Ken, apparently the resistance of the voicecoil is hardly independent of temperature. This means that when using voltage drive, this impedance varies with temperature and with voltage drive this causes distortion. This is known as thermal compression and current drive fixes this problem because the power through the voicecoil is no longer dependent on its resistance.
For headphones, I've heard the improvement is not a lot.
- keantoken
For headphones, I've heard the improvement is not a lot.
- keantoken
Any links on that subject? Would this mechanical damping be frequency selective or reduce the efficiency of the driver over a broad band? I'm trying to picture a mechanical equivalent of a notch filter tuned to the drivers Fs and Qms but I'm coming up blank.
I stand by my remarks. Your objections #180 (except zobel as shunt which we agree)
are not based upon fully though out reason. There is nothing magical "electrodynamic"
that operates only upon a fixed magnetic field and a current. Nothing gets away from
mass, inertia, breakup modes, leakage, hysteresis. What factors you don't control, are
not gonna wake up and suddenly pay attention just cause you switched to a current
mode.
Back EMF (Voltage) is a poor servo at low frequencies for sure, maybe all frequencies.
But perhaps the only simple method fast enough to work the full range. You propose
to ditch a bad servo altogether on a presumption that the cure (back EMF) is worse
than open loop disease? I think we are missing the boat that no voltage, current, nor
power guarantees a transducer will do the exact thing we ask.
Like you compare rotten apples to rotten pears, and tell me the pears ferment better.
What??? I think the whole argument is rediculous. If you gonna fix it, well then fix it...
We can start by studying how the flux in a gap shifts due to the influence of the coil,
and see that its a complex problem not easily controlled by any single variable.
are not based upon fully though out reason. There is nothing magical "electrodynamic"
that operates only upon a fixed magnetic field and a current. Nothing gets away from
mass, inertia, breakup modes, leakage, hysteresis. What factors you don't control, are
not gonna wake up and suddenly pay attention just cause you switched to a current
mode.
Back EMF (Voltage) is a poor servo at low frequencies for sure, maybe all frequencies.
But perhaps the only simple method fast enough to work the full range. You propose
to ditch a bad servo altogether on a presumption that the cure (back EMF) is worse
than open loop disease? I think we are missing the boat that no voltage, current, nor
power guarantees a transducer will do the exact thing we ask.
Like you compare rotten apples to rotten pears, and tell me the pears ferment better.
What??? I think the whole argument is rediculous. If you gonna fix it, well then fix it...
We can start by studying how the flux in a gap shifts due to the influence of the coil,
and see that its a complex problem not easily controlled by any single variable.
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Ignore an overheating voicecoil by increasing voltage to keep current constant.
That fixes the compression... But since power is voltage times current, we are
only making things run hotter, till thermal failure. And still don't address any of
the problem what happens to the other 95%+ of the power we put in a speaker
that don't come out as sound. If we only control <5%, what did the rest do?
I'm betting not all of it went straight to heat without doing other mischief.
I just don't buy that current mode fixes anything. Its just a different bag of
unsolved problems that sound slightly different than ones we are used to.
Hi,
Actually, neither. We just need to build the damping of the fundamental resonance into the mechanical system of the Driver.
The mid 30's "System Eckmiller" Studio Monitor driver did exactly this, using a number of means.
Probably because that is not is how it works.
It is possible to counteract a mass-spring systems resonance with anti resonance, but it is not an easy thing to make.
But we only want to replace the damping of the Voltage drive amplifier short circuiting the voice coil and thus the back EMF of the driver. The Voice coil is usually around 70% of the Impedance, around 6 Ohm for an 8 Ohm Driver.
If we have a driver with a slotted Alu voice coil former we could link across the slot with a resistor of around 6 Ohm to give us the same damping as if we had the Amplifier producing voltage drive.
The bottom line is that you need the way you think when you finally put the horse before the cart, instead having the horse behind the car and trying to drive backwards. But prior art is surprisingly extensive and once you realise how much easier the cart is to drive you might get somewhere.
The problem is that in current HiFi/HighEnd systems active speakers are not well regarded (for good reasons, most actives are not very good) and to get the best from current drive active systems with individual drivers having individual Amp's and equalisation as well as of course active crossovers.
