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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
kavakat1 OP
106 posts
 
Geoffkait

Knowledge is everything. I am prepared for the consequences. Please explain. 
shadorne's avatar
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shadorne
7,467 posts
 
Steel works great for RFI noise. However magnetic fields of low frequency will still penetrate the chassis.

Mu-metal is needed to protect from the common source of low frequency magnetic field noise from AC power transformers.

Good news is magnetic fields are very local so separating a power amp (with a large transformer) from other components is usually enough.

Before going to great lengths to modify gear

1) Buy well designed gear  to begin with and you won’t need band-aids

2) Use XLR as RCA are woefully inadequate when it comes to protection from RF, ground loops and magnetic field induced hum.

3) A good XLR cable is Canare L-4E6S
kavakat1 OP
106 posts
 
I have heard a lot about Mu-metal lately. What is it? where do you get it? How is it applied?
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shadorne
7,467 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...
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