The term that was being discussed was Reverse Current which is different from Back EMF.
Just because there is some back EMF in a system, doesn't mean that it is large enough to force current back into the source.
Please again read my post #8625 which is also:
http://www.diyaudio.com/forums/lounge/234829-funniest-snake-oil-theories-863.html#post4619448
"Of course there is generally no actual reverse current, that's just another audiophile myth."
For there to be a reverse current the voltage across the load must actually be greater than the voltage provided by the source.
I included the word generally because there are some rare exceptions by which there could be a reverse current.
For example, if speakers were really ignition coils with a operating set of on/off contacts points then they could generate a large voltage. More generally this would be an example of a highly nonlinear and inductive load. Speakers are relatively linear in comparison. Line level inputs are generally very linear.
Speakers are known to produce "inductive kick backs" under circumstances where they are highly nonlinear because they are heavily overdriven into highly nonlinear operation. This is not High Fidelity.
In audio, loads are generally passive and relatively linear which makes the sort of inductive kick back required to generate a voltage high enough to cause current flow back into the source, very difficult or impossible.
Some power amplifiers, particularly those used in pro audio do have clamping diodes at their output which are a kind of emergency safety valve in case they are used with speakers that are being vastly overdriven.
If the load is passive, the load either has to be exceptionally nonlinear (such as having a set of contact points embedded in it) or contain its own source of energy.
Understanding speaker impedance curves helps explain this. Actual hands-on experience, even as a hobbyist can help. Speakers are reactive, but generally the reactance is limited to +/- 180 degrees and there is generally a significant resistive component. They are thus linear enough and lossy enough that the kind of reactance and nonlinearity required for creating an back EMF that is greater than the applied signal is very unlikely.
All inductors create a back EMF. This is a consequence of energy storage within the magnetic field. This is a consequence of the storage, not a result of non linearity.
All speaker voice coils will have an inductance associated with them, so will store and return energy to the source. That is how the output stage of a "B" or "AB" will be forced to run in four quadrant operation.
Power transformers connected to line but with no secondary load will draw a line current, but it will be 90 degrees out of phase with the voltage, this a consequence of energy being stored and then returned.
Nonetheless, I see no reason back EMF was invoked by soongsc in a discussion of grounding and earthing...that confused me.
ps. What is really interesting in the measurement of the inductance of large speakers is the return of energy to the driving source when the energy is actually the stored energy of the cone motion. In free air, it makes the results rather weird, and the inductance measured at and below free air resonance is terribly inaccurate due to the returned motional energy. A better method of measurement of the VC inductance is to place the cone face down to get as close to locked coil measurement. To get the absolute accurate coil inductance while it is in the gap requires filling the gap with epoxy...not on my woofers... Same goes for the frequency dependent resistance of the VC as a result of gap forming metal eddy losses. That unfortunately, eliminates measurement of the motional resistive eddy losses (drag losses), as well as inductive shedding due to coil motion through the gap..
John
All speaker voice coils will have an inductance associated with them, so will store and return energy to the source. That is how the output stage of a "B" or "AB" will be forced to run in four quadrant operation.
Power transformers connected to line but with no secondary load will draw a line current, but it will be 90 degrees out of phase with the voltage, this a consequence of energy being stored and then returned.
Nonetheless, I see no reason back EMF was invoked by soongsc in a discussion of grounding and earthing...that confused me.
ps. What is really interesting in the measurement of the inductance of large speakers is the return of energy to the driving source when the energy is actually the stored energy of the cone motion. In free air, it makes the results rather weird, and the inductance measured at and below free air resonance is terribly inaccurate due to the returned motional energy. A better method of measurement of the VC inductance is to place the cone face down to get as close to locked coil measurement. To get the absolute accurate coil inductance while it is in the gap requires filling the gap with epoxy...not on my woofers... Same goes for the frequency dependent resistance of the VC as a result of gap forming metal eddy losses. That unfortunately, eliminates measurement of the motional resistive eddy losses (drag losses), as well as inductive shedding due to coil motion through the gap..
John
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Which is of course, a consequence of the tribo-electric effect of a gas flowing out of an orifice..
Ya can't win, I tell ya!!
Oh, almost forgot..Isolated Receptacles is NEC 250.146(D).
John
ps. What damping factor thread?
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You started out with a pretty accurate and succinct explanation of DF:
http://www.diyaudio.com/forums/solid-state/287072-damping-factor-explained-not.html#post4620228
"I find it easier to view DF as an impedance in series with the speaker. But that doesn't help explain to the layman..."
And while we are into correct statements from that thread this one is also very good:
http://www.diyaudio.com/forums/solid-state/287072-damping-factor-explained-not-2.html#post4620302
"Yes. This is partly why the impedance of a speaker varies with frequency."
Always good to see your explanations John. Back EMF got into the discussion when someone posted a link for cables that prevent reverse current. But back EMF could also return current through the ground depending on the direction of cone movement.
Regarding loudspeaker inductance measurement, Dr. Klippel does give interesting results from his measurement system. But your explanation also gave me an idea for a simple jig to hold the cone in place.
