Ahah...
That's the whole point of the exercise, that we may well have a unique 'hard cone' driver that does not offend in this area.
I give credit where credit is due, it is influenced by Troels Gravesen view of this driver as well as a conversation I had with him back in 2017. At that time there were three versions of the SB17 driver, NRX fibre cone, MFC polycone (both are soft cone) and that he clearly thought I should have gone with MFC as I am using only an uncorrected series inductor, as that in this area the polycone was better suited in his opinion as I understood it.
Eventually we had to go over to the MFC anyway as they made less suited changes to the NRX2.
That left the NBAC aluminium not even considered.
And here Troels wrote something on his website that changed my mind. He listened to the playing MLS signal through a raw driver and hear its character and the character he expected with the aluminium driver was not there. The hard cone harshness banished in an aluminium driver. I will let Troels do the speaking:
"Frankly, I never thought I'd do a speaker from all aluminium (cone) drivers... the midbass was harsh on my ears. Later the manufacturer modified the drivers (cone curvature) for better performance... When I first set up this SBA driver and turned on the MLS signal from the CLIO I thought I'd done something wrong - or was suffering temporary loss of high-frequency hearing . Well, I hadn't. Usually you can hear from the very MLS signal if a driver is trouble or if it's smooth on the ear. This SBA driver was smooth on the ear. Apparently the cone design with the ribbed imprints does its thing in reducing cone break-up. I even found a manufacturer using the 8" version as midrange driver i a 3-way system up to 1800 Hz! Quite a bold choice I'd say."
[My underlining.]
http://www.troelsgravesen.dk/SBAcoustics-61-NAC.htm
The he also did CSD (Waterfall) plots on the three drivers:
He rates the poly (MFC) best for 1st order, then aluminium is 2nd and the paper/fibre (NRX) is last. The surprise is that the aluminium is not last.
The NRX has a slight issue around 5-6KHz which was small enough for me to leave uncorrected (no LCR). The same goes for the polycone. Look at the aluminium and there are no issues up until around 10KHz, which is high enough for me to leave uncorrected. But clearly I will be guided by my own CLIO measurements, which is also the system that Troels use.
Like Troels, I have avoided aluminium and hard cones since around the early 90's when I was playing around with Jordan 50mm aluminium drivers. I remember that I even designed a pair for the late Allen Wright in those days.
So yes, when the guys down at Monash University (Melbourne) started playing with this driver, then we did a deal, they would pay for the drivers, I would pay for the boxes and crossover etc. And now it is all here. The "NAC" version is coming, but will it be official... that depends on how it works out.
I hope to have further news during April, but there is no strict timetable here, it will all happen in its own time. If memory serves me right, it took me 6-7 months to get the ULD done.
My hat off to Ulrik Schmidt at SB Acoustics, I think he may well have done a first. And it is not an expensive driver at that.
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Straightforward MDF, exactly as per the website, all 25mm plus the one piece of 18mm that makes the front panel 43mm thick:
https://customanalogue.com/elsinore/elsinore_4.htm
Are you going to try the same waveguide? The ceramic tweeters' faceplates are different, is it going to work? (let me answer: we'll see!!! 🙂)
To lump or not to lump, that is the question?
But I see what you mean.
I am definitely going to produce some things/tests in this area. Your summation was interesting re Force Factor and AES papers. As you yourself seems to get is that we need more than that, we need something that can unify our thinking: Distortion measurements. I believe this is the key to get a whole (even wholesome) view of the subject. I am not looking for any unifying theory, more like correct thinking. We are all so used to think in terms of voltage, even a newbie can understand what they see on an oscilloscope, voltage vs time. Try put current on a scope. You can't unless you convert to voltage and that's complicated to explain to the same newbie. And voltage and current are only sync'd if the load is purely resistive.
Not when it looks like this. This has to be the starting point:
This is 2KHz below, into a 6.5" driver, where Yellow is the voltage of the amplifier.
This is 2KHz below, into a 6.5" driver, where Red is the current of the amplifier.
Note the commonality here (I have chosen my words very carefully). Yes, both are products of the amplifier.
The amplifier is producing the voltage, we can all agree upon that. Where there may be a reluctance is to state that the current we see above is also a product of the amplifier. The driver that triggered this event, it iself does not produce current, but it can modify the current almost at will. Then what is happening to our precious Force Factor? Can you see that 30° of current phase shift (to the right)? That is a time window (of opportunity) where bad things (like distortion) can happen? So we can have distortion both in amplitude (of current) and in time? What is the time window in 30° @ 2KHz? Will it produce sidebands when triggered (IMD)?
