Building a Faraday's cage ?

[CS]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

 

[martin griffith]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

Can you hear the noise, does it get picked up by the microphone(s)?


martin

 

[CS]

Can you hear the noise, does it get picked up by the microphone(s)?


martin

If the signal is amplified it gets very noticeable

 

[Rene Tschaggelar]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

You need two cages inside each other connected
at a single point and earthed there to get a
decent attenuation. There have a filter plate
where the signals are passed throuigh the walls.
The door and possible windows can be a problem
but are solvable.
For the lower frequencies, iron would be the choice.
I'd expect an attenuation in the order of 150dB
or better. Note that the quantum limit is at 180dB,
there is no better faraday shield.

Rene

 

[mc]

If the signal is amplified it gets very noticeable

Are you quite sure this is from fields and not from noise in the amplifiers
(power supply ripple, etc.)?

 

[Rheilly Phoull]

You need two cages inside each other connected
at a single point and earthed there to get a
decent attenuation. There have a filter plate
where the signals are passed throuigh the walls.
The door and possible windows can be a problem
but are solvable.
For the lower frequencies, iron would be the choice.
I'd expect an attenuation in the order of 150dB
or better. Note that the quantum limit is at 180dB,
there is no better faraday shield.

Rene

Dont forget the foil hats !!
In the real world one plays the 'axe' wherever the gig happens

 

[[email protected]]

After looking at your spectrum, I'd take a look for switching ballasts
for flouresent lights around you. Studios, and laser labs, should only
have incandescent.

Steve Roberts

 

[CS]

You need two cages inside each other connected
at a single point and earthed there to get a
decent attenuation.

I'm a complete ignorant in this matter - can you please explain why two not
one and what material and how thick (copper is pretty expensive here) ?

For the lower frequencies, iron would be the choice.

How thick ?

I'd expect an attenuation in the order of 150dB
or better. Note that the quantum limit is at 180dB,
there is no better faraday shield.

Whoa ! I need only 20dB or something like that hehe i just need to remove
that ugly peaks you can see on the picture i posted earlier - i want them to
drown in the noise floor.

 

[[email protected]]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

Before you spend time and money on a Faraday cage, read this:

http://64.70.157.146/pdf/Bondingcableshields.pdf

 

[CS]

Are you quite sure this is from fields and not from noise in the amplifiers
(power supply ripple, etc.)?

Yes i'm sure - the dirt disapears when i turn down the volume on my guitar.

 

[CS]

After looking at your spectrum, I'd take a look for switching ballasts
for flouresent lights around you. Studios, and laser labs, should only
have incandescent.

Steve Roberts

1 No lights were on at that time.
2 I'm pretty sure it is from power cables inside my walls - i can detect
them (the cables) with my guitar.

 

[CS]

Before you spend time and money on a Faraday cage, read this:

http://64.70.157.146/pdf/Bondingcableshields.pdf

I believe i have good enough cable. As i said in a different branch of this
thread the dirt disapears when guitar volume is turned down to zero so i
think it must be pickup picking all this unwanted frequencies - it is
shielded properly inside guitar but it can't be shielded outside - it has to
"look" at the strings

 

[John Larkin]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

The three field types are magnetic, electrostatic, and
electromagnetic.

Forget magnetic shielding. Enough iron to give any useful shielding to
a room would collapse the structure of a house.

Electromagnetic shielding, aka RFI screen room, is difficult and only
keeps out high-frequency fields. Google "emi screen room" or somesuch.

You achieve good electrostatic shielding (block capacitively-induced
hum) with any conductive coating on the walls: foil, screen wire,
metal sheets. Just connect and ground them all. Some modest
electromagnetic shielding will result, too. A water pipe is a good
low-frequency ground.

But none of this should be necessary if cabling and grounding are
right.

John

 

[CS]

Electromagnetic shielding, aka RFI screen room, is difficult and only
keeps out high-frequency fields. Google "emi screen room" or somesuch.
Thanks

You achieve good electrostatic shielding (block capacitively-induced
hum) with any conductive coating on the walls: foil, screen wire,
metal sheets. Just connect and ground them all. Some modest
electromagnetic shielding will result, too. A water pipe is a good
low-frequency ground.

So copper foil is enough ? How thick should it be or is that not important ?

But none of this should be necessary if cabling and grounding are
right.

Replacing wiring inside my walls is planned for a future (too expensive
now).

