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Re: Newbie view: have to be 'politically correct' to assylum insiders or beat up

Posted by Steve Eddy on November 24, 2001 at 03:39:15

In Reply to: Re: Newbie view: have to be 'politically correct' to assylum insiders or beat up posted by john curl on November 24, 2001 at 01:47:02:

Steve, you are arguing with two well experienced design engineers, who have actually contributed technical papers in the audio field. Together, Jon R and I have multiple decades of experience with speakers, amps, mathematical calculations, etc.

So? How many times do you have to be told that one's claims do not stand or fall based on how many papers they've published or how many books they have on the shelves, but rather on the validity of their claims? Why has this fundamental concept still not sunk in with you?

It is unwise to attack us, unless you can actually find some real fault in our arguments.

Which I did. And you have completely ignored it in this post, instead you dance around it by bringing up a bunch of things which have absolutely no relevance to the argument I made which proved your claim to be false. Why don't you address the argument which proved your claim false?

Once again, your claim:

Jon R. , this shows that Steve doesn't understand the underpinnings of negative feedback. Of course, negative feedback generates the correction voltage to counter the EMF of the loudspeaker, etc. Read a book, Steve.

FACT: To counter a voltage requires the application of an equal voltage of the same magnitude and polarity as the voltage you wish to counter.

FACT: Two voltages in parallel, each of the same magnitude and polarity results in a voltage of that same magnitude and polarity across them.

FACT: If an amplifier applies a voltage of the same magnitude and polarity as a voltage imposed across its output, the voltage across the amplifier's output will be of that same magnitude and polarity.

That's it, John. QED. Game, set, match. If as you claim an amplifier is applying a counter voltage equal to and of the same polarity as the voltage imposed across its output, then the output voltage of the amplifier MUST be equal to that voltage. But if the amplifier's input voltage is zero, it's output voltage MUST also be zero.

You can't have it both ways, John. The amplifier cannot simultaneously have BOTH zero volts AND some other voltage across it equal to and of the same polarity as a voltage imposed across it.

I'm sorry, but in spite of whatever papers you have written, or how much experience you've got, or how many books you have on your shelves, your claim is patently and provably incorrect. Any two voltages in parallel of equal magnitude and the same polarity will result in a voltage across them of that same magnitude and polarity.

This is BASIC ELECTRONICS, John. And anyone with two flashlight batteries, a couple of pieces of wire and a volt meter can prove this beyond any doubt.

You claim that a loudspeaker is NOT a generator, but I have proven by experiment that it is!

I claimed no such thing. I said that a loudspeaker being able to double as a microphone was irrelevant to Jon's claims as his claims were regarding only that energy input to the loudspeaker by the amplifier.

A microphone is a generator!

Congratulations on your new discovery. Better late than never I suppose. I discovered this when I was 9 years old with my Radio Shack 101 Electronics Experiments kit whose 2" speaker doubled as a microphone depending on the circuit.

A speaker will behave as a microphone when it is moved by an outside force, or even its own inertia or resonances.

The issue was regarding how much of the energy from any cone resonances ultimately made it back into the electrical portion of the driver (i.e. the voice coil). Not whether or not it was even possible.

How do you get an inductor to be a generator?

Uh... er... um... Gee, I dunno, Wally. Maybe wiggle it back and forth between Mary Ellen's thighs, er, I mean a magnetic field? Just a wild guess seeing as I don't know much about these things.

Is it represented by your model? No, you left it out in your simplified model of a loudspeaker.

Yes. Because it's irrelevant as Jon's claims had nothing to do with energy being input to the system from external sources other than the amplifier. And in that respect, it does model the "generator" effect of the voice coil. Except that in this context, it's not actually generating energy, but rather storing it. Which is why it's modeled using energy storage elements; inductors and capacitors.

You attacked my model of negative feedback, yet there is nothing wrong with my model.

I don't recall your presenting a model. But if your model has the amplifier outputting a voltage of the same magnitude and polarity as any voltage imposed on its output above the voltage the amplifier would normally be outputting, then I'm afraid there's plenty wrong with your model, at least as it relates to typical voltage source amplifiers.

Look, just test it yourself. Take one of your preamps and with the inputs grounded, put a 1.5 volt flashlight battery across its output (er, assuming it's not capacitively coupled). If your model is correct, then you should measure 1.5 volts across the battery. You'd have to. Since if your preamp's outputting 1.5 volts if the same polarity to counter the 1.5 volts from the battery, it would be ABSOLUTELY NO DIFFERENT than if you'd simply taken another 1.5 volt battery and tied it across the first. In which case you MUST end up with 1.5 volts across them.

ps. You want the amp to act like a virtual short on a battery, not to stop current from flowing. Where did you get any other idea?

From your claim of course. Once again, you said:

Of course, negative feedback generates the correction voltage to counter the EMF of the loudspeaker, etc.

The only way to COUNTER a voltage is to apply a voltage of the same magnitude and polarity. So if the amplifier is generating a COUNTER voltage to the EMF, then it MUST be generating a voltage of the same magnitude and polarity. In which case no current would flow.

That's why "back EMF" is also called "counter EMF." Because it's of the same polarity as whatever voltage is across it. And that's why back EMF appears to the amplifier as an increased impedance. The counter voltage of the EMF causes less current to flow.

Now, if you want to amend your claim and use some term other than "counter" then that's a different matter. But your claim as it stands is simply incorrect. And I have only been addressing your claim as you stated it. If you stated it incorrectly, then don't blame me for "attacking" it.

se

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