One thing I have not totally figured out is that there was a time when smoothing speaker impedance created better results sonically, currently working on amplifier does seems not always true. So this is quite confusing.
edit: the words "not clear" means I don't understand...
As well, "reverse current through the ground" is not clear.
I find that many of the white papers...well, actually much of the explanations out there... really shred grounding, bonding, emf, reverse current...to a pulp.. it makes understanding what is being said rather difficult.
It also doesn't help when explanations which try to explain emf as non linear and inductance miss the mark entirely as well.
Given the complexity of the real problem, it's important to go back to the start and understand the nature of the beast..most people out there, including engineers and technicians, don't have a really good grasp on inductance and magnetic energy storage.
I blame that on history, we've all been brought up on vacuum tubes...
I'm reminded of a recent medical question asked of my wife.....when did you give up smoking....
Answer: Before you were born...
John
Since the discussion centers around AC signals, it's not clear what is meant by "preventing reverse current".
As well, "reverse current through the ground" is not clear.
I find that many of the white papers...well, actually much of the explanations out there... really shred grounding, bonding, emf, reverse current...to a pulp.. it makes understanding what is being said rather difficult.
It also doesn't help when explanations which try to explain emf as non linear and inductance miss the mark entirely as well.
Given the complexity of the real problem, it's important to go back to the start and understand the nature of the beast..most people out there, including engineers and technicians, don't have a really good grasp on inductance and magnetic energy storage.
I blame that on history, we've all been brought up on vacuum tubes...
I'm reminded of a recent medical question asked of my wife.....when did you give up smoking....
Answer: Before you were born...
John
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I'm not claiming any special expertise here (other than usual EE qualifications), but the safety ground is for safety. It is necessary for insurance and can be needed in some situations also for continuing lifespan.
Safety ground can, however, cause problems with ground loops in unbalanced cabling in audio systems. I did some brief numerical analysis (in an example case) about it here in a blog, along with a way to design unbalanced inputs to eliminate or strongly reduce the problem. If interested, please see:
http://www.diyaudio.com/forums/blogs/bwaslo/1309-ground-loop-noise-why-what-you-might-do-about.html
A very similar setup can be done for typical "totem-pole" type inputs, I keep meaning to add that to the blog with another example, but time has been tight....
Safety ground can, however, cause problems with ground loops in unbalanced cabling in audio systems. I did some brief numerical analysis (in an example case) about it here in a blog, along with a way to design unbalanced inputs to eliminate or strongly reduce the problem. If interested, please see:
http://www.diyaudio.com/forums/blogs/bwaslo/1309-ground-loop-noise-why-what-you-might-do-about.html
A very similar setup can be done for typical "totem-pole" type inputs, I keep meaning to add that to the blog with another example, but time has been tight....
WTF has that got to do with what I wrote? You need to try sighted reading. I'm afraid double blind just doesn't work, as you amply demonstrate time and time again.
And I just love your inference that a love of experimentation implies that an individual is untrainable. That's an Arnyworld classic. You love condescension so much just can't help yourself. At this level it has to be categorised as an OCD.
Bonkers.
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This can be done and is done without resorting to separate ground spikes...
Tony Waldron's EMC rants are interesting on this but cant find them, the usual site is down.
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One reason I have always been taught is the fact that while current always follows the path of least inductance, the actual path varies according to frequency, so lower frequencies prefer the path of least resistance and as the fre2quency increases it moves to the least inductive path and so on. With audio interconnects and other single ended connections that rely on a co-ax cable, the shield is often the problem, being more resistive in comparison to the systems earth connections (often large gauge wire) thus lower frequencies especially those associated with mains based liner power supplies (and the mains frequency) will follow the earth connection path creating a huge loop and coupling where you don't want it to couple and creating hum. Using a system wide star earthing just makes this problem worse. Separate and control paths with bonding with allow resistance to control where loops are and to minimise unknown loops sneaking in is one way... I refer to Henry Ott, Ralph Morrison my self.
Totally agreed.
The counterpoint is that ground rods are highly variable in their performance, and could be the weakest link in the system. This may be a justification for separate ground spikes for the general ground and the technical ground.
OTOH, the best solution is to have one really good earth ground. It is all you need.
It was a great opportunity to obtain yet another demonstration an immature mind's melt down, of total childishness and complete inability to interact well with mature humans, not to mention being utterly condescending.
The annals of human psychology suggest that people who are overwhelmed with themselves are highly attracted to subjectivism and more particularly solipsism, because it gives them the control over the universe that they need.
In contrast, many of us are quite happy to be constrained by the laws of physics and polite conversation.
Sure that wasn't impedance?
I've looked at a number references about grounding just lately to make sure my thinking was refreshed. They pretty consistently said impedance, which IMO makes this statement a better generality.
arnyk said:
Am I the only person to see the faintest hint of discord between these two statements in the same post?arnyk said:
The big discord might be seen in posts by people who are supposedly totally uninvolved but feel compelled to become involved.
OTOH with all the aliases and phoney names around here, there may be some direct involvement.
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