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Seems like any equipment in a metal case is protected from rfi

Looking atFaraday cages in Wikipedia
Here's a quote:

A Faraday cage operates because an external electrical field causes the electric charges within the cage's conducting material to be distributed such that they cancel the field's effect in the cage's interior. This phenomenon is used to protect sensitive electronic equipment from external radio frequency interference (RFI). Faraday cages are also used to enclose devices that produce RFI, such as radio transmitters, to prevent their radio waves from interfering with other nearby equipment. They are also used to protect people and equipment against actual electric currents such as lightning strikes and electrostatic discharges, since the enclosing cage conducts current around the outside of the enclosed space and none passes through the interior.

Why are we trying to quiet the rfi to and from our amps, transports, etc when the metal case already does it? 

kavakat1
shadorne's avatar
shadorne
7,477 posts
 
You can buy Mu-metal in sheets - lots of devices that need magnetic shielding use it - medical instruments, power transformers and in the past on CRT tubes on instrumentation.

I suppose you could buy it to shield amplifier tubes from the magnetic 60 Hz and higher harmonics power supply transformer noise but most designs I have seen do not seem to bother. Speakers that are designed to be placed close to CRT tubes (old TV) probably have mu-metal sheets on the inside.

Mu is a Greek letter which has been adopted as the symbol for magnetic permeability (not the same as D’Arcy’s permeability). Mu-metal is mostly nickel iron.

Transformers cores are made from a similar high permeability material but Mu-metal is usually conductive and very soft which is bad for a transformer core.
randy-11
1,913 posts
 
also... if your equipment is properly designed, you don't need it

and to me that means it has provisions for XLR/balanced runs

one thing I find odd about some manfs. is they claim high end but offer only single ended...
geoffkait's avatar
geoffkait
23,365 posts
 
RF is like germs. It’s like Chickenman. It’s everywhere! We're drowning in a sea of photons. Since RF travels at lightspeed it’s eveywhere at the same time. It’s inescapable. It infiltrates any and all holes or gaps anywhere. It enters the unused wall outlet prong holes wherever they might be. RF then contaminates the house wiring (unshielded), then RF enters the electronics via power cords. The PC shielding only protects against external RF. Hel-loo! Regardless of the metal chassis. Since RF is also produced by microchips INSIDE electronics such as CD players not only is everything inside the chassis contaminated but the signal going to the amp or preamp is also contaminated. The enemy is inside the gates!
nonoise's avatar
nonoise
11,041 posts
 
A quick look at Wiki states that any hole or vent has to be significantly smaller than the RFI/EMI wavelength in order to stop it. Good luck with that. It enters through any connector not used as well as any cable not completely shielded. Also, AC brings it through your PC. 

Even galvanic isolation inside your component (if utilized) won't stop stray fields from contaminating each other. You can obsess your butt off about it but there are more important things to consider, unless you want to go the Howard Hughes route.

All the best,
Nonoise
kavakat1 OP
115 posts
 
So, would a sheet of mu-metal placed on the bottom of each shelf between components help? I have a NAD integrated amp, and one shelf below is my OPPO 105. Shelf is MDF
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