If you achieve the same acoustic transfer function regardless of where you placed the cap then I would basically expect to see the same behavior. But that is not what you said. Your comment was that the LRC network made the amplifier's damping unnecessary. The damping arises dues the the current generated in the loop around the driver by the back EMF produced but the driver's motor. If the impedance of the loop, including the VC impedance, is Z then the damping force is -BL x (Vb/Z) where Vb is the back EMF. If a driver is connected directly to an amplifier then adding an LRC network across the driver will have negligible influence on the loop Z unless the amplifiers output Z is on the order of the voice coil DC resistance.
The LRC network you used was important when you had the cap after the amplifier because if flattened the impedance seen by the cap to look more like a pure resistance and thus yield a 1st order HP response. Without the LRC the cap would resonate with the driver impedance peak and you would have had a very different looking response. But, when you moved the cap to before the amp you did two things: you significantly changed the loop impedance seen by the driver, thus the damping of the amplifier/driver system, and then you altered (dare I say equalized) the input to the amp such that the output of the midrange driver remained the same. The same basic response would be expected in such a case, given a predominantly linear system. But you should have added one more leg to the experiment; with the cap before the amp remove the LRC network. If the magnitude of the output impedance of the amplifier was much less than the resistance in the LRC shunt you would have observed the same result demonstrating that when a driver is directly connected to an amplifier such an LRC network has no affect on damping because it dozen't affect the loop Z seen by the driver, unless the amp's output Z is high.
But the experiment you performed was reasonable. It goes to dispel the often quoted advantage sighted by active crossover proponents that direct connection of a driver to the amp means the amp has better control over the driver. (I actually have a very different take on that statement which I may introduce tot he discussion at some point.) That is not the case as if the voltage across the driver's terminals is the same then the driver will behave the same. The problem is that the voltage must be the same. A driver's impedance is subject to variation from things like voice coil heating and variation of Le with excursion. The voltage delivered across a driver's terminals by a passive crossover is typically much more sensitive to such changes in driver Z than a driver connected directly to the amplifier with crossover before the amp (be it active or line level passive). A number of years ago I performed a quick study of this effect using a Vifa MG14 driver. I measured the voltage across the driver's terminals at different levels with the driver connected to a passive 2nd order low pass crossover. The results were as below:
I had initially suspected this change in response was due to VC heating and increased Re, but as revealed through simulations the effect was more a result of changes in Le with excursion. My thinking was that such behavior could explain why some passive speakers tend to sound harsh as the volume was increased. Obviously drivers which do not suffer from such Le modulation will not exhibit this effect.
ANyway, I understand what you were trying to get across, but you did the wrong experiment to show the effect of an LRC shunt on damping.
Please read the entire dialog. Stop taking things out of context and placing your own context on them.
And for what it is worth here is another installment of eqing a really bad looking driver. I'm sure you will find fault with it too.
You can mix the batter any way you like but you don't have a cake until you pour it in a pan and bake in in the oven.
For one, most active systems ignore the interaction between the load and the amp. Secondly, if the active system has the amp built in with space limiting constraints, the layout may be so tight that the small signal side is effected by the power side, thus increasing distortion.
I find that convincing John K. For me the case is settled.
fntn, i used the transmission line that was ( is ? ) on the Jordan webpage. I experimented a lot with stuffing. On top of the cabinet i put an external cabinet that was connected to the transmission line with a short reflex tube. That cabinet was also critically damped.
The result was a very flat impedance curve in the lower reaches. We call that cabinet on top an internal Helmholz anti resonator. It can be modelled quite well with AJ Horn. Of cause a cabinet like that does not have much output under say 100Hz but the midrange performance and imaging was rather good. I hope i can find it in my vaults but from outside it does not look any sofisticated.
fntn, i used the transmission line that was ( is ? ) on the Jordan webpage. I experimented a lot with stuffing. On top of the cabinet i put an external cabinet that was connected to the transmission line with a short reflex tube. That cabinet was also critically damped.
The result was a very flat impedance curve in the lower reaches. We call that cabinet on top an internal Helmholz anti resonator. It can be modelled quite well with AJ Horn. Of cause a cabinet like that does not have much output under say 100Hz but the midrange performance and imaging was rather good. I hope i can find it in my vaults but from outside it does not look any sofisticated.
Ted Jordan's VTL original design is without any stuffing, and as this, it is certainly not the most neutral speaker around, but stuffed has you say it is practically a closed box... And considering the driver params, the smothered TL box ...and the wailers, no wonder you get no bass at all...
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This is the Transmission Line i used : http://www.ejjordan.co.uk/articles/JX92sSystems.pdf
The Helmholz anti resonator was put on top as an extention and made the speaker ca. 10cm higher.
The Helmholz anti resonator was put on top as an extention and made the speaker ca. 10cm higher.
Be carefull with the caps you choose.
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When you hear significantly different sound quality from speakers of the same brand, you know something is far from ideal. The closer to perfection speakers get, the more closer in sound quality they should get.
The effect of enclosures can be clearly seen via impedance curve changes, however, it is not the whole story.
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An externally hosted image should be here but it was not working when we last tested it.
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GDO, the Jordan experiment was not to extend the bass response. I wanted to try if it is posible to build an anti resonant cabinet that has a flat impedance curve in the range of the fundamental resonance. I succeeded to a certain degree.
