Is guitar shielding a big fat hoax?

[Deleted]

Ok, we have been here for so long and subscribed in order to achieve this ideally-humbucking-like totally noiseless SC guitar. We have used all kinds of materials, conductive paint, aluminum, copper to create faraday cages, etc.
Until one day, I found that the ELF magnetic field which is the most harmful factor for a guitar pup (at least in my 220V 50Hz part of the world), cannot be filtered out by common electrical shielding techniques!! One either needs MU-METAL, or G-iron, or some other expensive material to truly block magnetic interference to the pups! I have done extensive searching lately, and found out that the values I get with the mGauss/uTesla meter in 3-axis match *exactly* the noise levels I get from my EMGs!!! but also from the rest of the pups, to the point I can predict the value of magnetic field in a *specific* dimension, *only* by placing the EMGs guitar in a specific orientation! So, in order to shield the guitar, I better shield the house, which will be very expensive, but that's another topic.

The question here is : since traditional electrical-conductivity-based Faraday cages are completely inefficient in shielding against magnetic fields, and since in my own experience, guitar pup humming is 100% connected with LF magnetic field interference, we are in a position to ask : Is guitar shielding (as we have been doing it) a big fat hoax?

[ashcatlt]

IDK if this helps any, but the point of shielding is not to block the EM radiation from getting to and wiggling the electrons in the coils, but rather to try to get it to wiggle both ends of the coil the same amount, the same direction, at the same time. The signal that we call our sound is the voltage difference between the tip and sleeve of the cable, and the shield helps to make sure that the EM/RFI noise is not different on the tip than it is on the sleeve.

[JohnH]

I think there are two different but related effects. When we suffer from 'hum' in a guitar, usually the most annoying aspect is not the low-frequency fundamental 50 or 60hz note, but the spiky 'buzz' that we hear as high frequency transients. Its caused by spikes and switching from such things as flouro lights and switched power supplies. Its largely generated at radio frequencies. The physics of supressing or reflecting these effects is such that just a very thin conductive skin, if grounded, even with a few small holes, can work very well. That's what guitar shielding can achieve.

But its much less effective on the base hum note, particularly caused by magnetic fields. To shield effectively against that requires a complete enclosure of very high conductiviy, such as several cm of metal
. A bit of foil does not much.

That's what I think happens, but I couldnt explain the theory of it.

[newey]

I think JohnH's explanation above is both succinct and correct.

We have debated this before, in several different contexts. Shielding isn't a hoax, but neither is it a panacea. There's a lot of variables in any given situation, and there may well be certain pickups, and certain electrical environments, where shielding will make no difference whatsoever. Jon Atchley, on the original GN site, said as much, that one should expect variable results.

But we don't have to speculate, as we have empirical evidence that shielding can sometimes provide a benefit under some conditions.

D2o's "How much benefit can we expect from shielding" started out as an evaluation of the (infamous) "Urthman wiring", but also provides a validation of shielding of that particular guitar in that environment. It doesn't prove any more than that, but his testing demonstrates that shielding can help reduce noise.

D2o does a good job of laying out his experimental conditions, and he controlled for the variables that he could. I see no reason to doubt his data.

For those members who came here more recently, those who don't recall the Urthman controversy, D2o provides a link to the original thread. Things haven't gotten that contentious around here since.

[Deleted]

Oct 14, 2015 15:51:43 GMT -5 JohnH said:

That's what I think happens, but I couldnt explain the theory of it.

That's what happens, I agree. In my case, almost all of the hum comes from 50Hz ELF magnetic field. And the receivers are the pups. I have got a problem in my house, whole neighbor, and city in general. In my house RF or lights is not so much of a problem, unless I place the guitar very close to the source. But when I approach the receiver/sensor (meter, jack, guitar, pup) to the particular area of danger or a mains socket, hum/numbers become very intense. I will buy a meter soon that is able to measure LF (low freq 1-300Hz band), both electrical and magnetic field and RF (radio/wifi/mobile freq, GHz band), and will do tests with hum.
As you said, to do proper magnetic shielding it takes either Mumetal or G-iron or Cobalt films or even thick (>=3mm) magnetic stainless steel sheets. The latter is the cheapest method but it will be so heavy and cumbersome to incorporate to the house walls. There is always the possibility that the wiring in our flat sucks as well.

[Deleted]

Oct 14, 2015 22:38:39 GMT -5 newey said:

I think JohnH's explanation above is both succinct and correct.

