It is already clear that a shorting ring will both lower inductance and raise effective resistance.
The front plate of a speaker, by virtue of being simply a hole in an otherwise continuous piece of metal, by design is in fact a shorting ring in itself. Since it also has high permeability, it both enhances the overall vc inductance, the overall flux, and dissipates because it is a shorted turn with some conductivity.
My hypothesis is that as a result of this shorted turn, the high frequency response of the speaker is compromised. That compromise will be measurable via Ls/Rs testing.
By cutting a slit through the entire front plate up to the gap OD, the shorting turn will be gone. So the hypothesized cause, that of a shorted turn, will be gone.
Testing of this new structure configuration will either prove or refute the initial hypothesis..
If it does indeed change the hf Ls/Rs characteristics, both drivers will then be sent to one of the participants in this thread for distortion measurements and possibly for audibility tests.
jn
My friend has a 30 watt IR 2-D laser, but the physical design is geared towards flat stock cutting. The depth of field is insufficient, only about 1/8th inch.
The class of laser to drop through 1/4 inch of iron scares me. Not a bad idea though.
Wire EDM would also be a good one, but the medium would probably have to be either paraffin or kerosene, as DI water may not play well with the surfaces due to rust. However, there are companies that have been able to wire EDM neo magnets, as the spark removed residue is no longer magnetic. But I suspect trying to cut iron at the same time might be a problem as the residue of iron spark discharge may be magnetic and trapped in the kerf.
jn
Velocity of the energized coil forcing time varying flux to react with pole tip and face plate, with nonlinear physical structure. Where to start?
jn
I must say that I'm surprised of this result. If this was an ideal resistor - should we not se only a linear loss in level? Why distorsion, Why FR change.
This must either be due to:
i) a non ideal resistor i.e. it has a reactive parts
ii) the driving amplifier is effected by the change in (linear?!) load
... which is it? or is it something else??
//
Divider composed of the series resistor and speaker impedance modulates the frequency response of the speaker. Nothing nonideal, nothing surprising. You can see it in every amplifier test in Stereophile. The bigger amplifier output impedance (= series resistor), the bigger deviations in frequency response. I am surprised that you are surprised 
.
.It certainly looks that way from your tests so far.
I sure hope the distortion going down isnt because the response is also. If so, there has got to be a better way.
THx-RNMarsh
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The misunderstandings out there are interesting.
I blame the measurements being used... Lowering inductance is thinking about only half of the impedance. If the effective resistance of the voice coil doubles while the inductance is going down, the plots may look like the impedance has been controlled, but it may not be the case.
Also, if the resistive increase is truly nonlinear, even less is being understood by the simple impedance/phase plots.
That is why I'm taking the Ls/Rs approach, to understand exactly what the electrical model is doing as I make physical changes.
In addition, if I can stuff a tap coil on the regular vc wind, I can use the tap signal to extract exactly what the voice coil resistance is dissipating, vs the overall dissipation including the shorting ring loss. Anyone with a good DSP setup can extract the exact losses with time that are being caused by the ring.
jn
I blame the measurements being used... Lowering inductance is thinking about only half of the impedance. If the effective resistance of the voice coil doubles while the inductance is going down, the plots may look like the impedance has been controlled, but it may not be the case.
Also, if the resistive increase is truly nonlinear, even less is being understood by the simple impedance/phase plots.
That is why I'm taking the Ls/Rs approach, to understand exactly what the electrical model is doing as I make physical changes.
In addition, if I can stuff a tap coil on the regular vc wind, I can use the tap signal to extract exactly what the voice coil resistance is dissipating, vs the overall dissipation including the shorting ring loss. Anyone with a good DSP setup can extract the exact losses with time that are being caused by the ring.
jn
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From what I've seen, skin resistance and eddy currents always shunt total impedance magnitude, not increase it. So when you compare a shorting ring to no shorting ring, you will always get lower impedance despite the increased resistive losses from skin effect. An increase in total impedance is only seen if you deliberately compare a real shorting ring with a perfectly conductive shorting ring.
Your inductive reactance may be 100 ohm, and your skin resistance 1kohm, but the skin resistance shunts the inductive reactance so your total impedance will decrease rather than increase.
If there are examples where eddy currents or skin effect increase total impedance rather than reduce it, I want to see them.
Your inductive reactance may be 100 ohm, and your skin resistance 1kohm, but the skin resistance shunts the inductive reactance so your total impedance will decrease rather than increase.
If there are examples where eddy currents or skin effect increase total impedance rather than reduce it, I want to see them.
If you examine my first inductor/copper tape test, you can see that the total resistance of the coil as seen by the meter increased very significantly with frequency while the L decreases.
The same occurred with the tweeter coil and shorting rings.
The Ls/Rs model is the best to use for these values of L and R. Do not confuse it with an Lp/Rp one, as you will go crazy trying to keep a mix between the two.
Any coil being driven with AC excitation by a meter in Ls/Rs mode, when a conductive object is introduced into the time varying field, the response of the meter will be to show Ls decreasing caused by the magnetic fields of the eddy currents, and the Rs will increase as the meter sees the loss as an increase in the system resistance. It does not see the eddy losses in parallel to the primary wire resistance.
I have re-attached the two jpegs being discussed, for clarity.
jn
The same occurred with the tweeter coil and shorting rings.
The Ls/Rs model is the best to use for these values of L and R. Do not confuse it with an Lp/Rp one, as you will go crazy trying to keep a mix between the two.
Any coil being driven with AC excitation by a meter in Ls/Rs mode, when a conductive object is introduced into the time varying field, the response of the meter will be to show Ls decreasing caused by the magnetic fields of the eddy currents, and the Rs will increase as the meter sees the loss as an increase in the system resistance. It does not see the eddy losses in parallel to the primary wire resistance.
I have re-attached the two jpegs being discussed, for clarity.
jn
Attachments
Yes and it does affect FR, a bit more pronounced on high-eff drivers.
In case you missed, as RNM posted :
- Marsh MFB ckt.pdf
- Marsh MFB_2.pdf
And Scottjoplin pointed to Rod Elliot's article on Current / Mix mode Drive.
OK. So it is not a universal cure and it has issues. Personally, I think that this kind of concentration on just one aspect of the speaker parameter overlooks more important parameters and brings more troubles than benefits. Much more complex and SOTA view is shown by Bruno Putzeys.
Kii Audio ::: electronics
Kii Audio ::: electronics
No, it is not, there are no universal cures, all distortion causes have to be tackled in parallel, like they did at Purify. Again, all this (partial) current drive can do is tackle the distortion of which the cause is impedance modulation. And this is not as far as I and others found a major consituent of driver distortion.
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The two distortion profiles are significantly and usefully different. The Marsh version shown has usefully lower distortion where it matters in the foundation tones of the music. The graphs are just one example of one 15" in a bass reflex cabinet perhaps not optimised to the Marsh amplifier. Getting rid of the normal 'double humped' bass reflex distortion characteristic in the 40-60Hz area would be of great benefit and for the price of a resistor and and some minor rewiring it's surely worth a try. Dan.
I disagree and the measurements show it is major contributor in bass region. Espec in region of LF resonance.
-THx-RNMarsh
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