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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: capacitive filters on speaker cables posted by cporada@cabnr.unr.edu on November 1, 2006 at 20:21:57:
A single 0.01 microfarad capacitor will work in some applications.However, all real capacitors have some parasitic inductance, and the combination of the inductance and capacitance results in a resonant frequency. The device acts like a capacitor up to the resonant frequency, then like an inductor above it. Generally, the smaller the capacitor, the smaller the parasitic inductance, and the higher the resonant frequency.
The point of these filters is to let the higher frequency noise energy on the cable go into the resistor, so a capacitor with a low resonant frequency will not allow higher frequency noise to be dissipated in the resistor. I measured some 0.01 microfarad capacitors and found resonant frequencies from 15 to 21 MHz. Cable resonant frequencies start at about 50 MHz for a one-meter cable and go up from there. The fundamental is inversely proportional to the length, so a two-meter cable starts at 25 HMz, a four-meter at 12.5 MHz, etc. There are many harmonics above these, so 15 to 21 MHz limitation from the capacitor is not very good for filtering these things, even with a long cable.
One way around this is to use a series of smaller capacitors in parallel with the big one. Each smaller capacitor maintains its capacitive behavior to its higher resonant frequency, so the parallel combination works like a better-quality capacitor. I like the sound of silver-mica caps in this service, and these are available in sizes as small as a few picofarads. I would use three or four in a series like 10,000, 1000, 100, and 10 pF, or any similar set of convenient values.
The resistor must also not have much stray inductance, so a metal film or metal foil type is best. Use a value equal to the characteristic impedance of your cable, if you know what it is, or ten ohms if you don't. If the resistor is much larger than ten ohms, scale the capacitor down accordingly so the product of R and C is about the same as 10 ohms times 0.01 microfarads.
A really luxurious installation would use a separate resistor for each capacitor, as this would avoid interactions among the capacitors.
The cleanest way to install these is to solder them to the ends of the cables. However, if you want to preserve the resale value of fancy cables, solder the R-C networks to silver spades and clamp them above the speaker cable spades under the binding post nuts.
As bartc said, you can simply stick the wires under the nuts to see if this tweak is going to do any good before you commit to the spades or soldering to the cables.
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Follow Ups
- Yes, and thanks to bartc. - Al Sekela 21:34:56 11/01/06 (2)
- Re: Yes, and thanks to bartc. - pkell44 18:24:11 11/02/06 (0)
- Geeze al.... - *Michael Z* 07:28:17 11/02/06 (0)
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