D
Deleted member 375592
These are the questions I would love to find answers to:
1. Why is the drivers' efficiency so low, about 1%? Where does 99% go?
2. The shorting coil current brings direct heat losses as in transformers with secondary shorted. How good is this heat for Nd magnets?
3. How much is the "slightly" lower sensitivity? In what frequency regions?
4. If the shorting ring is a kind of internal feedback, can it be done externally? What sensors would we need, where, and how?
5. For voltage drive with low Vcc/Vee - yes, sure. How much sense does the shorting ring make for current driving, modern parts, and DSP eq-ing?
1. Why is the drivers' efficiency so low, about 1%? Where does 99% go?
2. The shorting coil current brings direct heat losses as in transformers with secondary shorted. How good is this heat for Nd magnets?
3. How much is the "slightly" lower sensitivity? In what frequency regions?
4. If the shorting ring is a kind of internal feedback, can it be done externally? What sensors would we need, where, and how?
5. For voltage drive with low Vcc/Vee - yes, sure. How much sense does the shorting ring make for current driving, modern parts, and DSP eq-ing?
Two drivers on one channel current-drive amp? Parallel? = Barkhausen
Low range in voltage drive? = Barkhausen
Class D with cored output inductors outside the feedback loop? = Barkhausen
Best regards
Bernd
1) It is the poor coupling (impedance) between the membrane and the air that is the culprit - not so much the motor. Thats why horn exists. 99% becomes heat.
2) Not great per see but the how much heat really... the equivalent to the distortion reduced... i.e. << a % ?
3) ?
4) Just needs a complete model of the non linearity as a function of V, I , temp, time and frequency... 🙂 now let the DSP do its work.
5) ?
//
2) Not great per see but the how much heat really... the equivalent to the distortion reduced... i.e. << a % ?
3) ?
4) Just needs a complete model of the non linearity as a function of V, I , temp, time and frequency... 🙂 now let the DSP do its work.
5) ?
//
D
Deleted member 375592
After quite a bit of time spent on consideration of your arguments, I came to the conclusion that I was mistaken and you are absolutely right. Thank you!
D
Deleted member 375592
@TNT 1) I remember this argument... but at some point in time, I realized that it does not make much sense to me. There is no energy loss at the low-Z/high-Z boundary, right? You indeed need less energy exciting lesser air mass, same as driving on flat vs driving up the hills. Your engine's potential max power is not being used... what do I miss?
It's speculative, but I can try...
It sets up a parallel current path, so it competes against what current-drive tries to achieve, kind-of undermining it. I think there's some overlap in the benefits, but also some either-or choices that have to be made.
A copper sleeve reduces inductance, so the amount of amplitude modulation when multiple tones play simultaneously also gets reduced. There could also be a linearising effect, similar to using an underhung coil, because a copper 'shield' can be designed to extend the displacement range where mechanical braking is linear.
However, there's Barkhausen noise, and related hysteresis effects. And it seems to me that eddy currents in the "secondary" copper will dilute the linearising effect of a high series impedance.
In this was true, could a device/contraption/modification be made that would improve the sensitivity around 10-20KHz for an ordinary dome tweeter, with a flat faceplate from say ~94dB/W/m @10-20KHz eg. BlieSMa T34Bwith (34mm dome with 104mm flat faceplate)… to 107 dB (33% efficiency)
I'm not asking for 100% efficiency (112 dB/W/m)
I'm not asking for 100% efficiency (112 dB/W/m)
Last edited:
Cabinet volume ~400L.
Horn loaded 15" woofers x2
Horn loaded 10" midranges x2
Horn loaded compression driver x1
Released in 1982:
Datasheet:
The approximately half-metre centre-to-centre distance between the driver axes is the same old issue that will produce comb filtering at any listening angle that is not perfectly aligned with the angle at which the crossover overlaps are tuned.
For a 1kHz XO frequency and allowing a 90° phase shift, the offset in the Z direction is 343m / 1000 / 4 = 8.575cm.
Using magic, this works out at a maximum listening angle of (approx.) 16° off-centre, for a modest 30cm distance between the drivers. All that "pro" audio c**p about 60x90° "coverage" is starting to grate.
On top of that the horn diffraction resonances are usually poorly managed, because most designers seem to have tunnel vision, over-focusing on the "official" horn segment going from throat/phase plug to the mouth, while ignoring the de-facto continuation of the horn as it envelops the speaker enclosure.
For a 1kHz XO frequency and allowing a 90° phase shift, the offset in the Z direction is 343m / 1000 / 4 = 8.575cm.
Using magic, this works out at a maximum listening angle of (approx.) 16° off-centre, for a modest 30cm distance between the drivers. All that "pro" audio c**p about 60x90° "coverage" is starting to grate.
On top of that the horn diffraction resonances are usually poorly managed, because most designers seem to have tunnel vision, over-focusing on the "official" horn segment going from throat/phase plug to the mouth, while ignoring the de-facto continuation of the horn as it envelops the speaker enclosure.
Last edited:
1. Acoustic domain is no different than electric, power is only developed in the real (resistive) part of the load impedance. Even with a loss-less motor and suspension overall conversion efficiency is low at a few % max, unless horns are used.
2. While the ohmic losses in the shorting ring do exist, they are orders of magnitude below the losses of the voice coil proper. Nd is available in different heat resistance classes and proper drivers use Nd that can tolerate more than enough heat.
