Nothing against series x-o's, when they work, but you posted a pict of Joe's crossover with that statement which isn't a series job. Notice you deleted the pict from you post, so...
Sorry, John. You lost me there. What picture did I delete? 🙂
Back to Joe's filter, anybody not understand this?
A VERY simple 1st/2nd order filter with impedance correction. Is there anything hard here?
Hi Chris
Because we usually see things from a "voltage model" perspective and that a "current model" is a very different beast.
Please note that you can use voltage amplifier and voltage source interchangeably. Same goes for current amplifiers, the are current sources. They are AC versions that have similar characteristics to DC current and voltage sources. Study those and you will get the idea.
It's difficult to explain the difference in a few words, only that the voltage perspective dominates everything and the current perspective gets relegated, partly because it is harder to comprehend. But it is not voltage that makes a cone move. So if we send current from a current source, that current will stay the same through VC, but if we send voltage from a voltage source, then that MUST be converted to current. But is there an opening for an error signal since when we are using voltage we are driving the VC and motor indirectly?
Argue the subject, which is technical, and keep away from ad hominem posts. Those are the forum rules. Play by them.
Let me try to help you.
I believe this is an artificial separation that does not help understanding. Ever since Mr. Ohm explained it to us, voltage and current are related through impedance. The VC has a certain impedance, and to get current through it you need voltage across it, and vice versa. The two cannot be separated.
You say 'It's difficult to explain the difference in a few words'- not really:
A voltage source delivers a voltage that stays the same no matter how much current is needed for that. A current source delivers a current that stays the same no matter how much voltage is needed for it.
There.
You can choose to drive the VC with a voltage source, which means that the current will be determined by the impedance, or you can drive the VC with a current source which means that the voltage will be determined by the impedance. These are two different but completely interchangeable views.
Now, the impedance of the VC is not constant; it changes with frequency, with temperature (and thus with power) and a few other things. So if you drive it with voltage, the current (which depends on the impedance) will also vary with the mentioned parameters. So why not drive it with current then - well in that case the voltage across the VC changes with those parameters. Same difference.
Depending on chosing voltage drive or current drive the frequency response and a few other things of the speaker that is attached to that voice coil can be manipulated. Since the force that drives the mechanical stuff depends on the magnetic field generated by the VC current, the thinking is that therefore current drive somehow makes the speaker perform better in the sense that it can have a flatter response and less distortion. However, although mother nature lets you freely exchange one thing for another, rarely does she give something for free. If you look at the speaker system from a wider perspective there are issues with current drive that are not present with voltage drive, and issues with voltage drive that are not present with current drive. That dreaded dichotomy again! The upshot seems to be that current drive works very well with drivers that are developed for it, while voltage drive works well with drivers developed for it - and the latter is the overwhelming majority of current production. In fact, I know of not one driver that is optimised for current drive.
Jan
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Hi Jan,
Of course you are right on all counts!
Hi Joe,
Way back in time, the pioneers of audio experimented with both current and voltage drive. Guess which method won? Yet, we have telephones which are current driven, not driven by a voltage. So the current allows variable voltage drops to occur without causing too many problems. An intelligent person can only conclude that both voltage and current drive operation is well understood. There must be more benefits driving speakers with a voltage source rather than a current source. Nothing you are exploring is new, nor is it a breakthrough. What it is, is an interesting mind experiment and great questions for an electronics course exam. Changing the open market is not going to happen or it would have already made that transition.
Best, the other Chris 🙂
Of course you are right on all counts!
Hi Joe,
That depends on the person, but I generally disagree with you on that point.
So, if you impress a voltage across the speaker terminals, it just sits there? No, it does create current flow which causes the cone to move (or diaphragm). Just as current flow will create a voltage.
You can't have one without the other. If you send a current through a driver, a voltage MUST be created. It's power, and power consists of both voltage and current components. You can't have one without the other.
I'll assume you are referring to a crossover. A crossover operates by increasing the impedance in series with a driver as you enter the cut-off region or by bypassing current. It does this whether you are driving the network with a voltage, or a current. The only difference is how you would describe how the crossover works by viewing it from a current or voltage standpoint. However, you could also treat it from a power standpoint, and that takes both views into consideration.
