Impedance and admittance are indeed defined as reciprocal quantities, no matter the circumstances.
YES.
Mills & Hawkesford - Distortion Reduction in Moving-Coil Loudspeaker Systems Using Current-Drive Technology is typical but they certainly weren't the first.
If you can measure acoustic distortion, you can prove to yourself that worthwhile benefits accrue whether you use cheapo mini computer speakers or the most expensive Golden Pinnae units.
I'll stick my neck out and claim if you don't measure less acoustic distortion with current drive, you probably have a wonky measurement. 😱
But non est tantum facile to make a good system using current drive. 🙂
IIRC, I published a circuit and results in The Audio Amateur before this AES paper. It follows along the lines given in the new book --- Current-Driving of Loudspeakers by Esa Merilainen. Esa has better emplimentation designs though. Something I measured with my motional feedback was not only lower THD but a slight shift in response to a lower bass cutoff freq.
Now that we are all on the same page ----- anyone going to make a pcb and try one of the ESA's circuits?? That would be 😎
Thx-RNMarsh
Now that we are all on the same page ----- anyone going to make a pcb and try one of the ESA's circuits?? That would be 😎
Thx-RNMarsh
Back in the day... when I was prolific in Audio --- I was thinking about the ACE-BASS system.... I saw a simplified diagram of it that got published for marketing/sales purposes. But, it seemed too complex and I didnt understand it and it wasnt being explained, technically. [Commercially the ACE-BASS died and with it the concept.]
I finally deduced that a series resistor (.27-.47 Ohms) was the only part of the ACE_BASS that was fundamentally needed and if I put it in series with the feedback resistor to ground, I might be able to reduce speaker distortion. I tried it with an VFA amp I had... and any amp would have worked as well. I then measured the before and after affects on speaker distortion and saw very good results.
Since no one else had ever published this simple idea, to my knowledge, I published it in The Audio Amateur magazine. It works well and is easy for any DIY'er to try. The data is there. It is now well known method. But the book referred to is much expanded on the idea and can potentially do better. I would start with this new book... my curiosity and experiment is still useful but now mostly as early historical work.
Thx-Richard Marsh
I finally deduced that a series resistor (.27-.47 Ohms) was the only part of the ACE_BASS that was fundamentally needed and if I put it in series with the feedback resistor to ground, I might be able to reduce speaker distortion. I tried it with an VFA amp I had... and any amp would have worked as well. I then measured the before and after affects on speaker distortion and saw very good results.
Since no one else had ever published this simple idea, to my knowledge, I published it in The Audio Amateur magazine. It works well and is easy for any DIY'er to try. The data is there. It is now well known method. But the book referred to is much expanded on the idea and can potentially do better. I would start with this new book... my curiosity and experiment is still useful but now mostly as early historical work.
Thx-Richard Marsh
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With respect to the distortion mania...the distortion of loudspeakers one could possibly measure is not the distortion you hear.
The center of our research is the psychology of auditive perception because only that matters.
For example analyzing the harmonics spectrum of a violin at some frequencies varies greatly
and the master violin player knows how change the spectrum in order to transport emotions. But despite of this varying distortion everyone identifies the sound source as a violin. A cello can be played in a manner that the first harmonic is 40 to 50 db below the second harmonic and higher order harmonics so it is seriously "distorted" but we hear clearly the first harmonic but do not hear a distorted cello.
The first archeologically unearthed man made instrument is supposed about 30.000 years old, a flute made from animal bones. Man supposedly invented many instruments since but only a few survived to our days.
Only those that "sound good". One important aspect - perhaps THE important - of psychology of auditive perception is a characteristic "fingerprint" of instruments which "sound good". The spectrum of harmonics has a spectrum in time domain, that is, the harmonics appear in a timely order , are not at all constant in amplitude and phase, and this "time series" make a cello sound like a cello entirely independent of "distortion".
Thus far more important - already essential- than the amplitudes of harmonics in case of technical sound field reproduction is their phase vs frequency and power.
Analyzing a couple of amps which excel with ultra low thd a high power it can be shown that these yet sound "not good" because said time series is entirely "unnatural". Here the one-triode-class A amp is unsurpassed as it behaves in this respect almost natural.
Distortion figures of loudspeakers don't tell anything practically demonstrable about the subjectively ( nothing else matters) assessed quality of sound reproduction.
The center of our research is the psychology of auditive perception because only that matters.
For example analyzing the harmonics spectrum of a violin at some frequencies varies greatly
and the master violin player knows how change the spectrum in order to transport emotions. But despite of this varying distortion everyone identifies the sound source as a violin. A cello can be played in a manner that the first harmonic is 40 to 50 db below the second harmonic and higher order harmonics so it is seriously "distorted" but we hear clearly the first harmonic but do not hear a distorted cello.
The first archeologically unearthed man made instrument is supposed about 30.000 years old, a flute made from animal bones. Man supposedly invented many instruments since but only a few survived to our days.
