What a coincidence, me too. As you put it the cable 'disappears' when its length is any 1/2 wavelength multiple, including the case when the multiple is zero (ie very short cable length compared to wavelength). In this case, at 1kHz wavelength is c 300km, so obviously this condition applies.
Then Zin = ZL
That is to say driving the cable is exactly like driving the load at the far end directly, the cable behaves as simple wire not as a transmission line. Doesn't matter whether it's coax, twisted pair, fig 8 or two coathangers looking like a Christmas tree, same applies. The simple lumped parameters associated with the wires is all that matters.
Don't blame me, I didn't write this stuff, it's all standard.
No. Wrong. Sorry. You're describing an ANTENNA when you talk about 1/4 and 1/2 wavelengths giving a resistive load. An antenna is a narrowband reactive load. And you still need to carefully consider matching cable impedance with them.
It's not a million miles from how an anti-reflection coating works in optics.
http://en.wikipedia.org/wiki/Anti-reflective_coatinghttp://
I'm talking about a cable that is terminated in its characteristic impedance. There is no reflected wave from the matched load, so no parasitic inductance or capacitance is measurable at the source.
But really, all we are talking about here is whether 500pF or a nH matters at audio frequencies. Or, interestingly, whether our speaker cable might be turning into an antenna at radio frequencies if we get sloppy in technique. 🙂
Thankyou billshurv for the earthing article. Shielded balanced line for the win, eh? 😎
You keep repeating that and it is not generally correct.
At this point, given how many actually competent people have told you that you're all wet, given that you haven't read the basic literature, and given that you're apparently unable to do the basic calculations, you might consider either putting a halt to your postings on this subject or spending some time boning up on the basics so you aren't continuing to post nonsense and wasting people's time.
IC has "world experts" on cable termination? You mean people who have read and understood undergraduate EM textbooks? Surely not!system7 said:
I used to work at IC (briefly) but I would hope that even less respected colleges have staff who understand transmission line theory, and so know it is irrelevant to audio frequencies (unless you are wiring an analogue long-distance telephone circuit - when it becomes very relevant).
Why, when at audio frequencies we know this is difficult and quite unnecessary?
Please can we kill off this persistent false meme that a short audio cable needs to be terminated in its characteristic impedance? It doesn't. This is fortunate, as the characteristic impedance is approximately given by sqrt(R/(j 2 pi f C)), which is (0.5-0.5j)sqrt(R/(pi f C)). R and C are distributed e.g. per meter (or foot for our US friends). Making a lumped circuit with wideband inverse square root frequency behaviour would be an interesting design exercise!
There may be reasons why a speaker cable could benefit from having an RF load applied which roughly approximates to the RF characteristic impedance. This will kill off any RF resonances, and so may help with amplifier stability and RF interference. For some reason people often seem to confuse these two quite different issues: audio termination (unnecessary, and probably impossible), and radio termination (could be helpful, and relatively easy). Sometimes it because they have a product to sell; sometimes it is because they have read a little about transmission lines and think they have understood a lot.
You've consistently misunderstood, system7.
When length is a very small fraction of wavelength, as is the case here, it doesn't matter what 'termination' or ZL is applied at the load end, the driven end always simply sees the load ZL plus the lumped properties of the wire. If you 'terminate' it with a teabag, the driven would see the impedance of a teabag as though connected via wire with lumped properties. It's the way it is, the law, it can't be changed even by appeal.
I think we are in agreement there.
And getting the conductors as close as possible to each other is hardly controversial:
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If we mean to avoid the speaker cable/speaker being an RF antenna, then the issue is one of screening or snubbing, and building a matched terminated transmission line is a misconcept here again. Unless we intend to transfer power between amp and speakers at c 100MHz ? 😉
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No. A speaker cable is a poor antenna (deliberately so, unless it adopts some peculiar 'hi-end' design). However, it can pick up RF and a resonance can increase the pickup. This is because a resonance only needs loose coupling to pick up a lot of energy. Damping a resonance reduces the pickup. The CR network which does this is sometimes called a snubber.luckythedog said:
Yes, but such has nothing to do with arranging for matched impedance termination of speaker cables as a transmission line. The ground return wire in a speaker cable might be considered an antenna per se, for example. It's a total goose chase, no evidence linking RF to the OP, and inconceivable for it to be widespread or repeatable or present in well designed amps.