We have debated this before, in several different contexts. Shielding isn't a hoax, but neither is it a panacea. There's a lot of variables in any given situation, and there may well be certain pickups, and certain electrical environments, where shielding will make no difference whatsoever. Jon Atchley, on the original GN site, said as much, that one should expect variable results.

But we don't have to speculate, as we have empirical evidence that shielding can sometimes provide a benefit under some conditions.

D2o's "How much benefit can we expect from shielding" started out as an evaluation of the (infamous) "Urthman wiring", but also provides a validation of shielding of that particular guitar in that environment. It doesn't prove any more than that, but his testing demonstrates that shielding can help reduce noise.

D2o does a good job of laying out his experimental conditions, and he controlled for the variables that he could. I see no reason to doubt his data.

For those members who came here more recently, those who don't recall the Urthman controversy, D2o provides a link to the original thread. Things haven't gotten that contentious around here since.

Newey, I'll have to read D2o's article, but I must note here, we are living in 2015, electric guitars and magnetic pups have been around since 50s, most ppl/companies/articles/posts talk about reducing 60Hz hum, and I have yet to find the words "Gauss" or "Tesla" or mV/m or μW/m2 in any "research" about guitar hum shielding or humbucking or pups in general. This I cannot explain. Hopefully soon, I will start measuring all the EMF spectrum and will try to correlate this with hum in its various aspects. In fact, I have found such a strong correlation between hum and 50Hz EMF that I think that the meter alone can do most of the work, leaving the EMGs (most noisy humbuckers I have) alone. Also I have a true single coil (and the only pup which is noisier than the EMGs) a 7-string dimarzio blazer SC RW/RP version, I'll do some tests with this as well.

[newey]

I must note here, we are living in 2015, electric guitars and magnetic pups have been around since 50s, most ppl/companies/articles/posts talk about reducing 60Hz hum,

True, but also note that most manufacturers do make some attempt at shielding things. Many use conductive paint in the cavity, for example, and most pickguards have a foil backing. Those things cost money, and manufacturers wouldn't bother if they didn't think there was a benefit.

[Deleted]

From D2o's post

Jun 14, 2008 17:04:34 GMT -5 D2o said:

The following tests were performed with the guitar being held in the same position, angle, distance, etc. every time.

alright, but the (this particular) devil is in the details (angle). One should "measure" hum in all 3-axis and then normalize. In my house at a particular angle EMGs are dead silent. Guess what, so is the Dimarzio blaze single coil. At this angle "maybe" classic faraday shielding filters out or reflects back RF waves, hence the absolute silence. But move the guitar 90 Deg up and ELF buzz becomes heavy again.

[newey]

The point is, the angle he chose was one where the guitar in question wasn't silent, it was noisy, as the clips show. And the shielding reduced it to some extent, at that angle. While another angle might be quieter, the shielding isn't going to add to the noise in any position.

To "normalize" noise across three axes would mean looking at the average of the hum in three different positions- but in this context, we aren't concerned with the average, but with the maximums. Cut the noise at it's maximum, and sure, the effect may be less at the quieter positions, or the reduction may not be detectable at all if the noise "floor" is low enough. But if we've chopped it off the top, we have accomplished the goal to some extent, even if imperfectly.

[Deleted]

The clips are no longer available, but my guess is that the angle he chose was not the worst (in my case the worst angle is with the guitar body parallel to the ceiling). Shielding might help get rid of high frequency EMF, this annoying trebly hiss, but not the LF (low freq) heavy hum. There is one phenomenon in physics called "skin effect", it has to do with conductivity and thickness of the conductor. This rule works in companion with the Faraday principle. For very low frequencies this thickness is rather large for most metals. (in the ranks of 8mm for aluminum, copper, etc). One has to use about 3mm of magnetic stainless steel class 430 in order to achieve some minimal magnetic shielding. It is the cheapest solution and costs about 50 EUR/m2.
One cannot shield a guitar's pups against LF. Shielding against LF magnetic fields (besides being impractical) would also shield against the string-vibration-generated EMF -> poor sound. So, for balanced coils humbuckers, there is absolutely no need for shielding. For unbalanced designs (like the EMGs), one has to live with the noise.
Those are my thoughts at this point. I need to do some testing when I get the EMF LF/RF meter.

[newey]

Well, you raise a question, but I don't think anyone has proposed that shielding does anything more than shield RF, not magnetic fields. The more basic question is, does a low frequency magnetic field cause noise in a guitar pickup in the first place? It certainly could in theory, but what would the frequency be, would it be audible, etc?

