Kuei Yang Wang said:
Hi Thorsten,
I largely agree with your views on this. But when you say, voltage drive is not needed to damp the cone, that may be technically correct, but wouldn't you say that it is something that can help. Full, complete mechanical compensation of the mechanical problems isn't possible I think. A little electrical help is nice.
The other comment I have is what you seem to advocate is an amp whose charateristics are matched to the particular speaker to use. That certainly will be good, but in practise that will be difficult. I wouldn't want to be in a position to have to mod my amp everytime I switch speakers. On the other hand, maybe I can have an amp with say a 3-pos switch (lo, med, hi) for speakers with lo, med or hi mech damping. Just thinking out loud.
Jan Didden
Konnichiwa,
Not only is this possible, but it has been done before. A 12" Coaxial Monitor Speaker developed for the German Radio in the late 1930's by Herr Eckmiller did exactly that, with the result that together with a competently designed X-Over the impedance response remained within better than +/-15% or thereabouts above 70Hz.
Why? It is helpfull in the same way as light was to drunk looking for his housekeys under a streetlight.
When asked by a policeman about it and where he had lost the keys the drunk pointed somewhere in the darkness and said "over there by my car"....
When the policeman asked why he did not look over there he said but the light is better here".
Some electrical damping is NOT helpfull because it makes us look in the wrong place....
Aone more argument for competently designed active speakers.
At any extent, you can make the amp continously adjustable easily.
Sayonara
janneman said:
Not only is this possible, but it has been done before. A 12" Coaxial Monitor Speaker developed for the German Radio in the late 1930's by Herr Eckmiller did exactly that, with the result that together with a competently designed X-Over the impedance response remained within better than +/-15% or thereabouts above 70Hz.
janneman said:
Why? It is helpfull in the same way as light was to drunk looking for his housekeys under a streetlight.
When asked by a policeman about it and where he had lost the keys the drunk pointed somewhere in the darkness and said "over there by my car"....
When the policeman asked why he did not look over there he said but the light is better here".
Some electrical damping is NOT helpfull because it makes us look in the wrong place....
janneman said:
Aone more argument for competently designed active speakers.
At any extent, you can make the amp continously adjustable easily.
Sayonara
Kuei Yang Wang said:
Nah. Nice joke, old, but still nice. But in practise, the speakers we and you are able to buy have a certain amount of mech damping that is not enough to compensate the mech defects (and some mech characteristics that are not defects but just, well, physics). So knowing that both mech and elec damping are available, why not use both. There's no law saying you can't...
Jan Didden
Konnichiwa,
There are some very notable and high performance exceptions if you also go along with using them open baffle.... ;-)
Other drivers can be modified by adding a flowresistance to have enough mechanical damping and this will generally be highly linear.
My point is that instead of worring about the "damping factor" (a cute misspelling often seen is "dumping factor" it is cute as it is accurate, much "dumping factor" and you really want to dump that amp) we should worry about sorting the problem directly. The overall benefits are material.
I used to have (again back in the 80's) an (active) speaker system that used current feed on the wideband midrange (and originally on the tweeter, until this was changed for a piezo) and a form of motional feedback on the woofers.
Considering the fairly cheap and basic (and small) drivers this system did play rather exceedingly well. Especially dynamics where superb, probably due to the absence of compression.
Now here is the rub. IS ELECTRICAL DAMPING actually available?
If so, how and HOW can it be linear, that is more linear than a simple mechanical solution?
There are many assumptions being made and lumped in under "dumping factor". Most assumtions are wrong.
Sayonara
janneman said:
There are some very notable and high performance exceptions if you also go along with using them open baffle.... ;-)
Other drivers can be modified by adding a flowresistance to have enough mechanical damping and this will generally be highly linear.
My point is that instead of worring about the "damping factor" (a cute misspelling often seen is "dumping factor" it is cute as it is accurate, much "dumping factor" and you really want to dump that amp) we should worry about sorting the problem directly. The overall benefits are material.
I used to have (again back in the 80's) an (active) speaker system that used current feed on the wideband midrange (and originally on the tweeter, until this was changed for a piezo) and a form of motional feedback on the woofers.
Considering the fairly cheap and basic (and small) drivers this system did play rather exceedingly well. Especially dynamics where superb, probably due to the absence of compression.
janneman said:
Now here is the rub. IS ELECTRICAL DAMPING actually available?
If so, how and HOW can it be linear, that is more linear than a simple mechanical solution?
There are many assumptions being made and lumped in under "dumping factor". Most assumtions are wrong.
Sayonara
Kuei Yang Wang said:
Well, isn't it? Isn't a low Zout adding to the already available (mech) damping?
I'm not saying it is more linear. You are right that given enough effort and ingenuity, you can built a speaker driver that is linear and has enough mech damping in itself. It just doesn't seem to happen. Why not? Economics?
Jan Didden
Konnichiwa,
You choose to make again many assumptions and then select a macro view of the subject that is abstracted to a level that makes it in effect useless to understand reality.
Try for a moment to cionsider the micro view and consider exactly how the "damping" happens.