I referred to a thread discussing a possible practical implementation quite a few years ago earlier on in this thread.
Ciao T
Actually, neither. We just need to build the damping of the fundamental resonance into the mechanical system of the Driver.
The mid 30's "System Eckmiller" Studio Monitor driver did exactly this, using a number of means.
Probably because that is not is how it works.
It is possible to counteract a mass-spring systems resonance with anti resonance, but it is not an easy thing to make.
But we only want to replace the damping of the Voltage drive amplifier short circuiting the voice coil and thus the back EMF of the driver. The Voice coil is usually around 70% of the Impedance, around 6 Ohm for an 8 Ohm Driver.
If we have a driver with a slotted Alu voice coil former we could link across the slot with a resistor of around 6 Ohm to give us the same damping as if we had the Amplifier producing voltage drive.
The bottom line is that you need the way you think when you finally put the horse before the cart, instead having the horse behind the car and trying to drive backwards. But prior art is surprisingly extensive and once you realise how much easier the cart is to drive you might get somewhere.
The problem is that in current HiFi/HighEnd systems active speakers are not well regarded (for good reasons, most actives are not very good) and to get the best from current drive active systems with individual drivers having individual Amp's and equalisation as well as of course active crossovers.
I referred to a thread discussing a possible practical implementation quite a few years ago earlier on in this thread.
Ciao T
Hi,
And the distortion current caused by applying a voltage to an iron filled coil is also fixed.
That happens with voltage drive too, as one simply turns up more to overcome compression.
The rest was dissipated in the voicecoil as heat. This is actually trivial to fix, in theory. Simply wind the voicecoil using a room temperature supraconductor. The voicecoil DCR becomes 0 and the power absorbed by the speaker becomes only that converted into acoustic energy.
Well, yes actually. Some is lost due to the eddy losses and related in the pole piece, which BTW is the stuff that causes most distortion in speakers in the midrange/treble.
Do you understand how an electrodynamic driver works?
No, I'm sorry, this is just not the case.
However your attitude is all too common... It was described by RAW as this:
"The true god of all was now the impotent "What Can I Do" and his dull brother "What We Did Yesterday" and his ugly and vicious sister "Get Them Before They Get Us".
Or as Mr. Fnord supposedly once said: "If you are doing its the same you always did, you are probably doing it wrong."
Ciao T
And the distortion current caused by applying a voltage to an iron filled coil is also fixed.
That happens with voltage drive too, as one simply turns up more to overcome compression.
The rest was dissipated in the voicecoil as heat. This is actually trivial to fix, in theory. Simply wind the voicecoil using a room temperature supraconductor. The voicecoil DCR becomes 0 and the power absorbed by the speaker becomes only that converted into acoustic energy.
Well, yes actually. Some is lost due to the eddy losses and related in the pole piece, which BTW is the stuff that causes most distortion in speakers in the midrange/treble.
Do you understand how an electrodynamic driver works?
No, I'm sorry, this is just not the case.
However your attitude is all too common... It was described by RAW as this:
"The true god of all was now the impotent "What Can I Do" and his dull brother "What We Did Yesterday" and his ugly and vicious sister "Get Them Before They Get Us".
Or as Mr. Fnord supposedly once said: "If you are doing its the same you always did, you are probably doing it wrong."
Ciao T
Can't we all just listen to the music...
Nitpicking like this made me quit these forums for years...I prefer spending time building illogical circuits b/c it's fun, and the music sounds great either way😉
But hey, I get it, without discussions we'd never get anywhere would we, so keep at it!
Cheers!
Nitpicking like this made me quit these forums for years...I prefer spending time building illogical circuits b/c it's fun, and the music sounds great either way😉
But hey, I get it, without discussions we'd never get anywhere would we, so keep at it!
Cheers!
Hi,
Mass & inertia are constants.
Are at least in one school of thought undesired and drivers should operate only below the breakup modes.
Mechanical hysteresis is not a necessary feature of a well designed driver, neither is air leakage (I assume that is your reference), at least not to any material degree.
Hopefully you were awake and declined to employ defective drivers?
