Shielding?

[Soulhunter]

Small question...

How to build shielding against EMI (psu, speakers etc.) ???


Bye

[TotalChaos]

Encase whatever in a faraday cage (a box made of a condutive material) Tinfoil works. Ground the box and EM signals shouldn't be able to penetrate the sheilding. It's just like the metal box around the actual tunning parts of a TV tuner on the circuit board.

[Soulhunter]

Originally posted by TotalChaos

Encase whatever in a faraday cage (a box made of a condutive material) Tinfoil works. Ground the box and EM signals shouldn't be able to penetrate the sheilding. It's just like the metal box around the actual tunning parts of a TV tuner on the circuit board.

Hrm, I thought this faraday cage thing would only work for high frequency fields (radio, tv etc.). Does it also work for low frequency sources like speakers?


Tia n' Bye

[TotalChaos]

The theory is that the potential inside a faraday cage is 0 volts. EM Signals shouldn't be able to influence the potential of the components inside.

It probably has to do with something like the capacitive and/or inductive reactance the grounding path has when we are talking about what frequencies can influence the electronics inside.

I wouldn't call myself an expert in electronics, but my semi-educated guess is that lower frequencies would be easier to block then higher. (well Hmmm on second thought, it does kinda shunt all signals. I should block them all well enough for most standards) The PSU on your computer uses a high frequency, and usually has a metal case around it. (Shouldn’t be much of a problem!?!?) Since I'm on this note, what do you mean when you are talking about EMI from speakers? Are you talking about the electro/magnetic fields produced by the voice coil? Do you want magnetic shielding from the magnets? Something else????

[Soulhunter]

Originally posted by TotalChaos

Since I'm on this note, what do you mean when you are talking about EMI from speakers? Are you talking about the electro/magnetic fields produced by the voice coil? Do you want magnetic shielding from the magnets?

Yeah, magnetic fields from speakers/magnets !!!


Tia n' Bye

[TotalChaos]

Magnetic circuits are just like electric circuits; short the circuit and nothing gets out. If you look at magnetically shielded speaks they have a magnetically conductive material (usually steel) housing around the motor structure. This effectively shorts the magnetic field. It's kind of hard to make something that fits the magnets. Maybe try a small piece of steel pipe (large enough to surround the magnets). Use a metal disc for the bottom. Good luck on this venture.... I hope it works. *crosses fingers*

[Soulhunter]

Thanks for ya help! In the meantime someone else suggested me the same solution. He said you can buy this "shielding caps" @ matched size in special audio-shops. So, seems I have to open my speakers, measure the size of the magnets n' buy/build some of this caps! Hope I dont b0rk something... ^^


Thanks n' Bye

[zilog jones]

Shielding CRT monitors that aren't already properly shielded - now THAT will be a challenge! Don't suppose there's any remotely easy way to do this without potentially killing yourself? I have a TV about a metre away from my monitor - I can't see any sort of substantial shielding inside them, and they don't get on well together...

[TotalChaos]

How are they affecting each other? The main things to watch out inside the CRT case are capacitors (any time) and the high voltage inductor circuit (during operation).

[zilog jones]

The TV makes the picture on the monitor kinda fuzzy. They're coming from the same socket as well, which probably isn't helping things. CRTs are the only thing I'm seriously scared of taking apart though so I don't think I'll actually do anything. Plus I usually have the TV off when using the PC anyway...

[TotalChaos]

Maybe the signal wires are tangled up with power wires!?!? I doubt the TV is actualy radiating EMI high enough to impose on the monitor itsself.

[zilog jones]

I don't know actually - I can't remember if they did have much effect on each. Maybe it was just the degaussers when turning them on...

[feedback]

Plug them into different outlets on different circuits. Also, you may try reversing the polarity to see if that helps. It's been a while since I cracked open a TV but I will tell you that those capacitors will hold a charge for days. Discharge them before you start fooling around inside or you will be highly stimulated by the electromotive force and current inside.:)