For one, if you look at the cumulative spectrum decay, the levels of continuous sound is way higher than harmonics compared against the main signal. Unless the listening tests show data that rule out the masking effect, I would have some doubt how accurate those tests are.What are they?
Rob
The subject of operating point of magnets is well explained in the pdfs of this site:
Theory
If you go through them, please start from the first one (basic parameters…), to the second (demagnetisation curve), to the third (working point…), then to the forth (magnetic materials) and finally to the fifth (computation of permanent magnetic fields).
In them, I found a few things that cleared some misconceptions in my mind.
They may be of help to you too. *PS
Regards
George
*PS They are a good common reference point for discussion as well.
Theory
If you go through them, please start from the first one (basic parameters…), to the second (demagnetisation curve), to the third (working point…), then to the forth (magnetic materials) and finally to the fifth (computation of permanent magnetic fields).
In them, I found a few things that cleared some misconceptions in my mind.
They may be of help to you too. *PS
Regards
George
*PS They are a good common reference point for discussion as well.
The Linkwitz study is interesting but a little confusing in terminology. He is trying to model the midrange distortion he sees in 3 drivers. First attempt is related to how inductance changes with position in a symmetrical driver and a non-symmetrical driver. Distortion is much higher than expected so the model is found inadequate.
In the second look he considers the solenoidal force and the second harmonic it should generate. Again the predicted distortion is much lower than the measured. The model is inadequate.
For a third look he talks about Le vs. i but is actually looking at flux modulation: "The magnetic field strength generated by the voice coil current produces nonlinear increases and decreases of the static magnetic bias flux density B that is generated by the permanent magnet." (Emphasis mine, no mention of steel
) In other words flux modulation happens.In this case one driver has the distortion he predicts considering this particular factor. The second is 16dB better than predicted due to the presence of a shorting ring. So flux modulation creates a high but predictable level of midrange (low excursion) 2nd harmonic. A shorting ring knocks it down 16dB better than predicted.
Some of the confusion throughout this thread is that better quality woofers employ a number of improvements aimed at various performance issues. Copper caps and silver plated cores will reduce inductance and extend bandwidth. Undercut core poles will improve symmetry, reduce variation of inductance with position and reduce LF (high excursion) distortion. These are different issues.
The dominate cause of midrange 2nd harmonic distortion is flux modulation pushing the operating point around a hysteresis loop of ferrite magnet material. The shorting ring knocks it down to the point where the remaining distortion is a function of cone resonances.
David S.
Eureka! I have isolated the tiny misunderstanding we have been going back and forth about! Le vs. i and flux modulation are one and the same distortion mechanism. When flux modulates with changing values of i, the permeability of (forgive me!) *iron* changes, shifting Le.
While I fully agree that permanent magnet material of any kind has a hysteresis loop, I still think you're ignoring the elephant in the room--iron has a hysteresis loop, too! And perhaps more importantly, its magnetic permeability varies with the flux it carries.
We've both stated our positions pretty clearly, and no other magnetics gurus are entering the fray, so we may have to agree to disagree on exactly where the bad stuff happens. I say iron, you say ferrite--potato, potahto... let's call the whole thing off.
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Uh oh.
If "to err is human," then maybe to fess up is divine?
I made an unequivocal assertion a few posts ago that
Well, something in the back of my mind made me uneasy, so I went digging through a bunch of literature. And guess what? I was wrong. ..Or not entirely right, which is only a little bit less bad.
To set the record straight, yes, flux modulation does lead to Le(i) distortion, but there is a fine distinction between flux modulation distortion and Le distortion.
Following is an excerpt from a Klippel document that has disappeared from their website but still can be dug out of the Internet Archive:
http://web.archive.org/web/20050301182645/klippel.net/download/bin\AN11+-+Flux+modulation.pdf
It defines the two phenomena and outlines how their very similar effects can be untangled from one another empirically to determine which is dominant in a given test case.
If "to err is human," then maybe to fess up is divine?
I made an unequivocal assertion a few posts ago that
I even bolded it--about as emphatic as I ever get.
Well, something in the back of my mind made me uneasy, so I went digging through a bunch of literature. And guess what? I was wrong. ..Or not entirely right, which is only a little bit less bad.
To set the record straight, yes, flux modulation does lead to Le(i) distortion, but there is a fine distinction between flux modulation distortion and Le distortion.
Following is an excerpt from a Klippel document that has disappeared from their website but still can be dug out of the Internet Archive:
http://web.archive.org/web/20050301182645/klippel.net/download/bin\AN11+-+Flux+modulation.pdf
It defines the two phenomena and outlines how their very similar effects can be untangled from one another empirically to determine which is dominant in a given test case.
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Dave,
An interesting sidelight of this Klippel excerpt is how it informs what you mentioned earlier in this thread--how high-output-impedance amplification led to a reduction in measured distortion from a loudspeaker. It's forehead-slapping simple, but I missed it earlier:
High output impedance largely overcomes Le(x) and Le(i) nonlinearities in loudspeaker motors by preventing them from affecting VC current. (Flux-modulation would still manifest in this case, though.)
