Subwoofer magnetic sheilding question

(snip)

I tried this for a TV centre speaker and it does NOT work.
I even annealed the iron sheet (our company has access to a
heat treating furnace - don't try it at home!)  Still did
NOT work! Actually it gave a very slight attenuation to the
magnetic field so the centre speaker could be about 1 inch
lower before changing the picture colour at the top - no
good, of course.

(snip)

Cheers,

Roger

--
Roger Jones, P.Eng.
Thornhill, Ontario,
Canada.

"29 years in Quebec - took the freedom train"
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In , on 03/11/03
   at 06:11 PM, "y.i.oda" said:

If you have a magnetic problem the colors will shift and moving the
subwoofer will cause the color shifts to move around on the screen.

If you are observing interference such as lines that move slowly up
and/or down the screen, then there is a design problem with the
subwoofer. You can easily diagnose this by unplugging the subwoofer
power cord without moving the subwoofer. If the problem suddenly stops,
then you know it is an electronics problem with the subwoofer. If so,
you may be able to improve the situation by plugging the subwoofer into
a *GOOD* (not the $10.00 variety) noise reducing surge suppressor and
keeping as much separation between the TV's antenna lead and the
subwoofer.

If you are using cable rather than an antenna, consider the possibility
that the cable system is causing a problem. Many cable systems are
poorly installed and maintained. I recently installed a very expensive
plasma set and found a very faint purple line slowly falling through
the picture. At first one would blame this on the set because all
inputs were effected, however unplugging the cable antenna system cured
the whole mess. (there are solutions to this problem)

---

An academic side note: many of us wish that you had not described this
as "EMF signal interference". I assume that you meant "EMI". Others
will assume that you meant "magnetic coupling between the subwoofer and
picture tube". A better choice would have been to describe what you saw
on the screen. Did you see a stationary color change, moving lines,
random bits of color? Did the picture change with the subwoofer output?

------------------------------­-----------------------------
SPAM: u @ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
------------------------------­-----------------------------

WOW, I just finished hooking up all my power source and coax cable for my
entire AV system and the sub to a new highend Acoustic Research *noise
reducing* surge protector re: Barry's recommendations. Everything is clear
as silk now and the BONUS is the surge protector I picked up came with
shielded coax cables which have somehow increased the overall quality and
color of my digital cable source (probably had lousy cables in the first
place).
Thanks all for the incredible input which helped me understand what I was
dealing with, I'm one happy camper now!
BTW, this unit was $109CAD and well worth it, check it out here
http://www.araccessories.com/s urge/ar10s.asp and get them at
Futureshop/Bestbuy

In article <3E717166.902C6 @sprint.ca>,

At one time, I was in a business where we needed a *really well
shielded* 5-inch CRT. Cold-rolled steel will attenuate a large field
quite a bit; there will be some leakage, but it doesn't saturate very
easily. Mu-metal can attenuate a *weak* field quite a lot, but a
not-very-strong field will saturate it.

It took a three-layer box -- two layers of 18 ga. cold-roll with a final
internal box of Mu-metal, to do the job. And it was not cheap.

Isaac

Man, you've been in my house haven't you.
To describe the issue, I have dotted lines running diagonally across, left
to right, upwards on my screen. The lines won't show up unless there is
*some* bass going through the sub (music or movies primarily) and will show
synchronization and intensity as the bass source increases/changes. I have a
digital cable box and was considering moving the box itself to see what
difference I find. I did have to move the sub power to another plug-in as I
was experiencing a ground loop which cause minor humming. I'm not
experiencing any other issues.
I'll take your advise and first move my cable source, purchase a noise
reducing surge suppressor and see if moving it is my last and undesirable
resort.
Personally I've never worked with a product that has 1500 watt power
amplifier like what's built into this sub...

Thanks very much for the feedback too.

http://www.sunfire.com/product s/subsuperjr.shtml

Just move it away - subs can be nearly anywhere if they are
crossed over below 80 Hz or so.

Cheers,

Roger

PS. It's not "EMF", its a static magnetic field.

--
Roger Jones, P.Eng.
Thornhill, Ontario,
Canada.

"29 years in Quebec - took the freedom train"
------------------------------­---------------

In <%2Cba.202004$na.7756 @news2.calgary.shaw.ca>, on 03/12/03
   at 08:18 AM, "y.i.oda" said:

[ ... ]

Just disconnect the cable signal where it enters the cable box and take
care that the metal connector on the cable does not touch anything that
is connected to your system.

Does this subwoofer have a separate power supply? If so, try moving the
power supply away from the video cables and the TV set.

Keep the subwoofer power cord away from the other cables -- especially
the video cables. If the power cable must cross the audio or video
cables, cross them at right angles and avoid parallel runs and loops.
Keep all cables as short and neat as you can.

Since your problem is so fierce it will be easy to get instant feedback
and see if moving something helps or not.

------------------------------­-----------------------------
SPAM: u @ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
------------------------------­-----------------------------

In article ,
 DPie @TheWorld.com (Richard D Pierce) wrote:



And since the magnetic field falls off as the fourth power of distance,
it doesn't take much of it...

Isaac

In article <5ksba.448223$Yo4.18885 @news1.calgary.shaw.ca>,

Since "EMF" means "electromotive force" and is a term that does
NOT describe magnetic fields and interference, and there are
other further confusions of terminology on this website,
methinks these people are selling no better than the proverbial
pig-in-a-poke. "mumetal" is a specific, treademarked alloy, and
is NOT useable as these people describe. In other words, this
stuff is NOT mumetal, which is FAR more expensive and requires
special annealing at elevated temperatures once it is formed to
shape to take on its shielding properties.

Frankly, I think this stuff is junk. If youy want to spend the
money and try it, it's up to you, it might do a little, it
probably won't help much at all.

Ny the way, the proper term for this kind of interference is
"EMI" or electromagnetic interference, and that's NOT the
problem you have. You have simply, static magnetic fields. EMI
referes to alternating, often high-frequency fields. Note there
mention of "microwave ovens" in their blurb.

--
|            Dick Pierce            |
|   Professional Audio Development  |
|   1-781/826-4953  Voice and FAX   |
|       DPie @world.std.com       |

Thanks for the feedback. I found some product material -
http://www.lessemf.com/mag-shl d.html which indicates Nickel is the best EMF
dampning. I'm wondering if I could simply create a cardboard shield wrapped
with the foil on this webpage and place this between my sub and the TV.
Think that would help?

"Richard D Pierce" wrote in message

Kool info, appreciate it!

"Richard D Pierce" wrote in message

In article ,

The reason they limited the shielding probably has little to do
with the fact that it's a 9" cube, it's more likely it's a
matter of manufacturing costs. Proper shielding doesn't take up
much space, it does, however, take up money.

Tinfoil (actually aluminum foil) will do absolutely nothing,
nada, zilch, zip. Copper, lead, zinc, and such, all will have
absolutely NO effect. A sheet of mild steel MIGHT work, and
might make it worse..

The only way to shield a speaker is to properly design the
magnet itself for low emission. And you can't do that on an
existing system such as you have. Thus, the ONLY reliable
alternative is distance.

--
|            Dick Pierce            |
|   Professional Audio Development  |
|   1-781/826-4953  Voice and FAX   |
|       DPie @world.std.com       |