Actually, I do not presume. I worked with back emf derived MFB in the 80's. Outside the frequency domain and generally at very low frequencies it considerably worsened objective (measured) and subjective performance. I eventually switched to electret microphones, which are not particulary linear, but much more so than back-emf.
Correct. However current drive removes one absolutely major and one minor source of performance impairment that is unneccesary, when using electrodynamic drivers (when using electrostatic drivers the reverse of course is true).
Hmm, more like comparing a slightly wrinkled and old (lain in the basement all winter?) apple to a rotten and wormy pear. One you can eat, the other is probably not even good for making perry.
Trivial to fix. Saturate the magnet system.
So far you seem to say that badly designed drivers cannot be rescued by current drive. On this we agree.
As long as you want to simply continue "business as usual" current drive does not help.
If you want to remove the major performance impairment sources in electrodynamic drivers fixing the magnetic field (hence I was mentioning it so prominent) so it is not modulated by the voice coil field (try a CCS driven fieldcoil with enough current to saturate the pole pieces toroughly) and remains constant across the linear excursion range of the driver (not trivial, but doable) AND driving the resulting driver with a modulated dcurrent (and avoiding construction details that introduce hysteresis) you will have a system that is by far more free from performance impairments than what is offered these days.
But (again, as I remarked earlier), the Speaker industry has zip interest in this kind of technology, nor does it (or much of the rest of the electronics industry) consider "High Performance Audio" relevant. And as High End audio (including Studio systems) lacks anything like the required market size to sustain it's own infrastructure, the stuff offered by the main stream electronics industry is what we desperately try to get the best from (and I agree with you, it often produces a choice between rotten apple and rotten pear).
Yet the debate here is less about what is being done, but should/could be done. Not that I hold much hope that it will be (see above in my comments on approaches to technology and life)... 🙂
Ciao T
Mass & inertia are constants.
Are at least in one school of thought undesired and drivers should operate only below the breakup modes.
Mechanical hysteresis is not a necessary feature of a well designed driver, neither is air leakage (I assume that is your reference), at least not to any material degree.
Hopefully you were awake and declined to employ defective drivers?
Actually, I do not presume. I worked with back emf derived MFB in the 80's. Outside the frequency domain and generally at very low frequencies it considerably worsened objective (measured) and subjective performance. I eventually switched to electret microphones, which are not particulary linear, but much more so than back-emf.
Correct. However current drive removes one absolutely major and one minor source of performance impairment that is unneccesary, when using electrodynamic drivers (when using electrostatic drivers the reverse of course is true).
Hmm, more like comparing a slightly wrinkled and old (lain in the basement all winter?) apple to a rotten and wormy pear. One you can eat, the other is probably not even good for making perry.
Trivial to fix. Saturate the magnet system.
So far you seem to say that badly designed drivers cannot be rescued by current drive. On this we agree.
As long as you want to simply continue "business as usual" current drive does not help.
If you want to remove the major performance impairment sources in electrodynamic drivers fixing the magnetic field (hence I was mentioning it so prominent) so it is not modulated by the voice coil field (try a CCS driven fieldcoil with enough current to saturate the pole pieces toroughly) and remains constant across the linear excursion range of the driver (not trivial, but doable) AND driving the resulting driver with a modulated dcurrent (and avoiding construction details that introduce hysteresis) you will have a system that is by far more free from performance impairments than what is offered these days.
But (again, as I remarked earlier), the Speaker industry has zip interest in this kind of technology, nor does it (or much of the rest of the electronics industry) consider "High Performance Audio" relevant. And as High End audio (including Studio systems) lacks anything like the required market size to sustain it's own infrastructure, the stuff offered by the main stream electronics industry is what we desperately try to get the best from (and I agree with you, it often produces a choice between rotten apple and rotten pear).
Yet the debate here is less about what is being done, but should/could be done. Not that I hold much hope that it will be (see above in my comments on approaches to technology and life)... 🙂
Ciao T
Mass and inertia are only constants when all of it moves together as a unit,
exactly why I mentioned the breakup modes. Back EMF, was only referring
to this servo as a standard freebie you get from voltage driven voice coil...
We are converging toward an agreement on the other details.
exactly why I mentioned the breakup modes. Back EMF, was only referring
to this servo as a standard freebie you get from voltage driven voice coil...
