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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, 03:23 AM   #31
subwo1 is offline subwo1  United States
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Quote:
How is it exactly that a speaker is an AC generator but an inductor isn't?
An inductor is passive and is only able to store energy in a magnetic field (normally temporary). A speaker is a mechanical system which can actively convert the mechanical energy of a moving voice coil into electricity as the coil cuts through the lines of magnetic force (from a permanent magnet) during this physical motion. When the speaker is producing a sound, it is a motor, when it is moving in response to sound or simply pushed with fingers, say, it is a generator. The modeling with passive components is good in the standard use of the speaker, when driven by an amplifier, and that is what we care about here.
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Old 23rd April 2004, 04:50 AM   #32
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by subwo1
An inductor is passive and is only able to store energy in a magnetic field (normally temporary).
Last I looked, loudspeaker drivers were passive as well. And they also store energy.

Quote:
A speaker is a mechanical system which can actively convert the mechanical energy of a moving voice coil into electricity as the coil cuts through the lines of magnetic force (from a permanent magnet) during this physical motion.
Actively convert? What's the active element in a loudspeaker driver?

Quote:
When the speaker is producing a sound, it is a motor...
How does calling it a motor change its fundamental electrical behavior?

Quote:
...when it is moving in response to sound or simply pushed with fingers, say, it is a generator.
But we're not talking about it moving in response to sound or being pushed with fingers. We're talking about it being driven by an amplifier.

But if you want to look at it in that context, then would you also call an inductor which is being impinged upon by a time varying magnetic field a "generator" as well?

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The modeling with passive components is good in the standard use of the speaker, when driven by an amplifier, and that is what we care about here.
Sure. So if we're talking about it being driven by an amplifier, then where does the "AC generator" come into it?

se
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Old 23rd April 2004, 05:10 AM   #33
PMA is offline PMA  Europe
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OK. Here is the more complex model, acoustical side included. But nothing is changed from the point of view of the amplifier.
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File Type: gif a1speaker.gif (6.3 KB, 391 views)
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Old 23rd April 2004, 05:15 AM   #34
peranders is offline peranders  Sweden
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First cycle distortion - Graham, what is that?
Nice explanations (but I don't understand a thing....) but how can you measure this new distortion and how does is relate to music reproduction? It seems that noone knows really what Graham is talking about.
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Old 23rd April 2004, 05:46 AM   #35
andy_c is offline andy_c  United States
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Oh, you actually want to measure it? Well, there's always a troublemaker in every crowd .

I'm thinking that you might be able to find a function generator capable of tone bursts with controlled start phase (set to zero) and very low "first cycle distortion", with an external trigger pulse to start the tone burst. Then a computer controlled digitizing scope or waveform digitizer, whose sampling was started by the same pulse that triggered the tone burst, might be used. The digitized data might be sent to a computer over the GPIB bus. The computer program that controls all this could also compute the FFT of the incoming samples and display them on a graph.

I don't really know if a suitable tone burst generator exists, nor have I tried to figure out how many bits of resolution you'd need for the sampling. I'm just dreaming here. But I did work for about 10 years in computer controlled RF/microwave test equipment, so it's not total BS, only partial.
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Old 23rd April 2004, 06:03 AM   #36
PMA is offline PMA  Europe
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Quote:
Originally posted by subwo1

An inductor is passive and is only able to store energy in a magnetic field (normally temporary). A speaker is a mechanical system which can actively convert the mechanical energy of a moving voice coil into electricity as the coil cuts through the lines of magnetic force (from a permanent magnet) during this physical motion. When the speaker is producing a sound, it is a motor, when it is moving in response to sound or simply pushed with fingers, say, it is a generator. The modeling with passive components is good in the standard use of the speaker, when driven by an amplifier, and that is what we care about here.
Oh no. The resonant circuit in the speaker electric diagram is really the what you are speaking about (exchange of the energy).
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Old 23rd April 2004, 07:34 AM   #37
traderbam is offline traderbam  Canada
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Quote:
What's the active element in a loudspeaker driver?
The permanent magnet.
Quote:
would you also call an inductor which is being impinged upon by a time varying magnetic field a "generator" as well?
Yes. That's how a generator works.
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Old 23rd April 2004, 07:38 AM   #38
peranders is offline peranders  Sweden
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First cycle distortion - Graham, what is that?
Quote:
Originally posted by andy_c
Oh, you actually want to measure it? Well, there's always a troublemaker in every crowd .
I still say that this distortion isn't a separate phenomenia (hard to spell).

It's just step response
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Old 23rd April 2004, 07:50 AM   #39
phase_accurate is online now phase_accurate
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The problem with this kind of distortion has nothing to do with either:

Feedback
driver Back EMF
FFT behaviour

It is simply generated by expecting the wrong outcome of the simulation. A simple lowpass would generate the same kind of distortion with the same type of signal.
The signal in question is NOT a SINUSOID but the multiplication of a Sinusoid by a step function. Every lowpass will definitely distort such a signal, like every filter would distort a dirac pulse !
The signal in question and the Dirac pulse have something else in common: The do NOT EXIST IN THE REAL WORLD !

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Old 23rd April 2004, 08:02 AM   #40
jan.didden is offline jan.didden  Europe
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Yeah! Nothing beats knowing what you are talking about....

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