Dynamics of reality
It's been a busy week in UK for blowing things up as we've had Diwali and bonfire night next to each other. Took sprogs 5 and 6 to their first fireworks display saturday night. I'd almost forgotten how satisfying the kick in the chest was from a professional grade firework. Some cracking echos off nearby buildings as well.
I know, I've been locked in too long...
It's been a busy week in UK for blowing things up as we've had Diwali and bonfire night next to each other. Took sprogs 5 and 6 to their first fireworks display saturday night. I'd almost forgotten how satisfying the kick in the chest was from a professional grade firework. Some cracking echos off nearby buildings as well.
I know, I've been locked in too long...
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Jan, it is. But that is not what I said and certainly not in that context, I was talking how the driver impedance modulates the current of the amplifier, something that a very highly respected source has called "impedance modulations" and if I used that here, the bricks would start flying through the air aimed at poor me. But that phrase is here to stay.
Why did I chime in? I saw Billshurv posting about a 'fix' (a solution) that Purifi had used in their driver. I suggested I knew what the fix was, and then was accused by him of 'weaponising' the word 'fix' and that was weird because I was quoting him two days later. He forgot that it was his word and it meant 'solution.'
This is where "impedance modulations" are suppressed by the driver's inductance changing with excursion (but it does change with frequency). This is what Purifi says is the fix or solution. Flat inductance. A driver that does not have this characteristic will cause "impedance modulations" of the current of the amplifier.
Jan, do you remember something that Menno did with the modified Hypex amplifier at ETF17?
He played this modified Hypex Class D amp for us and it had three settings, 0R, 3R and 18R. He asked if we could hear the difference between the three settings. We could. So could he. In fact I remember pretty clearly that the speakers were yours(?). Did you hear the comparison?
Menno made it clear he preferred it when the settings was 18R o/p Z and I assume the speakers were 8 Ohm nominal and the DCR of the main driver around 6R. This almost means a ratio of 3:1 - closer to the ratio of 5:1 that Esa Merilainen and I had agreed many years was the minimum requirement for current drive to give us the benefit.
So Menno was at least going down that way and we could all hear it, and it was for the better, even if the bass driver was operating closer to its mechanical Q than its electrical Q.
Menno then asked if "lower damping factor" leads to better sound? I made it known to him that this was an area I had a deep interest in and thought it had to do with the current of the amplifier and that the current phase angle would be much flatter. But later realised this was only half the answer. I told him at ETF18 that "I am convinced we are listening to the current of the amplifier and not directly to the voltage." His precise answer was "and the good news is that we are going to be able to prove that." I think that proof has now arrived from a number of places/angles, including Lars Risbo because I put the statement to him as well and got an "excellent point you made" and I stated categorically "Once again, the key is the quality of the driver and there is no substitute, there is no short-cut" and got a "thanks."
So back to Menno. That high 18R output impedance is what suppresses those "impedance modulations" of the amplifier, and Purifi has software that does in fact measure this, and it causes audible distortions.
While we don't want the hassle of current-drive, it does suppress "impedance modulations" very well. It is the amplifier's current that gets modulated and causes distortion, and that is harder with current drive.
BUT!
I am sorry to use capitals, but people just don't want to believe me:
I AM NOT IN FAVOUR OF CURRENT DRIVE AND WE DON'T NEED IT.
Please, I am very sorry to use capitals, but will people please take notice?
What Purifi is doing get getting the quality of current drive, but showing we do not need it. Goodbye current drive. Au Revoir!
There are several methods that can be employed with lesser drivers than Purifi, which are very expensive:
1. Use a series resistor, but not a good solution. Only partial solution.
2. Use a parallel resistor, I suggest 8R with 8 Ohm, and most amps are OK. But still only a partial solution.
3. Add a precise amount of external (linear) inductor in series with the non-linear inductance, for example, a driver that measures around 0.15mH at 2KHz and add a 0.47mH inductor and -3dB at the crossover frequency, this is very effective and audible.
