That only applies to resonances creating an impedance peak but completely ignores there are resonances that create an impedance dip. While that doesn't apply to a lot of speakers, it's not a thing you can ignore since a lot of mid domes, low fs tweeters with a back chamber and different bass enclosures have such a behaviour. There's no conpiracy, just plain physics. You might not like it but it still applies, no matter if you are agreeing to it or not.
Oh, I forgot, did you know the BL is impedance dependent? And that the BL isn't even mentioned in the page you've linked?
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Deleted member 375592
This is what I do 100% agree with. I do not see how the current drive can be applied to woofers, especially in ported enclosures, or to tweeters, either dome or ribbon/AMT. Even more, the current drive is of low value to many Nd drivers with little or no shorting aka Faraday ring. The current drive appears to be quite useful for some midrange, including some domes, I tried HiVi D7500. Some - but not for all. It is not a universal "cure-all".
Bl - see equation 11.5.5.
Bl - see equation 11.5.5.
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Deleted member 375592
A good example of what current drive and cone mods can do to a driver is shown here on SB16PFCR25-4. CAD36 on Solen.ca (~USD25). Here is a picture of the cone with foam tape applied:
Then you put a thin layer of expoxy glue (or whatever else you prefer). Your hand skills matter - mine are horrible. The added mass inevitably results in the sensitivity loss. The better are your skills - the lower is the sensitivity loss.
Here are H2, H3, and H5. red is voltage drive, yellow is current drive, greep is current drive with foam, cyan is current drive with foam with expoxy.
Then you put a thin layer of expoxy glue (or whatever else you prefer). Your hand skills matter - mine are horrible. The added mass inevitably results in the sensitivity loss. The better are your skills - the lower is the sensitivity loss.
Here are H2, H3, and H5. red is voltage drive, yellow is current drive, greep is current drive with foam, cyan is current drive with foam with expoxy.
I completely agre to that. The issue is, that doesn't apply to every speaker. On some, you have to realize that the amplifier principle is inferior to other (conventional) amps. That doesn't make the amp bad but you have to accept it's not an universal solution for every speaker. If you know the limits of it, it can be amazing but if you ignore it, it's possibly abysmal worse to a conventional amp, which can cope with ~98% of all speakers.
Current drive amps are a remarkable concept but if you are ignoring its limitations, it's often worse than a voltage dependent amplifier. The correct use of it is imperative. And its use is a lot more limited than a 'conventional' amp. It's great if you can use it to its peak performance, most instances will not profit from the amplifier principle though.
Interesting. Not long ago, I was listening to a system for which the bass drivers were EQd to a way-too-low frequency (as if getting 15Hz output from a 10" driver was realistic). When sound effects got down there, I didn't hear the sound of voice coils crashing but instead heard a modulated "shhh" sound from the drivers. I attributed that to air maybe getting squeezed out of leaks in the drivers or box. Might that have instead been Barkhausen noise?
(The EQ has since been corrected to a more realistic LF cutoff).
mikets42, can you tell me what you mean by "ESS"? I'm not familiar with that acronym.
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Joined 2003
Flattening the impedance curve is generally already done by adding more hardware and complexity, such as shorting rings, and oversized magnets to strongly saturate the iron pole pieces.
In addition, the dampening effect from shorting rings is hard-wired and 'dumb' in the sense that it cannot be unplugged if you want active control. So the whole approach goes against the trend to simplify hardware, and refine the control techniques up-stream (e.g. with electronics and software).
Well no, it's not. I speculated in another thread some time ago, that high and low frequency behaviour is kind-of opposite in the voice coil.
Anywhere near the bass resonance, expect the central active part of the coil to 'hog' voltage, because the mechanical impedance generates voltage mostly in the middle where the coil's interaction with the magnet is greatest. Similarly, I would expect the current to also have local slopes, because the electrons are undergoing acceleration. (It's not as simple as marbles in = marbles out!) With voltage control there's electro-mechanical feedback that automatically generates impedance peaks / limits the current, which is no bad thing.
At higher frequencies however, inductive reactance starts to become the dominant source of impedance. Since the inductance can be modulated in response to current and coil displacement relative to the iron core, it's favourable to swamp that with a much larger, linear impedance in series.
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Uhm, no. In dynamic speakers you want to avoid saturation since that creates unlinearities and distortion. Oversized magnets are used to extend the magnet field strength above the technical Xmax. Or to keep the extend of power compression down.
No. The main reason to have shorting rings is to keep distortion down and keep the induction of the coil down, equally to extend the high frequency extension as to keep the distortion down. The trend to simplify hardware doesn't have anything to do with it since dsps and amps are so much cheaper nowadays and are so easily able to compensate for some drivers shortcommings that often the dsp is used to compensate for too cheaply built drivers. Shorting rings are an excellent way to keep the distortion down but 'modern' speakers are often built that cheaply as possible because 'the dsp will fix it anyway'.