3. ???
4. Yes. The shorting ring creates an opposing field to counteract the field modulation in the magnetic circuit caused by the voice coil field. And thus it mainly works for higher frequencies. But it can be replaced with a driven stator coil that even works at LF & DC. Some PA Driver from 18sound offer a stator coil. And then you have field coil drivers.
In both cases, driving them with a properly sized fraction of the VC's current does the trick sufficiently, making BL(i)=const.
5. Stabilizing the magnetic circuit is a beneficial for current drive as it is for voltage drive. The main idea of current drive is to avoid the additional distortion from the modulation of the voltage-to-current transfer impedance (the position-dependent static VC impedance) in voltage-drive mode, and by this also removes BL(temp) aka power compression and de-alignment, It cannot help for BL(x), BL(i) and several other distortion mechanisms.
D
Deleted member 375592
3. Often stated "adding shorting ring results in slightly lower sensitivity". I have not seen a reference to experimental data showing what "lower" means. 0.2 dB? 2dB? 20dB? It shall depend on the type, mass, and geometry of the shorting ring too.
There is a well-known formula for efficiency: ~Fs^3*VAS/QES, which can be reformulated in several ways. There are quite a few simplified interpretations of these formulas which may be misleading. There are also works like "Maximum Efficiency of Compression Drivers" by D. B. (Don) Keele, Jr. and others discussing nominal and true efficiency, and arguing that true efficiency 100% can be approached. None of them, AFAIK, mention shorting coils.
Back in the 70s, when amplifiers were of much lower power, the drivers were quite a bit more efficient. It seems that the current "status quo" design of drivers is the result of evolutionary development with many trade-offs taken along the road, both explicit and implicit. I wonder if current driving may help in changing the trade-offs towards higher real efficiency.
There is a well-known formula for efficiency: ~Fs^3*VAS/QES, which can be reformulated in several ways. There are quite a few simplified interpretations of these formulas which may be misleading. There are also works like "Maximum Efficiency of Compression Drivers" by D. B. (Don) Keele, Jr. and others discussing nominal and true efficiency, and arguing that true efficiency 100% can be approached. None of them, AFAIK, mention shorting coils.
Back in the 70s, when amplifiers were of much lower power, the drivers were quite a bit more efficient. It seems that the current "status quo" design of drivers is the result of evolutionary development with many trade-offs taken along the road, both explicit and implicit. I wonder if current driving may help in changing the trade-offs towards higher real efficiency.
Revisiting the formulae, not that math inclined, it looks like making Qes lower would increase efficiency, and Qes goes toward zero if Re goes toward zero. Perhaps superconductivity is reality within some years as technology advances very rapidly today, and even faster tomorrow. Perhaps something else also changes and it wouldn't work. Anyway, technology to rescue. Perhaps we can get rid of electro dynamic transducers even, who knows 🙂
Last edited:
This is a very very common oversimplification that stems from a mistaken interpretation of Lenz's law, which actually states that the induced magnetic field (by the shorting ring) opposes the changing of the original field and thus not the original field itself. This makes a night and day difference, and thus with AC signals, the field induced by the ring is always in 90° lag relative to the original field - not opposite to it (assuming only that frequency is yet low enough that the stray inductance of the ring can be neglected).
Therefore, the combined field even increases somewhat to begin with. How then does the field reduction come about? It happens due to the transformer action, where the image of the ring (secondary) resistance appears on the primary side, in parallel with the voice coil inductance, thus partly shorting it (hence the term shorting ring). This shunt resistance reduces the inductive impedance of the driver wherefore the voltage dropped across it and hence the magnetic field gets reduced while voltage across VC resistance respectively increases.
There is no doubt that demodulation rings -- that's their official name -- do work exactly as the name suggests, reduce the modulation of both the inductance vs. position; Le(x), and the force factor vs. current; BL(i). That's why even extreme underhung motor still profits from a demodulation means even though Le(x)=const but Le(i) is not. Another way to get there is saturated gap so it can't be modulated anymore.
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_11_Flux_Modulation.pdf
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_11_Flux_Modulation.pdf
Last edited:
Indeed. I would not be able to formulate it symbolically like some of the minds here, but I can intuit a lot based on observation. CRTs were very instructive about electron behaviour. I was taught that like charges repel each other, but most teachers never really delved into electrons actually flowing as current.
I noticed a fast stream of electrons tends to "pull" other electrons into their wake in the same direction (hence, CRT beams were basically self-focusing, and only needed relatively crude coils to control the beam angle). But the pulling only makes sense with relative motion, hence the lag.
I have the "feeling" that this thread is overblown by voltage drive mobsters.
Best regards
Bernd
D
Deleted member 375592
This picture implies the second harmonic to be the result of Le(i)... how does it agree with experimental data of the 2nd harmonic barely affected by current vs voltage drive, and the 3rd harmonic being invariant to excitation level?
Klippel is a good guy, but he is centered on sub-woofers. IMHO, the area of applicability of his approach ends at `~200Hz. Here the focus is on the midrange where the distortions commonly rise with frequency - which contradicts to and is outside of the scope of his theories.
@ETM Do I understand correctly that there is no true (in the "classical" sense) theory that explains the reduction of harmonics by shorting coil and can predict the level of distortions?
Last edited by a moderator: