Indiglo: That looks very similar to the infinity servostatik. I need to compare with my old sub. I was thinking going a few steps further and trying to move towards the sort of promise that NXP claimed and never delivered. Segmented electrostatics also show promise with enough segments, but they bring their own slew of problems 🙂.
Throw enough tech at the problem and sure we can reduce something by a gnats chuff!
Throw enough tech at the problem and sure we can reduce something by a gnats chuff!
There's lots of ways to measure position, fast and with precison, without loading a cone these days - if anyone wanted to do it they could. You could even use several, and try and compensate for the cone distorting in shape. No one seems to be doing it, either amateur or pro.... I wonder why....
Yes, Joe does use inappropriate terminologies and this causes confusions.
The key to what Joe is saying is that reactive currents need to be contained within the loudspeaker 'system' and then the loudspeaker appears as an 'ideal' resistive load to the driving amplifier.
The crux of the matter is that most (economical) amplifiers that are blameless when driving pure resistance loads are not 'blameless' when driving strongly reactive loads.
Dan.
Why the objection? Persistence is not a bad thing. Besides, there has been a LOT of progress and there is now more traction on this than ever. We are able to draw on other people's experiences, even some really good raw and solid measurements. I give others credit where it's due. a new more high resolution measurement is being developed - once a train gets momentum, then it becomes harder to stop. So maybe get on board rather than trying to stop it.
George, you do realise that a moderator must have started that thread!!!
I certainly have no memory of doing it - and I would not have used "Back-EMF and flat impedance" as the title. So I definitely did not start it. (Did Pano?)
So maybe you have over-rated my efforts? Never mind. Sigh.
Cheers, Joe
PS: As it seems I have the right to edit the first post, so I did, just to set the record straight - so check it out.
www.diyaudio.com/forums/solid-state/329854-emf-flat-impedance.html#post5572601
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What is this obsession with the 'new' word. I haven't even used that word.
That made me chuckle.
My Dad used to work for Philips as an engineer.
I used to work for Panasonic.
In a few days I will be 67. You would be surprised at my track record. I have been around, know what I mean? 🙂
Cheers, Joe
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Just to remind us how far away audio is from the bleeding edge Atomic clock performance enabling geodesy below the centimetre level | Nature
I know they are talking to get funding, but the possibility of using atomic clocks to measure gravity waves is somewhat mind boggling.
I know they are talking to get funding, but the possibility of using atomic clocks to measure gravity waves is somewhat mind boggling.
You have missed the obvious. The distortion is current distortion of the amplifier. The amplifier is only able to keep distortion low when looking at the voltage. This is a clear as the nose on your face. I am sorry, but not getting it, you are completely wrong.
Not at all. RM has just posted shortly ago that he senses that back-EMF is at the heart of this. Indeed the mechanism that explains it is rather straight forward, if not entirely obvious. The back-EMF modulates the current side of the amplifier and creates current distortion. The current sense resistor converts this into an accurate representation of what the current of the amplifier is triggered into doing. This now becomes the input of the speaker, not the voltage, but the current. This now becomes what is translated into dB-SPL that we hear at the front of the driver in a box.
There is absolutely nothing new here. This is always how it has been.
It also proves why a current source produces less distortion than a voltage source. Now the back-EMF cannot modulate the current of the amplifier, now the voltage across the current sense resistor looks a lot cleaner. A current source cannot supply reactive current, the voltage source does so happily, and now we got audible and measurable increase in distortion, but via microphone and on the current (actually the input) side of the speaker.
It also proves once and for all that a dynamic driver ignores the voltage of a voltage source, it simply reacts to the current that the amplifier supplies, the voltage becomes secondary.
The voltage of the amplifier tells us what we should be hearing, but the current tells us what we are actually hearing.
And at the heart of this altered current is the back-EMF impedance of the driver. Yes, I said impedance, because at any frequency you can indeed measure that back-EMF impedance and give it an Ohm value.
And thus it has always been. Just take a closer look. 🙂
I don't have difficulty grasping that. In fact I expect that. That is what is meant by a voltage source. Where are all these people who think otherwise?Joe Rasmussen said:
I am afraid the rest of your paragraph got lost somewhere between what you mean to say, and what I seem to be reading on the screen. Maybe you are saying that the load impedance sets the current drawn from a voltage source? Such deep thought!
