Sorry Joe, there is no distortion for any case not that any actual measurements will convince you the talk and speculation with no substance will just keep on rolling.
Well,
If F = BLI, then it must be Current.
Now what? So, what is next .....?
-RNM
But surely a nonsense question. The force applied by the voice coil is proportional to the current through the voice coil, note that is not one of the options offered by Joe. However there are many sources of force applied to the speaker diaphragm, not just the voice coil. There is the compliance of the suspension, the compliance of the air, the compliance of the air in the enclosure if there is one, etc. I'm sure if JN was here he could offer some insights into the magnetic circuits. There are many reactive elements, both mechanical and electrical, which store and release energy in the loudspeaker system. This is all very basic stuff.
Not at all.
Options? What options?
EXACTLY!
Et cetera indeed!
That's right!
But it is hardly basic then. What are all these things doing? That is what I am on about. Maybe you didn't you realise that.
Consider the bi-directionality involved, that one way you have the driver acting as a current device (as we agree on for the reasons even you stated) driven by a low source impedance voltage source (voltage controlled means no current control) and that those "reactive elements" and more (as you again stated) and yet those rogue elements in turn causes the speaker to act as a generator - that generator is in itself a voltage source. This is now referred to as back-EMF where the F is voltage, so there is no mistaking there.
Now all I ask is this, how is this affecting the current of the amplifier? After all, we agreed that the driver is a current device. If the current through the coil that defines motion (not voltage), then is it not important to examine what kind of current the amplifier supplies, it is what you are listening to.
Now some people get this, others don't. I am not the one that decides if they do.
Next indeed.
It means that we are listening to the current of the amplifier, not its voltage.
An inconvenient truth. Even an uncomfortable thought.
What if we can measure negligible distortion on the voltage side of the amplifier and yet put a tiny 0.1R in the return leg, then a tiny voltage that is proportional to the current of the amplifier will be formed. We can now compare the voltage of the amplifier with its current. If they are not the same, the question has to be asked, which of the two are we actually listening to?
What if harmonic distortion of the driver (not the amplifier's) shows up on the current side? That is coming from the speaker's imperfections, cone resonances and all sorts of things.
This needs to be taken seriously and it is. Not so much here, but it is a really hot topic and I am hoping that it will lead to exciting things.
Hans van Maanen has already shown that amplifier's feedback can create high order distortions when the amplifier transitions from Class A to Class B, when current and voltage are not tandem in time (phase). Sudden nasty bursts as the voltage feedback struggles (may point to current feedback as superior?). So how an amplifier reacts on the current may well define how good it sounds, its sound quality. So this may lead to better amplifier design too?
Interestingly, tube amplifiers are far more impervious to current being distorted. They may well have higher voltage distortions. But distorted current gets fed back right through the voice coil, just as F = BLI tells us.
Interestingly, that equation can be reversed. It is bi-directional and it can be both at the same time (current device and voltage source, since F is force or voltage). It takes mental effort.
This must have been extremely miserable class AB amplifier if it behaved as you have described. Or, intentionally miserable design.
Go ahead and make your own measurements on a normally designed amplifier. Go ahead and also make measurements on acoustical side. Did you? I did and there is nothing to see, with a non-idiotic amplifier.
Such theories are on the same level as a Flat Earth theory, to me.
See attached from AK4497 EVM datasheet. Looks like a serious problem...
I'm not sure why anyone takes Rob very seriously in terms of claims. He is marketing his product in that video. He mentions anecdotes like his kids heard changes watching cartoons. The old wife-in-the-kitchen thing.
View attachment 768693 View attachment 768694 View attachment 768695
My point was, I have always noticed this particular DAC artifact he refers to and newer DAC's appear to be improving. The 4499 is the best I've seen.
T
OK. You will never find unless you see. I suggest you tell Hans van Maanen that his amplifiers are rubbish, I will keep out of the firing line. Duck!
OK Joe, this is your "devil" - I am able to setup such measurement very quickly. This is a distortion of speaker current, speaker driven by a fine low distortion class AB amplifier. The output stage is in A to AB (B) transition zone. Idle current 100mA. 1 pair of output devices. See the distortion level. Any high orders?? I apologize for some mains spectral lines, the setup uses 2 x 10m cables from my lab room to the listening room, so the loops are unavoidable.
Yes I am stating that if there are high order distortions the amp is rubbish. However, Ohm's law is valid and if the impedance would have gross and strange non-linearities, they will reflect in speaker current, regardless it is class A or class B. It just must not be a rubbish.
Attachments
I managed to create a quasi-dynamic multitone by using two adjacent bins per frequency rather than one. This gives a beating of the frequency, its level drops to zero one time within a block of samples, the beat frequency is the bin width. I had to use a larger base multiplier (11 instead of 7) so that the IM components have enough space**) around them as they become wider, too. With some artificial 2nd and 3rd order added, the IM components can be up to 6 bins wide.
With phases all set to zero the waveform looks like a normal multitone which is amplitude modulated as a whole whereas with random phase each frequency has its individual zero amplitude point and it sounds like that, a detuned pipe organ chord which each note swelling up and down at a slow rate at different points in time.
**) For NFM we have to look at the spaces, not the IM components (which are there even if the distortion is fully static). And compare the noise floor in those spaces with the noise floor of a simpler signal, or silence. I tried to do this with my RME Adi-2 Pro in loopback, but alas, no difference found.
