Careful there Bill, I do a kiddies science fair demo where I drop a BIG N50 supermagnet down a copper pipe and it takes 20-30sec to fall 2'. The visa would be versa as they say, that is the magnet on a string and drop the pipe.
Scott. We always have agreed. Well, except for the Alzheimers, I suspect it isn't helping me...😉
The major thing I've brought into play is the concept of the load to line mismatch causing a change in the settling time of the system. The RLC model can certainly predict that, however that has NEVER happened. The simplistic t-line model totally predicts (accurately) that the system will have a phase shift dependent on the mismatch..And given how poorly every speaker on the planet maintains it's load impedance both statically and dynamically, the ability to properly model these shifts is pretty bad.
I only point out simple ways to reduce these load impedance related delays, and that is by reducing the line Z. Not an expensive thing to do, as I pointed out with multiple zips.
Had wire vendors did the proper LCR modelling to show the lessening of the settling time delays, we would not be having this discussion.....but then again, if they had done that, they'd be out of business as well, no?
Everyone believes that the energy being delivered to the speaker happens at the speed of the prop velocity of the cable. That is not true, the cable can only deliver energy that has the V/I ratio of the cable. Extreme mismatches, which are standard for audio speakers as made today and zip, cannot deliver that energy with one transit of the signal.
I enjoyed bateman's articles, but I understand they never made it to publication. I suspect he kept them too high level for the target audience, so was rejected.
I hope he is doing well
jn
I lost the comment about an aluminum tube vs copper for the eddy drag experiment.
No, aluminum will not work as well. Copper is far better at eddy current braking than aluminum.
I tried 1/4 inch thick aluminum as a windmill eddy brake disk with a neo magnet, it had less than half the drag of a copper disk of the same thickness and velocity. Granted, it was by feel during my building process, but the copper was definitely better.
Thickness also matters too. 1/8th inch copper was not as good as 1/4. I didn't have any 3/8th or 1/2 to try, I was in a hurry and it was 1 in the morning..
jn
No, aluminum will not work as well. Copper is far better at eddy current braking than aluminum.
I tried 1/4 inch thick aluminum as a windmill eddy brake disk with a neo magnet, it had less than half the drag of a copper disk of the same thickness and velocity. Granted, it was by feel during my building process, but the copper was definitely better.
Thickness also matters too. 1/8th inch copper was not as good as 1/4. I didn't have any 3/8th or 1/2 to try, I was in a hurry and it was 1 in the morning..
jn
Well aware of that, but if you are firing a projectile any distance, especially to impress you would not use copper. way too much pain to build to get enough energy into it to overcome the mass difference even tho the eddy currents are higher. With military budgets or the sort of current capabilities JN has access to the rules are different.
Made a Tesla egg with a group at school as well. The original Tesla made was teeny. Ours was the size of a large hens egg.
John, responding to "system7"'s complete inability to engage in any followup to this thread.
A complete waste of time. Ignore list + 1
A complete waste of time. Ignore list + 1
Cliff, I don't quite know WHAT to respond to here. Just for a moment we had 6 constructive posts on the trot, but then it's going back to personal insult level.
Frankly, I think you and billshurv can hang your heads in shame. Too much to apologise, I guess. jneutron and scott wurcer seem to be on the money.
I think we've pretty much covered it all now. Anyone want to summarise? 🙂
Frankly, I think you and billshurv can hang your heads in shame. Too much to apologise, I guess. jneutron and scott wurcer seem to be on the money.
I think we've pretty much covered it all now. Anyone want to summarise? 🙂
How about we just remove the personal aspects from this, the world will not hover over the results of audibility of cable lifters.
Don't understand the technicalities but If one presumes that proximity to floor affects speaker cable it still defies the judgement that nothing happens to wires, circuit tracks or terminals, if they are inside an amplifier but once out of an amplifier all surfaces in close proximity affects it till it reaches speaker, where they are immune again.
Regards.
Regards.
I understand what you post, just do not happen to agree with it for well established and valid reasons. And yes, the argument here in the first instance is whether correct TL modelling is helpful, significant or meaningful, versus lumped modelling - which is a matter of extent. It's your prerogative to ignore or not address points which prima facie contradict your pov, but then you've not provided argument otherwise so its obviously not convincing......
Let me ask an open question or two, based on the case of driving the speaker cable with an audio bandwidth limited waveform derived from an ideal step change, the fastest audible rise time by definition. The driving waveform has a well known, ideal curve shape. 1) in your proposition how would the shape of the observed waveform at the speaker end deviate from the ideal curve at the driven end ? 2) Why can I not observe any such deviation ?
Lathwaite was a clever chap when working on his magnetic stuff, but hopelessly out of his depth when working with gyroscopes. They can be counter-intuitive, and my experience is that some engineers can be flummoxed when faced with something counter-intuitive.simon7 said:
My point was simply that quoting an IC prof as an authoritative source can fail to convince anyone who is old enough to remember Eric and his spinning tops.
