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First cycle distortion - Graham, what is that?
First cycle distortion - Graham, what is that?
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Old 23rd April 2004, 08:35 PM   #81
subwo1 is offline subwo1  United States
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But all of those elements are passive. Not active. The only active elements involved here are the tubes and/or transistors in the amplifier. Everything else is either resistive or reactive.
Your definition of active is more specialized than mine.

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But that's ultimately just energy being returned to the system. Not from an external energy source.
Your definition of the electronic component is broader since the voice coil is what I was considering.

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You mean like how the collapsing magnetic field around an inductor is being converted back to electrical energy?
The magnetic field is electromagnetically part of the inductor which is an electronic component considered a normal part of the electrical circuit while the cone is not part of the circuit.

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Which takes me back to my previous question. How is it exactly that a speaker is an AC generator but an inductor isn't?
An inductor can only convert a finite amount of stored energy back into electricity while a motor like a speaker used in reverse can do it indefinitely. A battery is not even considered a generator since its energy is only stored also.

I propose we retire this line of discussion.
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Old 23rd April 2004, 10:01 PM   #82
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by traderbam
By that definition a speaker isn't "active". But it does rely on a permanent magnet which is an "external" field source as opposed to an external voltage source as it were.
But it isn't active. Which was my point.

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In any case I think your questions are about what the differences are between motors, ac generators and inductors.
Actually my questions are about what I asked originally. Which was:

What's the fundamental difference between the back EMF of the loudspeaker and the back EMF of any other RLC resonant circiut?

The answer it appears, disregarding issues wholly irrelevant to the issue of the supposed "FCD" such as flicking the cone with your finger, is "none."

Electrically, the fundamental behavior of a loudspeaker is that of an RLC resonant circuit. The back EMF of the speaker is fundamentally no different than the back EMF of an RLC resonant circuit.

se
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Old 23rd April 2004, 10:08 PM   #83
millwood is offline millwood  United States
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Originally posted by Steve Eddy
Electrically, the fundamental behavior of a loudspeaker is that of an RLC resonant circuit. The back EMF of the speaker is fundamentally no different than the back EMF of an RLC resonant circuit.

se
I think that's correct.

a 2ndary issue, one that some of us seemt o be arguing for, is that the RLC circuit does not represent the exact behavior of a real speaker in every circumstance. For example, the speaker emf may deviate fromt hat of the rlc circuit when it is overdriven.

That is true. But end of the day, the back emf from an rlc circuit is foundamentally the same as the back emf from a speaker. That seems to be the concensus here.
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Old 23rd April 2004, 10:09 PM   #84
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by subwo1
The magnetic field is electromagnetically part of the inductor which is an electronic component considered a normal part of the electrical circuit while the cone is not part of the circuit.
Since the cone is fixed to the voice coil, that makes the cone decidedly part of the circuit.

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An inductor can only convert a finite amount of stored energy back into electricity while a motor like a speaker used in reverse can do it indefinitely.
It can only do it indefinitely if you indefinitely keep putting energy into the system. Same holds true for an inductor.

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Old 23rd April 2004, 10:25 PM   #85
fdegrove is offline fdegrove  Europe
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Hi,

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Since the cone is fixed to the voice coil, that makes the cone decidedly part of the circuit.
The circuit would be exactly the same without the cone.

Cheers,
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Old 23rd April 2004, 10:27 PM   #86
fdegrove is offline fdegrove  Europe
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Hi,

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It can only do it indefinitely if you indefinitely keep putting energy into the system. Same holds true for an inductor.
And if you pull the plug all active circuitry becomes rather passive all of a sudden...I wonder why...

Cheers,
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Old 24th April 2004, 12:53 AM   #87
john curl is offline john curl  United States
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You folks are really confusing me. First, a loudspeaker is NOT just an inductor. In fact, that is a very small part of the speaker circuit. The moving loudspeaker is a resonant SYSTEM all of its own that CAN be represented by an 'equivalent' R, L, and C model. Also, loudspeakers are microphones and pretty good ones at that, so any sound in the room can be put back into the loudspeaker an emf generated across the speaker terminals. What about a resonant cabinet? What about a port?
Loudspeakers may be 'simply' modeled as an equivalent RLC circuit, but that is not their complete response in the back EMF.
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Old 24th April 2004, 01:34 AM   #88
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by john curl
You folks are really confusing me. First, a loudspeaker is NOT just an inductor.
No, they're not. Who said they were?

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In fact, that is a very small part of the speaker circuit. The moving loudspeaker is a resonant SYSTEM all of its own that CAN be represented by an 'equivalent' R, L, and C model.
Yes. Because that's how it appears electrically to the amplifier.

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Also, loudspeakers are microphones and pretty good ones at that, so any sound in the room can be put back into the loudspeaker an emf generated across the speaker terminals.
Sure. But what has that to do with the issue of FCD?

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What about a resonant cabinet? What about a port?
Those also model as RLC equivalents.

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Loudspeakers may be 'simply' modeled as an equivalent RLC circuit, but that is not their complete response in the back EMF.
Sure, the model doesn't account for microphonics, but then that hasn't anything to do with the FCD issue.

Remember, Graham's plot illustrating what he was referring to as FCD used an idealized loudspeaker model using nothing but ideal RLC components.

What prompted me to reply here was this notion that the "back EMF" of a loudspeaker is somehow fundamentally different than the "back EMF" of an RLC resonant circuit, looking at loudspeaker back EMF as a voltage source driving the amplifier's output (i.e. the "AC generator" notion) rather than the reactance of the energy storage mechanism that it is.

As an aside, it's interesting to note that with a typical dynamic loudspeaker driver, the "back EMF" is greatest at the driver's resonant frequency (Fs), and at that point, current and voltage are in phase and the loudspeaker presents a purely resistive load to the amplifier.

se
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Old 24th April 2004, 09:14 AM   #89
traderbam is offline traderbam  Canada
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Sure. But what has that to do with the issue of FCD?
I'm looking for a "smilie" named "red herring" but can't find it.
1st cycle distortion doesn't bother me...it's the distortion on all the subsequent cycles that I notice.

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What prompted me to reply here was this notion that the "back EMF" of a loudspeaker is somehow fundamentally different than the "back EMF" of an RLC resonant circuit.
You seem to be mixing concepts up here. A speaker or motor or generator need not resonate at all. EMF is not a resonance effect. Resonant circuits do not have "back EMF" - this is to do with the opposition to force caused by a current flow within a magnetic field. Resonance is an entirely different thing.
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Old 24th April 2004, 04:20 PM   #90
Steve Eddy is offline Steve Eddy  United States
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Originally posted by traderbam
I'm looking for a "smilie" named "red herring" but can't find it.
Red herring? This thread is solely about FCD.

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1st cycle distortion doesn't bother me...it's the distortion on all the subsequent cycles that I notice.
Hehehe. True. But the issue here is FCD.

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You seem to be mixing concepts up here.
I don't believe I am.

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A speaker or motor or generator need not resonate at all.
But dynamic loudspeaker drivers are a inherently resonant devices.

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EMF is not a resonance effect. Resonant circuits do not have "back EMF"- this is to do with the opposition to force caused by a current flow within a magnetic field.
Back EMF is really nothing more than Lenz's Law in action and is a fundamental property of simple inductance. So a circuit which includes inductance, which includes RLC resonant circuits, do indeed have back EMF.

If you build the RLC loudpeaker model, the impedance peak at Fs is every bit as much due to back EMF as the impedance peak at Fs in a dynamic loudspeaker driver.

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