The voltage is 'regulated' because it is a voltage source, but the current is un-regulated and now produces around 30° phase shift due to
Esa Merilainen wrote his book on current-drive (I am not a fan) and in 342 pages, on page 57 is the single most important sentence of the entire book:
"...the resulting current is a mixture of the original signal and a spurious signal corrupted by the speaker's own mechanical, electrical, acoustic properties and circulated in the feedback process."
[Think of 'feedback' more like something that is continuously feeding back on itself, circulating in a loop. This is a crucial concept to understand.]
Of course Esa will then tell you that only current-drive will save the day and we have to throw away voltage sources because, in his opinion, they are all wrong.
But I say no, figure out practical ways to deal with current distortion and you don't have to throw away amplifiers and also, the speaker designer's job is now made more difficult than ever, because it is his job to get the load right. Yes, I know, it means I have put myself in the poop now, but that is OK since I have already been here for the last ten years.
Is it measurable? You betcha - and I believe I have found ways to come up with meaningful measurements that is not textbook but actual physical events captured and that these will definitely have an affect on the sound. One measurement I have conceived should show that a voltage source can only control the voltage and that current unrelated to the voltage occurs. The way this measurement is done will be unlike anything that has been seen in any textbook. I have shared the method with some confidantes of mine and asking them if it will work. They seemed to think I was on to something and that it will bne successful. It involves multiple amplifiers that are not electrically connected and two speakers and sound bursts in excess of 110dB-SPL.
Back to the use of the word lumped. Just calling it 'lumped' is not wrong, I like that you put it that way because sometimes that is what we need to do. But we have lumps within lumps too. For example, the drivers used in Elsinores have on about 30% of the VC is inside the magnetic gap. That means that only 30% of the voltage is inside the gap, but thankfully we have 100% of the current in there. So whatever we do we have to keep certain things primary and here it must be the relationship between current and that critical total lumped characteristic you call Force Factor. Lose that relationship should equal to measurable distortion. But that means we must measure something beyond the voltage of the amplifier, we must measure the current of the amplifier - and we must start with measurements of a single driver where all the current is going through the one VC. That is current distortion whilst also doing voltage distortion, do both measurements, indeed do it simultaneously.
Does that make sense to you?
Distortion and phase shift are different things. Phase shift like this is not a bad thing.
Joe,
Any particular reason for choosing the SB26CDC and not the SB26ADC which is 1 dB more sensitive?
Is it because the SB26CDC is smoother in the higher frequencies (mainly beyond 20 KHz)?
Any particular reason for choosing the SB26CDC and not the SB26ADC which is 1 dB more sensitive?
Is it because the SB26CDC is smoother in the higher frequencies (mainly beyond 20 KHz)?
Attachments
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Yes, this was something that needed to be sorted out and we have a solution, details to come later. A ring is needed and I can include some with Waveguides.
The choice was not done by me, it's a long story and involves the sponsorship involved.
I never said that phase shift was a bad thing. That was not meant to be implied.
BTW, are you aware that a current source cannot produce current with a current phase angle? The summed current of the amplifier will always be 0° - but if the current is divided then on the legs of that division there can be a current phase change. But the summed current back into the amplifier, no.
Yes, a current source can produce current with non-zero phase.
Speaker current is expected to vary with the varying impedance. If you hold it steady with a current source it changes the response. You equalise the signal to the current amp and the current phase angle varies in accordance with the response.
Hi Joe and guys here,
Explications above may be almost obvious to anybody being familiar with passive electric composants physics, especially when adding the parallel résistor that your exemple shows Joe, but may I emphasise that, as son as you add that resistor (or anything in parallel to the voice coil), you are not concerned anymore about the phase of the current as it is plotted, because it is that of the amplifier's output...and you don't care about the amplifier's output voltage either, because this is not the closed loop parameter (assuming a current drive amp). The only thing you'd be interested in would only be the driver's current with respect to what it should be, because this is then, into this system, the only thing you'd hear.
Idéally, you'd want to close-loop control the driver's cone position with respect to the modulation signal...but folding back to control the driver's current is à trade-of between accepting some imperfections introduction vs easiness of implementation.
My 50p...
Explications above may be almost obvious to anybody being familiar with passive electric composants physics, especially when adding the parallel résistor that your exemple shows Joe, but may I emphasise that, as son as you add that resistor (or anything in parallel to the voice coil), you are not concerned anymore about the phase of the current as it is plotted, because it is that of the amplifier's output...and you don't care about the amplifier's output voltage either, because this is not the closed loop parameter (assuming a current drive amp). The only thing you'd be interested in would only be the driver's current with respect to what it should be, because this is then, into this system, the only thing you'd hear.
Idéally, you'd want to close-loop control the driver's cone position with respect to the modulation signal...but folding back to control the driver's current is à trade-of between accepting some imperfections introduction vs easiness of implementation.
My 50p...
"Will the driver current distortion be reduced with the 8R parallel resistor in place? If so by what magnitude?"
