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In Reply to: Re: Carbon fiber & Isodamp posted by audionutge@yahoo.com on December 6, 2006 at 23:50:15:
cable shielding cause ringing? What do U mean by "ringing" and what property of the shielding would cause this?Confused,
Follow Ups:
Cables that are long compared to the wavelengths of the disturbances on them can act as resonators. Like any other resonance phenomena, the basic requirement for an observable oscillation is underdamping: the dissipative path for energy is less available than the pathway(s) of storage and return.Cables that resonate are those with low resistive losses and impedance mismatches at the ends. Unfortunately, this describes just about all audio cables. These cables are short compared to audio wavelengths, but, doubly-unfortunately, the radio frequencies at which they do resonate interact with the audio signal through intermodulation distortion.
Cables resonate in modes that have to do with the number of conductors and their geometry. Simple coax has two basic types of modes: normal and common. A shielded cable has more types. One type involves the shield versus all other conductors. This is what Alan means by the shield "ringing." Even if the shield were to be connected to the audio ground wire at both ends (not recommended for other reasons), it would still support a ringing mode from end-to-end, and that mode would affect the audio in many circumstances.
So, "cables that resonate are those with low resistive losses and impedance mismatches at the ends". As you say, this describes just about all audio cables!! :-((How does one create an impedance MATCH at the ends?
Regards,
The common design approach for audio interfaces is low impedance in the source and higher impedance in the load, with negligible power loss in the cable. The high resistance Van Den Hul interconnect cables are a notable exception. The common approach guarantees mis-matched impedances and resonant behavior in the cables unless other damping measures are employed.Since the resonances are in the UHF band and far away from the audio band, it is possible to provide damping through an old trick called "dynamic loading." This approach loads the cables with resistors and uses capacitors in series to prevent the resistors from drawing power from the audio band. This is how Walker Audio High Definition Links work for speaker cables.
The complex behavior of shielded interconnect cables presents significant challenges for damping resonances, and the sizes of the connectors make DIY dynamic loading difficult. This is all I'm going to say about the technology, as I do have some information that is proprietary to others. IME there is considerable audio benefit to damping electrical resonances in cables, and I believe that a large part of the "synergy" of cable matching to audio gear has to do with differences in resonant behavior among cable designs.
Check out some of Al Sekela's posts as well here and on Tweaks about standing waves in cables, "ringing", etc.
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