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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Re: No, because the power cord is a resonator. posted by Presto on February 14, 2007 at 18:22:53:
Some RF energy needs to be present to initiate the resonance. The resultant resonant tones can be much larger than the initial input, depending on the Q. Think of an organ pipe: it sounds a strong tone with a modest white-noise input.The requirement for resonance is reflection at both ends of the cable for standing waves. These waves are at frequencies where the cable length (between reflecting ends) is an integer multiple of half the wavelength. The cable can support lots of harmonics (integers larger than 1) as well as the fundamental (integer 1). Some RF noise must be available to stimulate the harmonics, unless the cable itself has some intermodulation distortion.
The RF noise environment can be a mixture of white noise, strong tones at particular frequencies, and a scattering of tones from things like digital signal transitions. Every noise source is different, so it is somewhat of a puzzle to find the ones that most strongly affect your audio system, and the cords or cables that are most sensitive to them.
The issues surrounding power cord and cable sonic behavior share the basic property of RF resonance, but the same cable or cord model may behave differently in different systems, with different RF noise environments. The cord or cable may have adequate damping measures built in to it so that it has superior performance in many environments. However, if the environment were perfectly quiet, then the cable resonance and damping properties would not matter.
This means audiophiles can do simple things to improve their sound, by experimenting with non-audio equipment noise sources under their control. Even if the audio cables and cords are resonant objects, because they lack proper damping, reducing the noise environment reduces the ability of the cables and cords to generate the strong tones that affect the sound.
Look around for sources. Unfortunately, many appliances these days contain computers and switching power supplies. Both of these can be strong sources of RF noise. My worst source was a TiVo digital video computer, which thankfully died after some power surges. Its replacement is quieter, and I've taken measures to filter the noise it makes from the AC power wiring. I've also found that a combination microwave/convection oven is a bad noise source.
Unfortunately, not all noise sources are under domestic control. Even after all the local sources are filtered or removed, the external ones will still cause trouble. This is why cables and cords that are damped against RF resonance will provide further improvements.
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Follow Ups
- A cord resonates at its fundamental and harmonics. - Al Sekela 09:56:02 02/15/07 (1)
- Well thought out and thorough reply Al - thanks! - Presto 16:11:34 02/15/07 (0)
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