When talking about wires at audio frequencies we are several orders of magnitude down the scale of complexity from black hole entropy.
Only a few pages back you were still talking about using the RF characteristic impedance approximation at audio frequencies. In what sense is that the correct transmission line method? A short cable loaded with an impedance significantly less than its characteristic impedance will act as a filter. Electromagnetic theory makes it quite clear that provided that the wavelength is sufficiently larger than the apparatus then it is quite OK to use the lumped approximation - it will give the same result as a correct full wave calculation (but not necessarily an approximate full wave calculation). If not, we would need to change Maxwell's equations.
Anyway, we are still waiting for an IC prof to confirm that your view on cables is right and all the textbooks are wrong.
Yes. A cable is 'short' in the context of the spectrum of vibrations or waves it is propagating. When that is true, as it always is here at audio, 'characteristic impedance' has no meaning. This is because the impedance seen by the driver looking into the cable, in the context of being the source of vibrations or waves, is simply the load impedance (including the lumped parameters of the cable) no matter what load impedance is applied.
Laithwaite had some kind of mental block with gyroscopes, BTW. I never could see his hang up, its just Newtonian mechanics. Such things happen to all manner of people then..........!
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From the pics and video's I've seen, I suspect the mass of copper is meaningless. I think (but am not sure) that the projectile they are accelerating to mach 7 give or take, is tungsten. Tungsten is heavy. Either that, or depleted uranium. Copper may as well be aerogel.
Ah, thank you.
Other than repeating the RF approximation garbage I learned 40 years ago (give or take), you've not provided any well established "reason".
And no, you still do not understand. Unfortunately, part of what I've detailed falls within system control theory, latency.
Again, your statements indicate a lack of understanding of what is being stated. I welcome your questions, but not simple repeating ad nauseum of generic approximations designed to make it easy for undergraduat engineers.
Excellent, a reasonable question.
You cannot observe it as a consequence of the level of effect, the complexity of the load, and the nasty technology behind measurement of high current slew rates within a low impedance circuit.
Think about what I've been saying. The load impedance variation at the end of a horribly mismatched line to load will cause frequency dependent time delays on the order from "none" to 20, 30 microseconds depending on the load impedance dip, the cable impedance with rise at audio frequencies, and such second order effects as the variation of inductance and eddy current dragging losses within the vc slot.
I am very, very good at that type of measurement, having put in over 10 thousand hours doing so before the year 2000. (somebody's simplistic definition of "expert")
You cannot even measure a time delay of 5 uSec in a 1Khz waveform accurately within a circuit loop having 4 ohms impedance, the CVT b dot trapping errors in every NI resistor out there prevents that. That is why I make my own, presented here in the past with pics and accompanying theory. The best I've been able to make so far has been measured at 250 picohenries (designed at a 60 picoH, alas real world size makes the measurement quite difficult), with negligable magfield trapping.
I find the same both here and at work with physicists. (and engineers of course).
totally agree.
BINGO....give that man a ceeeegar!!!! IT's about time.
Now, think about that filter's response when the filter's characteristics are dependent on the load value, and then, how speakers have a load value which is dependent on frequency.
jn
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My apologies luckythedog, you asked two very good questions, I answered only 1.
With a step input, the settling time will be dependent on the line length, it's prop velocity, and the load impedance. In my gallery is a graph showing the settling time dependency resulting from that mismatch. I run the load from 1 to 20 ohms, using a 100 ohm cable 20 feet long. If you notice, the settling decay runs out into the ten microsecond or so with lower impedances. Note also that I used 100 ohms arbitrarily. Actual zip characteristic impedance at audio frequencies is significantly higher, well over 200, 300 depending on actual frequency. So a real zip cord will have delays even longer than this plot set.
To duplicate this using sines on a real speaker requires current measurement accuracies that are very significant challenges.
Scott W has already duplicated this result for one load value and one line impedance using an LCR model. So the settling is real, but nobody has considered the load variation in this respect.
settling_graph - My Photo Gallery
Cheers, john
With a step input, the settling time will be dependent on the line length, it's prop velocity, and the load impedance. In my gallery is a graph showing the settling time dependency resulting from that mismatch. I run the load from 1 to 20 ohms, using a 100 ohm cable 20 feet long. If you notice, the settling decay runs out into the ten microsecond or so with lower impedances. Note also that I used 100 ohms arbitrarily. Actual zip characteristic impedance at audio frequencies is significantly higher, well over 200, 300 depending on actual frequency. So a real zip cord will have delays even longer than this plot set.
To duplicate this using sines on a real speaker requires current measurement accuracies that are very significant challenges.
Scott W has already duplicated this result for one load value and one line impedance using an LCR model. So the settling is real, but nobody has considered the load variation in this respect.
settling_graph - My Photo Gallery
Cheers, john
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