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

I could tell you but then I’d have to kill you.


Geoffkait

Knowledge is everything. I am prepared for the consequences. Please explain. 
Geoffkait

Knowledge is everything. I am prepared for the consequences. Please explain. 
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
I have heard a lot about Mu-metal lately. What is it? where do you get it? How is it applied?
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.
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...
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!
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
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
nonoise
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.

All bets are off how small or big a space has to be to stop or prevent or disallow an electromagnetic wave once the Schumann frequency raised its ugly head. You know, the 7.8 Hz wave that sets up in a listening room when generated by a Schumann frequency generator, since the wavelength of that particular frequency is around, what 26,000 miles? Yet it has no problem fitting into the room. Yeah, baby!
Geoffkait,
Since you mentioned it, I use Clone Audio's Schumann Generator to defeat all that nasty electronic smog. Better detail, instrumental/perfomer separation, layering and soundstage.

I can't wrap my head around how a 26,000 mile generated wavelength can fit in my room, so maybe only a fraction of it's length is generated since a wall wart is used as a power source. However it works, I'm glad I have one.

All the best,
Nonoise
Electromagnetic waves are very flexible. 😀 The Schumann frequency waves wrap around the room. It would have to be the full wavelength as shorter wavelengths wouldn’t be 7.8 Hz. Can electromagnetic waves enter the component via unused input/output RCA jacks on electronics, even though the chassis case is metal? I wouldn’t bet against it. It's also interesting how a Schumann CD can generate a 7.8 Hz acoustic wave in the room through any speakers, even computer speakers, no?
 
kavakat1 OP
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

Since the primary culprit of magnetic fields by far is the large transformer, the ideal solution is to completely wrap the transformer with one or two layers of mu metal, which is quite flexible (and SHARP). As I recall one layer absorbs 77% of the magnetic field whereas a second layer increases the performance to 95%. A space of 1/4" should be maintained between the two layers. The correct type of mu metal is low frequency high permeability mu metal.
Mu-metal tends to lose its properties after it is bent, unless it is annealed. Same with many other magnetic exotics.
That’s why you always use annealed mu metal, which all of it is these days, since annealing improves performance considerably. Why wouldn’t you anneal it? And why you wrap the transformer without putting sharp bends in the metal, easier I suppose for toroidal transformers than for square type. Just ask for Ultraperm.

My point is that wrapping in mu-metal is not straightforward.

"Why wouldn't you anneal it?" Perhaps because most people don't know that they should?

you can not isolate from all RF period lower Frequencies are easier. The sun bombards us with RF, every cell phone every wireless device is bathing you in High frequencies. shorter the wave length the smaller the holes in the cage need to be. I’ve been in shielded rooms on the Navy base that use 12" of various types of shielding the doors are 12" thick and the door seals have multiple copper wipers all around and they still let in some frequencies. so don’t worry too much focus on the ones that are audible.

oh Terry9 once you bend any metal you get micro fractures so when you anneal the metal, heating and cooling under control you remove the micro fractures. This is a point for wires to consider don’t bend them to much and too often.

glennewdick
oh Terry9 once you bend any metal you get micro fractures so when you anneal the metal, heating and cooling under control you remove the micro fractures.

Mu metal is annealed by the manufacturer prior to shipping. That’s why bending annealed mu metal won’t produce micro fractures like unannealed mu metal. Think of it like cryogenic treatment, which is what it is. The molecular structure of the annealed alloy is much more homogeneous and less brittle and more ductile. Obviously for toroidal transformers no sharp bending is involved when wrapping the transformer. You just make a "hat box." Mu metal is quite soft and malleable so for square transformers use a cylinder shaped tool to form the alloy into gradual bends around the transformer, thus avoiding sharp bends. Problem solved!

