John Curl's Blowtorch preamplifier part II - Page 2804 - diyAudio
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Old 8th October 2012, 10:33 PM   #28031
wayne is offline wayne  United States
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Controlling current paths is certainly a big issue even if using Aluminum. Found that one out the hard way.
I remember seeing a magnet for Aluminum that worked by inducing eddy currents Popular Science I think.
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Old 8th October 2012, 11:07 PM   #28032
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Thanks S.A.G. for your link. It does describe how many, many cases are made, but unfortunately, it is not a SHIELD, so far as I can tell.
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Old 8th October 2012, 11:26 PM   #28033
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A good rule of thumb might be that you need about 10-15 times thicker aluminum than steel to get the same low frequency magnetic shielding. However, at much higher frequencies, aluminum may win out.
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Old 8th October 2012, 11:39 PM   #28034
fas42 is offline fas42  Australia
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Quote:
Originally Posted by bcarso View Post
I will say that having heavier speakers does help to prevent them from bouncing around as much. I'm about to use double-sticky tape on some ones on my desktop in lieu of weighting them down with tungsten.
Try 4 decent sized balls of Blu-Tack precisely at the points of the corners, press the speaker down hard on the goo so that the speaker feels like it's glued to the desk -- see what that does for the sound ...

Frank
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Old 9th October 2012, 04:13 AM   #28035
RNMarsh is offline RNMarsh  United States
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Default EMI-RFI shielding

At high freqs (>100KHz-1Mhz) the signals are reflected rather than absorbed. Thin metal works just as well for them. The lower the freq, the greater is the penetration into the metal and thicker or more efficient metals, such as steel, are needed. -RNM

Last edited by RNMarsh; 9th October 2012 at 04:18 AM.
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Old 9th October 2012, 04:25 AM   #28036
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Quote:
Originally Posted by RNMarsh View Post
At high freqs (>100KHz-1Mhz) the signals are reflected rather than absorbed. Thin metal works just as well for them.
Not necessarily, no.

It depends on whether the interference is primarily E field or H field in nature. If it's primarily E field, then reflection loss is the most effective and high conductivity materials such as copper or silver are the most effective. If it's primarily H field, then absorption loss is the most effective and ferromagnetic materials or thick paramagnetic materials are the most effective.

se
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Old 9th October 2012, 04:30 AM   #28037
fas42 is offline fas42  Australia
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Originally Posted by Steve Eddy View Post
Not necessarily, no.

It depends on whether the interference is primarily E field or H field in nature. If it's primarily E field, then reflection loss is the most effective and high conductivity materials such as copper or silver are the most effective. If it's primarily H field, then absorption loss is the most effective and ferromagnetic materials or thick paramagnetic materials are the most effective.

se
Steve, in the typical home listening environment what could be a source of interference that was predominantly H field, that was of a frequency greater than 100kHz?

Thanks,
Frank
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Old 9th October 2012, 04:40 AM   #28038
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Swtichmode power supplies come to mind.

se
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Old 9th October 2012, 05:38 AM   #28039
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Swtichmode power supplies come to mind.

se
Like a PC ?
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Old 9th October 2012, 05:45 AM   #28040
kevinkr is offline kevinkr  United States
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Like a PC ?
Many DVD, BD, and universal players, LCD and plasma TV sets, laptops, B&O Ice Power module equipped power amps, USB chargers, etc.
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