Yes, economics, the NIH (not invented here) principle and of course the great true god of all is now, the impotent What Can I Do and his dull brother What We Did Yesterday and his ugly and vicious sister Get Them Before They Get Us.
And the countries who stand a chance to really invent things and change things drastically (eg emerging econimies like Chine) are happy to copy and play catchup ionstead of innovating.
I figure the human race is screwed....
Sayonara
janneman said:
You choose to make again many assumptions and then select a macro view of the subject that is abstracted to a level that makes it in effect useless to understand reality.
Try for a moment to cionsider the micro view and consider exactly how the "damping" happens.
janneman said:
Yes, economics, the NIH (not invented here) principle and of course the great true god of all is now, the impotent What Can I Do and his dull brother What We Did Yesterday and his ugly and vicious sister Get Them Before They Get Us.
And the countries who stand a chance to really invent things and change things drastically (eg emerging econimies like Chine) are happy to copy and play catchup ionstead of innovating.
I figure the human race is screwed....
Sayonara
Circlotron said:
...but the current controlling the FORCE is working against the spring constant of the cone suspension - this WILL convert the FORCE into a linear DISPLACEMENT (assuming the suspension is made to exibit a linear behaviour - i.e. is operating in the same plain as the DISPLACEMENT).
Now, I don't know much about dynamic loudspeakers, however from a first guess I would assume the conversion of linear FORCE into DISPLACEMENT using a conventional suspension will follow a sine/cosine function. Any thought on this anyone?
I can post an image if this isn't clear.
Hi,
Since digital precision equalization exist, infinite Z out isn't a problem (theorethically). Response (mainly a rise in output with frequency) can be easily compensated.
I'm thinking in using some digi amps with balanced inputs, where a current feedback arrangement could be easily done (Coldamp or Hypex). Do you see any problems with this?
Regards,
Roberto
Since digital precision equalization exist, infinite Z out isn't a problem (theorethically). Response (mainly a rise in output with frequency) can be easily compensated.
I'm thinking in using some digi amps with balanced inputs, where a current feedback arrangement could be easily done (Coldamp or Hypex). Do you see any problems with this?
Regards,
Roberto
Hello everyone,
Just want to add my own experience on current driven loudspeakers:
With an excellent compression driver loaded with a horn with very reduced reflexion from mouth to throat, the frequency curve within the bandwith is nearly the inverse of the impedance curve.
With the TAD TD2001 on such a horn (Marco 320Hz) when voltage driving is used you can see the on the frequecny curve the famous 1600Hz-1900Hz of the TAD2001 the origin of which is welle explained by Ken Kinoshita in the papers:
Design of 48mm Beryllium Diaphragm Compression Driver
Preprint Number: 1364 Convention: 60 (April 1978)
Authors: Kinoshita, Shozu; Yoshimi, Toshikazu; Hamada, Hiroyuki; Locanthi, Bart N.
The Influence of Parasitic Resonances on Compression Driver Loudspeaker Performance
Preprint Number: 1422 Convention: 61 (October 1978)
Authors: Kinoshita, Shozo; Locanthi, Bart N.
You can see the shape of the frequency curve I obtained on this
http://www.musique-concrete.com/mesures.htm
In blue voltage drive in pink the very linear curve obtained usisng my Shabda amplifer (Zout = 53ohms)
If you can read French (but the garphs are easily understable for non french speaking persons ) you can read the little document I wrote about the linearization of the 1900Hz hole in the frequency response curve of the TD2001:
http://www.musique-concrete.com/guide_fichiers/creux19.doc
You'll find in this docuemnt a very enlighting compraison between the impedance cureve of the TD2001 loaded by the horn and its frequency response curev on the same horn. Every peculiar features of the frequency response curve possess its equivalent but reversed on the impedance curve
Best regards from Paris,
Jean-Michel Le Cléac'h
3.) Added linearity.
Just want to add my own experience on current driven loudspeakers:
With an excellent compression driver loaded with a horn with very reduced reflexion from mouth to throat, the frequency curve within the bandwith is nearly the inverse of the impedance curve.
With the TAD TD2001 on such a horn (Marco 320Hz) when voltage driving is used you can see the on the frequecny curve the famous 1600Hz-1900Hz of the TAD2001 the origin of which is welle explained by Ken Kinoshita in the papers:
Design of 48mm Beryllium Diaphragm Compression Driver
Preprint Number: 1364 Convention: 60 (April 1978)
Authors: Kinoshita, Shozu; Yoshimi, Toshikazu; Hamada, Hiroyuki; Locanthi, Bart N.
The Influence of Parasitic Resonances on Compression Driver Loudspeaker Performance
Preprint Number: 1422 Convention: 61 (October 1978)
Authors: Kinoshita, Shozo; Locanthi, Bart N.
