Hi Vacuphile
RE speaker cables as transmission lines.
I have observed the following experiment carried out which I believe proves that
speaker cables do act as transmission lines. A similar test was published by
Stereophile some years ago with the same results.
A signal comprising a 1Khz 1V square wave is applied to a typical length (3Meters)
of any speaker cable by any type of amplifier. The end of the cable is loaded by
a variable resistor.
First this resistor is set to be much larger than the cables nominal characteristic impedance and the waveform at the amplifier end is observed with a scope.
The leading edge of the square wave will be seen to be composed of a series of steps like a stair case. The time interval between each step corresponds to the time a reflection would take to arrive ie about 15nsecs for a 3 meter cable. The multiple
reflection die away at the rate you would expect given the amount of reflection
due to the mismatch at each end of the cable.
Now if the resistor is adjusted to match the nominal characteristic impedance
the steps disappear.
This behaviour proves for me that the cable is acting like a transmission line. I
would be interested if there is any other explanation.
Its an easy test to try to prove it for yourself.
RE speaker cables as transmission lines.
I have observed the following experiment carried out which I believe proves that
speaker cables do act as transmission lines. A similar test was published by
Stereophile some years ago with the same results.
A signal comprising a 1Khz 1V square wave is applied to a typical length (3Meters)
of any speaker cable by any type of amplifier. The end of the cable is loaded by
a variable resistor.
First this resistor is set to be much larger than the cables nominal characteristic impedance and the waveform at the amplifier end is observed with a scope.
The leading edge of the square wave will be seen to be composed of a series of steps like a stair case. The time interval between each step corresponds to the time a reflection would take to arrive ie about 15nsecs for a 3 meter cable. The multiple
reflection die away at the rate you would expect given the amount of reflection
due to the mismatch at each end of the cable.
Now if the resistor is adjusted to match the nominal characteristic impedance
the steps disappear.
This behaviour proves for me that the cable is acting like a transmission line. I
would be interested if there is any other explanation.
Its an easy test to try to prove it for yourself.
Please, MaxTownshend, first, compensate your loudspekers motional and selfic impedance in order to get the flatest impedance you can. Second, change the position of the amortissment materiel in your inclosure (in the middle of each lengh, instead at on the panels), and mesure the changes. Then compare the sound difference..
Now, compare the ones of two different cables ?
Did you will continue working on cables magic ?
Now, compare the ones of two different cables ?
Did you will continue working on cables magic ?
No a match terminated system has a pure real impedance at all frequencies. Not enough loss angle at 5.6 milli-ohms/m to make much difference.
Please provide a reference to this. On the surface it makes no sense at all.
Now you're stabilizing the amplifier. If it sees 8 Ohms at an angle of 0 degrees why would it need a Zobel? The Zobel does nothing for the speaker/cable interface.
The rest of this is such nonsense it's not worth the effort, we go from matched impedances to "bouncing back and forth" signals with only 5% of each bounce transfered (where that number came from I would like to know). You obviously have something to sell.
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Scott,
Few speaker cables are 8R CI.
Many are way over 100R CI.
My point was more subtle though.
Somone asserted that "transmission line theory does not apply to short runs of cables".
That statement is patently wrong.
We may argue that at audio frequencies speaker cables are too short to exhibit transmission line behaviour at audio frequencies, however that is different to saying "it does not apply", in fact it illustrates that it does apply.
Ciao T
Few speaker cables are 8R CI.
Many are way over 100R CI.
My point was more subtle though.
Somone asserted that "transmission line theory does not apply to short runs of cables".
That statement is patently wrong.
We may argue that at audio frequencies speaker cables are too short to exhibit transmission line behaviour at audio frequencies, however that is different to saying "it does not apply", in fact it illustrates that it does apply.
Ciao T
1- Does not this variable resistor load change the behavior of the amplifier ?
2- Agree, but do not agree it has, at the involved frequencies, a so noticeable auditive impact ;-).
Least than hundreds of others factors in your amplifier or loudspeakers design, situated in the audio frequencies range. You better look-at them first, don't you agree?.
Some can be afraid looking to the class D signals. The same can love how some of them sounds.
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Please find me "any type amplifier" that will put clean 15ns edges on a 1kHz square wave. And a low resistance pot that's good to 70MHz.
BTW the total distance is 30ns travel out and back.
SY
My post was to describe an experiment that shows that speaker cables
act as transmission lines to debunk one of the "myths" as Thorsten said.
15ns is indeed a short time but the reflections continue for a considerable
time. If we can get the fact established re transmission lines then we
can move on to whether the reflections can cause sonic differences
dont you think.
My post was to describe an experiment that shows that speaker cables
act as transmission lines to debunk one of the "myths" as Thorsten said.
15ns is indeed a short time but the reflections continue for a considerable
time. If we can get the fact established re transmission lines then we
can move on to whether the reflections can cause sonic differences
dont you think.
It is a fact that at audio frequencies speaker cables are too short to exhibit transmission line behaviour. Just as it is a fact that chlorofyl is green.
Therefore: Transmission line theory does not apply to the speaker cables that I use.
Agree again. In between thousand of ten time more noticeable other sonic differences you can hear, and mesure, between Ops, resistances technology, circuit designs, printed boards designs, and, (looks like a joke) loudspeakers materials.
Is this Serious ?
Zeta, i can confirm your assertion, made some experiments on this long time ago.
I decided to forget about that at the same time i had stopped to look in a microscope the result of the work of my home vaccum cleaner.
I remember, in the research and development office i was working in 40years ago, we had reduced by a factor of 10 the distortion of our amplifier only by changing the design of our printed board (symmetry of the output stage , point where the CR was took).
I prefer to work on that kind of thinks than on the sonic differences between gold, coper and silver ;-)
I decided to forget about that at the same time i had stopped to look in a microscope the result of the work of my home vaccum cleaner.
I remember, in the research and development office i was working in 40years ago, we had reduced by a factor of 10 the distortion of our amplifier only by changing the design of our printed board (symmetry of the output stage , point where the CR was took).
I prefer to work on that kind of thinks than on the sonic differences between gold, coper and silver ;-)
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SY
Sorry not to make it clear. Considerable time meant the time for over 100 reflections in the experiment I witnessed. This is from memory so its not exact. It showed that there were multiple reflections which could affect the sound (or not).
Again why doesnt someone else try it? Surely its worth doing to prove once
and for all the transmission line behaviour. I could (and probably will) repeat
the experiment for myself but somehow I doubt that even then I will be believed.
Sorry not to make it clear. Considerable time meant the time for over 100 reflections in the experiment I witnessed. This is from memory so its not exact. It showed that there were multiple reflections which could affect the sound (or not).
Again why doesnt someone else try it? Surely its worth doing to prove once
and for all the transmission line behaviour. I could (and probably will) repeat
the experiment for myself but somehow I doubt that even then I will be believed.
On the contrary, the transmission line theory always applies, and if you are careful enough to model the losses vs frequency you would get pretty good results.
Let's up the ante, and say S parameter analysis also applies. So if you had the speakers audio frequency S parameters and placed your 8 Ohm line model in there you have no choice but to use the tiny fractional wavelengths. Now substitute the lumped R/L/C and plot the difference.
Speaker parameters are unfortunately not stationary with power level and I'll bet that makes more of a difference.
I have I just don't have an audio amplifier with 15ns edges, please point me to one.
There must be dozens of amplifier reviews out there with squarewave response plots.
As i said, i believe-you. I know too it need some very high performance equipment, and a EMI protected room.
What i know for sure, i was unable to correlate this acrobatic and funny experiment with any listening experience.
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