I guess you could call DIYaudio social media. Online is not more difficult; you just have to use words to convey meanings. If people don't 'get it', it could be that they are thick or it could be that you are not expressing yourself clearly enough or it could be that they believe you are mistaken (and have probably tried to say so).
You treat us like idiots then complain about our attitude? Sorry, I am being combative again.
Makes you wonder why these audio manufacturers spent time and money in R&D for motional feedback loudspeakers then abandon it all some years later. Obviously they were aware of the benefits.
When you think about it measuring cone movement shouldnt be that difficult at all, inside an iphone is an integrated circuit only few mm in area that has both a 6-axis Gyroscope and Accelerometer.
When you say "back-EMF impedance" do you actually mean 'impedance'?Joe Rasmussen said:
A speaker designed to give a good response from a voltage source will take whatever current it needs to achieve that. This is not a fault.
I assume the 'distortion' you mention is measured acoustically? An electrical measurement tells us nothing.
The 1R test shows us that the current is distorted. That may tell us nothing about acoustic distortion. It could be that the distorted current is partly cancelling acoustic distortion. So the 1R test does not point the way; it may confuse the way for some people.
Surely the whole point of speaker distortion is that what we hear coming out is not what we put in? We know that the current drawn tells lies about frequency response, so how do we know that it tells the truth about distortion?
Why do you even have to say stuff like that? I just don't get it, maybe you are more concerned with ego than the science?
In fact, there has been some really good comments here, haven't you noticed?
Of course it does, maybe time to brush up on the topic.
I put this to an authority that must be respected (no, I am not going to do name dropping as that would be insensitive) and I stand by that statement and it is solidly based.
The motion of the coil responds only to the current in the coil, that response is an acoustic output. This shouldn't even be argued about. Classic 'garbage in, garbage out' and you can match the distortion of the current with the distortion of the dB-SPL of the driver - it can be measured. If you don't believe, then do the test, I challenge you.
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Certainly, and that is why measurements on acoustical side are provided as well with conclusion
Proudove buzeni repro a zkresleni repro
I am always assuming at least some elementary knowledge of circuit theory and acoustics - electric-acoustical transducers, so I assume people are not confused. Contrary to my optimism, even some people involved in audio design seem not to understand very basics.
Distortion seen in current with a voltage drive only reflects speaker nonlinearity converted to the electrical side. On the acoustical side, we can see both mechanical and electrical issues reflected in distortion.
No. The 'current distortion' does not come from the amplifier, it comes from the speaker. Whether this current distortion produces or partly cancels acoustic distortion is something you don't seem to have demonstrated - forgive me if I missed it. You talk as though the current distortion is necessarily a bad thing; you need to show this, not assume it. We know that the linear 'distortion' of the current (i.e. less current drawn near the bass resonance) is a good thing; so good that if you use current drive you need to achieve the same result via pre-compensation.Joe Rasmussen said:
Maybe this is your fundamental misconception? Restated again as
I am afraid he will never understand this. Maybe some more waving with "back-EMF"?
You are giving the impression to having found a new solution to decades of existing knowledge of which a number of companies already had products since the late 60's. Your solution of equalising the crossover network to appear resistive is not really inventive. The fundamentals of electromagnetism in a loudspeaker transducer is well understood.
I've always assumed that the amount of correction is small before the next problem gets the way* and, as the sub market got more competitive it wasn't worth the hassle. I think Demian knows a lot of what happened behind the scenes.
If you think infinity they had some eyewateringly expensive speakers that used the tech. The sub I have was $1600 in 1988 so $3500 now. The average sub sells for under $500! But a few still fly the flag for servo feedback.
*at the end of the day its the cone position you want to know and that might not be the coil position.
This reminds me of monty python and the holy grail "Oh but if I went 'round sayin' I was Emperor, just because some
moistened bint lobbed a scimitar at me, they'd put me away!"
If said person WAS an authority AND spoke to you as an authority then he would have stuff to back up the statement that he would be happy for you to reference.
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