You can see the shape of the frequency curve I obtained on this
http://www.musique-concrete.com/mesures.htm
In blue voltage drive in pink the very linear curve obtained usisng my Shabda amplifer (Zout = 53ohms)
If you can read French (but the garphs are easily understable for non french speaking persons ) you can read the little document I wrote about the linearization of the 1900Hz hole in the frequency response curve of the TD2001:
http://www.musique-concrete.com/guide_fichiers/creux19.doc
You'll find in this docuemnt a very enlighting compraison between the impedance cureve of the TD2001 loaded by the horn and its frequency response curev on the same horn. Every peculiar features of the frequency response curve possess its equivalent but reversed on the impedance curve
Best regards from Paris,
Jean-Michel Le Cléac'h
phase_accurate said:
3.) Added linearity.
GRollins said:
Tosh, bunkem and twoddle.
While the statement "Without voltage you will have no current" is perfectly valid, the statement that there is no such thing as current drive is complete lunacy.
I suggest you look up the terms "independent variable" and "dependent variable".
Fundamentally the motion of a coil in a magnetic field follows: F = BLi (i.e. the integral of magnetic flux, multiplied by the coil inductance and the current through the coil gives rise to a force at right angles to both the magnetic field and the current through the coil).
Ignoring all other forces on the cone, the above dictates that the acceleration of the cone is directly proportional to the current through the voice coil (ignoring non-homogeneous magnetic field across the voice coil), therefore it is the current that we wish to control to control cone movement.
Now, assuming voice coil impedance is not complex (i.e. purely resistive) then yes, your argument stands up - we can control voice coil current directly by controlling the voltage across the voice coil. However as driver impedance is frequency dependent we cannot and therefore directly driving a loudspeaker with a controlled current seems like the obvious choice.
Jean-Michel, if you still have the graphs and .doc you linked to in the quoted post of yours, I'd be obliged if you could repost them as the links are dead. I'm doing some research into high output Z amps and compression drivers/flares and this is one of the few comments I've found on this subject.Jmmlc said:
Cheers
I'm fairly sure I've read about this being tried in the past. Unfortunately I cannot recall where, or by whom.
Thinking about it, this is analogous to an output impedance directly proportional to that of the driver itself - there are numerous examples (online) of amplifier projects that approximate this, for example:
http://sound.westhost.com/project56.htm
I hope this is useful.
Pashley said:
annex666 said:
This claims power feedback :
http://www.stan-white.com/a_doc_pwtr_1.htm
Hi forr,
Good reference. My comments.
Voltage NFB provides accurate voltage output.
It is the reactive loudspeaker characteristic which modifies the power response of the system, no matter what type of amplifier might be used.
The solution for accurate reproduction is a low Q loudspeaker system design, because fancy passive/NFB based compensation networks cannot work in the same (delayed energy storage) time frames without modifying on-going (power) throughput.
Firstly, if the driver has Q it takes additional power to dynamically start its cone moving linearly, also to stop it, plus secondly, variable power levels according to frequency in time frames which lag the amplifier's live signal waveform. Controlling one aspect will introduce group delay to the other, and introduce audible characteristics.
I am not saying that the resulting reproduction would be dissonant, but it would not sound realistic.
Cheers .......... Graham.
Good reference. My comments.
Voltage NFB provides accurate voltage output.
It is the reactive loudspeaker characteristic which modifies the power response of the system, no matter what type of amplifier might be used.
The solution for accurate reproduction is a low Q loudspeaker system design, because fancy passive/NFB based compensation networks cannot work in the same (delayed energy storage) time frames without modifying on-going (power) throughput.
Firstly, if the driver has Q it takes additional power to dynamically start its cone moving linearly, also to stop it, plus secondly, variable power levels according to frequency in time frames which lag the amplifier's live signal waveform. Controlling one aspect will introduce group delay to the other, and introduce audible characteristics.
I am not saying that the resulting reproduction would be dissonant, but it would not sound realistic.
Cheers .......... Graham.
annex666 said:
Those are not really (dynamically) "variable impedance amplifier". They are just examples of a few ways to get whatever (constant) output impedance one may want to obtain.
Although as you say it may somewhat approximate "power-drive", unless the speaker has a constant, purely resistive impedance (which of course it doesn't have) it is not really the same thing.
forr said:
not really either.
Again, AFAICT, also this one is no more than just a "low DF" drive. And just like the aforementioned SS example, it too make use of "mixed-mode" (voltage and current) NFB to keep the output impedance (relatively) high.
IMHO there is nothing special about the UL arrangement with respect to this aspect. Just add more current and/or less voltage NFB and you can get the same behavior from triodes or the other way around (more voltage and/or less current NFB) to get it from pentode mode. As shown in the previous link, it can be done with SS too...
To make a true "power-drive" you'd need an "amplifier" (...more properly a "servo") which e.g. senses both the load voltage and current, calculate the instantaneous product of the two (that is, a signal proportional to the actual instantaneous power in the load - independently from the instantaneous value of the load itself!) and use that signal in an NFB loop to make sure that it is always proportional (by a constant "gain") to the control signal (e.g. the input voltage).
One way or the other, you should get: Vout * Iout = K * Vin^2
not an easy thing to do if the load is not a fixed resistor...
...and, AFAIK, something that no-one have tried so far.