't be enough.

Thanks for the initial response. I'd like to explore this one level
deeper.

First off, I've found this selection of magnets at Parts Express:
http://www.partsexpress.com/webpage.... tGroup_ID=571

I haven't been able to find any other sources of donut magnets
in my google searching, although I feel that they must be a somewhat
common item that are available for other purposes as well. Anybody
have suggestions for alternate sources. (hopefully a local one where
I could try a number of them)

Second, is there any tips on first pass sizing? Like, where do I
measure
on the driver to find the diameter (outer and inner) that I need? I
assume
that it is the back? Should I look for magnets that are exactly that
size,
or smaller/bigger? It seems that magnet strength would matter as
well.

Thanks,
Collin


"Rusty Boudreaux" wrote in message ...
"Collin Ong" wrote in message
om...
I have a bookshelf speaker that is well matched to the rest of
my
surround system, but the problem is that it is not shielded, so
putting it on top of the TV causes distortions in the picture.

I'd like any comments or experiences, particularly on the
effectiveness of various methods and whether they had any
effect on
sound quality.

I'd move the speaker farther away or buy a shielded one.

Getting the right sized bucking magnet can be difficult. Too
small and the cancellation is insufficient. Too large and you
have the same problem only reversed in polarity and a more
complex field distribution. If you have a toolbox of magnets you
might try various ones. The one with the LEAST attractive or
replusive force one is the one you want. Beware that the reverse
magnet can and often does change the driver parameters.

The cup method is usually used to redirect the residual field
AFTER you already added the bucking magnet. The cup alone
probably won't be enough.

On 24 Sep 2003 14:26:51 -0700, (Collin Ong) wrote:

I have a bookshelf speaker that is well matched to the rest of my
surround system, but the problem is that it is not shielded, so
putting it on top of the TV causes distortions in the picture.

The best shielding has always been a few inches of air.

In article ,
(Collin Ong) wrote:

I have a bookshelf speaker that is well matched to the rest of my
surround system, but the problem is that it is not shielded, so
putting it on top of the TV causes distortions in the picture.

I've found a few methods described online to add shielding to a
speaker:
- bucking magnets (example:
http://www.partsexpress.com/pe/showd...duct_ID=122474) which
are placed on the back of the driver in reverse polarity to cancel out
the field. I have concerns about the effect this will have on sound
quality.

The bucking magnet can actually strengthen the speaker's magnetic field
a bit. It's holding back the field that would normally radiate out.

- wrapping the driver in magnetic shielding foil
(http://www.lessemf.com/faq-shie.html#speakers) which can get pretty
expensive but should have less effect on the sound character of the
speaker.

This would probably short the magnet so it's weaker.

- surrounding the speaker magnet with some off-the-shelf metal can(s).
I found a webpage previously that described using some sort of duct
fittings for this but can't find the link again.

I'd like any comments or experiences, particularly on the
effectiveness of various methods and whether they had any effect on
sound quality.

Thanks,
Collin