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In Reply to: Very Interesting...... posted by drlowmu on April 22, 2007 at 18:39:32:
Hi Jeff,
there has been a lot of dicussion about this at another site. The conclusion was to use 1/4" thick aluminum when you need to shield low frequency magnetic fields. This gives you somewhere between 5 to 10db attenuation at 60Hz, depending on what formulation of aluminum you use. Its pretty much purely resistivity based, the higher the conductivity of the material and the thicker the sheet the more attenuation you get.Copper would work fine, but its cheaper to go with the thick aluminum rather than the thick copper.
The experience was that using the aluminum sounds better than the steel. The theory being that the steel relies on the BH curve which is not all that linear but the aluminum is using eddy currents which are far more linear.
I tried this in my preamp, I was getting some hum from the filament transformers (the BDT tubes are quite sensitive to external magnetic fields). I used some .375 aluminum plate between the tubes and the transformers and it made a significant improvement. I haven't tried the steel sheet yet though.
John S.
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- 1/4" aluminum - John Swenson 23:46:45 04/23/07 (0)
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