Way back in time, the pioneers of audio experimented with both current and voltage drive. Guess which method won? Yet, we have telephones which are current driven, not driven by a voltage. So the current allows variable voltage drops to occur without causing too many problems. An intelligent person can only conclude that both voltage and current drive operation is well understood. There must be more benefits driving speakers with a voltage source rather than a current source. Nothing you are exploring is new, nor is it a breakthrough. What it is, is an interesting mind experiment and great questions for an electronics course exam. Changing the open market is not going to happen or it would have already made that transition.
Best, the other Chris 🙂
Voltage is converted to current using the impedance of the speaker. Not an ideal R. One of the issues voltage drive brings.
With a voltage amp the increased T decreases the drive. Increase the R with a current amp and the power output increases. For a speaker dedicated to use with a current amp, XO topology changes. A parallel XO with a voltage amp acts like a series XO with a current amp, and visa-versa.
dave
Hi Jan
I hear what you say, but he also said he was a newbie. So there was a context to consider.
That is what I have been saying too.
Have you ever tried to explain it to an audio club, then the secretary writes up a report to the club afterwards and gets it completely wrong, and it is the wrong interpretation that sticks. Explaining things from a current perspective can be challenging. For example how the mode is related to the source impedance and how accurate current can be tracked is a source impedance thing. You will get a few eyes staring straight ahead.
All I was saying, and I do think you know what I mean, that the concept of voltage drive/source is quite easy to comprehend, even showing a newbie (and he was, so he said) an oscilloscope's z-y axis' present amplitude and time, and they see it because it is intuitively easy.
Yes, we ALL know Ohm's Law, alas I fear if I say anything going beyond that, we will be going down the KL route (and it isn't in Malaysia) about the fact that we need to be see beyond that we we all know and understand: That sending current into x Load, the voltage becomes a function of that. That sending voltage into x Load, the current will be a function of that. That part is easy. So if we stick to that orthodoxy, then everything else becomes ridiculous. Is this not the position you and others have taken, effectively drawn a line in the sand?
Bottom line is that Ohm's Law works predictably with straight resistive values, no argument there, but even John towards the beginning of this thread opened the discussion when he mentioned the V/I function. How accurate is that with a dynamic Load, where various EMF changes the impedance(s) and where I have observed that even those, like VC inductance changes with input stimuli and is not a constant as it varies also with frequency - there is potentially stuff going on here that maybe just worth a look at. The inductive EMF is just a part of it. There are aspects of thermally loading the VC, that too is not a constant along its length... but better stop there. Things we know and things we don't know, the known unknowns?
What we know is that voltage drive is an indirect way of causing motion in a motor. But is that straight forward V/I conversion?
Please understand that I am not in the current drive camp, that misnomer has been placed on me I fear and then becomes very hard to shake. Even John clearly misunderstood that - or gave me that impression.
Bottom line, is there something 'rubbery' going on here? Is that V/I function that predictable, when I know there are dynamic elements that may interfere with it (testing driver for T-S Parameters easily shows some of those up)? If so, then I would like to find out something concrete - and it seems we can work together or fight over it. The latter I don't think will have a happy outcome. It's not exactly 'hidden variables' - I wouldn't go that far, but there are things to look at.
I would love to change the tenor of this whole discussion - rather than argue from entrenched positions. I am pleading here.
Cheers, Joe
PS: Despite all the aggravations, none that I have enjoyed, it has not all been a fruitless exercise. As Solomon said, "one face sharpens another". I just wish it could have been more fun and just plain an open case of brainstorming ideas. It does work surprisingly well.
Hi Dave,
Increasing resistance increases power dissipation. The increased resistance increases I-R losses, and that is a problem for current drive as well.
Any crossover operates by diverting power away from the driver. That is a universal constant. Look at it from a current standpoint if you wish, but the physics of the situation remain the same..
