Sigh...ya give me a line just crying for humor, and whaddya do?
Miss it..
Sheesh..your no fun
John
For more on Characteristic Impedance and the such, Jim Brown has a very nice paper:
Transmission Lines at Audio Frequencies, and a Bit of History
http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf
Figures 1 & 2 are very interesting.
Transmission Lines at Audio Frequencies, and a Bit of History
http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf
Figures 1 & 2 are very interesting.
"Thus, at audio frequencies,
a cable less than 2,000 ft long is no more complicated than its series resistance and parallel capacitance. As the cable becomes
longer, or as frequency increases, the cable will begin to behave as a transmission line."a cable less than 2,000 ft long is no more complicated than its series resistance and parallel capacitance. As the cable becomes
simple like a pimple!
Figure 3 is the one that seals the deal. Is your interconnect 2 miles long? If not, then guess what, the lumped RC (with R being the terminating resistance and C being the cable capacitance) is perfectly accurate to well above any possible audible limit.
Since this thread is about interconnects he`s wrong. Speakercables is just about eliminating resistance by using heavy gauge solid(!) wires, but when it comes to signal-level wiring things is a bit more tricky.
line level, or signal level cables impose the same loadings on the source as a speaker cable imposes on it's source.
The sources see the complex impedance of the cable added to the load at the far end.
The source should, if designed competently, be able to drive that complex impedance.
Seems like a reasonable point of view. I'm probably going to sim it and see what comes out. But I'm sure it's not that simple. Low frequency performance during listening seems to somewhat follow the impedance variation below 30Hz. Maybe if a model is found, then interconnects can be significantly better.
Impedance variation of what? The amplifier input impedance, as measured from the other end of the cable? Is what you were actually measuring? Of course that affects LF performance, depending on whether there is a coupling cap or not. Nothing to do with cables, though.
That is what was being measured. Tried a few amps, results had similar trends. But what you mention is very interesting. If there is an input coupling cap, the impedance will rise at low frequency. I've also been looking through various input designs of amps and preamps, there seem to be quite some variation.
Last edited:
From figure 2 the velocity of propagation of DC is 1% of the speed of light?
Is there really a .5us delay between the high and low audio frequencies in a 1m cable?
The Telegrapher's Equation is bit more complete.
So what I was trying to mention on the Blowtorch thread is going on here.
However it does explain G and how the mu metal was used!
Just a quick look at the graph, I will plead guilty to not calculating it. .2us would be 1.44 degrees of phase shift at 20K, so 3.5m of interconnect would have enough phase shift to be perceived according to to Schroeder or Neve!
Easy enough to measure! But not on my things to do list, yet.
Interesting read. Thanks for the link.
I was particularly interested in several items.
1. The analysis showing how the actual load impedance affects the signal transmission to the load. (perhaps that was forgotten)
2. His explanation that even though the line starts to approach the 50 or 75 ohm impedance within the audio band, that can be ignored for audio up to 2 thousand feet long. Doesn't seem to be internally consistent.
I always have concerns whenever an article is written to attempt to debunk something..they never work out right..
Cheers, John
I think there is some confusion of dphase/dfrequency and actual propagation delay here. The time it takes for an RC circuit to reach 50% has nothing to do with speed of propagation.
You also might find this paper interesting:
"Cables, Transmission Lines, and Shielding for Audio and Video Systems"
http://audiosystemsgroup.com/TransLines.pdf
More (about 60) of Mr. Brown's papers at Audio System Group.
Audio Systems Group, Inc. Publications
Jim Brown is the AES committee chair on EMI/RFI (EMC).
Last edited:
- Status
- Not open for further replies.