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In Reply to: RE: "How electricity flows in an AC circuit" posted by geoffkait on May 02, 2022 at 06:24:52
I vote 3
A coax cable is identical to any other in that the currents flowing in the two paths as a result of a load at the far end, are ALWAYS equal but opposite.
Coax cable is a configuration that has the least resistance and inductance because the magnetic fields the current in the conductors produce,, do not escape (and become a series L). The geometry of RF cables is aimed at having a particular ratio between the series L and parallel C which when more than around 1/2 electrical wavelength long,. give the cable an impedance of say 50 Ohms. That impedance can be made higher by making the center conductor smaller in diameter and the diameter of the shield larger (reducing the parallel C) TV coax is usually 75 Ohms vs 50 Ohms for say RG-8 radio cable.
Coax is not glamorous but low loss and more flexible variants of RG-8 works great for speaker cables, all the parameters are better and if the cable is long enough they begin to matter so far as effecting the loudspeakers output.
Follow Ups:
From paragraph in my original post,"The signal does not travel in the center conductor."
"The signal travels in one direction only, from source to the load."Please comment.
Edits: 11/05/22 11/05/22 11/05/22
So perhaps we are talking about two different views, a more conceptual one, like the signal travels in one direction from the source through the system, to the speaker.
What i am talking about is how that "signal" is transferred via wires as a current and voltage through two paths or a pair of conductors to the loudspeaker. Where the current that makes the voice coil move and produce sound is traveling equally in both conductors but in opposite directions and if a coax is used, equally on the inner and outer conductors.
To have a complete circuit, where a signal can be transferred electrically, you need both paths, with AC like audio one is positive when the other is negative. "Ground" is often used for one of those paths.
The paragraph I quoted was mixed up to a certain extent. That paragraph was actually referring to the energy contained in e and B fields located outside the conductor. The Poynting vector energy flux points in the direction of free electron motion. Current and voltage are scalar quantities so they do not travel or have any direction. What does travel and have direction are the free electrons, the moving charges. Free electrons are physical entities whereas current and voltage are not. This will become important on discussions of directionality.
Edits: 11/07/22 11/07/22
AC does flow back and forth in a coax cable or it would not be AC.
Current doesn't flow back and forth, technically speaking. Current is a scalar quantity, it has no direction, it has no velocity, it's calculated according to amount of free electron flow, total charge per unit time. Only the free electrons move back and forth in an AC circuit. The picture of how electricity works is further complicated by adding the concept of Poynting vector and energy flux outside the conductor in electric and magnetic fields. Having said that we're stuck with common occurrence of term, "alternating current."
Edits: 01/17/23 01/17/23 01/17/23
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