RF termination of the RF line can affect RF pickup on what is, in effect, a leaky line. This has nothing to do with audio 'termination' of an audio' transmission line'.luckythedog said:
Both cables together can also form a monopole. RF termination at the speaker end does not affect this.
None of this has anything to do with cable lifters, which I believe to be complete nonsense.
is it possible that cable lifters can have audible effects on an amplifier or reproducing system that is already suffering from instability?
Sure, if the instability is caused by something like a partial break in the wire so that adding the lifter pinches it back into place, or if the instability is caused by something like...a 100 watt television broadcast antenna running under a floorboard.
I would suspect that unless seriously deficient, line level gear should be filtered in it's operating range anyway. I could be wrong and I'm sure someone will pipe up with an example or 20, but gear should be filtered as part of it's design.
well i could be wrong but from what i've learned over the years from servicing gear only confirms what i've been taught.which is if physically moving any part of an electronic device results in a noticeable performance change there's a problem.
so i contend that if moving a speaker cable changes how the system performs it not a mod or enhancement it's an indicator of a problem.
so i contend that if moving a speaker cable changes how the system performs it not a mod or enhancement it's an indicator of a problem.
Well, GKF, we've had a lively squabble over cable lifters. 🙂
Whether you use lumped parameters, or transmission line theory, you end up with smallish effects at audio frequency. The most I could get was about 1% tonal effects from the cable. And that's not distortion either, just tonal.
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A cable inductance of 1uH really shouldn't affect a 50uH tweeter very much. 😕
The earthing (aka common-mode) problems with a 5m unbalanced cable don't look huge either.
So unless you have a very weird factor coming into play here, I think most of us are stumped by this. But it's made us think. 🙂
Whether you use lumped parameters, or transmission line theory, you end up with smallish effects at audio frequency. The most I could get was about 1% tonal effects from the cable. And that's not distortion either, just tonal.
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A cable inductance of 1uH really shouldn't affect a 50uH tweeter very much. 😕
The earthing (aka common-mode) problems with a 5m unbalanced cable don't look huge either.
So unless you have a very weird factor coming into play here, I think most of us are stumped by this. But it's made us think. 🙂
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This whole argument about the characteristic impedance of cables is irrelevant to the original poster's question about the use of cable lifters.
He has not changed his cables but has simply raised them a few inches on blocks and concluded there is a difference in the sound he now hears, nothing more than that.
Whether that stacks up with a common sense view of what is rational or not is open for the individual to decide, but if nothing has changed (apart from a few inches of elevation) .......then nothing has changed but one's perception.
C.M
He has not changed his cables but has simply raised them a few inches on blocks and concluded there is a difference in the sound he now hears, nothing more than that.
Whether that stacks up with a common sense view of what is rational or not is open for the individual to decide, but if nothing has changed (apart from a few inches of elevation) .......then nothing has changed but one's perception.
C.M
I guess if one had an aeroplane and decided to put it on high wooden blocks (lifters) rather than leave it on the ground it could be thought of a flying experience in itself.
The mind is easily tricked into believing things without having a reference to rely on.
C.M
The mind is easily tricked into believing things without having a reference to rely on.
C.M
This is not a topic relevant to common sense - the latter is quite useless here, I'm afraid.
Regarding a few inches of elevation - to go to extremes, it can make an enormous difference in an electrical sense ... someone hovers his bare foot a couple of inches over a rail system's third rail, then decides to reduce the clearance to nothing ... 🙂
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