[flipper]

On Sun, 23 Dec 2012 14:59:30 +1100, "Phil Allison"
wrote:


"flipper"

Well, I suppose we just wouldn't mention that to be a transmission
line at audio frequencies the cable would have to be miles long.


** Not this stupid red herring again !!!

I though only ****wit radio hams misunderstood the topic of transmission
lines so badly.

The theory of "electrically short" transmission lines says they act like
pure capacitors if unterminated and like inductors if shorted.

I know about "electrically short" transmission lines but sending audio
over a few meters of cable is not just "electrically short," it's
ridiculously short and renders any notion of 'characteristic
impedance' irrelevant. At audio frequencies the conditions for it to
have meaning simply don't exist any more than it matters if your audio
gets to the speaker at .6 or .9 the speed of light.

As with
longer transmission lines, when terminated by a resistance equal to the
line's characteristic impedance - there is almost no upper limit to the
frequency range.

You should try measuring that 'almost no upper limit' sometime. You'll
be sorely disappointed but we weren't talking about 'any frequency'
anyway. The purpose is to send audio and not 1 MHz, or some other
'almost no upper limit' red herring.

Move the frequency up high enough and "electrically short" begins to
have some meaning, but not at audio over a few meters.

Ordinary twin speaker cables are transmission lines, but with a
characteristic impedance of around 100 ohms - so when terminated by an 8 or
4 ohm resistor show high frequency roll off above the audio band due to
series inductance. Specially made cables ( woven conductor or strip lines)
with a characteristic impedance of 8 ohms show no such roll of.

I don't care what the "above the audio band" roll off is and have no
idea why a speaker would either.

Mostly this roll off hardly matters, but a few cases exist where the
speaker's impedance falls to a low value ( 1 or 2 ohms) at or near the top
of the audio band

Which rules out any notion of supposedly 'impedance matching' the
alleged mythical 'transmission line'.

and then it can matter quite a bit. The original QUAD ESL
is one example and even the AR11 has a huge dip in the impedance at 5 to 6
kHz

The unfortunate speaker cable finds itself stuck between the
amplifier, a low-output impedance voltage source, and the loudspeaker,
whose impedance and phase are all over the place. As such, the actual
impedance with which the speaker cable works is effectively zero,
because it is electrically short in the ridiculously extreme and
connected across an amplifier having negligible output impedance. As a
result, a loudspeaker cable is categorically not a 'transmission
line'.






.... Phil