Building a Faraday's cage ?

CS · 2006-06-26T13:08:58+00:00

Hi :)I have a small bedroom recording studio full of electromagnetic fields(mainly 50hz+harmonics up to ~3,5khz from power cables in walls).Here is how it looks on Adobe Audition's spectrum analyzer:I'm planning to build a 2m x 2m Faraday's cage/booth to protect activeelectric guitar pickups from external electrostatic and electromagneticnoise 20hz-96khzPlease suggest best material (copper ? aluminium ? iron ? or maybe acombination of different metals), how thick should it be and how to get ridof the current in a situation where no true ground is available.How many dBs of attenuation should i expect ?Thanks in advance.ps. If this is not the right newsgroup to ask this question please suggestthe best one.

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GregS 20 years ago

Power conditioners can introduce noise. Guitars are terrible for noise. I see Faraday cages all the time here. Mostly a 5 sided box with the front open. Most of these cages are made from aluminum window screens. They reduce electrostatic noise. Many times power strips are toward the rear of the cage, but NO AC 60 Hz power can enter the cage area via power cords. I carry a electrostatic and magnetic noise sniiffer. I recently added a photodiode so I could hear light noise. Sources of the electrostatic noise can easily be tracked down, but ground loops and 60 Hz wiring are simply tricky. Also around here, we suggested there be problems, so new building are constructed with aluminum backed wallboard. It helps, but of course its not perfect, but gets the job done of reducing intense fields. Having the AC wiring contained in a conduit also reduces electrostatic noise to a very high degree. You can also buy shielded AC cords. Isolation transformers usually help.

greg

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John Jardine. 20 years ago

?

That massive 50Hz peak looks distinctly odd. Maybe it's not actual 'pickup' but conducted mains leakage type currents. Curiosity piqued, I stuck a 1.5H coil into a X100 lo-noise amp feeding a normal spectrum analyser, looking at 20Hz to 1kHz with a 5Hz filter. Just sat it on the bench near the incoming feeder, the only other powered kit being the PC. Virtually no 50Hz component was present (-90dBm, 7uV) but big peaks of 150Hz, 250Hz, 350Hz, 450Hz, all about 20dB higher at about -70dBm, 70uV. That was it though, all other components were sitting in the grass at the -100dBm level. Powering up a lot of other kit made little change to the display. john

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CS 20 years ago

U¿ytkownik "Rene Tschaggelar" napisa³ w wiadomo¶ci news:44a022ea snipped-for-privacy@news.bluewin.ch...

Thank you very much :)

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pbdelete 20 years ago

Is this due the wavelength ..? (one point at node, one at maximum = short)

How does this quantum limit work..? Makes me curious.. :)

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Phil Allison 20 years ago

"CS"

** That hum is being injected MAGNETICALLY into your guitar's pickups.

A Faraday cage will have NO effect on it - whatever !!

FORGET IT !!

Your ONLY option to eliminate the hum is to get a guitar that has " hum-bucking " pickups.

The hum problem YOU are having is WHY they were invented, way back in the

1960s.

Most musicians learn to live with it by orienting themselves when playing to minimise the hum and/or using a *noise gate* to silence the hum when the guitar is not being played.

BTW

I can hardly believe how many F*****TS posters here have given you the WRONG answer for such a common problem.

...... Phil

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Howard Eisenhauer 20 years ago

Q.- Do you have a PC & monitor running in your studio? Nearby?? The switching supplies in these things, especially the cheap "No Name" ones, are just F___ing horrible for generating noise, both radiated & back fed on power lines. Those harmonic spikes on your mains certainly arn't coming from your power utility, something is generating them locally. If your guitar is picking them up out of the air its VERY local. Have you tried connecting a 600 ohm termination to the cable instead of the guitar to see if you still have the noise?

Beyond that I'd have to say theres also a problem with the cable shielding setup, when properly terminated audio cables shouldn't have any problem with cancelling out common mode or shielding differential noise.

H.

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Phil Allison 20 years ago

"Howard Eisenhauer"

** Kindly read this and learn something about magnetically induced hum.

formatting link

...... Phil

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Phil Allison 20 years ago

"Phil Allison"

to CS

** That hum is being injected MAGNETICALLY into your guitar's pickups.

A Faraday cage will have NO effect on it - whatever !!

FORGET IT !!

Your ONLY option to eliminate the hum is to get a guitar that has " hum-bucking " pickups.

The hum problem YOU are having is WHY they were invented, way back in the 1960s.

** OK - it was actually developed by Seth Lover in the 1955:

formatting link

....... Phil

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Rene Tschaggelar 20 years ago

The first shield radiates to the inside what the induced currents on it surface flow. The efffects are multiple. You have to visualize the multitude of frequencies and fields that are possible to propagate.

The worst are nearfield magnetic, eg a train passing

5m from your house. At the time of CRTs, it was impossible to work during the time the current flowed through the rails. And it wasn't shieldable. As John Larkin said, for a decent magnetic shielding, eg 120dB up, you need substantial amounts of iron.