4. Equalise the current of the amplifier flat through the critical midrange and then also use the inductor - and now you have the sound of current-drive with a voltage source.
Experimenters are trying these very things right now. This is happening. And it's a good thing. It's going to grow, I am sure.
Purifi:
These is truly remarkable drivers and worth a Wow! and I am ordering 8 drivers from them this week and I have two friends down here are also ordering 8 sets each.
Below is what a normal good driver does, and as bad as it looks, this one is actually well above average and has very low inductance, but just not flat. The inductance increases in the negative position (in) and decreases in the positive position (out). So when a mixture of lower frequencies and higher frequencies, we have significant "impedance modulations."
Below the three positions are simulated based on a real driver made by Peerless, simulated in SoundEasy:
The Blue line simulates the cone in the negative (in) position. The Red is centered. And Green is in the positive position (out). All three posistions are with Xmax and linear p/p excusions.
Now what happens when we put a series 18R resistor in series, this is what Menno did:
A noticeable improvement. Improved sound.
Now what if we put an 8R in parallel?
I see this as more pratical and more effective, but that 8R resistor needs to be a decent size as it will get hot.
Anybody can try this and report back here. I urge them as they likely have something around that they could use. I know that in my workshop I'd find something to do the job.
Please Jan, I have put a lot of effort into this. I have suggested to Menno in a copy of a discussion paper that I sent to him that 8R should have been tried. In fact, when I think of it, we should have tried that at ETF17 and the Hypex amp set to 0R - it need not have been modified.
The context of all this is that I want to use voltage source amplification and want the lower distortion of a current source, but with much lesser problems than current drive.
It's all about lower distortion and using voltage sources.
Regards, Joe
Jan, it is. But that is not what I said and certainly not in that context, I was talking how the driver impedance modulates the current of the amplifier, something that a very highly respected source has called "impedance modulations" and if I used that here, the bricks would start flying through the air aimed at poor me. But that phrase is here to stay.
Why did I chime in? I saw Billshurv posting about a 'fix' (a solution) that Purifi had used in their driver. I suggested I knew what the fix was, and then was accused by him of 'weaponising' the word 'fix' and that was weird because I was quoting him two days later. He forgot that it was his word and it meant 'solution.'
This is where "impedance modulations" are suppressed by the driver's inductance changing with excursion (but it does change with frequency). This is what Purifi says is the fix or solution. Flat inductance. A driver that does not have this characteristic will cause "impedance modulations" of the current of the amplifier.
Jan, do you remember something that Menno did with the modified Hypex amplifier at ETF17?
He played this modified Hypex Class D amp for us and it had three settings, 0R, 3R and 18R. He asked if we could hear the difference between the three settings. We could. So could he. In fact I remember pretty clearly that the speakers were yours(?). Did you hear the comparison?
Menno made it clear he preferred it when the settings was 18R o/p Z and I assume the speakers were 8 Ohm nominal and the DCR of the main driver around 6R. This almost means a ratio of 3:1 - closer to the ratio of 5:1 that Esa Merilainen and I had agreed many years was the minimum requirement for current drive to give us the benefit.
So Menno was at least going down that way and we could all hear it, and it was for the better, even if the bass driver was operating closer to its mechanical Q than its electrical Q.
Menno then asked if "lower damping factor" leads to better sound? I made it known to him that this was an area I had a deep interest in and thought it had to do with the current of the amplifier and that the current phase angle would be much flatter. But later realised this was only half the answer. I told him at ETF18 that "I am convinced we are listening to the current of the amplifier and not directly to the voltage." His precise answer was "and the good news is that we are going to be able to prove that." I think that proof has now arrived from a number of places/angles, including Lars Risbo because I put the statement to him as well and got an "excellent point you made" and I stated categorically "Once again, the key is the quality of the driver and there is no substitute, there is no short-cut" and got a "thanks."
So back to Menno. That high 18R output impedance is what suppresses those "impedance modulations" of the amplifier, and Purifi has software that does in fact measure this, and it causes audible distortions.
