I think that the back EMF is so highly non linear that it is hard to quantify. It is so dependent on the motor design and voicecoil length in the gap and any stray fields. It is extremely positionally dependent and becomes greater at higher excursions. This is one of my arguments for short coils in long gaps and a Faraday ring. I don't see any way you can make this linear with an equal hung voicecoil or overhung voicecoil, there is just to much asymmetry in the magnetic field from both the coil and gap geometry.
Just my 2 cents worth of observation on this part of the subject.
Just my 2 cents worth of observation on this part of the subject.
I'm not an EE, just a serious audiophile. But looking back at history, there are two individuals that I know of in the US audio engineering pool that have used the cartridge and the tape head in the feedback paths of their respective preamps; Keith Johnson in the Fairchild MTIS tape system and then in the Gauss Electro-Physics-Cetek tape duplicating system and John Stevens in the Stevens multi track recorder. Westrex used feedback in the 3D cutter head and amplifier system. Why isn't the phono cartridge and the tape head ever placed more frequently in the feedback path to linearize the playback? Thanks, Ray
Not to talk about membranes and suspensions+ crossovers + box in a multiway speaker... ;-)
And not to forget a speaker is a microphone too, so, the room...
Would that it were so simple. In fact there is a considerable range of opinions and attitudes, although there are, periodically, attempts to classify that fall short by trying to enforce imagined dichotomies. The most prominent is the subjective versus objective. A subset of this is the embracing or shunning of controlled tests.
The level of emotion imparted by posters is also quite variable, with particular topics like Bybee gadgets inspiring derision, mostly stemming from the absence of convincing physical mechanisms and measurements.
This thread is a bit of a free-for-all of course. Although nominally devoted to John's designs and followed by some for that, it is more of a general anything-goes exchange now, although sometimes we veer back to electronics. When it seems topical I've inserted a few actual schematics and even given breadboard performance results.
The things to be braced for, as a poster, are claims that combine sighted tests with attribution as to the physical mechanisms. There are folks here who know physics pretty well, even if they acknowledge that there is much left to be learned in the field. But when basic electromagnetic and electromechanical theory applies, problems with hypotheses that invoke these are going to be noticed and brought to our attention. There are plenty who really want to understand, have others understand, and are not just posting to close off further inquiry.
In other threads there is a good deal more rancor at times, but usually not on the scale of the more purely subjective fora. More commonly someone will build something and praise the original inventor, while commenting on soundstage enhancement etc. All based on sighted tests or pseudo-sighted (my wife heard it from the kitchen and noticed the change immediately). Many involve pride of ownership and are rich with expectation bias. And perhaps this is as it should be, given the name of the site. Diy audio is recreational for most who follow it.
"Not to talk about membranes and suspensions+ crossovers + box in a multiway speaker... ;-)
And not to forget a speaker is a microphone too, so, the room..."
Yes. to add to the confusion.
How about some current mode amplification Bill to add to all of this. There is nothing theoretically wrong with the premise I don't think. Just a different approach to the application of power.
CFA vs VFA, voltage application vs current application for driving a mechanical device.
And not to forget a speaker is a microphone too, so, the room..."
Yes. to add to the confusion.
How about some current mode amplification Bill to add to all of this. There is nothing theoretically wrong with the premise I don't think. Just a different approach to the application of power.
CFA vs VFA, voltage application vs current application for driving a mechanical device.
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There were some current mode graphs posed about 25000 posts ago. I am certainly intrigued by the claims of a 10dB reduction in distortion that some claim to measure, but I have never sat down to get my head around the practicalities of using it in my system. Or to put it another way, I have a lot of other things to sort before that is a worry.
Bill,
Get yourself a copy of the book: Current-Driving Of Loudspeakers by Eas Merilainen if you want to look into current driving speakers any further. I'm told by others, including I think Bcarso, that there are a few errors in his thinking but it does cover the concept fairly well. Perhaps he is a bit over enthusiastic about the implementation but there is nothing wrong with the concept. You do have to make some serious changes though vs voltage amplification and how you have to implement this. What I have still to figure out is what exactly he would change in the actual speaker itself to optimize their use with current drive, that is not clear at all.
Get yourself a copy of the book: Current-Driving Of Loudspeakers by Eas Merilainen if you want to look into current driving speakers any further. I'm told by others, including I think Bcarso, that there are a few errors in his thinking but it does cover the concept fairly well. Perhaps he is a bit over enthusiastic about the implementation but there is nothing wrong with the concept. You do have to make some serious changes though vs voltage amplification and how you have to implement this. What I have still to figure out is what exactly he would change in the actual speaker itself to optimize their use with current drive, that is not clear at all.
Going back to the earlier M1 example, having your input amplification via a
Common Base mode connection inserts the source into the "feedback" as
the cartridge's impedance is the degenerative component.
I think he is on track most of the time, but one can almost see the "true believer" gleam in his eye. And there is a trace of bitterness as AES (I don't know who made the decision) refused to run an ad for the book in the journal. The cover likely played a part.Well Brad recommends the book, so that's two votes. Bear in mind my interest in driving something you would take pity on me for (ribbon)
I encountered him in an online e-letter and my first reaction was negative, as I believed he was advocating driving just any loudspeaker from a high-impedance source---which would disastrously affect frequency response, particularly with voice-coil-level crossovers in place for a multiple-driver system. But as I read on and followed up with his subsequent online contributions, I realized he was a lot more sophisticated than this. So I bought the book. I also reviewed it on Amazon, mostly positively.
But he claims powerful and audible positive effects for current drive of loudspeakers designed for the purpose, and with proper equalization. He even gives sample circuits and board artwork! The problem is, once again, expectation bias. But to do a proper comparison of the effect of the method on loudspeaker performance is virtually impossible as going in you are comparing voltage-driven apples with current-driven oranges.
He is fighting an uphill battle for the adoption of the approach, as a great many loudspeaker designers are quite content with the status quo of voltage drive. And for marketing to devotees of mix-and-match audio, there are no current-drive amps or loudspeakers designed to work with them (I think, at least at this time).
The one immediate advantage of current drive for a given transducer is the absence of compression due to voice coil heating and the rise in d.c. resistance. This also leads to higher dissipation and potential thermal runaway, but he anticipates this and presents protection circuitry examples.
I tried to get a couple of people to look at the material and got no response. Despite their claims, I have found most loudspeaker and transducer designers to be quite conservative.
Mechanical damping?
As you drive a loudspeaker from a higher and higher source impedance, it's resonant behavior becomes dominated more and more by Qms, which is usually quite high. So you'd need some mechanical damping to tame it.
se
Well Brad recommends the book, so that's two votes. Bear in mind my interest in driving something you would take pity on me for (ribbon)
Esa has the first 43 pages (and other articles) available on his web site.
http://files.kotisivukone.com/currentdrive.ota.fi/tiedostot/sample2.pdf
Seekers of sensation might similarly consider the natural proposition of an MM cartridge coil in the cathode circuit of a common grid valve circuit..... NB grid circuit also remains available for feedback BTW ....... or try similar FET topologies......
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