[Deleted]

Oct 16, 2015 9:36:56 GMT -5 newey said:

The more basic question is, does a low frequency magnetic field cause noise in a guitar pickup in the first place?

IMHO not only does LF magnetic field cause noise to the pups, it is the prime source of what we know as hum, the classic 50Hz/60Hz hum. All my pups respond so similar to the LF mGauss meter, someone could say I almost don't need the meter! But I hope to have more accurate quantitative results soon, as the meter I have ordered measures LF/RF.

[Deleted]

To the question about whether LF magnetic field has any effect on the hum, lets consider that the strings themselves produce a LF magnetic field, and that guitar pups are exactly designed to sense this magnetic field. Strings vibrate at frequencies ranging from about 62Hz (low B), or 82Hz (low E) to about 660 Hz high E at 24th fret. I'll try to measure this as well by placing the meter as close to the strings.

[newey]

lets consider that the strings themselves produce a LF magnetic field, and that guitar pups are exactly designed to sense this magnetic field.

Not quite my understanding of it. The magnetic field is produced by the magnets in the pickups. The vibration of the (metallic) string perturbs that field, thereby inducing a current in the windings of the pickup, which is the signal we hear. It is the movement of the field that matters, a static magnetic field won't induce a signal, noise or otherwise.

The pickup senses RF noise from the environment by a different mechanism- the windings of the pickup act as an antenna. They will do so even if you remove the magnets from the pickup.

[Deleted]

Oct 16, 2015 17:58:13 GMT -5 newey said:

The magnetic field is produced by the magnets in the pickups. The vibration of the (metallic) string perturbs that field, thereby inducing a current in the windings of the pickup, which is the signal we hear. It is the movement of the field that matters, a static magnetic field won't induce a signal, noise or otherwise.

So the vibration of the strings are "moving" the field you say? That's how I understand it as well. The field of the magnets/stable strings is static. In order to have alternating electric current produced, one has to force an alternation to the magnetic field as well. Which means that the forces of the magnetic field are not even there without the strings. It's the presence of the ferromagnetic nickel, cobalt, etc which is part of the magnetic phenomenon. Will have to look more on this.

Oct 16, 2015 17:58:13 GMT -5 newey said:

The pickup senses RF noise from the environment by a different mechanism- the windings of the pickup act as an antenna. They will do so even if you remove the magnets from the pickup.

Alternating 60Hz EMF IMHO is inducing the pup's coils in the same manner that the combination of strings/magnets does. If you think about it it is exactly the same thing. I'll have to look into the antenna analogy.


I find this whole thing interesting. Brushing up knowledge we got ages ago is fun!

Edit : the only comment I can make about the antenna theory, is that it might be so for RF, but for LF the coils should have length of a magnitude of 5000 Km.

[newey]

Let's not forget that, if you are measuring magnetic fields and measure anywhere from about 0.25 to 0.65 microTeslas (25 to 65 Gauss), that is to be expected anywhere on Earth, it's the strength of the Earth's magnetic field. That's a tiny amount, much less than a typical magnet that you'd stick on the refrigerator. But the field from the refrigerator magnet extends much less out into space as it is so small, whereas the Earth's field extends out hundreds of miles into space.

As I said before, it's the movement of the field that matters. (The Earth's magnetic field changes over time, but very slowly. At any given point and any given time, it is relatively static)

50 (or 60) MHz noise propagates as a moving wave from our household lines as the AC current alternates at that frequency. If we went back to Edison's original DC system, we wouldn't experience it.

It seems to me no meter is necessary to test your proposition that LF magnetic fields cause noise through guitar pickups. Get a noisy guitar, get several relatively strong magnets, place them near the guitar pickups while the guitar is plugged in and see what it does to the noise level. My prediction would be that it does nothing so long as you don't move the magnets. At least, it won't change the noise much, it will probably affect the tone in a negative way.

[Deleted]

Oct 17, 2015 8:48:36 GMT -5 newey said:

Let's not forget that, if you are measuring magnetic fields and measure anywhere from about 0.25 to 0.65 microTeslas (25 to 65 Gauss), that is to be expected anywhere on Earth, it's the strength of the Earth's magnetic field.

