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Old 29th November 2012, 01:45 PM   #30361
DF96 is offline DF96  England
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Quote:
Originally Posted by jneutron
Trivial when the load at the other end is exactly compatible with the line. Not so when we require the line support a current/voltage characteristic which is not what the line is designed to support.
Non-trivial, true. Straightforward, though. Given a line, and a load, then currents and voltages can be calculated anywhere. RF designers do this all the time. They consider lines with lengths which are significant when compared with a wavelength. Audio is simpler in that sense. I can't quite put my finger on what it is you seem to have failed to grasp. I assume you have read the standard textbooks on the full transmission line theory? Most just give the simpler RF plus small attenuation model.

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You have adopted the assumption that interchannel delays are unimportant.
No, I have assumed that interchannel delays due to this phenomenon will be negligibly small. Your calculation gives total delay, not interchannel delay - which will be much smaller.
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Old 29th November 2012, 01:48 PM   #30362
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Yes, ticknpop,even I am having trouble deciphering what I even wrote so many decades ago. It must have been important to me then. A class note?

Last edited by john curl; 29th November 2012 at 02:04 PM.
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Old 29th November 2012, 01:54 PM   #30363
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Of course, you are right DF96. Once the channel delays are subtracted from each other, there isn't much left.
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Old 29th November 2012, 01:55 PM   #30364
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Help! I found an old notebook with some of my stuff that has been stored for at least 25 years. It goes back to 1959 for the first entry, so it is interesting (to me).
However, this page has an entry that must be between 45 and 50 years old, but I can't exactly place its origin. Can any of you math wiz's help?
The last is the relationship between the divergence of the E field as a result of the volume density of charge. Spinoff of the electric fux theorum (electrostatics).

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I can only recall when they are written on bar napkins, the notebook throws me off.....
Yah, the threw me off...so did the penmanship..

jn
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Old 29th November 2012, 01:57 PM   #30365
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Sometimes, penmanship is hard to maintain when you are taking notes from a lecture, at least for me. I'm sure I understood it well enough, then, but that was almost 50 years ago.
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Old 29th November 2012, 02:01 PM   #30366
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Haven't you guys ever seen a spiral notebook before? What throws me off is the WATER DAMAGE. I have to keep this notebook in my lab, away from the living quarters, as it smells so moldy, but it is an INSIGHT for me to find it, when most of my past history was lost in the firestorm over 21 years ago.
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Old 29th November 2012, 02:04 PM   #30367
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Originally Posted by DF96 View Post
Non-trivial, true. Straightforward, though.
Semantics. But we agree.

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Given a line, and a load, then currents and voltages can be calculated anywhere.
Nobody has stated otherwise.

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I can't quite put my finger on what it is you seem to have failed to grasp.
That much is clear.

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No, I have assumed that interchannel delays due to this phenomenon will be negligibly small. Your calculation gives total delay, not interchannel delay - which will be much smaller.
Your model of human hearing needs to be reconsidered, as it is quite flawed.

An image within a soundfield which is not centered within the soundfield will shift position with respect to a central image when both channels are delayed the exact same amount.

This is where you are lost. Your understanding of human hearing capability is only valid for monophonic reproduction.

I went through this learning curve about 12 years ago. You are at the start of a journey, I hope you take it.

Your E/M and physics is very good. That is not what you are missing.

jn

ps. My statements are not meant to be condescending..my apologies if they appear as such.
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Old 29th November 2012, 02:05 PM   #30368
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You are of course, incorrect.

There are 4 very important things you must remember.

1. There are no lumped element models presented which consider the speed of propagation along the cable. At the microsecond level where humans ability to discern interchannel temporal differences, this can not be ignored.

2. A load at the far end of a cable which has a V/I characteristic which is not identical to that cable, will require a different current than that which the cable will propagate at it's characteristic velocity. The RLCG model assumes instantaneous communication.

3. Measurement of these delays within the audio band is extremely difficult given the overall lack of ability of most to understand and implement a wideband test setup with the necessary capabilities, as well as a lack of adequate hardware.

4. Discussion with you regarding our different thinking on this topic has been nothing but pleasure for me. I do not care if you are wrong, or if I am wrong. This discussion is the way it should be. I thank you for this.

jn
It is useful to bear in mind that signal propogation in cables with typical dielectrics is on the order of 1.5 ns per foot. This varies only a little bit as a function of mis-termination. We should also not confuse phase lag created by LCR lumped-element effects with propogation delay.

Many loudspeakers become inductive at frequencies above the audio band, and it is often beneficial to include a Zobel network at the loudspeaker terminals (or inside the loudspeaker) to maintain its nominal resistive characteristic to high frequencies. This tends to mitigate speaker cable transmission line effects at high frequencies. There is a discussion about this in my book "Designing Audio Power Amplifiers". Often that "nominal" resistance can be set to the characteristic impedance of the cable, so that at high frequencies the cable sees an approximately-matched far-end termination.

It can be especially interesting to measure the impedance vs frequency as seen looking into a 10-foot length of speaker cable when it is terminated in (a) a short; (b) an open; (c) 100 ohms (often near the characteristic impedance of many speaker cables); and (d) 8 ohms. This measurement should be done out to at least 10 MHz.

Cheers,
Bob
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Old 29th November 2012, 02:09 PM   #30369
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Many of the variables reported by listeners which drive engineers nuts are unknown from one place to another. For example, lets say you do not have a wood floor raised from the earth. But instead, live in a high-rise apartment/condo. A steel and concrete floor/walls... a ground plane. Does that grounded flooring (concrete and rebar/I-beams) change the cables L or C, coupling or interference when placed against the floor (ground)? Test it rather than assume. What affect would there be when you raised them off the ground/floor? [I'm not telling] -RNM
Hi Richard,
My speaker cables are raised from the floor by ceramic insulators.
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Old 29th November 2012, 02:10 PM   #30370
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All this implies, regarding time delays and impedance matching, to me, is that connecting cables can therefore be VERY IMPORTANT as they might upset time delays with frequency that might possibly be detected by the human ear. A wonderful approach to answering why cables do not usually sound the same.
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