We are converging toward an agreement on the other details.
Thanks for the explanation. Yes I was definitely thinking in a different ballpark than a resistor when you said "mechanical" damping.
Hi,
My suggestion is electrical. But it has the merit that existing drive units are easily adapted.
The original Eckmiller driver had a classic Spider (that is one with legs - where the name originated - not a flat preformed colth disk) and each leg of the spider was damped using a grease-pot style damper with the addition of aperiodic damping of the rear cone by having a basket a lot like a sieve.
Modern polymers can probably offer other options of resonance damping in a moving system as well.
The point I was trying to make however is that we do not need to use the Amplifier to damp the cone oscillation at resonance and other then reducing drive unit cost doing so (as is common) actually does not provide any performance benefits, but many dis-benefits.
Yet the practice being established we are caught in a vicious circle.
Practically all Speaker makers make speakers designed for voltage drive. So if I make Amplifiers and wish to stay in business I need to make Amplifiers that drive these speakers well. Anything else is financial suicide. But with all Amplifiers being made to offer voltage drive, they will not drive a speaker designed for current drive well at all. As there no amplifiers to drive such speakers making any would be strongly prejudicial to a company's satying in business. So.... <return to the beginning of the paragraph and keep reading>
This is why I gave my various experiments in the 80's on how to improve speakers "the active way" (read MFB, Current Drive etc.) eventually and instead worked on how to get good sound in the context of the systems as they are, as opposed to "how they should be".
Ciao T
My suggestion is electrical. But it has the merit that existing drive units are easily adapted.
The original Eckmiller driver had a classic Spider (that is one with legs - where the name originated - not a flat preformed colth disk) and each leg of the spider was damped using a grease-pot style damper with the addition of aperiodic damping of the rear cone by having a basket a lot like a sieve.
Modern polymers can probably offer other options of resonance damping in a moving system as well.
The point I was trying to make however is that we do not need to use the Amplifier to damp the cone oscillation at resonance and other then reducing drive unit cost doing so (as is common) actually does not provide any performance benefits, but many dis-benefits.
Yet the practice being established we are caught in a vicious circle.
Practically all Speaker makers make speakers designed for voltage drive. So if I make Amplifiers and wish to stay in business I need to make Amplifiers that drive these speakers well. Anything else is financial suicide. But with all Amplifiers being made to offer voltage drive, they will not drive a speaker designed for current drive well at all. As there no amplifiers to drive such speakers making any would be strongly prejudicial to a company's satying in business. So.... <return to the beginning of the paragraph and keep reading>
This is why I gave my various experiments in the 80's on how to improve speakers "the active way" (read MFB, Current Drive etc.) eventually and instead worked on how to get good sound in the context of the systems as they are, as opposed to "how they should be".
Ciao T
I finally found a speaker I ripped out of a karaoke machine today, and decided to see how it sounded. I also decided to test out series resistors.
I was surprised by the quality of the speaker. It has a black cloth surround, treated with what I guess is some sort of drying oil, like boiled linseed oil. Black dust cap (mylar?).
The surround is large enough to accommodate decent excursion, and as such toms sound good. Deeper bass than you would expect from a 3.5" speaker.
I wouldn't hesitate to say it was still a piece of crap if it didn't sound better than my $80 Kevlar cones... Unfortunately, I only have one because the karaoke machine only had one speaker...
Using a 25 ohm rheostat as a series resistor, it seems to sound less militant. The sound doesn't bite so much, things sound smoother. I don't know if this is because of equalization changes. Speech is more legible. It is easier to relax while listening. (this is out of a single speaker, mono)
Instruments don't obscure each other so much. Bass instruments have less bite.
For this speaker at least, I would consider current drive because series resistors, to me, improved the sound.
- keantoken
I was surprised by the quality of the speaker. It has a black cloth surround, treated with what I guess is some sort of drying oil, like boiled linseed oil. Black dust cap (mylar?).
The surround is large enough to accommodate decent excursion, and as such toms sound good. Deeper bass than you would expect from a 3.5" speaker.
I wouldn't hesitate to say it was still a piece of crap if it didn't sound better than my $80 Kevlar cones... Unfortunately, I only have one because the karaoke machine only had one speaker...
