Clueless,
I'm sorry - you are misusing the term "impedance matching".
When you have tranmission lines - and you do "impedance
matching" - you make the impedance of one element exactly
the SAME as the upstream components.
For example, if you have a transmission line with twin-lead -
the type that's used for antenna connections to TVs - that's
a 75 ohm transmission line. When you want to terminate the
transmission line - you use a 75 ohm resistor. That's
because a 75 ohm resistor looks to a twin-lead transmission
line like an infinite length of twin-lead transmission line.
THAT is impedance matching - making the impedances the SAME
hence the term "matching".
I would use the term "coupling" not "matching" in the example
you give with the tube amp. Even with the transformer -
the output impedance of the tube amp is not 2-8 ohms.
In fact, the ratio of the output impedance of the amp to
the load impedance of the speaker is called the "damping
factor" and it is not unity [ 1.0 ] in a good stereo setup.
For the amp to exert good control on the speaker - the
damping factor is usually a few hundred. That is the
output impedance of the amp is around a few thousand ohms.
In an audio system - the interconnects ARE transmission
lines - typically 47k ohm transmission lines.
I believe we have a semantics problem here. You evidently
well understand how amps and speakers work. However, you're
evidently unfamiliar with the terms "transmission lines"
and "impedance matching". These are well defined terms in
science and electrical engineering.
Courtesy of the Institute for Telecommunication Sciences:
Transmission line definition:
http://www.its.bldrdoc.gov/fs-1037/dir-038/_5565.htm
Impedance matching definition:
http://www.its.bldrdoc.gov/fs-1037/dir-018/_2679.htm
Dr.Gregory Greenman
Physicist
I'm sorry - you are misusing the term "impedance matching".
When you have tranmission lines - and you do "impedance
matching" - you make the impedance of one element exactly
the SAME as the upstream components.
For example, if you have a transmission line with twin-lead -
the type that's used for antenna connections to TVs - that's
a 75 ohm transmission line. When you want to terminate the
transmission line - you use a 75 ohm resistor. That's
because a 75 ohm resistor looks to a twin-lead transmission
line like an infinite length of twin-lead transmission line.
THAT is impedance matching - making the impedances the SAME
hence the term "matching".
I would use the term "coupling" not "matching" in the example
you give with the tube amp. Even with the transformer -
the output impedance of the tube amp is not 2-8 ohms.
In fact, the ratio of the output impedance of the amp to
the load impedance of the speaker is called the "damping
factor" and it is not unity [ 1.0 ] in a good stereo setup.
For the amp to exert good control on the speaker - the
damping factor is usually a few hundred. That is the
output impedance of the amp is around a few thousand ohms.
In an audio system - the interconnects ARE transmission
lines - typically 47k ohm transmission lines.
I believe we have a semantics problem here. You evidently
well understand how amps and speakers work. However, you're
evidently unfamiliar with the terms "transmission lines"
and "impedance matching". These are well defined terms in
science and electrical engineering.
Courtesy of the Institute for Telecommunication Sciences:
Transmission line definition:
http://www.its.bldrdoc.gov/fs-1037/dir-038/_5565.htm
Impedance matching definition:
http://www.its.bldrdoc.gov/fs-1037/dir-018/_2679.htm
Dr.Gregory Greenman
Physicist