The 800lb guerrilla that impacts how we deal with resonance is the lack of control the applied voltage exerts on the driver's voice coil as energy storage increases. To regain control, the most effective method is to either incorporate a negative feedback scheme or increase mechanical damping. Feedback systems work fine up to a point since they are with present technology very bandwidth limited and can cause the system to suffer from compression. Precise mechanical damping (such as with a damped transmission line) has a proven track record and is not as limited by bandwidth issues or compression. Active amplification presents another useful asset which when used with the appropriate signal shaping can reduce energy applied to the driver in the resonance region in accordance with the driver's energy storage characteristic. The energy that would have to be dampened in a passive network would simply not exist and thus a sizable chunk of the control problem would be eliminated or greatly reduced.
E=IZ ?
It is more like;
P=I^2 * E
Or
P=E^2 / Z
Depending if the amplifier is a voltage source or current source or some where in between.
DT
All just for fun!
Yes, Mills and Hawksford discuss the potential benifits of current drive in their 1988 paper. How time flies. How little progress has been made.
So you are saying that you can control the driver's behavior at resonance by using active equalization. Hip, hip hurray! Tally-ho
Excuse me for editing you post, but this is perhaps the first ststement you have made that I agree with.
I believe I touched on the potential of feedback earlier - as has Joachim - we don't need to rehash covered ground.
I'm not an expert on Audio Physics stuff - I do believe that like us - Joachim is a fan of transmission lines for the reasons I've been spouting in this thread. Perhaps he can make sense of the distinctions I've been trying to point out. No matter what I do, it doesn't seem to register with you and the discussion has more than once come full circle.
It is not "just a transfer function that provides voltage/current signal". Mechanical damping can resolve energy storage and the non linear distortion that accompanies it. The linear process of equalization cannot.
Now if you say the sentence above thirty times, or better yet, write it down thirty times - maybe it will sink in.
Energy storage at resonance is in no way a linear phenomenon - otherwise the distortion it causes would have been solved a long time ago by EQ. Again, the problem gets back to what actually controls the voice coil's motion. When the coil's impedance is hovering around 50 to 60 ohms and it is normally 8 ohms, it's a pretty safe bet that current isn't controlling its motion at resonance - no?
Mechanical damping is either going to be a linear element of a nonlinear element. If it is linear it can have no effect on the nonlinear aspects of the system. If it's nonlinear then whether distortion increases of decreases is a complex issue and more likely than not, distortion will increase.
Where is energy stored? In mass, in capacitance, in springs, in inductance. Certainly there can be nonlinear components here but for a driver operating in it nominal range the storage mechanisms are predominantly linear. And correctable by linear corrections. Again, no argument that a linear correction can not reduce (or increase) the nonlinearity.
Now, if you don't think that the current through the VC controls the driver motion at resonance you are mistaken. It is no different than any other oscillator. At resonance it just requires less current to sustain the motion. And, as I said, the current can be introduce to oppose (damp) the motion as well. It is, as you put it, just a matter of shaping the signal so that the desired current is applied. It's not magic.
Distortion is in no way necessary part of resonance. we have been there before. Resonance is a characteristic of any 2nd (or higher) order system. If the system is linear there is no distortion.
You seem to consistantly blame nonlinear bahavior on certain aspect of the system behavior such as: resonances introduce nonlinearity, stored energy introduce nonlinearity, breakup introduces nonlinearity. That is just not the case. The behavior will have nonlinearity if the components in the system have nonlinearity. An RLC oscillator will not have nonlinearity becase it oscillates. It will have nonlinearity because one or more of the elements is nonlinear.
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I did not say that i like transmission line better then closed or reflex. My main speaker is a very wide open baffle and i have m-dipole subwoofers. The subs are active and i filter the main baffles with a cap in series with the poweramp. I have 3 parts in the passive crossover of the main baffles. One coil in front of the wideband and a cap and coil on the horn ribbon tweeter. See my MPL thread that is currently not very active. In total an extremely simple but effective design. What i whould like to try next here is put the Scan wideband in a cabinet and try both active and passive. I have already described the experiment earlier. If i can aceave the same acoustic transfer function ( i asume i can ) i will measure distortion too with a multitone signal. I did not plan that but i could try the Scan wideband in an open back pipe ( transmission line ) and do the same test.
Not sure where you're getting that from. The buildup and release of stored energy is not linear. The damping of that energy is essentially resistive in nature which "tracks" the non linear curve as it is a percentage of stored energy - increasing as it increases, decreasing as it decreases. With EQ, there is no "adjustability" to suit the non linear behavior that results from different drive levels and frequency of applied signal within the resonance band. If EQ could do that - it would no longer be "EQ" and would fall more into the category of feedback.
And with that - good night!
Hi,
Phase Distortion is a concern. First, if the X-Over and drivers are within production tolerances and you are in the far-field (> 3m) it is minimised. I optimised the whole thing to have pretty decent summed step/impulse response.