Using a 25 ohm rheostat as a series resistor, it seems to sound less militant. The sound doesn't bite so much, things sound smoother. I don't know if this is because of equalization changes. Speech is more legible. It is easier to relax while listening. (this is out of a single speaker, mono)
Instruments don't obscure each other so much. Bass instruments have less bite.
For this speaker at least, I would consider current drive because series resistors, to me, improved the sound.
- keantoken
Actually, if we are to use this method the get the same damping as the voltage amplifier provides, one turn is not enough, but it would need a shorted second coil with the same number of turns as the primary coil.ThorstenL said:
However, if we do so, the damping coil generates just equal electromotive forces (motional EMF and inductance EMF) as the active voice coil does, and these EMFs would then bring back the same detrimental effects that are just avoided by current drive.
So, it is the mechanical damping supported by suitable cabinet filling materials that are useful, and I also think it would not take long to develop these if only some effort were put to it. Even now there are rubbers that yield free air Qm values of around 1.5; and according to my tests with copious cotton cloth stuffing, the value can yet be considerably lowered from this.
Often it is not even necessary to reach to the 0.7 since with a slightly higher value, the mild boost that develops in the 100 Hz region can be used for benefit to compensate some part of the baffle step.
With existing gear, it is feasible to employ some degree of electrical damping for the resonance region (a series RCL network in parallel with the driver) and keep the impedance level high elsewhere, as the benefits of current drive appear mostly in the mid and treble regions.
I have sorted out and treated these effects:
Voice coil acting as a microphone for the sound waves reflecting from the cabinet interior and passing through the diaphragm
- Voice coil acting as a microphone for the sound waves from adjacent drivers
- Mechanical and pneumatic non-idealities of the moving parts causing unpredictable EMF-effects
- Bl-variation causing modulation of impedance's angle and hence phase modulation of current at middle frequencies
- Position-dependent inductance of voice coil causing both amplitude and phase modulation (as in post #66)
- Voice coil inductance depends strongly on current level (without any displacement) causing non-harmonic distortion
- Magnetic coarseness of iron causing harmonic distortion, hysteresis and Barkhausen noise
- Resistance changes caused by temperature variations and manufacturing tolerances
- Program-dependent contact resistance variations in connectors and switches
These are pretty similar observations to mine when I made my first experiments in the early 90's and what I've been experiencing ever since. Hold on what you have found.keantoken said:
I've been able to test series resistors with some hi-fi drivers lately. Results are the same. It is easier to turn up the volume without people complaining. I currently use 25 ohm resistors in stereo with Wild Burro BetsyK's. I can use such a high value since it's an open baffle and I need bass. Response is pretty flat to my ears.
I'm pretty pleased for now. I want to upgrade my amp soon, to exclude the possibility that it's simply reacting positively to the higher load impedance. Higher load impedance would change crossover characteristics, towards a more seamless crossover region AFAIK which would decrease higher order harmonics and improve small-signal linearity (it always bugs me that AB amps distort the most during the first watt...).
- keantoken
I'm pretty pleased for now. I want to upgrade my amp soon, to exclude the possibility that it's simply reacting positively to the higher load impedance. Higher load impedance would change crossover characteristics, towards a more seamless crossover region AFAIK which would decrease higher order harmonics and improve small-signal linearity (it always bugs me that AB amps distort the most during the first watt...).
- keantoken
ETM, I did buy your book and I find it informative. However, I find it to be a 'double edged sword' sort of like the books written by Doug Self. I like your use of math. This is often presented in too difficult a form in many technical papers, or ignored by many popular writers. As you show, math is important, and with some effort from the reader, understandable.
The other side of the equation is your written opinions of areas outside your general research, such as TIM. Here, you make strong statements, but they really don't help the situation and are not useful in general. I have found this in other researchers who find speaker problems fascinating, and tend to think that electronics amplification is a very poor relation in the contribution to overall sound.
I still recommend this book.
The other side of the equation is your written opinions of areas outside your general research, such as TIM. Here, you make strong statements, but they really don't help the situation and are not useful in general. I have found this in other researchers who find speaker problems fascinating, and tend to think that electronics amplification is a very poor relation in the contribution to overall sound.
