Building a Faraday's cage ?

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:
http://img158.imageshack.us/img158/4522/dirtysilence7th.jpg

I'm planning to build a 2m x 2m Faraday's cage/booth to protect active electric guitar pickups from external electrostatic and electromagnetic noise 20hz-96khz

Please suggest best material (copper ? aluminium ? iron ? or maybe a combination of different metals), how thick should it be and how to get rid of the current in a situation where no true ground is available.

How many dBs of attenuation should i expect ?

Thanks in advance.

A faraday's cage will keep out unwanted electrostatic noise, but not electromagnetic noise. Those are different entities, though often occuring simultaneously..

For magnetic shielding it's much harder - mu-metal caging would cost you a fortune..

Jakob E.

[quote author="gyraf"]A faraday's cage will keep out unwanted electrostatic noise, but not electromagnetic noise. Those are different entities, though often occuring simultaneously..

For magnetic shielding it's much harder - mu-metal caging would cost you a fortune..

Jakob E.[/quote]

Hi gyraf
Thanks for your reply

So will for example copper block 50hz noise from power cables ? Is this type of noise electrostatic or electromagnetic ?

I may be mistaken, but i think i remember an experiment from elementary school where i could block some of an ordinary magnetic field (from a magnet) with a 1cm thick piece of metal (iron ?) or is it my imagination ?

I dont need to block all fields - my primary goal is to reduce that 50hz noise - i want a nice smooth white noise floor not that ugly buzzing.

Magnetic fields can't be blocked, only diverted. The lower the frequency, the more material to divert it.

Chances are, that your guitar-related problem are mainly electrostatic - but I can't promise that.

Jakob E.

Quick thought:

Electrostatic stuff is usually "buzzzzy", and can be reduced by chicken-wire type faraday shielding. Electomagnetic is "hummmmmmmmy" and you're stuck with it. If it's the type of hum that a stratocaster picks up at certain orientations, you really have to work around it. All efforts to eliminate that sort of thing are usually stratospherically expensive, or utterly ineffective.

Keith

Try this:

Wind about 10 turns of enamelled copper wire round a toilet roll tube and cut the tube down to the length of the turns. Secure with sticky tape and bring the ends out to an XLR plug (pins 2 and 3). Wire this up to a microphone input using a standard 6m XLR cable, and connect to an amplifier and monitor speaker with fairly high gain in the pre-amp. Now walk round the room, sliding the coil over the walls (turns parallel to the wall), and see if you can locate points at which hum is much louder than at others. If you can, then the hum is magnetic, and a standard Faraday cage is not going to help you.

If you find a restricted area that is the only source of hum fields (e.g. a light fitment), then you could consider containing the fields in that area using tinplate (mild steel plated with tin) screwed to the wall, ceiling etc. around the area. The magnetic field is diverted along the high permeability steel, greatly reducing the field in the surrounding air.

[quote author="SSLtech"]Quick thought:

Electrostatic stuff is usually "buzzzzy", and can be reduced by chicken-wire type faraday shielding. Electomagnetic is "hummmmmmmmy" and you're stuck with it. If it's the type of hum that a stratocaster picks up at certain orientations, you really have to work around it. All efforts to eliminate that sort of thing are usually stratospherically expensive, or utterly ineffective.

Keith[/quote]

Can you tell me what can produce this electromagnetic hum ?

[quote author="Boswell"]Try this:

Wind about 10 turns of enamelled copper wire round a toilet roll tube and cut the tube down to the length of the turns. Secure with sticky tape and bring the ends out to an XLR plug (pins 2 and 3). Wire this up to a microphone input using a standard 6m XLR cable, and connect to an amplifier and monitor speaker with fairly high gain in the pre-amp. Now walk round the room, sliding the coil over the walls (turns parallel to the wall), and see if you can locate points at which hum is much louder than at others. If you can, then the hum is magnetic, and a standard Faraday cage is not going to help you.
[/quote]

Can't i do it with my guitar ? It can detect power wires in my walls.

[quote author="Boswell"]If you find a restricted area that is the only source of hum fields (e.g. a light fitment), then you could consider containing the fields in that area using tinplate (mild steel plated with tin) screwed to the wall, ceiling etc. around the area. The magnetic field is diverted along the high permeability steel, greatly reducing the field in the surrounding air.[/quote]

I'll try this method.

Thanks

:?: You do know that if you got singlecoil pickups near dimmer switches are bad news :?:

[quote author="mikeyB"]:?: You do know that if you got singlecoil pickups near dimmer switches are bad news :?:[/quote]

Active humbuckers and no dimmers and crt turned off

[quote author="CS"]Can you tell me what can produce this electromagnetic hum ?[/quote]
AC power running through looped or coiled wires; to a greater or lesser degree, just about anything containing transformers...

-And don't forget that everything in your room can do this. -How do you know that you have a problem from outside the room?

Most buzzes/hums that I deal with are either caused by or worsened by calamitous power layout/distribution. After that the next most common cause is poor grounding practice. Too many grounds is as bad as not enough.

If I had a dollar for every time people thought that power conditioning or a faraday shield would cure it when neither would do any good, I'd probably have enough for a Soundcraft channel strip by now...

Keith

Keith

I don't know if he cage thing is going to work but you could consider to shield the strat itself with copper foil on the inside. This method is known to reduce some of the unwanted noise. other possible problems could be the dreaded pin 1 problem try a google search for "Hummer" and "Pin one problem" and you will get some info!

[quote author="just.sounds"]I don't know if he cage thing is going to work but you could consider to shield the strat itself with copper foil on the inside. This method is known to reduce some of the unwanted noise. other possible problems could be the dreaded pin 1 problem try a google search for "Hummer" and "Pin one problem" and you will get some info![/quote]

It is not a strat and it's pickups are not single and it's already shielded inside.

Sorry my bad! Maybe the shielding has become disconnected What also can be a solution is to use power from one outlet only.
(just thinking out loud here)

[quote author="just.sounds"]Maybe the shielding has become disconnected[/quote]

It works.
I can check it by turning crt on and pointing pickups towards and then away from it.

I might be wrong here but isnt a -90db noise floor pretty damn good for an electric guitar? Some of my tube recording gear is only around -65db...


M@

[quote author="SSLtech"][quote author="CS"]Can you tell me what can produce this electromagnetic hum ?[/quote]
AC power running through looped or coiled wires; to a greater or lesser degree, just about anything containing transformers...[/quote]

So i can be pretty sure that most of the 50hz hum/buzz comes from electrostatic fields if there are no coiled or looped power wires in my house and every transformer is properly shielded or not running.
Right ?

[quote author="mattmoogus"]I might be wrong here but isnt a -90db noise floor pretty damn good for an electric guitar? Some of my tube recording gear is only around -65db...


M@[/quote]

Noise floor is good only if that noise is really a noise not a constant quiet
A flat.

Ab will sound good for example with Eb and another Ab one octave higher , but it can sound horrible with other chords.

Remember that the 50hz hum/buzz is present at all times - i can hear it under long sustained notes.

What happens when you unplug your guitar and short the input?

Samuel

[quote author="Samuel Groner"]What happens when you unplug your guitar and short the input?

Samuel[/quote]

I get a nice smooth noise floor without those ugly peaks.