Me too... I haven't read through the whole theory yet. Just the abstract. I guess the -180dB are the thermal noise floor at room temperature in comparison to the ambient EM-noise.

Rene

Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net

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CS 20 years ago

U¿ytkownik "Phil Allison" napisa³ w wiadomo¶ci news: snipped-for-privacy@individual.net...

Hmmmm then why every good electric guitar (including mine) has a Faraday's cage ( conductive paint or copper foil) inside - just for fun ? :D

the

I have two humbuckers in my guitar and i don't need another one. ;)

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CS 20 years ago

U¿ytkownik "Howard Eisenhauer" napisa³ w wiadomo¶ci news: snipped-for-privacy@4ax.com...

That signal on my analyzer picture was recorded with crt monitor turned off.

All those spikes get louder when i move my guitar closer to the cable (going to a ceiling lamp) inside the wall. The buzz gets quieter when i switch the light off ( i even tried this experiment without a lightbulb to see if the buzz comes really from the wire and not from a working lightbulb )

????? I know almost nothing about electronics , so if you can explain in layman terms i would be grateful :)

I think my cable is ok. It is high quality and short - it gives me no noise when the guitar volume is turned all the way down.

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Phil Allison 20 years ago

"CS"

** That is a simple * ELECTROSTATIC * shield - you jerk off.

Has NO effect on a MAGNETIC field .

** What guitar?

What "humbuckers" ??

I reckon YOU are full of S*IT !

....... Phil

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Phil Allison 20 years ago

"CS"

** That hum is being injected MAGNETICALLY into your guitar's pickups.

A Faraday cage will have NO effect on it - whatever !!

FORGET IT !!

Your ONLY option to eliminate the hum is to get a guitar that has " hum-bucking " pickups.

The hum problem YOU are having is WHY they were invented, way back in the

1960s.

Most musicians learn to live with it by orienting themselves when playing to minimise the hum and/or using a *noise gate* to silence the hum when the guitar is not being played.

BTW

I can hardly believe how many F*****TS posters here have given you the WRONG answer for such a common problem.

...... Phil

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Phil Allison 20 years ago

""CS" = Complete S*****ad

** That hum is being injected MAGNETICALLY into your guitar's pickups.

A Faraday cage will have NO effect on it - whatever !!

FORGET IT !!

Your ONLY option to eliminate the hum is to get a guitar that has " hum-bucking " pickups.

The hum problem YOU are having is WHY they were invented, way back in the

1960s.

Most musicians learn to live with it by orienting themselves when playing to minimise the hum and/or using a *noise gate* to silence the hum when the guitar is not being played.

BTW

I can hardly believe how many F*****TS posters here have given you the WRONG answer for such a common problem.

...... Phil

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pbdelete 20 years ago

What distance and hole diameter should be used?, a prof suggested 1/2 wavelength for the holes at least. But things like micros have 1/65 wavelength.

I well not accept trains then ;)

Another perspective on this scale is that atoms work as wavelength conductors depending on how large the holes between them are. So any glass have holes that are at least 700 nm wide. While an parabole could use cm/mm wide holes and still be conductive enough for radio signals.

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CS 20 years ago

U¿ytkownik "Phil Allison" napisa³ w wiadomo¶ci news: snipped-for-privacy@individual.net...

pickups.

Faraday's

It clearly has a big effect on power wires in my walls - i can hear a loud noise if i put my emg707 very close to a wire in my wall and that noise gets much quieter if i turn my guitar 180 degrees to face away from the wall and hold the pickup at the same distance to the wire.

good enough - emg707 & emg81-7

Like everyone else few hours after a good meal ;)

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jasen 20 years ago

guitars use unbalanced cables.

Bye. Jasen

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Phil Allison 20 years ago

"CS" = a Complete S*****ad

** YOU ARE A COLOSSAL F****NG IDIOT !!! .

That scenario PROVES the direct opposite !!!!!!!!!!!!!!!!!!!!!

** Damn shame those two heaps of s*it do not actually *buck* hum very well.

Try a " Les Paul " with original PAF Gibson humbuckers.

Bet it is silent as a graveyard in the same room.

....... Phil

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CS 20 years ago

U¿ytkownik "Phil Allison" napisa³ w wiadomo¶ci news: snipped-for-privacy@individual.net...

loud

Ok if i am an idiot and you know better then you must be smart enough to eplain to an idiot why "That scenario PROVES the direct opposite" ?

well.

My guitar (in my room) is ~30 dB quieter than my cousin's (genuine) strat.

Do you realize that there is no humbucker on this planet that will buck 100% of hum ?

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John O'Flaherty 20 years ago

=B6ci

ets

nd

If you can look at what load is fed through those particular wires, you might be able to turn it off as an experiment. If there is no load on the wires, there will be no current or magnetic field. If the noise is still present, you could conclude that it's electrostatic.=20

-- john

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