 

[Rene Tschaggelar]

I'm a complete ignorant in this matter - can you please explain why twonot
one and what material and how thick (copper is pretty expensive here) ?


How thick ?


Whoa ! I need only 20dB or something like that hehe i just need to remove
that ugly peaks you can see on the picture i posted earlier - i want them to
drown in the noise floor.

20dB is not really a faraday shield, it is a toy.
And thus a single shield should be sufficient.
Low frequency is coupled magnetically, and magnetically
only. Thus iron should be sufficient. Iron means
iron and not steel, nor stainless, chrome nickel, or such.
By the way iron is better than copper at these frequencies.
Magnetic nearfield attenuates as r^3 and not as r^2,
I guess 1 mm or so should be sufficient.


Rene

 

[John O'Flaherty]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

I note the 50 Hz fundamental is about 20 db higher than the next
highest harmonic. If it's constant in amplitude and phase, you might
be able to null it by injecting an adjustable amplitude and phase 50
Hz signal. It might be cheaper to do that until you can do your
rewiring. On the other hand, if you thrash around a lot while
recording, the amplitude and phase might not stay constant!

 

[John O'Flaherty]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

Another thought occurred to me. Could you mount another magnetic
pickup on the guitar in the same orientation, but not under the
strings? It should pick up exactly the same fields as the first, for
fields originating more than a few feet away. Subtract its output from
that of the first. Then it wouldn't matter if you moved around while
recording. I don't know what these things cost, but it might be
cheaper than a construction project.

 

[Abstract Dissonance]

Another thought occurred to me. Could you mount another magnetic
pickup on the guitar in the same orientation, but not under the
strings? It should pick up exactly the same fields as the first, for
fields originating more than a few feet away. Subtract its output from
that of the first. Then it wouldn't matter if you moved around while
recording. I don't know what these things cost, but it might be
cheaper than a construction project.

This is called a humbucker pickup. It does get rid of the hum but also has
a distinctively different sound then "single coils".

 

[Abstract Dissonance]

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.

ps. If this is not the right newsgroup to ask this question please suggest
the best one.

I have noticed that with my guitar when I play I can reduce the noise to a
minimum depending on the orientation of the guitar. It would depend on if
the noise is omnidirectional or not but it might work.

With the faraday cage you might try some copper mesh and see if that works.
It should be relatively cheap to build. I seen them do it on Myth Busters.
I'm not sure if it will get the low freqencies though.

Another thing to do is to insulate the guitar's electronic cavities using
copper foil or a special paint. These will reduce the hum.

Besides those things you probalby know you can buy noise reducers, power
conditioners, etc...

You mgiht try to replace your AC with a HF AC then convert back down using a
transformer at the wall outlets. Using about 20khz AC then convert down at
the outlet should help. I'm not sure how big the transformer would be
though and how efficient it would be. It might not need converting though
if the devices hooked up to it use only DC(but convert from AC). The
problem here, I think, is when the devices use the frequency of the AC to
determine "time" or for some type of modulation.

You might even be able to do this without replacing the current power
sources. Just turn off the breaker to them then run you an extension cord
but have this HF AC run through it. If you are drawing more than 15 amps
though you would need to get a higher powered connection. (maybe from the
230V washer/dryer connection or something similar). All you would need is
two transformers that can convert to the 120V mains and some type of
frequency converter.

i.e.,

Mains->AC freq converter->cabling->AC freq converter->devices.

With transformers thrown in to convert voltage if needed.

If your interested in doing this it might be a quick fix. You would need to
get the specifics though and might cost a few hundred dollars. You could
then insulate the cabling and conversion devices so they reduce the noise
even more. You would need to ask about the specifics of freq conversion and
such to get that info. There might be a good way to do this efficiently and
cheaply.

Anyways, Just some ideas

Jon

 

[John Larkin]

So copper foil is enough ? How thick should it be or is that not important ?

Any thickness is a solid electrostatic shield. Aluminum foil would
work, too... just staple the seams fairly well; if you use copper, you
can solder, which is better at RF. Either will kill the annoying
harmonics of 60 Hz which are capacitively induced from power lines and
fluorescent lamps and such. Thin metal used like this is a moderate RF
shield and useless for magnetic fields, which aren't usually the
problem here.

Replacing wiring inside my walls is planned for a future (too expensive
now).

Use conduit, either rigid or the much easier MX (flex) stuff.

John