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Rosco Bodine
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It's not just a concern for power grids .....
Actually the same considerations are *very* important
in antenna circuits and their connecting cables being matched to the amplifier circuits , to minimize signal losses
receiving or transmitting .
And dittos for audio circuits . The quality of the audio
and the power transfer are better when there is an impedance matching front to back .
Same for data cables and phone lines .
It's all about having a phat pipe 
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12AX7
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Audio circuits are too short to give a damn about impedance. Telecom does.
Tim
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Rosco Bodine
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Electrovoice matching transformers must have been an anomaly huh ? Dittos for equal length stereo speaker wires , and "impedance spec" for the
speaker coils
and crossover networks ....all that impedance stuff
just a total waste of time for audio . L-pads for balance control too I guess , just total nonsense .
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12AX7
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Those are for maximizing power transfer, where either the power is low enough to matter (mics) or high enough that loss would be akward. I meant
(forgetting to specify) in regards to transmission line theory, especially in line-level signals.
BTW, with modern amplifiers, does it really matter than a speaker is 8 ohms? Or 4, or 2, or 16, or 600 ohms? What would an actual impedance match
be?
Tim
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DerAlte
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Matching load impedance to the conjugate of the load impedance gives you the maximum power transfer possible. In your audio amp cases this is not the
case, such as your push-pull 6L6's. Here you are matching to the load-line impedance, which is determined by safe tube operating area. This is not a
true impedance match.
The semiconductor amps nearly always use a emitter follow output and heavy NFB. The output impedance is near zero so you don't try to match that. Put
an 8-ohm speaker on it and you get X watts, say. A 4-ohm will give you 2X. A 0.1 ohm speaker - weel, you'll probably blow the transistors.
The same reasoning applies to a power grid. Here you also have to take account of line losses. This design is a matter of engineering economics. Very
complex.
In communication line systems, matching is not optional, it's essential to avoid echoes leading the pulse distortion or bad frequency respose. Here
you have to match the source to the transmission medium impedance (possibly free space) at one end ( for maximum power transfer) and match the load
to the medium ( for maximum power transfer and minimum reflection) The same priciple applies in optics to reducing reflection and increasing
transmission by coating lenses and mirrors. Same mathematics, same theory as transmission lines. Learn the maths behind it and you'll be able to apply
it generally...
Regards,
DerAlte
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unionised
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IIRC the original contention was "AC on long transmission lines has in addition to the usual
IR losses , AC reactance losses due to the inductance and capacitance of the long transmission lines , as well as EM radiational loss . There is also
ionization and leakage"
The losses are not due to reactance. If the lines had zero resistance the losses would be near zero.
There are losses by inductive coupling, but these are small.
There are losses due to dissipation in the effective capacitance of the insulation, again these are small particularly where the insulation is mainly
air.
The loss due to the fact that the power factor is less than 1 is easy to deal with; thats what PFC caps are for.
These equations
"
Inductive Reactance (in ohms)
X sub L = 2 pi F L
where F is frequency in Hertz and L is inductance in henrys
Capacitive Reactance (in ohms)
X sub C = reciprocal of 2 pi F C
where F is frequency in Hertz and C is capacitance in farads"
don't have any real bearing on these losses.
The output of modern amplifiers is (as has been said) near zero thanks to negative feedback. Connecting a matched load would cripple the amplifier.
The "impedance" given for a loudspeaker is just a means to express the voltage required to drive the speaker to a given power. It is usually far from
constant across the audio spectrum.
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Twospoons
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Matching an audio amp to loudspeaker impedance is rather non-sensical anyway. Loudspeaker rated impedance is only a nominal value - the actual
impedance is complex (has real and imaginary components) and varies considerably across the audio band.
Helicopter: "helico" -> spiral, "pter" -> with wings
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