|
|
|
|
Speaker wire - another fine theory
(Stewart Pinkerton) wrote in message
While this is all true, the reality is that most speaker cables have a
characteristic impedance of 50-100 ohms, and are connected to a load
of less than 8 ohms driven from a source of less than 1 ohm. To a
close approximation, this *is* a shorted termination.
But Dick made the *general statement* that as the spacing increases,
the inductance increases. This is not always true.
For example, if the cable has a characteristic impedance of 4 Ohms,
and if the loudspeaker load is 8 Ohms, the amplifier will see a
resistive /capacitve load.
For the above case, 20 ft of cable, at 20 kHz, would be 7.98 -j 0.031
Ohms. If the wires are seporated a little, the cable's input impedance
becomes *less capacitive*, not more inductive. One can *not* make the
general statement, that as speaker wires are seporated they become
more inductive.
The problem comes from trying to look at a transmission line as lumped
constants. Let me give you a challenge. I understand that ordinary zip
cord has a characteristic impedance of 50 Ohms. Using lumped
constants, tell me what is the input impedance of 20 ft of (16 gage)
zip cord, terminated by an 8 Ohm resistor.
Bob Stanton
|