Hi macgyver10,
Your oscillator output impedance is 500 ohms. Since the cables are designed to be driven by a low impedance source you may want to enlist an amplifier's help. Consider a worst case amplifier with a damping factor of 1, giving an 8 ohm output. Common solid state amps normally go from a DF of 40 and up, even at higher frequencies.
Granted, your choice will exaggerate the influence of the cables (as you stated - no argument there). You may have some capacitive correction that is needed across your 500 ohm output impedance to zero your test fixture at the very least. I am being picky. 😉
-Chris
Your oscillator output impedance is 500 ohms. Since the cables are designed to be driven by a low impedance source you may want to enlist an amplifier's help. Consider a worst case amplifier with a damping factor of 1, giving an 8 ohm output. Common solid state amps normally go from a DF of 40 and up, even at higher frequencies.
Granted, your choice will exaggerate the influence of the cables (as you stated - no argument there). You may have some capacitive correction that is needed across your 500 ohm output impedance to zero your test fixture at the very least. I am being picky. 😉
-Chris
My idea wasn't to single out Hiraga. He's name turned up, is all. And I use lie in a very broad sense. ("Sound reproduction" is an example of a lie that is universally accepted.) But mostly it was a response to:
Hiraga is clearly more of an authority on cables than the Pope. But it still doesn't prove that cables make a difference. It only proves that Hiraga thinks they do.
Hiraga is clearly more of an authority on cables than the Pope. But it still doesn't prove that cables make a difference. It only proves that Hiraga thinks they do.
Q: "Why would impedance mismatch and ringing not exist in speaker cables? Or if it does exist, why would it not be audible?"
A: the cable is too short compared to audio wave length for impedance mismatch to have any effect. In other words the rise/fall time of audio signal is waaayyyy too long.
A: the cable is too short compared to audio wave length for impedance mismatch to have any effect. In other words the rise/fall time of audio signal is waaayyyy too long.
The characteristic impedances of speaker cables (except for types deliberately designed to have high capacitances and notorious for their own amplifier incompatibilities) are typically much higher than at least that of the amplifier, if not the speaker, at any frequency much below the megahertz range. The impedance discontinuities, while arguably not very significant in the audible range, may have significant repercussions at RF frequencies where digital componentry and Class D amplifiers are known to generate a significant amount of noise that may interact in a way resulting in sonic consequences with amplifiers having conditional stability and/or gain and slew rate limitations in these frequency ranges.
A somewhat related argument is raised against SACD's significant out of band HF noise signal which is widely considered to deteriorate the sonic quality of some amplifiers having slew rate and linearity/open loop gain limitations above the audible range.
A somewhat related argument is raised against SACD's significant out of band HF noise signal which is widely considered to deteriorate the sonic quality of some amplifiers having slew rate and linearity/open loop gain limitations above the audible range.
anatech said:
This would be good advice if the oscillator was not part of the LMS test system. The 500ohm output impedance is specifically designed to be used as a voltage divider which the analyzer then uses to derive the low impedances. LMS stands for Loudspeaker Measurement System and it has been specifically designed for this purpose. It works extremely well and actually has some advantages over FFT systems. In other words the fact that this test was done with this system is significant. It's designed for the purpose of measuring impedance in the audio range. I use it for deriving T/S parameters, and later with a calibrated MIC (and an amplifier for drive current) match impedance curves to SPL graphs for extremely accurate x-over fit.
However, I'm considering that my choice of resistor value was poor (I've been "schooled") so I don't see why I couldn't try the test again and actually terminate with a loudspeaker. You can't get more "real world" than that, and I can still invert and remove the impedance curve of the speaker which will leave me the intrinsic impedance of the speaker cable.
Does anyone take issue with that M.O.P.?
Typo: I meant to say that the characteristic impedance of most speaker cables is higher than that of the amplifier and/or speaker much above the audio range.
koolkid731 said:
That makes sense, as even a 1/4 wavelength at 10 KHz would be somewhere around 7Km!
But riddle me this:
I can easily see ringing in video cables starting at ~2Mz or lower. That's a 1/4 wave of 36 meters. Certainly I have used cables that long and longer, but the ringing is also visible with much shorter cables, on the order of 1m or less. Why?
Never have tried to see if signal ringing had a direct correlation to cable length, but it might be interesting to measure. If it does, then it shouldn't be a problem in the AF band. If not - then it must be something else.
panomaniac said:
When you're talking about "ringing" do you mean as the result of standing waves? The unterminated coax cable would appear as a "mirror" to the RF signal, voltage would be at maximum, and current would be zero. The length of the cable WRT the wavelength of the signal (actual wavelength will be affected by VF for the cable, about 75% for RG-6) will be significant to the standing wave amplitude as you approach the 1/4 wave, 1/2 wave lengths.
I'm not sure that the "full wave needs to fit in the cable length" for this to be significant. You theoretically could produce a standing wave with a cable half the length of the signal wavelength.
