Impedances for audio cables...

Discussion in 'General Electronics Chat' started by Externet, Dec 25, 2014.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Hi.
    Do you know of any charts or standards for thin, thick, balanced, unbalanced, oem, consumer... dozens of types...?

    Or any manufacturer just uses and sources whatever ? Examples... those triples used for externally connecting audio L,R, composite video; those used wiring audio equipment internally...
    I suppose they are referred to 1 KHz.
     
  2. Papabravo

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  3. Externet

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    Well, unbalanced coaxials are built with dimensioning inner, outer, spacing, dielectric dimensioning; and that corresponds to a certain characteristic impedance. Same for balanced, conductor diameters, spacing, twists per lenght, shield or not... also yield characteristic impedances.
    Curious of what is used for audio industry.
     
  4. Papabravo

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    Feb 24, 2006
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    I don't think there are any consistent standards that people apply. Most people have a psychological hangup about the use of inferior "speaker wire" despite the evidence that it makes no difference. The "audio industry" has no opinion on the matter either unless they are trying to sell you something you don't need. Unshielded zip cord with sufficiently low DC resistance works as well as the exotic "magic" wires.
     
  5. Externet

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  6. bertus

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  7. #12

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    Nov 30, 2010
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    I have done the math on driving impedance for an audio cable in order to find the absolute minimum battery power required to drive x number of feet of cable with y db loss at 20 KHz. It's about keeping the Class A driver resistance low enough to drain the charge out of the picofarads in the cable at the highest frequency of interest. Oddly enough, Crutschow independently designed a low power Class A driver with just about the same impedance I arrived at.

    If you have more picofarads in your cable than I had, you would want a lower driving impedance, lower than 3.3K. What is the typical driving impedance of a modern power output stage? WAY lower than 3.3k! A crude look at the math shows more than 150,000 feet of cable would be required to interfere with the high frequencies.

    So, that's my take on it.
     
  8. alfacliff

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    Dec 13, 2013
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    audio coax isnt rated by the manufacturers for impedance like rf coax. audio cables are just shielded to prevent noise. you can use rf cables for audio, but audio amps and such just use shielded cable. the twisted pair used in lamp cord and speakers usually works out to 50 ohm impedance for rf, but what is it at audio? does it really matter? not really, the current handling capacity of the wire does at high power, but not the impedance.
     
  9. nsaspook

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    For audio cables (electrically short) in a house or even a large business venue it's not a concern usually but I worked with dry audio lines that were sometimes a hundred miles long at navy shore stations that had to be impedance matched for maximum power transfer and reduce echo from reflections in long distance telephone circuits using 600 ohm CT audio transformers with 600 ohm balanced cable. What matters is how much of the total waveform is traveling on the wire (electrically long) as fields from source to load. When that percentage gets to be above a few percent the field difference between ends becomes important as the transmission line reactive lumped components become non-negligible.
    http://www.allaboutcircuits.com/vol_2/chpt_14/5.html
     
  10. #12

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    100 miles = 528,000 feet.
    Seems compatible with my estimate of more than 150,000 feet. ;)
     
  11. crutschow

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    Mar 14, 2008
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    So for normal audio runs the cable impedance is not normally a factor so is not mentioned. It's only for distances where the electrical cable length approaches 1/4 wavelength for the highest frequency of interest do we become concerned about cable impedance and matching impedances.
     
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