Doing so, please note that you are therefore changing the current applied to the driver, unless the amp is controlling précisément this as the feedback parameter.
The very best one could do, when closing the amp control loop using a voltage or a current directly taken from this system, would simply be to reduce distorsion to the level intrinsically introduced by the driver itself (how could it be else), not below... to go below that distorsion level requires to sense the driver's "output"= the cône position that is, so that the mechanical part of the driver would also be into the control loop, not outsider of it.
Doing so would then make the sound from the cone to be free from driver's electromechanical imperfections as the loop would correct any in real time tanks to the feedback loop...
Doing so, please note that you are therefore changing the current applied to the driver, unless the amp is controlling précisément this as the feedback parameter.
The very best one could do, when closing the amp control loop using a voltage or a current directly taken from this system, would simply be to reduce distorsion to the level intrinsically introduced by the driver itself (how could it be else), not below... to go below that distorsion level requires to sense the driver's "output"= the cône position that is, so that the mechanical part of the driver would also be into the control loop, not outsider of it.
Doing so would then make the sound from the cone to be free from driver's electromechanical imperfections as the loop would correct any in real time tanks to the feedback loop...
A few posts have been deleted due to Joe Rasmussen accidentally posting something that was destined for PM.Apologies to members who's posts were in direct response to this and were removed as a result. These posts will be returned to you for your future consideration.
My thanks to Moderation Team. My apologies as well. It was my mistake.
Re parallel resistor, take the example below:
Last week, I spoke to a guy, his name is Isaac. He has this speaker:
Revel M126Be
We are talking around $7500 retail.
I suggested that he get some 8R2 10W resistors from his local Jaycar store, he actually got some 15R and 18R and put them in parallel and got 8R18 from two 10W resistors, both channels of course. This was about midday.
He later called in the afternoon, he had put them across the speaker terminals. He was very suppressed, described the improvement very obvious and that he had disconnected and connected them a number of time. The difference was not small. Much easier on the ear, soundstage improved, much more natural tone, less synthesizer sounding which to him is the opposite sound of natural.
Of course, the frequency response is not changed, so he must be imagining this. I have to say that he is not the everyone that has heard this simple trick and I am not into mass-hypnotising people.
So what is going on?
There has to be something physically happening, as in something in physics, and explain this.
I believe I have figured out why. It is also the reason that leads us to understand that using voltage sources is going to continue being a practical solution and not necessarily need current-drive to get that improvement.
Edit/PS: May I mention that there are now a number of commercial speaker designers out there, that are already aware that parallel resistors improve the sound of a speaker when incorporated into the crossovers. They don't seem to be 100% sure why. And they are silent about it. We are speaking about substantial speaker brands. So this is already happening, it is definitely going on!
Re parallel resistor, take the example below:
Last week, I spoke to a guy, his name is Isaac. He has this speaker:
Revel M126Be
We are talking around $7500 retail.
I suggested that he get some 8R2 10W resistors from his local Jaycar store, he actually got some 15R and 18R and put them in parallel and got 8R18 from two 10W resistors, both channels of course. This was about midday.
He later called in the afternoon, he had put them across the speaker terminals. He was very suppressed, described the improvement very obvious and that he had disconnected and connected them a number of time. The difference was not small. Much easier on the ear, soundstage improved, much more natural tone, less synthesizer sounding which to him is the opposite sound of natural.
Of course, the frequency response is not changed, so he must be imagining this. I have to say that he is not the everyone that has heard this simple trick and I am not into mass-hypnotising people.
So what is going on?
There has to be something physically happening, as in something in physics, and explain this.
I believe I have figured out why. It is also the reason that leads us to understand that using voltage sources is going to continue being a practical solution and not necessarily need current-drive to get that improvement.
Edit/PS: May I mention that there are now a number of commercial speaker designers out there, that are already aware that parallel resistors improve the sound of a speaker when incorporated into the crossovers. They don't seem to be 100% sure why. And they are silent about it. We are speaking about substantial speaker brands. So this is already happening, it is definitely going on!
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How would you define "the amplifier's output" as being?
The "driver's current" is what? Is it not the amplifier's current? Sure, some of that current might flow through the VC voice coil, depending on other components. But does not the current originate from the amplifier.
If 50% of the current goes through the 8R parallel resistor at circa 200 Hertz because the driver's impedance there would be close to 8R as well.
But let us take a super critical frequency with regards to the ear @2KHz and that typical impedance is 15 Ohm with an average driver, then much more than 50% of the current is going through the 8R resistor is now near 85% and the driver is 35%. The current through our resistor is very stable at nearly all time, the driver current is anything but stable. But the total current of the amplifier is more stable. Note the underlining and how carefully I am choosing my words and what they mean.
