I run 75R at each end of 75R coax speaker cable.....adding these resistors is easily audible, removes hf dirt.
Dan.
Mark, Please show me those "tiny steps" that would have rise time fast enough to create reflections. I am asking for measurements. Otherwise it is nothing but further audiophile hypothesis. And we speak about speaker cable. If the square generator with ns rise shows nothing, when feeding power amp, what do you expect from tiny steps? Unless you show measurements, it is only a further pseudotheory to me.
Have you looked into the reflections in your listening room and what they do to the replayed sound quality?
I know Pavel and Bonsai are choosing to ignore this, but others will find it quite illuminating.
http://www.waynekirkwood.com/images/pdf/Cyril_Bateman/Bateman_Speaker_Amp_Interaction.pdf
Go to The bottom of page 6, heading "Cable Reflections."
Note that figure 8 is an actual scope photo showing the driving voltage and the REFLECTED wave coming from the load.
And, it's at 10Khz.
But I will admit, he cheated. He used a really really long length of cable.
4.9 meters.
Another paper Zung linked us to, published in 1997, shows reflections measured using 1786 hz.
And his reflection bridge measures REFLECTIONS down to 1Khz on room length cables that are terminated mismatched.
Honestly, some here remind me of the guy standing in the middle lane of the highway, screaming at the top of his lungs that there is no such thing as gas powered or diesel powered vehicles...only to be run over by a tractor trailer..
jn
ps and in the link zung provided
http://techdoc.kvindesland.no/radio/measurements_simple/20051021151535899.pdf
details were provided to assist others to make a bridge capable of 1Khz to 1Mhz operation.
On page 638 and 639, schematics, discussion, and lo and behold, a few more of those "pesky" scope photos showing those DANG reflections at 1786 hz..hmmm, last I recalled, that was considered an audio signal frequency.
http://www.waynekirkwood.com/images/pdf/Cyril_Bateman/Bateman_Speaker_Amp_Interaction.pdf
Go to The bottom of page 6, heading "Cable Reflections."
Note that figure 8 is an actual scope photo showing the driving voltage and the REFLECTED wave coming from the load.
And, it's at 10Khz.
But I will admit, he cheated. He used a really really long length of cable.
4.9 meters.
Another paper Zung linked us to, published in 1997, shows reflections measured using 1786 hz.
And his reflection bridge measures REFLECTIONS down to 1Khz on room length cables that are terminated mismatched.
Honestly, some here remind me of the guy standing in the middle lane of the highway, screaming at the top of his lungs that there is no such thing as gas powered or diesel powered vehicles...only to be run over by a tractor trailer..
jn
ps and in the link zung provided
http://techdoc.kvindesland.no/radio/measurements_simple/20051021151535899.pdf
details were provided to assist others to make a bridge capable of 1Khz to 1Mhz operation.
On page 638 and 639, schematics, discussion, and lo and behold, a few more of those "pesky" scope photos showing those DANG reflections at 1786 hz..hmmm, last I recalled, that was considered an audio signal frequency.
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Scott Wurcer, can you please set Pavel straight?
I am not claiming reflections cause problems at audio frequencies on short lines, only that they always exist (even though often negligible). There is no sense in having people here who don't know any better believing incorrect claims by Pavel.
I suspect only two here believe his incorrect claims.
I guess actual measurements are no longer valid if they are looked at after their "use by" date..
jn
As a good engineer, I look at actual tests, schematics, and continuously evaluate my thinking if what I see contradicts what I believed.JN wrote “Read my response to Pavel.”
No. At audio frequencies TLE’s are a nonsense.
I suspect as a good engineer you absolutely know this . . .
Watch out for that tractor trailer..
jn
Reflections are caused by the boundary conditions at the ends,
and happen regardless of the shape of the input waveform.
A short circuit at the far end means that the voltage there is zero,
requiring an inverted polarity reflected wave (of the same but mirror imaged
shape) traveling back toward the source. This reverse direction wave
combines linearly in amplitude with the original wave within the line.
An open circuit at the far end causes the reflected mirror imaged wave
to be of the same polarity and shape as the original, traveling back to
the source, combining linearly in amplitude with the original wave in the line.
A load equal to the characteristic impedance at the far end gives no reflections, and
the voltage at the load end is equal to the amplitude of the original wave at that instant.
Similar actions happen when the reflected reverse wave reaches the source end,
if the source end does not have a source impedance equal to the characteristic impedance.
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Completely irrelevant. Attached is the Fourier transform and the reconstruction of a staircase signal, grossly approximating a half sine.
Now imagine a 24bit staircase approximation of a sine and figure out what is the difference to an ideal delta function. The reflections may occur on components which are far away from the delta function, which are virtually zero, whatever scale you are looking at.
If you mean transmission of serial digital data over a cable, that's also irrelevant; some simple math will show immediately that since all pulses are suffering the same "reflections", the clock recovery will fix any timing errors. Pathological cases excluded, of course.
Attachments
True story: I was with a friend driving down a narrow country lane, a tractor and trailer had pulled up by a gate into a field. The driver had just opened the gate and was heading back to the tractor so I waited for him to pull into the field. He drove the tractor into the field, but the trailer remain where it was... except....... I saw the trailer follow the tractor momentarily and then it seemed to jump back to starting position. I said to my friend, did you see what I just saw? He said, what, that the trailer moved and then moved back?Watch out for that tractor trailer..
Perhaps irrelevant you, but there are still reflections (or one continuous reflection). Either way reflection occurs, like it or not. And I think you already know that. Pavel seems to think that reflection only exists if he can see it on a scope. SWR meter doesn't count, apparently.
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True. And the sun sends out tons of harmful radiations as we speak. Be afraid, be very afraid, you cannot ignore them.
This, as much as your reflection story, is called FUD in my book, YMMV.
Please stop with the exaggerated BS. I do not claim crazy consequences, never have. Maybe you are thinking of someone else.
The recent links provide a more detailed discussion, my sims from long ago just covered a basic example to show the equivalence of results. The resistance by some IMO comes from thinking the t-line approach is required in all cases.
Please stop quoting irrelevant facts, reflection exists even for a 1Hz signal sent over a 1cm transmission line, open or short ended. This is what I call an irrelevant fact, your example with a DAC signal before reconstruction, sent over a TL, is as much.
My takeaway is that the resistance is because they were taught in school that the t-line approach is useless when the line is << wavelength within the line.
As has been clearly shown, that is not the case.
For my personal analysis, it is much more convenient to use as I do not have any software to do a 20 to 200 section cable model as you and Cyril did. And the mismatch understandings to me are very clear using T-line.
It is just another tool in the engineers toolbox.
jn
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