Soon, i think many of the expensive so called audiophile loudspeakers do not go for a strictly neutral balance. They rather try to find a spectacular "home sound" that creates a cult following. When i entered the scene with my Audio Physic loudspeakers back in 1985 i had a lot of trouble in the beginning because they measured rather flat and many found them sterile and "cold". Well, i kept on track and success set in. People got used to it and then they had trouble with speakers that boom so i had my own cult following. I think John K. said ones ( and that impressed me ) : "whatever floats your boat". Let´s be fair, the perfect loudspeaker does not exist but we may come closer. And that has nothing to do with a ruler flat response and very good off axis behaviour. That can be had with modern measurement equipment and simulation. Where it is still lacking is in dynamic expression. Believe me, when my son playes the french horn 3 stories up in my rather big house i know it is "life".
Soon, i think many of the expensive so called audiophile loudspeakers do not go for a strictly neutral balance. They rather try to find a spectacular "home sound" that creates a cult following. When i entered the scene with my Audio Physic loudspeakers back in 1985 i had a lot of trouble in the beginning because they measured rather flat and many found them sterile and "cold". Well, i kept on track and success set in. People got used to it and then they had trouble with speakers that boom so i had my own cult following. I think John K. said ones ( and that impressed me ) : "whatever floats your boat". Let´s be fair, the perfect loudspeaker does not exist but we may come closer. And that has nothing to do with a ruler flat response and very good off axis behaviour. That can be had with modern measurement equipment and simulation. Where it is still lacking is in dynamic expression. Believe me, when my son playes the french horn 3 stories up in my rather big house i know it is "life".
You expereience about the "home sound" is exactly the same as my experience. It is also true that realistic sound has nothing to do with ruler flat response as measured and applied in the most popular way. This is much due to the complexity of wave front and interaction among the vaious diffraction and reflection sources. As you have already mentioned. Once the wave leaves the diagragm, there is nothing we can do prior to it that will improve the situation. I have some relatives that play the sax, some friends that play the violin, etc. My experience is that the dynamics first come with clean sound with micro detail, then power driven pushes the dynamics to more realistic levels without the hash that increases with level.
As you have already mentioned. Once the wave leaves the diagragm, there is nothing we can do prior to it that will improve the situation. I have some relatives that play the sax, some friends that play the violin, etc. My experience is that the dynamics first come with clean sound with micro detail, then power driven pushes the dynamics to more realistic levels without the hash that increases with level.
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Joachim, in any event I think my initial statment may have been a little strong. There is some interpretation involved and that depends on what direction the light is shining from. Perhaps the important point about damping and passive vs active is that with a passive, what ever network is between the amp and drivers, if it results in the desired transfer function then the net damping in the system ultimately has to be what it takes to achieve that response (the same applies for the active system). The idea that actives are better because the amp has better control over the driver is really irrelevant. What matters is that the driver is controled, not so much what controls it.
The more important issue would seem to be how the current through the VC is affected by dynamic changes in the VC impedance for actives and passives. We spend a lot of time looking at voltage transfer functions across the driver with little consideration that current is actually the driving force. Whether the x-o is active or passive, the current through the VC is affected by this variation of VC Z.
True. I did a lot of measurements with the Klippel and distotion in the voltage is mostly low measured with an amp of conventional construction but it shows up in the current.
There you can also see why Alnico sounds better. It gives lower distortion in the current.
When i talked about my experiment i only wanted to tell that the time domain behaviour of an active and passiv version can be made very similiar. The acoustic transfer function being the same so the step response is the same. That does not mean they sound the same so i should repeat the experiment and also measure distortion at high levels.
There you can also see why Alnico sounds better. It gives lower distortion in the current.
When i talked about my experiment i only wanted to tell that the time domain behaviour of an active and passiv version can be made very similiar. The acoustic transfer function being the same so the step response is the same. That does not mean they sound the same so i should repeat the experiment and also measure distortion at high levels.
You mean you spend a lot of time looking at voltage transfer functions across the driver. Speak for yourself. Some of us who've been in the business of building loudspeakers have known for many years that current in the motor is the true measure of the end result - acoustic power delivered. Since you're finally coming around to understanding that - I'll give you one big "Hip Hip Horraaaaay"
Passive damping of the current is always desireable because you never know what kind of amp the speaker is going to be connected to. Current source is great, but it also depends on how the current source is designed. In the past, I've looked at preventing back EMF from feeding into the amp, only in the past year or so have I started to look more deeply into driver damping which was stimulated by other aspects in audio design. Measuring the distortion across the driver terminals is probably one of the ways I found more useful.
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To measure distortion in the current you need a current sensor in line with the speaker.
Just measuring distortion at the driver terminal fed by a conventional volatage drive amplifier does not show much because the high damping factor of the amp short circuits the speaker. What you will see is the influence of the cable. This is the case when the driver is directly fed by the amp ( active ). What happens when the driver is connected to a passive crossover needs more research on the other hand i think.
Just measuring distortion at the driver terminal fed by a conventional volatage drive amplifier does not show much because the high damping factor of the amp short circuits the speaker. What you will see is the influence of the cable. This is the case when the driver is directly fed by the amp ( active ). What happens when the driver is connected to a passive crossover needs more research on the other hand i think.
Not if you have passive components in between like an XO. Changing the passive components do change the distortion. I agree that cables also make a difference, but I'm sure you don't want to turn this into a "cable thread" I have a 45cm cable story in the last one that was closed.
I have a 45cm cable story in the last one that was closed.
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I don't think it's that simple. But I've never tried to model it. I only change the components, listen, measure.
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