From what I measured, readings about 0.3->0.7 mGauss (=0.03->0.07 μTesla) seemed pretty normal level, the minimal I got in the problematic room. EMGs sounded pretty good at those levels (as did all the rest of pups, minus maybe the SC, which hums slightly more than the EMGs at the 0.7 mGauss axis). If we have earth's magnetic field of 0.3 mGauss at each of the 3 axises, the total field has intensity equal to sqrt(x^2+y^2+z^2) = 0.52 mGauss, you can't get much lower than that. EMGs started to hum ugly above the 0.7 mGauss level (at a specific axis, I gather the Z axis)

Oct 17, 2015 8:48:36 GMT -5 newey said:

It seems to me no meter is necessary to test your proposition that LF magnetic fields cause noise through guitar pickups. Get a noisy guitar, get several relatively strong magnets, place them near the guitar pickups while the guitar is plugged in and see what it does to the noise level. My prediction would be that it does nothing so long as you don't move the magnets. At least, it won't change the noise much, it will probably affect the tone in a negative way.

My proposition was not this. My hypothesis is that traditional guitar shielding (faraday cage with a thin layer of conductive material) is ineffective to protect against what is known as 60/50 Hz hum, which IMHO constitutes the main source of what we call and sense as guitar pup hum. Shielding might help filter out the RF noise, so the guitar should be (more) silent at a given angle (if we get lucky) (meaning with the pups perpendicular to the axis with the least measured MF intensity) but granted at the not so good angles (the rest of the angles) the guitar will start humming again loud. But all this will have to proven experimentally when I get the meters/materials. I just hope I didn't spend all that money for nothing.

[ashcatlt]

Oct 17, 2015 8:48:36 GMT -5 newey said:

50 (or 60) MHz noise...

...is inaudible. We know what you meant.

Back in the last couple years of the millenium we were "working" on building a studio complex from the ground up. Part of the "plan" was to remove all AC power from the studio building itself. Most modern gear runs on DC internally. It might take AC from the wall, but that just means it's got rectification and filters to create DC. So move all of that to some spot outside the studio and run DC only through the walls and you remove that whole part of the noise equation. We never got anywhere near that far, but we did end up with a really nice composting outhouse in the middle of a grapefruit grove.

[newey]

a really nice composting outhouse

Sounds a little small for studio space . . .

Yeah, Hertz, not MegaHertz.

Greek, I get what you're saying; I think JohnH's response right at the beginning of this thread covers this ground. I guess you lost me with all this talk of measuring magnetic fields, it's still the 50 Hz wave that you're concerned about. There are low frequency spectrum analyzers that go down that low, but they're pretty pricey.

(and, yes, I'm aware that we're talking about electromagnetic force here, that the two are interrelated. My point was, there are a lot of stray magnetic fields that we're not concerned about as they are static.)

And, why bother to try to measure the 50 or 60 Hz wave from household AC? We know it's there . . .

I guess we need to know your experimental protocol and what it is you're trying to achieve.

[ashcatlt]

I'm going to say again that it doesn't really matter how much those magnetic fields wiggle the electrons in the wire as long as it wiggles both ends the same amount in the same direction. Shielding has nothing to do with blocking EM waves, in fact almost the opposite.

Edit to add - The outhouse was 8' x 8' x 8' so we didn't have to saw anything. We used 2x10s (!!!) for the floor joists, and 2x8s for the roof. I laid some really nice slate tiles on the floor. It was pretty sweet. The toilet itself cost more than the structure.

[newey]

Ah, so it wasn't that the proposed studio got converted to an outhouse.

And Ash, I think you are correct in describing that it's what happens at both ends of the wire that matters.

At the outset, GD said:

So, in order to shield the guitar, I better shield the house, which will be very expensive, but that's another topic.

Shielding the house won't help (unless you go "off-grid" with something like a 12VDC system). As long as you have AC wiring in the house, you're going to get the 50Hz (or 60Hz, depending on your local utility) hum, it's coming from the wiring in your house.

You mentioned the Mu-metal shielding. I saw a roll, I guess it was a meter, for about 100 euros. That is expensive, but the tape looks to be about 10 cm wide or so, so a meter's worth, used judiciously, would probably do 3-4 guitars. They claimed the equivalent of 7-8dB reduction with one layer, more with multiple layers.

Still, I've taken the wife out to a nice restaurant and spent more . . .

[ashcatlt]

Oct 18, 2015 10:53:37 GMT -5 newey said:

Ah, so it wasn't that the proposed studio got converted to an outhouse.

No. We never really got started on the studio building itself. It was me and three other guys living in tents in a grapefruit grove. We had electricity, built that outhouse, pounded a shallow well, and had worked toward clearing the area for the studio, but domestic issues combined with certain changes to the early e-commerce market (the bursting of that first "tech bubble") conspired against us, and the project was abandoned. We made a little money selling the grapefruit for a year or two, but it wasn't sustaining itself and we had to let the property to.