While that's true, it doesn't make the current source amplifier perform any better. The goal is to keep the impedance rise on the top end of a driver low since that introduces distortion. A current source amplifier does not have an inherit advantage there since speakers are often designed to avoid that problem, be it by using drivers with shorting rings, pole core covers or by just using more ways and these drivers simply not being used in any critical range.
I agree. It's just that a current source amplifier isn't the only answer to that. Hundreds of thousands subwoofers and full range speakers behave greatly on existing voltage source amps. Yes, badly built speakers do not but they don't perform any better on current source amps. You can't compensate for horribly designed speakers by the amp design. That's neither the the right way to use them nor what's their duty.
Higher frequencies usually do not benefit from current drive since neither mid nor high frequency drivers are used at their resonance, which is the main argument for current drive. And since impedance compensation is a thing for decades, that's not even an argument, it makes current source simply obsolete, even tube amps can easily drive these without having impedance dependent 'bad behaviour'.
Current drive amps can perform amazingly. But that's only an advantage if your speaker is performing well on the needed characteristics. Most speakers are designed to perform best on voltage source amps, that means your setup will only preform reasonably if your whole chain (or at least dsp-amp-speakers) are perfectly set up for that purpose. If they are not, in 99,9% of the cases, a voltage source amp will perform a lot better.
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Deleted member 375592
Yes, they do, and yes, you can. See Dayton MB620 above, for example, as well as others. Moreover, some speakers on the current drive outperform most if not all voltage-driven speakers. I have shocked enough of my friends on auditions, and have seen their reactions. They called back saying that they no longer can listen to the high-end systems. I can (and did) support all my statements with reproducible hard-data proofs.
If you don't agree, please argue - am I all attention, but please provide supporting hard-data facts, such as objective reproducible measurements - not opinions nor beliefs, however strong they are.
No, it doesn't. If you saturate the magnetic gap, the VC exceeding the usual linear excursion will create a lot more distortion! That's why modern drivers are not designed to have a saturated magnet gap but to keep the magnet field on a very controlled mildly deviating intensity.
The maximal saturated magnetic gap was an issue of the late 70s horn drivers and thanks to god the compression drivers evolved from that!
If you want to use your horns above 3-4k and insist of having a supertweeter above 5-8k, that's probably a paradigm you want to follow but since modern CDs are capable to cover 3-5 octaves, that's thankfully a chapter of the past.
ICG / mikets42, observation from side if you don't mind:
So, both of you seem to be talking about bit different things while roughly on same page. Thought to point this out to prevent unnecessary word fight.
- ICG seems to be talking whole speakers driven by current drive amp is not good, because the frequency response gets worse than the same speaker driven with voltage amp.
- mikets42 is showing data how a single driver acoustic response gets way better distortion wise, and doesn't take stance on how a whole speaker should be assembled.
So, both of you seem to be talking about bit different things while roughly on same page. Thought to point this out to prevent unnecessary word fight.
Hi, I think main argument for current drive is to lower driver motor distortion getting into acoustic domain for the whole bandwidth, what ever that is for any given driver in any application. I think it's misnomer to attribute effects of current dirve to the amplifier, because all effects in acoustic domain are solely effect of high series impedance with the driver, so that driver doesn't emit it's own distortion or affect current to equalize acoustic response, nothing to do with the amp, everything to do with high series impedance with the driver.
Everything in current drive is how the driver itself affects circuit current, which all goes through voice coil and affects acoustic response, including the frequency response changing vs. voltage drive. In voltage drive the driver equalizes it's own response because it can reduce circuit current with it's effect on circuit impedance. So, in current drive situation, with high series impedance with driver, the driver cannot affect circuit current much at all, so it cannot equalize acoustic response or dampen itself electrically in the main resonance, so the frequency response is natural as it should because if driver can affect it's response it will emit all issues with it's electrical parameters changing with excursion and whatnot, hysteresis / barkhausen. The frequency response looks bad because ~all drivers are manufactured to make flat frequency response with ~0 impedance between it's terminals, the drivers are relied to manipulate circuit current to make certain acoustic response. It's the current through voice coil that is acoustic response basically, everything that happens in current appears in acoustic domain. Bad frequency response is no problem though, as we can equalize the response by manipulating current with the amplifier itself, with DSP. So, any current drive problem is just problem with a person designing a system, it's just another tool for speaker builders toolbox to utilize when appropriate.
I'm not sure current drive has any benefits on driver main resonance, perhaps it has, but great downside is need to add some extra acoustic / mechanical damping to the system, not sure if DSP is enough for the main resonance and some damping is needed in one form or another. Electrical damping is just way easier, so voltage drive seems very logical for driver resonance, but above that current drive wins hands down as shown by mikets42 data in this thread, and data elsewhere since way back.