While we don't want the hassle of current-drive, it does suppress "impedance modulations" very well. It is the amplifier's current that gets modulated and causes distortion, and that is harder with current drive.
BUT!
I am sorry to use capitals, but people just don't want to believe me:
I AM NOT IN FAVOUR OF CURRENT DRIVE AND WE DON'T NEED IT.
Please, I am very sorry to use capitals, but will people please take notice?
What Purifi is doing get getting the quality of current drive, but showing we do not need it. Goodbye current drive. Au Revoir!
There are several methods that can be employed with lesser drivers than Purifi, which are very expensive:
1. Use a series resistor, but not a good solution. Only partial solution.
2. Use a parallel resistor, I suggest 8R with 8 Ohm, and most amps are OK. But still only a partial solution.
3. Add a precise amount of external (linear) inductor in series with the non-linear inductance, for example, a driver that measures around 0.15mH at 2KHz and add a 0.47mH inductor and -3dB at the crossover frequency, this is very effective and audible.
4. Equalise the current of the amplifier flat through the critical midrange and then also use the inductor - and now you have the sound of current-drive with a voltage source.
Experimenters are trying these very things right now. This is happening. And it's a good thing. It's going to grow, I am sure.
Purifi:
These is truly remarkable drivers and worth a Wow! and I am ordering 8 drivers from them this week and I have two friends down here are also ordering 8 sets each.
Below is what a normal good driver does, and as bad as it looks, this one is actually well above average and has very low inductance, but just not flat. The inductance increases in the negative position (in) and decreases in the positive position (out). So when a mixture of lower frequencies and higher frequencies, we have significant "impedance modulations."
Below the three positions are simulated based on a real driver made by Peerless, simulated in SoundEasy:
The Blue line simulates the cone in the negative (in) position. The Red is centered. And Green is in the positive position (out). All three posistions are with Xmax and linear p/p excusions.
Now what happens when we put a series 18R resistor in series, this is what Menno did:
A noticeable improvement. Improved sound.
Now what if we put an 8R in parallel?
I see this as more pratical and more effective, but that 8R resistor needs to be a decent size as it will get hot.
Anybody can try this and report back here. I urge them as they likely have something around that they could use. I know that in my workshop I'd find something to do the job.
Please Jan, I have put a lot of effort into this. I have suggested to Menno in a copy of a discussion paper that I sent to him that 8R should have been tried. In fact, when I think of it, we should have tried that at ETF17 and the Hypex amp set to 0R - it need not have been modified.
The context of all this is that I want to use voltage source amplification and want the lower distortion of a current source, but with much lesser problems than current drive.
It's all about lower distortion and using voltage sources.
Regards, Joe
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Bill, I love you!
That is exactly the answer I would have given him. Bravo!
And yes, distortion reduction is worth it. That's my Holy Grail.
😀😀😀
We all have! Our local one on Saturday was great too, and I was similarly enjoying the "thump" and in our case the echoes from the surrounding hills...
Impedance modulation is simply that the driver impedance is different at different frequencies. Naturally, loading an amp with a load that changes with frequency, changes the current that the amp has to deliver with frequency (for voltage drive) or it changes the voltage across the driver with frequency (with current drive). Ohms law and all that.
I fail to see how that in itself causes distortion. Unless you call frequency response deviations 'distortion'? Some call that linear distortion and I can accept that. But non-linear distortion, the kind that adds harmonics? Maybe I miss something.
Jan
Have metal bands gone soft?
Wargasm singer'''s head '''held down backstage toilet by bouncers''' - BBC News
Ok I know this lot are 'Nu-metal' but I always thought a good fight after a gig was part of the fun of touring?
(Above all a bit tongue in cheek, I know that in 2021 no one should expect to be roughed up by security as there is no money in the chat show circuit telling the story years later).
Wargasm singer'''s head '''held down backstage toilet by bouncers''' - BBC News
Ok I know this lot are 'Nu-metal' but I always thought a good fight after a gig was part of the fun of touring?
