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Post by angelodp on Jun 25, 2009 13:35:14 GMT -5
Will very small breaks or tiny gaps or pin holes in the copper shielding for a strat nullify the hum canceling effect. Is it a question of tiny break in the shield allowing a small amount of noise in ?? I ask because the cavity I am shielding is quite irregular and its a bear to cover all areas, but i am trying. At the moment I do have continuity around the entire cavity, just these teeny little gaps??
ange
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Post by D2o on Jun 25, 2009 13:39:30 GMT -5
Hi Ange,
Teeny is fine. I don't know the exact point of teeny-ness, though.
Can you not just take little bits of leftover material and adhere it over the little gaps?
There would be no need for continuity in the little pieces used on those small gaps, so long as the Faraday cage has been achieved with what you have already done - these are more to be overkill safe in plugging any possible "leaks".
D2o
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Post by newey on Jun 25, 2009 16:04:34 GMT -5
Neither do I, but if I recall, Faraday's original cage used a mesh screen and not solid material, so "teeny" gaps should be ok. Since the source we are trying to shield is (mostly) 50-60 Hertz AC noise, the wavelength of that could be calculated (mind you, I can't do it, but it could be done.), and the size hole that would "matter" for shielding purposes could theoretically be calculated from that wavelength. I don't know, but I suspect that the size of hole you could have is actually fairly large. You can, but these bits would be superfluous if not electrically continuous with the rest of the shielding, and grounded. Remember, we're not building a lead box for Kryptonite here.
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Post by D2o on Jun 25, 2009 17:59:24 GMT -5
FWIW, GN2 member Woody had done some neat stuff in this thread on zero hum strat coils, in which he found that copper mesh of about 70 strands per inch was ideal to both shield and resist the formation of eddy currents.
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Post by ashcatlt on Jun 25, 2009 23:20:51 GMT -5
Since the source we are trying to shield is (mostly) 50-60 Hertz AC noise, the wavelength of that could be calculated (mind you, I can't do it, but it could be done.), and the size hole that would "matter" for shielding purposes could theoretically be calculated from that wavelength. It's somewhere just short of 20 ft depending on your elevation and temperature and whatnot. Of course, that ignores the fact that much of the noise that's really annoying is actually harmonics of that AC mains frequency. Plus the fact that the nearest source of noise doesn't run off AC mains, but maintains it's own clock which seesms to run a bit faster than that. Then there's all the other EM radiation flying around this crazy world we live in. But yeah, don't sweat a couple little holes. There's usually big gaps around the pickups and stuff, too.
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Post by sumgai on Jun 26, 2009 1:40:26 GMT -5
Hmmm, I wonder what would happen if...... The known speed of electrons is approximately that of the speed of light, about 299,792,458 meters per second (within an ideal vacuum), give or take a meter. That said, we need only divide that speed by our frequency, and we have the length of one complete cycle (from one positive peak to the same point on the next positive peak). This should look like: 299,792,458 / 60 = 4,996,540.9666... Call it 5 million meters, or a skosh longer than 20 feet. (And as substantiated by this calculator: Frequency versus Wavelength Calculator.) ash's number crops up from time to time on the intardweb because people do the "inversion" of frequency over time, then use the resultant number (1/60 = 0.0166666) for the division - a Romper Room No-No if there ever was one. Everything you need to know, or could possibly want to know, about frequency, wavelength, and time are all available here. (A study guide put out by the ARRL.) But ash is correct in stating that the true speed of light/electrons in an electromagnetic transmission medium is subject to many conditions, which can slow things down by as much as 3% under normal observable conditions. This just means that the wavelength will get a little shorter, but not enough to make a difference to us, eh? So how's that answer the original question? It doesn't, except to say that any hole in your shielding job is not 100%, and if you're gonna do the job, why not go the whole way and do it 100%? But..... yes, you can fudge where absolutely necessary. If the hole is small, and the results are still 99%, then if you can live with it, I won't castigate you. More discussion: If there were only one source of 50/60Hz electromagnetic hum, then we'd be free of any worries. But as ash points out, the problem comes about because there are so many sources, and they aren't all arriving at our pickups at the same time. What we're really getting is the end-product of intermodulation between all these sources, and it's just about inescapable in the modern world. Which is why we have "Quieting the Beast". QtB - Know it, Use it, Love it! Word. HTH sumgai
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