Secondly, I selected the actual X-Over frequency to fall into a "hole" in terms of the human auditory systems ability to detected Group-delay/Phase errors. In this case it helps that the crossover region is so narrow.
I do not as such think the crossover is necessarily better than others, but it makes the most out of the drivers and it hides it problems in a narrow region of poor hearing common to most humans.
In the end, it works.
The same crossover at 2500Hz may be a major sonic disaster (or not - I did not have the chance to try). What I have learned the hard way though is that if your crossover is not VERY LOW ORDER (say zeroeth or first) you will struggle mightily to make it work well, unless you go extremely steep.
Ciao T
BTW, phase distortion does not seem to be a major concern...
Phase Distortion is a concern. First, if the X-Over and drivers are within production tolerances and you are in the far-field (> 3m) it is minimised. I optimised the whole thing to have pretty decent summed step/impulse response.
Secondly, I selected the actual X-Over frequency to fall into a "hole" in terms of the human auditory systems ability to detected Group-delay/Phase errors. In this case it helps that the crossover region is so narrow.
I do not as such think the crossover is necessarily better than others, but it makes the most out of the drivers and it hides it problems in a narrow region of poor hearing common to most humans.
In the end, it works.
The same crossover at 2500Hz may be a major sonic disaster (or not - I did not have the chance to try). What I have learned the hard way though is that if your crossover is not VERY LOW ORDER (say zeroeth or first) you will struggle mightily to make it work well, unless you go extremely steep.
Ciao T
Hello,
What came first, current or voltage? Is there one without the other? Voltage by its’ self never did any work. Can watts stop the motion of a speaker cone, consume the potential energy of a drivers’ suspension, enclosures’ compressed air or the heat stored in the enclosure stuffing (adiabatic heat of compression).
For my day job I use a mechanical engineer’s version of a class D digital amplifier, Variable Frequency Drive to control the RPM of large HP electric motors. Rather than a fixed frequency (50Hz /60Hz) power supply to the motor the Hz is adjusted to meet the requirements of the driven pump or fan. Distortion, harmonics and noise are all factors here. Now the point, the digital controls can and do apply power to actively slow and stop motion that could take minuets to coast to a stop.
I am seeing actively monitoring the motion of a speaker cone and digitally controlling a class D amplifier to dampen / control or counter the stored energy in the system.
Is that volts, current or watts doing the work Guys?
Lots of tools in the box to pick from!
DT
All just for fun!
What came first, current or voltage? Is there one without the other? Voltage by its’ self never did any work. Can watts stop the motion of a speaker cone, consume the potential energy of a drivers’ suspension, enclosures’ compressed air or the heat stored in the enclosure stuffing (adiabatic heat of compression).
For my day job I use a mechanical engineer’s version of a class D digital amplifier, Variable Frequency Drive to control the RPM of large HP electric motors. Rather than a fixed frequency (50Hz /60Hz) power supply to the motor the Hz is adjusted to meet the requirements of the driven pump or fan. Distortion, harmonics and noise are all factors here. Now the point, the digital controls can and do apply power to actively slow and stop motion that could take minuets to coast to a stop.
I am seeing actively monitoring the motion of a speaker cone and digitally controlling a class D amplifier to dampen / control or counter the stored energy in the system.
Is that volts, current or watts doing the work Guys?
Lots of tools in the box to pick from!
DT
All just for fun!
I for one, would be one of those, as I'm not that knowledgable yet
Very interesting thread, but it gets me quite confused from time to time with all the "this is the only correct view" posts regarding damping and the like. I don't know which leg to stand on.
I for one, would be one of those, as I'm not that knowledgable yet
Very interesting thread, but it gets me quite confused from time to time with all the "this is the only correct view" posts regarding damping and the like. I don't know which leg to stand on.
Don't worry. Confusion can be a good thing. It's a sign that you're still thinking and not brain dead.
May I make a suggestion? Don't take my word for any of this. Pick up a text on Linear Control Theory. In it, you should find a treasure trove of information relating the concepts of damping, feedback, instability, transfer functions, and energy storage.
Now he's reduced to quoting himself.And with that. Class is dismissed. I have real work to do today.
Buh Bye!
I've learned a lot from John over the years. Anyone who may question his bona fides should go to his website and review the papers he's written over the years. I used his Excel spreadsheet, that he now provides for free, to design my current dipole system, using the UE as the crossover.
Then go to the website of fntn and check his background. Actually, I know of none and in fact only know of a web moniker. Here at diyAudio and over at the PE board, there's zero by way of profile info. Total web anonymity.
It's sad to see some of the nonsense of the sort paraded by fntn. Those of you who are still confused remain so because of that nonsense. Yet it is allowed to stand by most here. Sad, very sad.
You'll have to decide who you think is providing accurate information.
Dave
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