[newey]

Still, must have been fun while it lasted. I've always dug the idea of getting up in the morning and picking breakfast off a tree. A buddy of mine in San Diego had a lemon tree and a lime tree in his back yard, it made Happy Hour a breeze . .

Meanwhile, we've derailed GD's topic here a bit. But I like the "off grid studio" idea. I always had an idea to have a battery-powered rock band that could play anywhere. That would, of course, require first of all being in a band, which would require a whole lot more practice on my end . . .

[ashcatlt]

Oct 18, 2015 12:11:27 GMT -5 newey said:

Still, must have been fun while it lasted. I've always dug the idea of getting up in the morning and picking breakfast off a tree. A buddy of mine in San Diego had a lemon tree and a lime tree in his back yard, it made Happy Hour a breeze . .

It completely didn't suck! We had a row of oranges halfway across the grove and tangelos over at the far corner. Not long after, I moved to Belize where there was always a lime tree close at hand to mix with our rum.

Meanwhile, we've derailed GD's topic here a bit. But I like the "off grid studio" idea. I always had an idea to have a battery-powered rock band that could play anywhere. That would, of course, require first of all being in a band, which would require a whole lot more practice on my end . . .

As you know, my band uses all amp sims, and now a pretty efficient computer based system. That and a small PA connected to an inverter equals tailgate concert anywhere we choose to play. We used to joke about finding a driver, rolling down the windows, and playing while cruising "the strip". Heck, we could just plug into an aux jack on a modern car stereo! One of these days...

Edit - I also had a computer based recording setup in the sleeper of the big truck back when I was an over-the-road trucker. Recorded some pretty great stuff in some loading docks and truck stop parking lots.

Automobile alternators are really nasty for noise, but there are ways to keep it manageable.

[Deleted]

Oct 18, 2015 10:53:37 GMT -5 newey said:

You mentioned the Mu-metal shielding. I saw a roll, I guess it was a meter, for about 100 euros. That is expensive, but the tape looks to be about 10 cm wide or so, so a meter's worth, used judiciously, would probably do 3-4 guitars. They claimed the equivalent of 7-8dB reduction with one layer, more with multiple layers.

Still, I've taken the wife out to a nice restaurant and spent more . . .

I bought smth that is supposed to be better and shield against both LF and RH : www.yshield.com/eu/mf-mumetall-shielding-film-mcl61-width-61-cm-0.5-meter
It contains polyester, Cobalt, Iron, etc.

Going back to the humbucker noise talk, the whole (brilliant) idea in the design of the humbucker was to cut-off outside-induced currents, cancelling their noise, by bringing the hum from the two coils out of phase with each other (unwanted signal->current out of phase), while keeping the currents from the string vibration in-phase (wanted signal->current in phase).
The assumption in the humbucker design was that the external EMF will be there and create current in the coils! The problem in our house is not so much the limited power EMF from the 50Hz in the house, but rather power carrier lines sources from outside the apartment. This is what I am trying to study here. That's why the EMG tech was absolute with this : EMG pups are shielded (against RF) but due to their imbalanced design, (the two noise signals from each coil are apparently out of phase but unfortunately one is stronger than the other), they are helpless in an environment of abnormal LF activity. That's the price they have to pay for having a rather rich sound. I find it ironic that people consider EMGs .... completely noiseless (the are not), but sterile and compressed (they are very rich in harmonics).

[Deleted]

Oct 18, 2015 10:09:21 GMT -5 ashcatlt said:

I'm going to say again that it doesn't really matter how much those magnetic fields wiggle the electrons in the wire as long as it wiggles both ends the same amount in the same direction. Shielding has nothing to do with blocking EM waves, in fact almost the opposite.

