[sdiy] OT? Shielding a rackmounted computer

Mon Mar 24 16:40:15 CET 2003

You can shield magnetic fields from a monitor without 'covering'
the screen. The magnetic field tends to be concentrated more 
'sideways' ie parallel to the screen. A nice big sheet of Mu Metal
wrapped around the monitor will suck in almost ALL the field...

Its very expensive... and if there is substantial energy in the
field the metal gets hot.

Plain old IRON (or very soft steel) will work as well. Its cheaper
but has to be much thicker to be effective. VERY heavy. I used 12ga
mild steel... it was fairly effective

H^) harry

--------Original Message--------  

From: Martin.Czech at Micronas.com
To: "Karl Ekdahl" <_nial_ at yahoo.com>, <synth-diy at dropmix.xs4all.nl>
Sent: Mar 24 2003 12:33
Subject: RE: [sdiy] OT? Shielding a rackmounted computer

>Depends on what you mean.
>There are ways for interference:
>1. electromagetic waves, i.e. higher frequencys where E and H field
>are strongly coupled. A sheet of metal will completely damp these,
>i.e. : metal case. Depending on the upper frequency limit,
>cooling and other openings in the case will have some radiation leakage.
>Even for 1GHz the wavelength is 30 cm, so that should be ok.
>2. wire bound: this means that the computer distributes currents
>into the neighbourhood that in turn will transform into
>voltage difference do to ohmic, capacitive or inductive resistance.
>This is a big problem if you are connecting not only Midi
>(we recently learned about the Midi current loop and grounding)
>but also audio. Since all computer cases are grounded to mains
>and the plug in cards have signal ground connected to that
>this will then lead to massive ground loop problems, not only
>hum but also higher sizzle. Switching supply and CMOS processor
>says all. A good audio transformer will handle that.
>Of course not the individual problem of stray signal allready
>inside the sound card.
>The mains plug of a computer will also polute his local mains
>terminal, i.e. difference voltages may be observed in relatiopn
>to other mains ground outlets.
>3. Low frequency H or E field.  E field will be tamed with metal
>case again, but not H field. I.e.: computer monitor. I think
>that flat panel LCDs type screens should have less problems
>than the good old CRT. The 40...100Hz vertical scan rate
>H field of those is very difficult to shield, it would require
>thick sheets of magnetic conductive materials, and how could
>you then see the screen?
>m.c.
>-----Original Message-----
>From: Karl Ekdahl [mailto:_nial_ at yahoo.com]
>Sent: Freitag, 21. März 2003 18:59
>To: synth-diy at dropmix.xs4all.nl
>Subject: [sdiy] OT? Shielding a rackmounted computer
>Hello everyone, soon i will include my computer in the
>same rack as my musical equipment. Does anyone has any
>idea of how to shield the computer (custom built so
>any mod is o.k.) so it doesn't interfear with the
>other stuff?
>Thanks
>Karl Ekdahl
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