Speaker Cable lifters or stands?

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#381
jneutron said:
Within specific limits, they do indeed provide the same result. So we both agree that the t-line model is accurate and viable, despite the protestations of others.

Both models have merits for specific reasons.

The LCR model, even a single stage, is far simpler to use for bog standard analysis via simulations. However, to approach the accuracy of reality, it requires many stages which increases the complexity beyond most to simply envision. However, the fewer the stages, the worse the high frequency accuracy becomes. A single LCR is a lowpass.

The t-line model provides immediate understanding of the frequency response at the load from dc to daylight. And, by inspection, the system settling delay can be seen. One can even use an excel spreadsheet to determine the settling time of the signal at the load. It is a simple matter to plug in the line and load values and use the reflection coefficients to examine the behaviour of the system.

The T-line also provides the concept of a "cusp" in settling time of the load. To wit, when the line matches the load, there is no settling time, so the load follows the load with a delay equal to the transit time of the signal in the wire, 2 nanoseconds per foot. Trivially small. BUT, when the load impedance is two orders of magnitude below the line impedance, the system requires many hundreds of transits before the system settles towards the final value.

The T-line model introduces to the user the concept of line/load mismatch and resultant settling time dependence. Settling time variations which reach into human discernment with respect to ITD.

The LCR model does NOT easily show that, one cannot figure out the settling time by inspection. One cannot, by inspection, see that a specific value of L and C per foot, lumped as one element, will provide a DC to daylight response with NO settling time variation.

If we were talking about a load which does NOT vary it's impedance with frequency, this discussion would be unimportant as all signal frequencies would have the same settling time.



Yes. See above.


The reflections and rise time are of no importance to the velocity of propagation of the load energy, they occur as a consequence of physics.

The fact that you cannot see it when the rise time exceeds the transit time does not alter physics. It remains there, even though the typical layman cannot see it. So your statement that there is no such effect is blatantly inaccurate, consistent with a lack of understanding.

One only needs use a reflection bridge to discern the reflections which occur at audio frequencies in a typical speaker run..this has been done, and it has been written up as an article.. I do not know if Cyril eventually published it.



Again, your understanding is incomplete. You need to research this more. The fact that you cannot see clear reflections does not mean they are not there. Your beliefs require superliminal velocities through the cable. You need to understand that your argument defies physics.


You need more research and understanding. Do you have access to the cyril bateman articles as a start?

jn
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Hi JN
The transmission line view is also (I think) the best way to deal with horns of an arbitrary shape. The lumped view is pretty much what you have at / near the low end corner but above that, one has increasingly more involved.

I suppose the big difference is the horn is (ideally) acting as an impedance transformer as well but just as the electrical line has ideal “end” impedances, so does the horn although they are different at each end.

I can picture the signal bouncing back and forth in an improperly terminated T line, but I wonder of other arm waving arguments could be made going from the horn case to the cable.?

For example with the horn as T-line, the horn begins to have a usable “gain” over the direct radiating driver when it is about / approaching ¼ wavelength long. When around that low corner, the lumped view works well.
The horn & driver reaches the highest efficiency when it is about ½ wavelength or longer and here and above is where the T-line (slices) view allows one to predict the radiation pattern and other details while the lumped view is blind to them.

Could one make the same generalization about the Cable issue?
That is, if it were say 1/8 wavelength long or less at the highest frequency in question (electrically short) , that the lumped view would be pretty good?

If one put an electrical low pass filter (externally on the amplifier ) that would low pass 40KHz and below, aside from blocking the antenna action of the cables on the amplifiers output stage, what would the maximum length of cable one could have, using plain Jane RG-213 on a typical loudspeaker?
Best,
Tom Danley
 
#382
Hi Tom,

I'd have to think long and hard about the analogy. Horns vary their impedance along the length and I suspect along the cross section as well due to boundary effects, while cables generally do not. I don't know how to consider a cable transmission line that changes it's intrinsic L and C vs length. I believe the acoustic horn to be much more difficult a challenge in light of that. A mismatch at a horn mouth which reflects back into a changing section and impedance is also beyond my simple cable model.

My major area of concern is how the line to load mismatch affects the system's settling time, or delay. A low pass prior to the amp output certainly stops the staircase output, but it doesn't alter how long the system settles with a step input.

Ah, didn't answer.. The wavelength is not a concern at all in the audio band. If there are rf intrusion issues, then yes. But a zobel at the speaker cab kills that. The lumped model is a VERY good predictor of amplitude response, and with unvarying load, also phase. My concern is varying load.