I still recommend this book.
keantoken said:
Nice to hear you are continuing with positive results although 25 ohms doesn't yet make very ideal current drive. I encourage also others to experiment, and if one has access to a graphic equalizer or the like and knows the impedance curve, it may also be possible to eliminate most of the response difference.
Full range speakers usually suffer from cone break-up modes, that cannot be helped very much even by current drive, but even so, reducing the effects of the inductance EMF clears a lot of debris from the highs.
john curl said:
One of the goals was just to bring the practical math and especially the use of transfer functions closer to the ordinary, not so highly educated readership, and if I have succeeded in that, I may be satisfied with that part.
In general, however, I was and am hoping more attention to the main points of the book, which I have outlined in my last posting. The effects should also be quite easily reproduced with basic equipment.
Concerning TIM, I was able to conclude, based on the results obtained with my simple rise rate meter, that the maximum rate of change in a CD music signal very rarely extends to even half of that reached with a 20 kHz sine wave at the maximum amplitude. (I assume you mean this.) This is also quite consistent with other studies I have come across. While such findings may not be directly related to the main topic, I thought they still give some practical insight into the broader art of distortion hunting.
BTW, there is a review of the book in the July issue of Audioxpress, but, as one can expect, it concentrates mostly on the bass region and resonance damping, omitting the main arguments presented, notably the effects of inductance. More on that later.
First I apologize for jumping in this late. This topic is very similar to one that I have dealt with a lot in the past. In looking at the history of the last 50 years, it appears that not all speakers are designed to be 'voltage driven'. Some are what I call 'power driven'. 'Current drive' seems to be a variant of that.
Competing paradigms in amplifier and speaker design
If this is regarded as a hijack, we can cover it elsewhere, but it seems related.
Competing paradigms in amplifier and speaker design
If this is regarded as a hijack, we can cover it elsewhere, but it seems related.
In my experiments results seemed positive as long as I had series resistance above 4 ohms. I might go higher than 25, except here the bass becomes noticeably peaked. At 50 ohms and higher, the sound seems to lose life, and I attribute this to highly reduced lower midrange (this is the dip right after the bass impedance spike where AC impedance is close to DC impedance; this region suffers the most).
- keantoken
Consider Ohm's Law:
V is voltage,
I is current,
R is the load.
V/R=I
V/I=R
IR=V
VI=power
Current and voltage participate in power equally. So saying current drive is a variant of power drive is no more true than saying voltage drive is the same.
In fact, no amplifier can reach true voltage or current drive, though they have made heroic efforts. Any amplifier can only have an impedance between zero and infinity, and so they are all limited to some extreme of power drive. The only factor is the balance between current and voltage drive. If the amplifier has an impedance higher than the load, it is mostly current drive. If the amplifier's impedance is below the load, it is mostly voltage drive. And an amplifier with impedance equal to the load will be balanced voltage/current drive, which is closest to what you call power drive. I'm not sure if it is possible to make an amp which has balanced drive regardless of the load, however you can make a constant power amplifier for a fixed load.
- keantoken
Prior to the rise of the Voltage paradigm, no amplifier was able to act as a voltage source. At the time (1955-1968 or so) as the Voltage model was being developed, the attention was focused on flat frequency response from box speakers, and seems to have ignored other speaker technologies whose impedance curve was/is not based on resonance.
Anyway, it is true that the prior art (tubes) had variable output impedance and so there was no 'current source' model. That is why I call it the Power Paradigm. It is still around today in active use- any SET is operating in this way.
Tomick, an Electro Voice engineer, wrote an article about damping that speaks to this issue, and proposed a circuit that allowed you to set the amplifier's response to deal with a wide range of speakers, some requiring a DF of 20:1 and others needing 0.1:1.
Missing Link in Speaker Operation
As we all know, the industry settled instead on the compromise of the Voltage Paradigm. It is a compromise and the Power Paradigm has a lot of advocates as a result! I think the most telling is that the ideal Voltage Paradigm specs that resulted seem to tell you nothing about how the amp will sound, other than once you know what the specs mean, you know the amp will likely sound a little harsh.
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