---------
I also tried to isolate that obscure "state variable settling" with a variety of time domain tests... again to no avail as of yet...
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Not showing up in a measurement simply means that the measurement was looking for something else, or the person doing the measurement didn't understand what he was doing. For example, someone putting in a single sine wave and then looking for IMD may be disappointed. Someone putting in two sine waves at different frequencies might see IMD but fail to see the harmonics which will also be present.mmerrill99 said:
Most measurements look for specific things. There is an alternative, which is to look at the residual after a scaled copy of the input is removed. The problem is that this type of nulling test depends on the accuracy of the test equipment significantly exceeding the amplifier, and it can be thrown off-course by simple changes in frequency response. It is easy to find things in the output which were not in the input; it is harder to determine exactly what they are and see if they are audible when the input is present.
Not at all. Who said that IMD is only caused by sine waves? That would be a very ignorant position to hold. Measuring IMD is best done with sine waves, but only an idiot would think that it is only sine waves which give rise to IMD.
You don't seem to get that the amplifier does not see the world in the way that we do. It sees a voltage varying at its input and it tries to amplify it. It does not know and does not care whether the voltage is one sine wave or a Mahler symphony. It filters it and distorts it. We distinguish between harmonics and IMD, but the amplifier does not.
One sine wave will not provoke effects which depend on the signal amplitude, so we can use multi-sine tests to do that. Generally, if you want a useful measurement you need to keep the test signal as simple as possible so that you can analyse the output.
Nice to know that Bruno agrees with me.
Thanks PMA Joe seems to think these measurements are difficult to make and keeps putting off answering them.
OK. You will never find unless you see. I suggest you tell Hans van Maanen that his amplifiers are rubbish, I will keep out of the firing line. Duck!
Bruno Putzeys and John Siau both participate in online forums why don't you ask them.
It is precisely what the topic is about. If a speaker sounds different when you put something across its terminals then it is being fed a different voltage, which means that it is not being fed from a voltage source. You cannot have it both ways, except in your own private Universe where the laws of physics are different and electric charge is not conserved and the quasi-static electric field is not a conservative field so voltage is no longer defined.Joe Rasmussen said:
Yes, clearly elementary circuit theory is tough enough to confuse you and your friends.
No. This is (one of) your fundamental errors. Once you put a network across the speaker terminals you are no longer listening to the amplifier current. You are listening (as you were before) to the speaker current. The amplifier current has changed because it is now feeding the speaker and the added network. However, if the amplifier is a voltage source (which you keep asserting) then the amplifier voltage output will not change so the spesker sees exactly the same signal and produces exactly the same output. You cannot have it both ways: either the amplifier voltage changes (not a voltage source) or the sound does not change.
You cannot arbitrarily separate things like this. The amplifier has an output impedance, which should be low and linear. The speaker has an impedance which will be higher and less linear. So what? Provided that the amp output impedance is low enough and linear enough (which it will be if it is competently designed) there is nothing to worry about.
When someone bangs on about back emf (especially in connection wth speakers) it is usually a sign that they do not understand impedance and where it comes from. Sadly, in most cases they do not realise that they do not understand impedance but instead fondly believe that they have discovered a deeper meaning to impedance which eludes the rest of us.
I can't believe I'm "wrestling the pig" again.
The two sides of the either/or question you asked in your previous post, neither of which was correct, hence it was a nonsense question.
Why do you care about the current in the amplifier? You should only care about the current in the voice coil.
The two sides of the either/or question you asked in your previous post, neither of which was correct, hence it was a nonsense question.
Why do you care about the current in the amplifier? You should only care about the current in the voice coil.
If you ridicule something, then you will never understand it.
Huh? That is exactly what I care about. That's the ONLY thing I care about. Wow!
Because that is what we end up listening to, it is that current in the coil. But where does the current come from? The amplifier can control the voltage (low impedance assures that), but has ZERO control over the current in the voice coil.
Thank you!
Huh? That is exactly what I care about. That's the ONLY thing I care about. Wow!
Because that is what we end up listening to, it is that current in the coil. But where does the current come from? The amplifier can control the voltage (low impedance assures that), but has ZERO control over the current in the voice coil.
Thank you!
You don't see the contradiction in your own words?
Amplifier controls voltage (has required low output impedance) so shunt components don't change the current in the voice coil either therefore the current in the voice coil is the same in both cases.
Scott, about a year ago you, me and several other guys tried to explain this to Joe. This is a never ending story. Current and voltage drive was discussed as well. My web shows some comparison as well
Proudove buzeni repro a zkresleni repro
He (Joe) obviously does not understand Ohm's law. He does not understand that even the cleanest voltage source will supply distorted current if the load impedance is non-linear. He simply does not get it. He also does not understand that two parallel distorted currents may sum in an undistorted one, so he waves with additional resistor loading. I am also not sure that he understands that a pure clean current source will produce distorted voltage across non-linear impedance. And that the speaker is not a simple BLi but that there are much more sources of non-linearity that are not cured by a pure current drive.
Moreover, his fairy tales about class AB inability to drive complex load and about its apparent instability and additional high order distortion is annoying as well, at least. There is nothing that would persuade this guy that he is wrong, not speaking about the fact that he is unable to place any measurement supporting his pseudo-theories. This is one of the worst spread of fake information that may happen in diyaudio community, as it definitely has its followers.
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