(Above all a bit tongue in cheek, I know that in 2021 no one should expect to be roughed up by security as there is no money in the chat show circuit telling the story years later).
Ok, thanks for the reasoning and analogies on current drive's popularity. Which leads me to wonder why 4, 8, 16 Ohms on the speaker impedance as defacto values the audio ecosystem settled on?
I had read cars have 6 - 12V electrical systems because the light bulb filiment accommodating higher voltages is too floppy for use in a mobile machine. It had to be short and stiff to withstand the jostling about. Perhaps automobiles can move away from that voltage standard given all light comes from LEDs these days...
But why is it that way in a speaker voice coil? So they could sell more line matching transformers in PA installations? I do realize Hi-Z voice coil'd speaker have been made (Phillips), but those are certainly an outlier!
I had read cars have 6 - 12V electrical systems because the light bulb filiment accommodating higher voltages is too floppy for use in a mobile machine. It had to be short and stiff to withstand the jostling about. Perhaps automobiles can move away from that voltage standard given all light comes from LEDs these days...
But why is it that way in a speaker voice coil? So they could sell more line matching transformers in PA installations? I do realize Hi-Z voice coil'd speaker have been made (Phillips), but those are certainly an outlier!
Yes Jan, I think you have missed something. In fact, we are talking about something entirely different. Please consider this:
We all know that the impedance changes with frequency, that is how measuring the impedance comes about. Constant voltage, you measure the AC current as it varies with frequency and that current is in effect the impedance. So an impedance graph shows how current is impeded and not voltage. Everybody knows this. The impedance above a few hundred Hertz becomes gradually increased by the inductance. The inductance impedes current. Current decreases with frequency.
But that is not what this was about, there is some else that changes the impedance, excursions of the driver. Let me please explain:
This is impedance changing with excursion.
Red is when there is no excursion. Cone resting in the centre position, same goes for the coil.
Blue is when the cone position/excursion is negative, say 3-4 mm inward. The inductance has increased. The same goes for the impedance and the current is now less.
Green is when the position/excursion is positive, say 3-4mm forward. The inductance has decreased. The current has now gone up.
The driver now has three different impedance graphs. Indeed it has many depending on where the cone position.
This is like imagining measuring the impedance vs frequency with a DC offset and then getting a different impedance curve.
Now when you have a low-frequency content causing excursions, modulating the impedance of the driver whilst also producing higher frequencies with little or no excursions.
That is "impedance modulations" that Lars Risbo of Purify talks about. I think the phrase is here to stay. And it is distortion! And they measure it and it especially shows up in IMD distortion tests. Try 30-50 Hertz and 300Hz and aim for excursions 6-8mm p/p and that it is within Xmax rating of the driver (max linear excursion). You will clearly see the IMD distortion products.
But what is more, we must find ways to stop the driver from doing this. It means keeping the impedance constant by keeping the inductance constant at any one frequency and not changing with excursion.
And that is exactly how Purifi does it, this is their 'fix' for a problem they identified and they did something about it and the distortion reduction is very significant:
Amazing accomplishment!
When we do this we will have the major problem solved without having to use current-drive. Simple as that.
We don't need current-drive to 'fix' this problem (even if it has the advantage of suppressing this distortion because fixed current cannot be modulated).
Regards, Joe
PS: Many view so-called voltage drive, they just see the current in the sense of just having enough headroom. As long as the amplifier can handle it, all is fine. I think that view can be questioned in the view of the above. Even small errors in current from the amplifier can cause significant distortion. That is now the view of others too.
Joe, so what happens when 30-50 and 300 doesnt exist in the same driver? Say, you cross it way down at 100, such that all the displacement is happening in the big driver, with relatively little in the next one up. Would that have a similar effect?
Crossing that low does double duty; it keeps the IMD out of the woofer, because there's no I frequency to MD. It keep the cone of the next driver up centered in its travel range, because there's no frequencies going to it that would cause it to displace a lot.
Does current drive "do something else" other than fix the traveling inductance distortion?