A voltage, in order to control the voltage, must relinquish control over the current. It has to
There is no amplifier that can control both voltage and current. We have a situation where we have chosen control or the voltage, but then we have to be prepared that the amplifier can get up to all sorts of thing on the current, and current phase shift is but one thing out of many.
I have become aware that this is a very tricky topic to explain because we can get into all sorts of minutia and lose sight of the bigger picture. It has to be understood that all the flaws of a driver above 200 Hertz will show up in the Ei part of the impedance and no amfilifier can reduce driver distortion, not even current-drive
It does not seem to be well understood that current-drive does not reduce driver distortion, it reduces amplifier current distortion.
Yes, it is the amplifier that produces corrupted current and yes, that corrupted is because the driver is corrupt, that is, it has flaws. Always get the best driver and you will get lower distortion from the amplifier.
So there is no "driver's current" because it is the amplifier that produces the distortion.
All this should put pressure on the speaker designer, to employ techniques that tame the current by design because the amplifier can't do it.
I know the guys at Purifi have come to the conclusion, that the idea of an amplifier is to provide damping. There certainly is no such need above 200 Hertz. as Esa Merilainen has also pointed out. Esa thinks the only way to have control over the current is current-drive. To a degree he has a point. But the speaker designer can also do a LOT here when designing crossovers, but rarely do. And some use crude methods like parallel resistors simply because they hear the improvement (but don't seem to understand why and the don't tell you when they use them).
I would like to stop there, and know how the above is received, before I get on to the next step that needs to be explained:
What is the mechanism that triggers current distortion?
The answer is under the Ei symbol and a singular important characteristic of a non-perfect driver. And that Ei is a voltage source that occurs inside the gap of the driver itself and about 30% of the VC length.
Hello All,
I have been reading this stuff about how Inductance and Back EMF causes current distortion.
So I thought a bit about how to isolate the restive and inductive nature of a driver and measure it. You read the AES papers; in a lab setting the voice coil is blocked to isolate its movement. If you recall the motion of a voice coil is minimal in the Back EMF frequency range of a driver. A blocked voice coil is a good approximation.
On my bench are two Dale NH 250 4R (250 watt) load resistors in series with a Jantzen 1.0mH inductor. The test amplifier with current sensing resistor is an Audio Precision APx1701. Using the APx500 Acoustic response software the test plots show current decreasing with increasing frequency and very low levels of “current distortion”, if any.
There is no distortion to blame on Back EMF or “circulating” voltage feedback.
In this case at least, the amplifier is innocent, very low levels of distortion.
Thanks DT
I have been reading this stuff about how Inductance and Back EMF causes current distortion.
So I thought a bit about how to isolate the restive and inductive nature of a driver and measure it. You read the AES papers; in a lab setting the voice coil is blocked to isolate its movement. If you recall the motion of a voice coil is minimal in the Back EMF frequency range of a driver. A blocked voice coil is a good approximation.
On my bench are two Dale NH 250 4R (250 watt) load resistors in series with a Jantzen 1.0mH inductor. The test amplifier with current sensing resistor is an Audio Precision APx1701. Using the APx500 Acoustic response software the test plots show current decreasing with increasing frequency and very low levels of “current distortion”, if any.
There is no distortion to blame on Back EMF or “circulating” voltage feedback.
In this case at least, the amplifier is innocent, very low levels of distortion.
Thanks DT
I used to think much the same way you do.
There are about three ways I can tackle this, but please look at the next three graphics below:
You can measure the current this way.
Ignore the fact that it says "speaker current' when in fact that 1R current sense resistor is telling us what the current of the amplifier and a common mistake.
THERE IS A NOW A SPEAKER INVOLVED!
That changes everything!
Now apply voltage-drive (low Z):
This is a tweeter, but it could be done with other drivers using multi-tone stimuli.
Now apply current-drive (high Z):
WHOA!
YIKES!
THESE ARE ACOUSTIC MEASUREMENTS WITH A MICROPHONE!
(The above are measurements that you can inspect further and their context, done by Pavel, known as PMA on forums.)
(Three pages, make sure you see all three starting here: http://pmacura.cz/speaker_dist1.htm )
What is going on here. Let us think rationally and not look the other way. Science tells us that this has to be causal and that means it must have a mechanism that produces that result.
Does this mean that current-drive is the answer?
NO!
Because we can get that decrease in distortion with voltage-drive if we do the right thing. So I am not going to crusade for current-drive like some are.
(This is ironic because I have the key to make current-drive work so much better and the Elsinores already work with current-drive.)
Be absolutely sure, this is about distortion, in fact this is about measurable distortion. It is not phantom, and it does have an affect
What is the cause?
Back-EMF!
How do you think the back-EMF does to the current of the amplifier?
Can you see the culprit?
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Ok, so it follows from what you're saying that this can happen when phase angle is zero.