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TV & loudspeaker shielding.

post #1 of 11
Thread Starter 
Wanting to raise the height of my video-shielded center channel speaker, I recently moved it up to the TV's shelf, and sat my TV directly on top of the speaker. Previously, the speaker was below, on it's own shelf, separated from the TV by 3 inchs.

There's no noticable problems or discolouration in the video signal, but my center channel speaker now picks up a faint buzz, only when the TV is turned on. You have to be within a couple of feet of the speaker to notice it, but now that I know it's there.......

I was considering sandwiching some sort of sheet metal between two pieces of painted black plywood to separate the center channel and the TV to act as a shield.

Could this work?

If so, what would be the best metal? Copper? Lead?

Any other suggestions ? ( besides moving the speaker away from the TV )

Thanks
post #2 of 11
To sheild aganst the electric field of the TV, you need a conductive shield in a box around the speaker. If it is just on top of the speaker there will be no difference.

I am assuming that this is an electric feild problem because the speaker is already magneticly shielded so it won't interfere with the TV.

Make sure your cables running to the speaker are clear of any power cords and such.

As for material I would suggest you first try the cheapest thing to make sure that it will help. I recommend getting a roll of aluminium flashing and a pair of tin snips. I used Al flashing on my old amp to shield the inputs and try to get rid of a buzz caused by the AC coming into the same enclosre close to the jacks and it worked great, I couldn't hear any buzz after I did that.


Good luck
post #3 of 11
If the speaker is small enough, look for a cover off of an old PC (desktop).

(if it works, let me know as I have a web page about uses for dead computers)
post #4 of 11
Thread Starter 
Quote:
To sheild aganst the electric field of the TV, you need a conductive shield in a box around the speaker.
Do you mean top, bottom, and two sides? The front of the speaker obviously has to remain open and preferably the back as well.

Quote:
If the speaker is small enough, look for a cover off of an old PC (desktop).
The speaker's too big. But that is an interesting idea.
post #5 of 11
yes, the top, bottom, and both sides.

If you want to cover the front you can, that would most assuaradly get rid of the buzzing.....and everything else coming out of the speaker.
post #6 of 11
Quote:
Originally posted by CaptBubba
yes, the top, bottom, and both sides.

If you want to cover the front you can, that would most assuaradly get rid of the buzzing.....and everything else coming out of the speaker.
To compleatly sheild it, yes....

But since the TV is above the speaker, the RF would be only hitting the bottom provided there was a RF reflective survace a certain distance beneath the speaker.

:::::::______:::::::::::::::::::::::::::
:::::::|#TV #|:::::::::::::::::::::::::::
:::::::|####|:::::::::::::::::::::::::::
:::::::|_____|:::::::::::::::::::::::::::
::::::::::::::::::::::::::::::::::::::::::::
::::::::::::::::::::::::::::::::::::::::::::
::::::::::RF:::::::::::::::::::::::::::::::
::::::::::::::::::::::::::::::::::::::::::::
::::::::_____::::::::::::::::::::::::::::
:::::::| spk |:::::::::::::::::::::::::::
:::::::|_____|:::::::::::::::::::::::::::
:::::::::@@@::::::::::::::::::::::::::::
::::::::::@@:::::::::::::::::::::::::::::
:::::::::::@:::::::::::::::::::::::::::::::

Since RF radiates out from the source, I wouldn't think the bottom would be a requirement as long as the top had enough over hang of the front and back of the speaker and the sides went all the way down.

Thinking outside of the box: What is the TV sitting on? Copper mesh makes an excellent RF Shield, so steal mesh might do very well also.
post #7 of 11
Electric fields are different. Yes, they radiate outwards, but they go through conductors as if they wern't there. But when a conductive box is formed, the electric field inside is zero.

You can try just one side, but I doubt it will work.
post #8 of 11
You mean a Faraday cage. Yes, a complete box would compleatly eliminate RF (once grounded), but even though the RF passes through the conductive metal better than if it wasn't there, the metal still has an effect on the direction of travel of the signal.

The signal will want to travel with the metal as it is now conducting or facilitating the RF. Yes some will pass straight through and some will be conducted to the edges were it radiates out and (being slightly out of phase at this point) cancels out some of the other RF.

This is part of why a mesh works: the wires conduct the RF but change its direction and phase enough to negate the RF that passed between wires. And why grounding is so important: this absorbed energy will want to follow the path of least resistance, which the ground is.

Which reminds me: which ever of us is right, grounding should improve the "strength" of the shield.

So is the RF strong enough to over power the redirected RF? Maybe not.

mbriant, tell us what you do that works.
post #9 of 11
Thread Starter 
Quote:
mbriant, tell us what you do that works.
Will do. It may take me a while to get to it, but I'll let you know.

And thanks for the suggestions guys.
post #10 of 11
While it's true that a box will have zero electric field inside, flat planes also shunt electric fields. For example, if one uses a unbroken copper plane for circuits, the RF interference near the plane is greatly reduced.
post #11 of 11
I'm assuming that we are atalking about an electric field from the TV interacting with the voice coil(s) of your center channel speaker. If so you only need to shield the back of the driver. There are various drivers out there that actually have cans built around the magnet structure for magnetic shielding.

It could also be coming in through a crossover coil. Even easier to shield.

Lastly, if you feel that you need to shield the entire cabinet, you can put the shielding on the inner wall of the cabinet to hide it.

OK, that is about all of the "in the box" thinking that I can handle in one day.


gerG
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