I am hoping for a measurable positive in drivers that arent displacing much and hence, dont have the associated inductance variations with positional change. Thanks!
Crossing that low does double duty; it keeps the IMD out of the woofer, because there's no I frequency to MD. It keep the cone of the next driver up centered in its travel range, because there's no frequencies going to it that would cause it to displace a lot.
Does current drive "do something else" other than fix the traveling inductance distortion?
I am hoping for a measurable positive in drivers that arent displacing much and hence, dont have the associated inductance variations with positional change. Thanks!
It would take a long time to respond to all these things, but I can see that you are thinking and getting the general idea. May I say that this is where 3-Way should have an advantage with a dedicated midrange. Indeed Purifi now is bringing out a more dedicated midrange version. But here special attention should be made to the high-pass filter, I would use an LC null at whatever that in-box Fb, to kill excursions cold dead for the midrange driver.
For those into current-drive, I see this as the major advantage - that is to say that there are not others, but that is not where I am looking for answers because I don't want to use current sources, even though I have one, I haven't listened to it for two years or so.
2.5-Way also has an advantage, because they reduce the excursion as well, and in the Elsinores, by using four drivers in series-parallel, the reduction in excursion versus a target SPL is very large indeed. The 1mH series inductor to the midrange also suppresses the effect even more. It further reduces "impedance modulations" by nearly 3:1 using the SB drivers. The Purifi drivers can also be improved? But the series inductor value will be lower, but hopefully not by much.
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Hi Hans, I hear you.
Please be patient. One of the reasons I have not finalised measurements is because I am awaiting to get a special driver of vintage years. This has characteristics that I have been looking for, but they are very rare. But I know that Scan-Speak has made a limited release (originally not one of their drivers officially, but it seems it was made by them and sold under a different name), but I have sourced a pair of the original ones. But they are a on a slow boat from China. 😉 The whole suite of measurements will be highly scrutinised and documented so that others can repeat them exactly and get the same results. But the scrutiny will be done before anything goes public.
Please be patient. One of the reasons I have not finalised measurements is because I am awaiting to get a special driver of vintage years. This has characteristics that I have been looking for, but they are very rare. But I know that Scan-Speak has made a limited release (originally not one of their drivers officially, but it seems it was made by them and sold under a different name), but I have sourced a pair of the original ones. But they are a on a slow boat from China. 😉 The whole suite of measurements will be highly scrutinised and documented so that others can repeat them exactly and get the same results. But the scrutiny will be done before anything goes public.
Parasound too cheap?
Gobel + WADAX + CH Precision + A/V RoomService | Stereophile.com
So here we have a silly expensive system ($70k for a music server!) with JC1+ power amps but speaker cable costing more than the power amps. Can't help wondering if they had intended to use the $93k CH precision power amp and it broke/they sold it so put in what they had.
I can personally think of better ways to spend half a million, but I'm not a dentist 😀
Gobel + WADAX + CH Precision + A/V RoomService | Stereophile.com
So here we have a silly expensive system ($70k for a music server!) with JC1+ power amps but speaker cable costing more than the power amps. Can't help wondering if they had intended to use the $93k CH precision power amp and it broke/they sold it so put in what they had.
I can personally think of better ways to spend half a million, but I'm not a dentist 😀
$23,000/ for a 10' pair - highway robbery, the should have been 12' and now you are talking! 😉
Joe, Jan is modest enough to say that he is aware of all these. Besides, they have been discussed here for more than 5 years.
As Pavel said
https://www.klippel.de/fileadmin/_migrated/content_uploads/Klippel_Nonlinearity_Poster.pdf
Separated Loudspeaker Distortion
Current through a circuit or through a component is current.
Voltage across a circuit or across a component is voltage.
And impedance of a component is impedance.
I, E, Z are linked to each other (visit Georg Ohm’s and Gustav Kirchhoff’s laws) but they are distinct entities.
So, everybody should know that current is not in effect impedance (and everybody should be hindered from spreading misinformation).
George