Only those that "sound good". One important aspect - perhaps THE important - of psychology of auditive perception is a characteristic "fingerprint" of instruments which "sound good". The spectrum of harmonics has a spectrum in time domain, that is, the harmonics appear in a timely order , are not at all constant in amplitude and phase, and this "time series" make a cello sound like a cello entirely independent of "distortion".
Thus far more important - already essential- than the amplitudes of harmonics in case of technical sound field reproduction is their phase vs frequency and power.
Analyzing a couple of amps which excel with ultra low thd a high power it can be shown that these yet sound "not good" because said time series is entirely "unnatural". Here the one-triode-class A amp is unsurpassed as it behaves in this respect almost natural.
Distortion figures of loudspeakers don't tell anything practically demonstrable about the subjectively ( nothing else matters) assessed quality of sound reproduction.
Were we designing musical instrument amplifiers, euphonic distortion might be desirable. For accurate music reproduction, a lack of distortion is required.
Under the name of YST, formerly AST, Yamaha uses Erik Stahl's concept. It consists of using two active feedback schemes around the power amp to redefine the whole electrical circuit amplifier+loudspeaker.
Here, member Bjorno has built a speaker using it. He may give you the details. Type "ACE bass" in the DiyAudio search facility for many more informations.
of what distortion? What is accurate?
A physicist with some basic knowledge in acoustics could easily demonstrate that a recording of a sound field produced by a free air - no reflecting walls and such cannot accurately be reproduced in any living room. That is plain physics.
It is not possible. So what is accurate?
Not sure what this forum will be about. The current-drive or motional feedback works. Now what?
Thx-RNMarsh
Thx-RNMarsh
Whatever is accurate, measurable (and audible) distortion added after the fact is by its very nature not accurate.
ultra low thd amps in general also achieve superior flatness of audio phase and frequency response by using high loop gain feedback
high negative feedback reduces all measured errors - "ultra low distortion" is expected to be inaudible
this excludes the moldy strawman "low thd at full power Only" scenario - everyone here is quite up to speed on the necessity to achieve low distortion at all power levels - heavy output bias is really the norm for quality diy amplifier designs recommended here
and the actual psychoaoustic data can be summarized as our hearing needing only a very modest better than ~1% preservation of relative amplitudes of harmonics, or adequate phase accuracy to keep the waveform envelope from changing by ~1% - completely trivial levels of accuracy for an amp using 60 dB of feedback gain over the entire audio band and adequately biased output Q
as far as I can see accurate current drive amps are going to use negative feedback too but require current sensing - the cheapest, most linear is a series R which has to be sized as a compromise between S/N and power loss
but otherwise the Iamp is delivering very similar I,V to the loudspeaker as a conventional Vamp for the same sound output
the biggest numerical change is the added compliance V if you want to ride over voice coil heating resistance rise at high power
but otherwise the Iamp is delivering very similar I,V to the loudspeaker as a conventional Vamp for the same sound output
the biggest numerical change is the added compliance V if you want to ride over voice coil heating resistance rise at high power
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voltage drive= the speaker sees varying current depending on impedance.
current drive= the amplifier sees variation of the needed voltage.
From the speakers point of view the difference is enormous and the design approach on drivers, enclosures and filters must be reassessed.
current drive= the amplifier sees variation of the needed voltage.
From the speakers point of view the difference is enormous and the design approach on drivers, enclosures and filters must be reassessed.
Experiment eventually published in TAA 1985.
See John Curls blowtorch preamp thread in the Lounge --- # 29746. Shows THD reduction from speaker.
Ckt looked like this:... Not MFB?
View attachment Motional FB CKT.pdf
THx-RNMarsh
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That is not the point. It is say "phase distortion" of the harmonics of the sound field reproduction. The consequence is then the gain section as well as for ex current to voltage must be extremely fast. Thus the old low open loop gain + very high open loop upper cut off frequency ( i.e. open loop GBW) has its merits. That excludes negative global feedback.
Btw. most hi end active speakers employ current drive.
Mr. Marsh, this isn't Motional Feedback but Negative Output R.
I was playing with this in the early 70's and it might go back to Voight. Yamaha YST/AST is basically this with fancy EQ (Da Linkwitz Transform is just crude EQ)
We did an OEM for Yamaha and realised we knew more about their method than they did. It was a very satisfying OEM contract.
Most OEM contracts are about knocking another $0.02 off the price but Yamaha were really concerned to get the best sound. Tanaka, who designed the NS1000, headed the team that visited us. He really didn't understand dis electronics sh*t but his young engineers deferred to him in everything. They dug him out of retirement for this so we were honoured.
ACE bass is the most sophisticated of these techniques and far more powerful than Yamaha's AST/YST. Very few (?!) people understand it properly. I pontificate a little on this in #4331 of cfa-topology-audio-amplifiers
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Mr. Marsh, in my above post, I touch on the 'equivalence' of the various descriptions of what may be the same thing. I would not call your simple method/AST/YST/Voight/bla bla Motional Feedback but that's da pedant in me.RNMarsh said:
However, the advantages (and disadvantages) are real and worthwhile.
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Can you name some .. especially if there are links to their circuits & acoustic performance?hahfran said:
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