In fact we're talking about the difference between transmission lines and wires, there's a loose rule of thumb that for a wire to be considered a transmission line it needs to be as long as 1/100 the wavelength of the signal it's carrying.
Impedance matching would be important at this point to transfer as much POWER to the load as possible.
Audio signals, as mentioned, do not see standard cable lengths as anything approaching a transmission line, so they can be effectively treated as a simple piece of wire. In fact unbalanced line level audio connections are "bridged" from low impedances into high impedances to maximize voltage transfer. You don't start "matching" impedance (600ohm balanced) until the cable lengths begin to get very long (and you need common mode noise rejection) The same thing is essentially happening from a power amp to a loudspeaker, but the amplifier is considered a "constant voltage source" so as load impedance drops the amp is required to provide more current to maintain the same voltage across the loudspeaker terminals.
Riddle answered?
panomaniac said:
I'll see what I can do, but don't hold your breath...I don't see myself getting around to this until after Xmas. I have a 3.5 year old and a 2 year old under foot!
panomaniac said:
I was assuming that the "ringing" was due to signal reflections in the RF range, however "ringing" in AF on, say, a reproduced square wave is very often a function of limited bandwidth - essentially high frequency roll off.
Fourier showed us that!
>Do speaker cables make any difference?
i tend to use thicker cable if possible
and keep the run as long as the distance
required to cover
regards
john
i tend to use thicker cable if possible
and keep the run as long as the distance
required to cover
regards
john
Come to think of it - does the quality or type of air in the room make a difference as this can be equated to speaker cables in the sense it is just a medium (forgetting the effect of wall reflections which do effect the sound).
... sorry! This is getting silly - I will promise this is my last post on the subject.
... sorry! This is getting silly - I will promise this is my last post on the subject.
Hi guys,
never ending fighting?
forget the paper guys, the math is so general, so a simple way is prove it! Do spectrum test with 'audiophile' cable and without. You guys who feel difference, please prove it..... don't be afraid to know the truth.
I am waiting.....
never ending fighting?
forget the paper guys, the math is so general, so a simple way is prove it! Do spectrum test with 'audiophile' cable and without. You guys who feel difference, please prove it..... don't be afraid to know the truth.
I am waiting.....
macgyver10 said:
For gross fr, this is an easy thing to accomplish...but this loses the temporal accuracy entierly.
panomaniac said:Thanks guys for poking holes in the Stereophile article. That super slow speed in copper was bothering me all night! How could that be??
The propagation velocity of a e/m wave is really that slow, but it is for a TEM wave. Think of a room with copper shielding several inches thick. If you try to beam a signal against the wall, it will travel that slowly through the wall. That is not the same thing as passing a current through a wire, for that, the signal information will be comparable to lightspeed.
panomaniac said:
The mismatch and ringing does indeed exist, even at audio frequencies. But, because the lengths we are talking about are so short in comparison, there is no way to see these effects, as the cable will act as a lumped element for all practical purposes.
"Reasonably" is based on an expectation of sensitivity of humans of course. When one considers the sensitivity of humans to localization parameters, which is what we actually use when discerning a virtual image in the soundfield. To consider localization requires modification of the sensitivity parameters we consider as "audible".macgyver10 said:
macgyver10 said:
Perhaps not wild inaccuracies. If the subtle errors are of the order of magnitude of localization criteria, then the measurements will fail at supporting testability.
anatech said:
It's amazing that they sell that kelvin set, isn't it? They should put a big tag on the clips saying "don't even think about using these for anything under a microhenry".
anatech said:
While a PITA, just breathing on the clip setup requires redoing the short correction.
Nah, it's not patience..there was indeed many a cuss word involved..😉anatech said:
Cheers, John
macgyver10 said:
Ok, ok...I apologize for the use of that phrase..🙁
The use of a loudspeaker will confound the test way too much. It has far too many elements of storage to be practical at looking at a simple wire. Don't forget, you are only using one source and load, the real test will be amplitude/temporal when comparing two systems.
Using a pure resistance of the correct load (4 or 8 ohm) forces the cable under test to support the correct ratio of current to voltage. Because the load is far lower than the cable Z, this makes the inductive storage of the typical wire pair the dominant storage element. And that is a lagging storage element.
thoriated said:
It is typically higher from DC up. The cable Z is sqr(L/C) for all cases. In the audio band, L just has to include the internal inductance of 15 nH per foot per conductor.
panomaniac said:
I assume you are talking about edges. Ringing will be evident when the physical length of the impedance mismatch approaches the length of the transition..a rule of thumb is to make the mismatch area much smaller than the length of cable required for the transition to pass. If you are using 10 nSec per foot cable, a transition of 1 nanosecond will reflect off a discontinuity that is a foot long, and for transitions slower than that, the reflections will be less.
Cheers, John
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