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Speaker wire - another fine theory
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Bob-Stanton
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Speaker wire - another fine theory
(Stewart Pinkerton) wrote in message ...
On 18 Sep 2003 16:14:04 GMT, Don Pearce wrote:
On 18 Sep 2003 14:36:22 GMT,
(Stewart Pinkerton)
wrote:
On Wed, 17 Sep 2003 18:09:09 GMT,
(Bob-Stanton)
wrote:
(Stewart Pinkerton) wrote in message
No, it won't. Anyone who has dabbled in radio will tell you that you
need at least tolerably close load matching to get anything like a
proper resistive transmission line.
That is because at RF, the cable is usually many wavelengths long. A
cable will act as an impedance transformer, if the load is other than
the cable's characteristic impedance.
As for audio, a 20 ft long cable is only 406 E-6 wavelengths long (at
20 kHz). This is far too short to cause an impedance transformation.
Therefore, the impedance seen by the amplifier will be nearly the same
as the impedance of the load (loudspeaker). A cable will add a tiny
amount of resistance and inductance, but that will usually be
insignificant.
Now, since the amplifier certainly
won't have anywhere close to 8 ohms source impedance, and the speaker
won't be anywhere near to an 8 ohm resistive load over the vast
majority of its working range, you are in fact back to the lumped
capacitance model.
Trying to analyze a transmission line, (even a short one like an audio
cable) by using lumped constants, will always result in wrong answers.
Bob Stanton
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