Of all people that I know, you should understand better that heat in a voice coil isn't a good thing. That is why you design efficient loudspeaker systems, isn't it? Heat changes the T/S parameters, well the electrical ones anyway. The speaker itself becomes less efficient as it is heated. That isn't good for voltage or current drive.
-Chris
No it isn't. What exists is a current flow related to the voltage and instantaneous impedance. Nothing is converted except for power into mostly heat.
No, no, no, no
Increasing resistance increases power dissipation. The increased resistance increases I-R losses, and that is a problem for current drive as well.
Any crossover operates by diverting power away from the driver. That is a universal constant. Look at it from a current standpoint if you wish, but the physics of the situation remain the same..
Of all people that I know, you should understand better that heat in a voice coil isn't a good thing. That is why you design efficient loudspeaker systems, isn't it? Heat changes the T/S parameters, well the electrical ones anyway. The speaker itself becomes less efficient as it is heated. That isn't good for voltage or current drive.
-Chris
Hi Chris, I think I addressed most of your post in #348.
He said he was a newbie and my words were tailored accordingly. This is the crazy thing about social media - context gets totally lost.
Re crossovers, many of us are not that fond of them. 🙂
He said he was a newbie and my words were tailored accordingly. This is the crazy thing about social media - context gets totally lost.
Re crossovers, many of us are not that fond of them. 🙂
Current drives the speaker's motor. I = VR. R is the impedance of the speaker. And R is usually not constant with time, and with most drivers, frequency.
That is a much more accurate way to descibe it.
But with a current amp the heating voice coil does not affect things. One of the advantages of current drive.
As does the weather and the level of drive (whether it is part of the dynamics of the music or the setting on the volume control).
dave
Due to convection across the gap, when a VC is thermally loaded, the heat is not a constant along the length of the VC. Done driver destruction to confirm this - cheap drivers of course, but not that cheap. 🙂
With conventional structures, thermal damage is often worst at the front of the gap - where the VC sticks out from the front plate (under the dustcap). Also, tracking heat while 'destroying' driver, most of the heat is absorbed at the front plate and least at the rear plate, strongly indicating a J-curve. Underhung drivers would have a large advantage here, but they are also prone to be lower sensitivity and hence for a particular dBSPL has to dissipate a LOT more heat. So there is no such thing as a free lunch.
Actually, it is a disadvantage. Current drive will try to send exactly the same amount of current through a heated the voice coil (i.e. increased Rdc), increasing further the temperature of the voice coil, which increases Rdc, and so on...
Yes, it is also a disadvantage in that you can get thermal runaway… similar to the problem with bipolars. But if you are not running a PA, or listening at levels that will cause hearing loss it is unlikely to be a problem.
dave
dave
Chris this is a good point. The idea that because current determines the force, and that therefor current drive is somehow better by definition, is a fallacy. With a specific driver it may have advantages - and with another driver it is disaster.
Someone pointed out to me that electrostatics don't suffer from the voltage drive problems that an em driver suffers from. Yet, many em speakers sound as good or better then many els. The reason is that voltage drivers have a 100 years history of development, optimization and lots of trials. Because there is much, much more to driver performance than the current through the VC.
Voltage drive has a set of problems that have been worked for a century. Current drive has another set of problems which have gotten not nearly as much attention and understanding. An interesting technical challenge but worthless commercially.
Jan
Joe you DO realise that current drive only increases this problem, don't you?
Jan
You may have to check your history. I 1st started to glimse the world of more than voltage drive amps when i talked with a Western Electric amp engineer who said to me "why would anyone make an amp where the output impedance isn't the same as the speaker it is driving". I believe that voltage amps really came to the fore along with transistors.
dave
You could be right Dave, but the fact remains that voltage drive drivers have been so far tweaked and developed and tuned that they have a lead that will never be made up by the current drive enthusiasts. Not to mention the little detail of the state of perfection of voltage output amplifiers.
Jan
Jan
Never say never. But current amps being common is unlikely as long as speaker manufacturers (typically conservative) continue to make drivers assumming that they will be used with voltage amps.
dave
dave
Surely the case of amplifier output impedance being the same as speaker is just someone coming from an RF or transmission line background where you are trying to optimise power transfer?
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