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Post by pablogilberto on Dec 25, 2019 15:20:18 GMT -5
Hello! I have read the article Quieting the Beast under Custom Pages. I'd like to know the best practices when shielding a guitar. I know that you can use either a shielding paint or aluminum/copper foil for the cavity. Does anyone here did some experiments on the effects and differences of each one? I know that the main advantage of shielding a guitar is hum reduction. And through this, we can play on higher volumes / gain without the unnecessary (too much) hums. Also, this will allow us to hear those frequencies that are usually masked by the hum/noise. In effect, we produce richer tones. BUT I am also aware that shielding (generally) increases the capacitance of the circuit. Increasing capacitance means tone loss specially on the higher end (Treble). I have read some experiments by antigua where he measured the capacitance of cables with/without shielding. I have tried it myself and confirmed the increase in capacitance due to shielding. With this, I'd like to know the best practices when shielding a guitar. How can we shield effectively without introducing a huge capacitance that might alter the guitar tone. Can we pick materials? e.g. shielding paint, aluminum or copper foil? Can you share any technique or recommendation? Thanks for your help!
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Post by Deleted on Dec 25, 2019 15:50:15 GMT -5
Shielding is a good thing, (basic a Faraday Cage) the best times you can see Effects of things without shields is when you see a Webcam and it Flickers, that someone has a Motor near by upsetting the signals.
Easy to get "Slug Tape" is a copper tape
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Post by sumgai on Dec 25, 2019 15:58:09 GMT -5
.... BUT I am also aware that shielding (generally) increases the capacitance of the circuit. Normally when we speak of a Faraday cage (of which a shielded guitar is but one example), we are concerned only with "stray capacitance", i.e. the cage itself introduces no measurable capacitance that affects our test circuitry/device. If it did, then we're dealing with an improperly constructed Faraday cage. And at that, we're speaking of 'electrostatic capacitance' levels of accumulated charge, which are deucedly small, especially when compared to other currents to found within the cage, emanating from the device/circuit under test.
All the literature I've read, or can find to read, evolves around readings where the cages are small, but the current levels needed to be monitored are on the microvolt/microamp scale of things. Even then, the cognoscenti seem to prefer a caged environment for testing, instead of worring about any possible stray capacitance.
If that's good enough for the big brains, I'm sure not going to second-guess them! So, I wonder where you found this little tidbit that lead you to the conclusion that shielding a guitar can (or perhaps will) cause a loss of high frequencies. In other words, [Citation needed].
sumgai
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Post by pablogilberto on Dec 26, 2019 6:58:16 GMT -5
.... BUT I am also aware that shielding (generally) increases the capacitance of the circuit. Normally when we speak of a Faraday cage (of which a shielded guitar is but one example), we are concerned only with "stray capacitance", i.e. the cage itself introduces no measurable capacitance that affects our test circuitry. And at that, we're speaking of 'electrostatic capacitance' levels of accumulated charge, which are deucely small, especially when compared to other currents within the cage.
All the literature I've read, or can find to read, evolves around readings where the cages are small, but the current levels needed to be monitored are on the microvolt/microamp scale of things. Even then, the cognoscenti seem to prefer a caged environment for testing, instead of worring about any possible stray capacitance.
If that's good enough for the big brains, I'm sure not going to second-guess them! So, I wonder where you found this little tidbit that lead you to the conclusion that shielding a guitar can (or perhaps will) cause a loss of high frequencies. In other words, [Citation needed].
sumgai
Hi sumgai! Thanks for your reply! You can check out this post by antiguaguitarnuts2.proboards.com/thread/7725/capacitive-coupling-various-guitar-partsFrom here, it can be seen that adding shielding on cables have a huge effect on its capacitance. The capacitance is also affected when a cable is placed near or wrapped with a conductor sheet (aluminum). That's the reason why I think shielding introduces additional capacitance which will result to Treble loss. Let me know what you think. Thanks!
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Post by sumgai on Dec 26, 2019 22:59:20 GMT -5
Hi sumgai ! Thanks for your reply! You can check out this post by antigua guitarnuts2.proboards.com/thread/7725/capacitive-coupling-various-guitar-partsFrom here, it can be seen that adding shielding on cables have a huge effect on its capacitance. The capacitance is also affected when a cable is placed near or wrapped with a conductor sheet (aluminum). That's the reason why I think shielding introduces additional capacitance which will result to Treble loss. I think the first problem here is that you're conflating a cable with a cavity... and that's not a very good comparison. Let me explain.
In a cable (guitar or otherwise), we see two or more conductors running for a length in very near perfect parallel. This introduces a form of capacitance, even though the two conductors may be isolated by a distance, and even though their insulation materials may not act like a dielectric at all - the fact still exists that a capacitive effect takes place. How do we know this?
Not-quite-simple, but easy to understand once we examine it. The case is, there is also an inductance value that rises from that proximity between the two conductors within that cable. If we examine several factors, we'll see that there is an impedance between the two ends of the cable. Taking some measurements and doing some simple arithmetic shows us that we're really observing a compound impedance - it has both a capacitive reactance and an inductive reactance. Boiled down to simple terms, a cable is actually a filter! Yes, better cables usually have better performance characteristics (Marketing Feldergarb notwithstanding...), but one still needs to do a bit of investigation by the simple method of "trying it out". All the measurements in the world don't mean squat, if the thing drags your sound down into the mud.
So it happens that for most guitar cables sold since, well, since the beginning of electric guitars, the usual cable exhibits a fair amount of capacitive reactance, and that translates to capacitive impedance. Now recall that impedance is a term used in AC circuits, and by that I mean, circuits dealing with frequencies - IOW, not battery-like DC. If you've been playing along at home, you've already guessed that the higher the frequency, the more the capacitor wants to pass it through. Of course, that's per the given value of capacitance. Now, think on what I said earlier in this missive - a conductor wants to carry a signal, but there's a non-trivial capacitance between the two conductors within that cable, yes? And if there's capacitance, then a signal of sufficiently high frequency wants to pass through that capacitance, yes? Well, that's exactly why a cable tends to sound muddy - the treble frequencies are effectively not going to the amp, they're simply going through that capacitance to the other conductor... and as we already know, that conductor, regardless of what we call it, is actually the signal return to the source. Hence, a more-or-less standard guitar cable exhibits some treble loss. Better cables presenting less loss, for the most part.
Now, let's look at a guitar's control cavity. The first thing we see is imperfection - there are holes aplenty, for the pickups, for the controls, possibly the output jack, etc. Not a perfect Faraday cage. But certainly better than the alternative, that of no cage equaling full hum. But most importatnly, we'll build on what we learned in evaluating a cable. Ah, but that's easy - there are no runs of two parallel conductors... there's only the one conductor, that being the cage material itself. All manner of circuitry contained within the cage is of short duration betwixt any part of the circuit and the cage material so as to mean "nothing to see here folks, move along". In short, using the terms above, there's no capacitive or inductive reactance to be found, hence no filtering, and thence, no reduction in high frequencies. End of story.
Capice? Any questions?
HTH
sumgai
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