Keep about 1 inch away
The answere is about 2-3 cm distance -- signal carrying wires from ferrous metals. -RNM
The answere is about 2-3 cm distance -- signal carrying wires from ferrous metals. -RNM
That's because I normally work air and non ferrous. Sorry bout that..
You are indeed being more accurate. For a magnetic circuit, such as a gapped core, H will indeed be constant through the loop, whereas B will be dependent on mu..
j
Well, it seems that no affordable 'breakthroughs' have been made with shielding. Kind of disappointing, but it might reinstate why the CTC Blowtorch preamp cases were so thick and made with aluminum. Copper or silver would cost much more, of course.
To understand or estimate shielding thickness, shielding articles or reference books by OTT are very useful, for people who want to understand WHY aluminum shielding has to be so relatively thick.
To understand or estimate shielding thickness, shielding articles or reference books by OTT are very useful, for people who want to understand WHY aluminum shielding has to be so relatively thick.
Simple. The permeability of aluminum is about the same as that of air, so it can only shield against magnetic fields through eddy current losses. The thicker the material, the greater the losses.
se
Yabut...do you really understand...😉
It's only been stated about a bazillion times here..
j
John,
for an "out of the box" approach to chassis and enclosure design you may want to have a look at what HP did in the 90's here:
http://www.hpl.hp.com/hpjournal/94aug/aug94a2.pdf
Should be affordable even to DIYers...
Regards
Giorgio
for an "out of the box" approach to chassis and enclosure design you may want to have a look at what HP did in the 90's here:
http://www.hpl.hp.com/hpjournal/94aug/aug94a2.pdf
Should be affordable even to DIYers...
Regards
Giorgio
Wavebourn mentioned the notion of multiple perforated nonferrous nested shields a while back. Has any one had experience with those, or is in a position to analyze their effectiveness?
Of course for magnetic fields the most important thing is loop area. After that is made as small as practicable, orientation and distance. With a given piece though, once the best job is done with the internals, one is at the mercy of the end user.
The sense of value conveyed by the mass of the equipment is also quite significant to the end user's perceptions. I recall a business associate hefting a small powered loudspeaker and openly scoffing at how light it was. He had not heard of neodymium magnets and judged things from his experience with ceramic or alnico magnet motors.
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.
Of course for magnetic fields the most important thing is loop area. After that is made as small as practicable, orientation and distance. With a given piece though, once the best job is done with the internals, one is at the mercy of the end user.
The sense of value conveyed by the mass of the equipment is also quite significant to the end user's perceptions. I recall a business associate hefting a small powered loudspeaker and openly scoffing at how light it was. He had not heard of neodymium magnets and judged things from his experience with ceramic or alnico magnet motors.
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.
Don't need to understand it. Just have to have the right books sitting on my bookshelf. 😀
se
From the looks of it, that packaging doesn't shield magnetically, nor even electric field shielding.
Use ferrous nesting. Layers of ferrous material will behave anisotropically.
The layers closest to the source will try their darndest to divert the field through that layer. Gaps of mu=1 will tend to isolate the steel layers. If you had 50% packing factor of sheets mu=1000 with equal thickness paper sheets, then the effective mu along the sheets would be 500, but normal to the sheets it's very close to 1.(well, 2).
But one of the biggest offenders with respect to chassis is control of the current paths.
Got that right..
How's it goin steve?
jn
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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.
I remember seeing a magnet for Aluminum that worked by inducing eddy currents Popular Science I think.
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.
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.
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
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
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
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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
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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