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It's easy to impress people by showing them current drive depending speakers. But so does well developed voltage depending speakers, as long as you deploy them into applicable situations. Yes, current source amls can deliver great performance but so do voltage depending ones.
It's amazingly easy to argue on that. The damping factor increases with rising impedance on voltage source amps while it doesn't on current source amps since the feedback can't improve it. It's the inherent flaw of the current source amplifiers. Don't get me wrong there, current source amps can be amazing if the system / speakers are designed for this but there's no general advantage of this. Current source amps are deeply dependent on the speakers (even if the principle is aimed to the exact opposite) but physical circumstances (ie available amps) makes it impossible to fulfill the requirements except in very low spl situations.
Electrical damping has nothing to do with the amplifier beyond what output impedance it has, what impedance it presents between driver terminals as load for back EMF. The driver dampens itself if back EMF voltage can make current in the circuit, which it can in case of voltage amp which is basically a ~shortcircuit between as load for back EMF. Back EMF is voltage source in the driver and if can make current in the circuit it'll affect acoustic response.
Current amplifier has very high output impedance, which presents high load impedance for back EMF and prevents make much current at all so no electrical damping. I think it's counter productive to think about amplifiers at all, while thats the first intuition one should think it prevents to see how the driver functions, and what is the voltage and current drive hubbub all about, amplifiers have nothing to do with it except their output impedance. Replace the amplifier with ideal voltage or current source, so either short or open circuit, or use some impedance network if you want, and analyze the system from drivers perspective to see how it all plays out. It's all about circuit impedance in series with the driver, how much any disturbance to the cone (movement) can make current into the circuit, or magnetic hysteresis or possible other phenomena affecting circuit current. Any current in the circuit turns into acoustic sound.
Sorry I'm repeating the same stuff, I just see the whole voltage / current amplifier debate being a distraction and not productive at all, because it is completely irrelevant to fight about amplifiers because it's not about amplifiers but how driver can affect circuit current, and I see these kind of debates people not quite having complete picture on how it works, which makes the discussion hard as it's hard to understand how others think about the subject. Results using current amplifier and voltage amplifier are quite obvious, easily measured and simulated, which most often everyone agree on, they just think it differently why the results are like that, and then unnecessary debating starts. I'm hoping to help, get everyone on same page, see each others perspective on the subject so that constructive discussion could happen.
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That's a grave misconception, any back EMF handling is also dependent on the amplifiers inner resistance (=damping factor) - which is very bad on most current source amplifiers. To handle a 200 Ohm impedance peak, a current source amp has to be able deliver close to 60V to deliver 15W. The noise/hiss level of a horn tweeter is unbearable. And to deliver this, you need an amplifier capable of ~450W.
Excuse me but I don't see that reasonable to drive a horn tweeter. And if it's not capable of delivering the 60V, it's clipping. That can't be the solution
Yes, that's the same thing I explained above, you just think and explain it being something inside the amplifier that makes damping, while I generalize it just a resistor in place of amplifier, amplifier abstracted away so to see how the electrical damping works actually. Electrical damping works without amplifier at all, amplifier is irrelevant for driver to dampen itself via the back EMF. You can do this analysis easily on paper using basic circuit analysis, use Norton / Thevenin theorem to simplify the amplifier away, then analyze what happens when the cone moves.
You are correct that in order to deliver current to a high impedance load the voltage must be great, this is problem of the amplifier, not the driver, and here you are right this is one thing that makes using current drive amplifier problematic on driver main resonance. If you notice insanely high voltages are required, then perhaps the current drive amplifier is not right solution for that system. One could reduce the impedance peak with mechanical damping of driver resonance, which reduces voltage required to deliver the current. Key thing is, one can use any amplifier, and manipulate impedance other ways, if one wants to, to take full advantage how driver affects current and acoustic output. Getting stuck into amplifier prevents one fully utilizing this stuff.
Modern amplifiers can apparently do high voltages, so perhaps it's not too much of a problem today? Still, I'm not sure if there is any benefit from high impedance on drivers resonance.
Sorry about my posts as they contribute to word fight I mentioned earlier 😀 I just thought perhaps there is some help with my posts trying to bridge any gaps, help everyone see there is multiple ways to think about it.
ps. for compression driver, use voltage amp and put series resistor in between to get some benefits of "current drive" while simultaneously drop amplifier hiss. It makes frequency response peak at drivers impedance peak? use cap or coil to manipulate impedance further, simiultaneously dropping his and manipulating the frequency response. In addition use DSP to have full control on frequency response, while passive parts handle the impedance.
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The physics is what it it is - but you are right in one thing - a completely saturated gap will give a rising FR - this needs to be compensated with a filter - once you have this - driver end game. In a saturated gap, hysteresis disappear.
Why it is not present? Build a motor with saturated gap and see.. its not that easy - it will most probable require the addition of a field magnet.
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