Hooray for current amps!
An interesting sidelight of this Klippel excerpt is how it informs what you mentioned earlier in this thread--how high-output-impedance amplification led to a reduction in measured distortion from a loudspeaker. It's forehead-slapping simple, but I missed it earlier:
High output impedance largely overcomes Le(x) and Le(i) nonlinearities in loudspeaker motors by preventing them from affecting VC current. (Flux-modulation would still manifest in this case, though.)
Hooray for current amps!
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An analolgy: In the daytime, there are lots of variety fo sounds, so you will probably not hear the footsteps of people walking around. However, at night when all is quiet, same footsteps will become very clear. If the masking effect is significant enough, hi fi and mp3 will not be very distinguishable in terms of sound quality. This can be easily tested using verious speakers of various quality. You will find some where mp3 makes no difference.Hello Soongsc
Masking ?? Can you be more specific? When I hear masking effects I think of the masking our hearing does that allows MP3 compression to "work". Is that what you mean? The masking that our own hearing does?? If so how can you get around it?
Rob
Well, in the case of most solid state amps (low output impedance, touted as "high damping factor"), electrical damping largely happens in the amp output stage. Unfortunately, though, this enables the two inductance modulation distortion mechanisms inherent in many speaker motors--those associated with VC excursion and with ferromagnetic materials' varying permeability.
But if your amp has a very high output impedance (oh no! what shall we do without a high damping factor??), then it cares little whether inductance fluctuates, and its current waveform remains undistorted.
But if your amp has a very high output impedance (oh no! what shall we do without a high damping factor??), then it cares little whether inductance fluctuates, and its current waveform remains undistorted.
Exactly. IMO, amplifier Zout should serve the parameter goals of the loudspeaker system, not the other way around. This is especially easy to accomplish in an actively crossed-over system like a lot of serious DIYers use. It really opens up new worlds of possibility for using Low-Q prosound woofers in all kinds of alignments.
I'd love to see amp manufacturers revive the Z-matic feature. The Pass F1 is one of the only such amps I've seen recently. It lets you tune the Zout by swapping values of a resistor across the outputs.
I'd love to see amp manufacturers revive the Z-matic feature. The Pass F1 is one of the only such amps I've seen recently. It lets you tune the Zout by swapping values of a resistor across the outputs.
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Bill, glad to have you back. Last time I saw you posting, we were talking about a DIY Parthenon motor; I recall that you modeled a triple-Differential Drive XBL^2 motor and remarked upon its ruler-flat BL(x) curve.Well, in the case of most solid state amps (low output impedance, touted as "high damping factor"), electrical damping largely happens in the amp output stage. Unfortunately, though, this enables the two inductance modulation distortion mechanisms inherent in many speaker motors--those associated with VC excursion and with ferromagnetic materials' varying permeability.
But if your amp has a very high output impedance (oh no! what shall we do without a high damping factor??), then it cares little whether inductance fluctuates, and its current waveform remains undistorted.
Anyway, can you clarify how a high output impedance (transconductance, current source, etc.) eliminates the B(i) variation and all excursion-based distortion factors? As far as I know, the main benefits is elimination of i(temp), which is a linear distortion source.
Yeah, those were fun times. A bit earlier, before Adire Audio published illustrations of how XBL2 worked , I used FEMM to figure out what was happening and scoop their press release.
Took a bit of a break when the fam started growing. Now I have 4 kiddos, and it's nice to escape back to audio every now and then.
With a voltage amplifier, anytime a driver's impedance varies for whatever reason, the current waveform is distorted. On the other hand, a current amplifier isn't sensitive to impedance variations, so it shuts down loudspeaker distortion mechanisms caused by varying impedance. These include Le(i) (inductance modulation due to nonlinear magnetic permeability), Le(x) (inductance modulation over excursion) and, as you mentioned, power compression due to VC impedance rising with temp.
By extension, current amplification also stabilizes several motor-related T/S parameters across the operating power range.
It does NOT treat other distortion mechanisms tied to excursion, such as Kms(x) (compliance vs. displacement) and BL(x) (force factor vs. displacement.)
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Even if we stipulate that a non-constant Le(i) is a cause of distortion, fixing i(Re), which is what high output impedance does, does not necessarily stabilize Le(i) as i is dependent on the source.
I'm not sure how to approach Le(x) being affected by fixing i(Re). Have to get back to you on that.
I'm not sure how to approach Le(x) being affected by fixing i(Re). Have to get back to you on that.
About halfway back in the thread I describe a test I did with high impedance drive. The only distortion it reduces is the midrange distortion (2nd harmonic) due to flux modulation. LF distortion mechanisms due to nonlinear spyder or surround stiffnes or nonlinear B are not effected.
Flux modulation creates a back EMF that puts a distortion in the current. running closer to constant current reduced the effect and lowers the 2nd harmonic midrange distortion.
David S.
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