Your radiation pattern stuff is not single dimension, but a 3 dimensional spreading problem in a compressible media.. cables are much much easier IMO..
jn
 
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#384
SY said:
MLS. And guess what, you STILL have that order of magnitude variation when you do it with impulse or sweep.
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Interesting. How does one test the step response of a bass reflex, transmission line, or any tuned cavity? How many cycles (group delay) are necessary until the response rises to that of the specification?

And what is the difference in delay between a driver at 8 ohms at one frequency, and 80 at another, with a speaker cable 15 feet long with a characteristic Z of 200 to 250 ohms and a prop velocity of .2C? (inclusion of Rcable brings cable Z up and reduces velocity.)

It's a trivial calculation with a spreadsheet and T-line. But the beauty of the t-line model, is that by inspection I can see that a cable of 20 to 30 ohms minimizes the delay spread. I can even set the cable z to minimize midrange spread, without regard to bass since I don't localize bass that well..

And I can do that by simply running multiple twisted pairs, 5 or 6 of them, 16 or 18 awg.. bog simple, bog cheap.

So what's the problem? you don't like using t-line because it's always been glibly dissed? Too complex? (I know you, it's certainly not that). Sticking with the horde?

As I've always said: The analysis works (for speakers as well as for synchrotron high speed magnets), it predicts exactly what the mismatch does to the settling/delay, it's very easy conceptually, it provides great understanding with little cost..

And it can provide guidance...if one wishes to test the delay effect on one's own system, it doesn't require fancy cables. bog standard zip that's not garden hose size. Assue the zip is 200 ohm, parallel as desired. Cheap, easy, no brainer, and either it makes a difference, or it doesn't to the user.

It's not like I sell cables or anything..

jn

ps..do any of your mentioned systems measure the impedance of one frequency while pushing another? For example, a high level of 20 hz with a low level of 500 on the same voice coil? Can it see asymmetrical eddy current dragging caused by velocity? (the aforementioned I dL/dt)
 
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#387
Ummm... no. If the load impedance varies by an order of magnitude, matching a characteristic impedance is fantasy. And of course, the driving impedance is near zero.

Lumped approximation gives correct results. This isn't RF. This is bandwidth-limited audio.
 
#388
SY said:
Ummm... no. If the load impedance varies by an order of magnitude, matching a characteristic impedance is fantasy. And of course, the driving impedance is near zero.

Lumped approximation gives correct results. This isn't RF. This is bandwidth-limited audio.
Click to expand...

Ah, there's your problem....in a nutshell.

Who said match the load?? That's impossible with speakers.

Who said driving impedance is other than near zero? It's a requirement of the model.

You are right, this is not RF. So stop trying to shoehorn it using approximations which are only applicable to RF...

chemists...pfffft.. old chemists....pfffft, pfffft..😉

jn
 
#389
system7 said:
Some of us, from more mathematically informed backgrounds, have actually worked out something in this thread.
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Is that the 'clever clogs' version of "if you can't hear the difference then you are too deaf/poor/stupid"?

Tell us, pray, exactly how "mathematically informed" you are? Graduate level? (in what subject?) Postgraduate level? Postdoctoral level? Are you also 'physically informed'? Or 'chemically informed' - like certain parties on here? The nice thing about this forum is however smart/educated someone is there is always someone else who is smarter/more educated, from whom they can learn if they choose to. Please don't be shy.
 
#390
DF96 said:
Is that the 'clever clogs' version of "if you can't hear the difference then you are too deaf/poor/stupid"? Tell us, pray, exactly how "mathematically informed" you are? … Please don't be shy.
Click to expand...

At first I thought you were being unnecessarily “baiting”, but on reading the full comment which elicited your response, I can see why you jumped the shark. Must admit though, its been a fun thread. JimmyNeutron is haranguing about transmission lines, and angling into RF realms. Sy … isn't. But is getting dissed for being a materials-scientist / chemist. I get dissed for lots of things, almost all which are valid.

But it does make the thread interesting!

GoatGuy
 
#391
GoatGuy said:
Must admit though, its been a fun thread.
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Agreed.
GoatGuy said:
JimmyNeutron is haranguing about transmission lines, and angling into RF realms.
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No. Actually, I've been saying all along that it's not RF realm, and one cannot use RF approximations like "wavelength" when talking about system settling.
GoatGuy said:
Sy … isn't. But is getting dissed for being a materials-scientist / chemist.
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You most certainly read that wrong..Sy and I poke fun at each other at times, but I have the highest regard for him.
GoatGuy said:
I get dissed for lots of things, almost all which are valid.
Click to expand...
Welcome to the club. I'll send you a decoder ring...

cheers, jn
 
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