Hmm I guess humbuckers solve the problem with putting the hum's current in the opposite direction for each coil. The currents are not induced by the ends, but from the coils *in* the wire. EMF will not only affect the both ends but the whole length of the coil wire as well. That's why we have an alternating current of the hum frequency in the coil, living side by side with the alternating currents induced by the string's harmonics vibrations. So we have a phasma of many frequencies each creating a current with its own sinusoidal function (magnitude, period). With humbucking we look to bring the unwanted currents fight against the direction of their twin brothers at the opposite coils (via the reversed polarity trick). This article helped me brush up on the topic : www.seymourduncan.com/blog/the-tone-garage/how-hum-cancelling-works-part-1 , www.seymourduncan.com/blog/the-tone-garage/how-hum-cancelling-works-part-2
With single coils, and shielding, we may minimize the currents induced by RF. Unfortunately traditional shielding will do nothing to the LF EMF. I don't quite understand your POV, but what IMHO will happen with shielding or not, is that 50Hz hum will induce alternating current (of the same frequency) to the pup's coil. Why does shielding do nothing to the LF EMF? Because of this : en.wikipedia.org/wiki/Skin_effect . The copper/aluminum whatever shield should be about 1cm thick. And the pups should be inside it. And when inside, they could not be affected by the strings' movement. What's why I said that my only hope is shielding the whole guitar (impractical) or just the house. Or going DC like you did, but this cant help in my case, since the noise is coming from the neighborhood power lines.

[newey]

As long as you're plugging it into an amp running on household current, shielding the house won't help. And yes, the whole length of the wire is involved but ash's point is that we only care about what happens at the two ends of the wire.

[Deleted]

Oct 18, 2015 19:37:41 GMT -5 newey said:

As long as you're plugging it into an amp running on household current, shielding the house won't help.

Just think about plugging the guitar into a DC battery powered pre-amp and hearing via headphones. Measure the hum somehow, e.g. by ear noting down all other factors : angle, distortion level, noise gate off, etc. Then plug the guitar into the amp. Stay 1-1.5 meter away from the amp, and measure again the hum, retaining the above factors constant again. It will be the same as before. The mechanism that the pups coils sense the ambient alternating EMF field has nothing to do with any amp, unless you place the guitar so close to the amp that you are forcing the whole of the amp's weak EMF field onto your pups (in addition to the ambient EMF due to the house's wiring or outside sources). The 50Hz noise is there with or without the amp! If you could generate a 50Hz EMF wave of the same magnitude as the source of the hum but with 180 Deg delay, I bet you could make the whole area acting as a very big humbucker, but I think the radiation we would receive might be double instead of zero. So my assumption here is that shielding the house (against external EMF, like the power lines from across the street) (if possible) would certainly help.

Oct 18, 2015 19:37:41 GMT -5 newey said:

And yes, the whole length of the wire is involved but ash's point is that we only care about what happens at the two ends of the wire.

The alternating voltage that happens at the ends of the wire is the *consequence* of the electromagnetic induction, not its cause. And I fail to see how can any internal shielding impact any of this, i.e. interfere at the correct frequencies, angles, magnitudes as to make any difference. AFIIR in case of an explicit power source, e.g. battery then I=V/R, in our case we can understand this better by V~ = I~*R. Now this V~ and this I~ is not *one* sinusoidal function, but many functions corresponding to each frequency, including the base frequency, its harmonics and all the hum and noise combined.

[newey]

The 50Hz noise is there with or without the amp!

Of course it is. My point was that you have household current to run the amp, the current runs through wires which are inside of your shielding if you "shield the house"- it has to go to an outlet, into which is then plugged power cords- to your amp, refrigerator, PC and everything else electrical in your house. All those things are connected to the power grid, which is dutifully alternating that current 50 times a second. That 50 Hz wave is propagated throughout the entire grid. So you've got the same hum from your household circuits, as well as from nearby lines (although the nearby lines could certainly make things worse).

[Deleted]

Oct 18, 2015 23:18:37 GMT -5 newey said:

The 50Hz noise is there with or without the amp!

Of course it is. My point was that you have household current to run the amp, the current runs through wires which are inside of your shielding if you "shield the house"- it has to go to an outlet, into which is then plugged power cords- to your amp, refrigerator, PC and everything else electrical in your house. All those things are connected to the power grid, which is dutifully alternating that current 50 times a second. That 50 Hz wave is propagated throughout the entire grid. So you've got the same hum from your household circuits, as well as from nearby lines (although the nearby lines could certainly make things worse).

Aha I get what you're saying. My aim is to shield against the powerful external EMF, i.e. keep the whole thing at or under the 1m Gauss territory. I assume that the internal EMF will be weak enough for the EMGs. For some reason I have connected "low hum with EMGs" with "healthy environment to live in". Granted, the SC will hum because of the internal noise, albeit not that strong. From my tests, I have gathered that the unbalanced humbuckers (e.g. EMGs, blazes in 2,4 positions, DMZ FT2 and Chopper in parallel (don't ask me about this last one)) will hum very loud at specific conditions. I am willing to minimize this effect + have a better environment for the humans in it. The fact that SC will hum less (but still hum because of the internal ELF as you said) will be a bonus.