Timely tip: TAKE CARE WHEN HANDLING MU METAL. Always use those special metal-cutting scissors with beveled edges that makes a blunt edge on the alloy. It’s ok to use gloves when handling mu metal. Otherwise you will suddenly realize your fingers are bleeding since mu metal edges are very very sharp.
from Wikipedia:
Mu-metal objects require heat treatment after they are in final form—annealing in a magnetic field in hydrogen atmosphere, which increases the magnetic permeability about 40 times.[4] The annealing alters the material's crystal structure, aligning the grains and removing some impurities, especially carbon, which obstruct the free motion of the magnetic domain boundaries. Bending or mechanical shock after annealing may disrupt the material's grain alignment, leading to a drop in the permeability of the affected areas, which can be restored by repeating the hydrogen annealing step.


Pop quiz - What's the difference between heat tempering and cold tempering (Cryo)? Free sheet of Morphic Message Labels to the winner.

Geoffkait:

My answer would be: The temperature at which it is done. Please send asap.
That's very good. The Morphic Message Labels are in the mail.
RFI/EMI is a tricky beast to handle.

It is nearly impossible to make an enclosure 'tight'. As a former designer of military electronics that were required to survive EMP, it's quite a challenge even at much smaller audio scales. 

Thing about EMI/RFI susceptibility re: audio is all electronics - tube or SS - can convert very high frequency noise right down into the audio band via diode demodulation. And the higher the frequency, (like the microwave from cell phone systems) the harder it is to deal with.

Top issue for EMI entry is cabling to/fro the chassis - these are the real problem children. RFI walks along the cable skin and enters easily to your gear's nice metal box via audio connectors never designed for susceptibility control. Once inside, the RFI radiates all over using internal wiring. Even shielded cables, - although better than open wire - are nearly transparent to RFI at very high frequencies.

Re-engineering existing equipment is virtually impossible as to get real, testable results.
Another "enlitened" response. We have to start thinking outside the metal box and I really can't recommend enough the use of a Schumann Resonator to help defeat electronic smog. 

If you can get a hold of one it would be so easy to try and see if you can detect the benefits. Just place it close to and higher than your head when you sit to listen (5'or more is best) and set it up so you can easily unplug it at will. Listen to some very familiar recordings and judge for yourself. 

All the best,
Nonoise

enliten
RFI/EMI is a tricky beast to handle.

It is nearly impossible to make an enclosure ’tight’.

>>>>>Especially with all those unused Input and Output jacks. 😛 Then there is the issue of RF generated by microchips inside the chassis, as I pointed out, was it yesterday? Think inside the box!

As a former designer of military electronics that were required to survive EMP, it’s quite a challenge even at much smaller audio scales.

>>>>of course EMP is not the same thing as RFI/EMI. Be that as it may. And it’s not that difficult to deal with RFI/EMI in high end electronics. Audiophiles have been doing so for many years. A good start would be to power OFF all unnecessary appliances such as fridge, TV, room purifier, even a microwave oven in sleep mode generates RF. (It helps to have an RFI/EMI meter to, you know, see what you're up against.





  You could also consider Stillpoints ERS shielding sheets . 11x8 for $25, at Music Direct . Lay a couple on your equipment and see if you can tell a difference . Then attach in a semi permanent manner. Also when my sound is too tight , I switch from briefs to boxers 🤡.
Bullrider97
You could also consider Stillpoints ERS shielding sheets . 11x8 for $25, at Music Direct . Lay a couple on your equipment and see if you can tell a difference . Then attach in a semi permanent manner. Also when my sound is too tight , I switch from briefs to boxers.

No offense, but I find Stillpoints ERS stuff a mixed bag. A very mixed bag. In fact after playing around with relatively small pieces of it in two systems I was unable to find a single place where it improved the sound. Now, I admit it did *change* the sound, it made it wooly and phasey sounding. Not to belabor this any more than I have to, I found that even with a sheet of the stuff lying inert as it were on the coffee table it atill made the sound wooly and weird. The only way I could get back to square one was to actually burn the stuff. Folks have reported trying smaller and smaller squares of the stuff until the sound is good. I say smaller and smaller until the pieces are zero size. If ever there was a poster child for expectation bias this is it! Hope that’s not being too harsh. But, wait, there’s a silver lining. The price has not gone up in 15 years. In fact, it’s come down.😀