I believe voltage translates to cone velocity. It's a linear motor, after all. It will be a bit squishy because of the ohmic resistance, of course, and there is a restoring force to a central position.
Jeroen Belleman
On 30/06/14 19.20, Glenn wrote: ...
...
Bugger...
Please remember that from a "4 ohm" loudspeaker 3.96 ohm is from the voice coil resistance and 0.04 ohm (assuming 1% efficiency; 92dB/1W/1m) is from the acoustic impedance.
Glenn
Agreed.
However... one can use active feedback to get high impedance out without the power loss.
Marshall actually do this in some of their transistor guitar amps (MG series) in an effort to duplicate the alleged sound differences of the higher impedance of tube/valve amps.
Note, guitarists are not seeking fidelity.
Kevin Aylward B.Sc.
and then there's everything else:
random example
-Lasse
Fundamental theory shows that this is completely untrue. The falsehood is confirmed by measurements and by listening tests which I (and lots of other engineers) have conducted over many years on loudspeakers, disc and cylinder cutterheads, servo motors and other electromagnetic transducers.
Current driving completely nullifies the inherent motional-feedback effect of the back E.M.F. and allows resonances of the speaker, cabinet and air mass to take control. This is exactly what you do not want for good quality sound.
I cannot comment on that statement because it make no sense whatsoever.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Also, stepper motors positioning paper in front of ??
Remember those 'simple to use' Riga stepper motor driver chips that had the extreme advantage of going into current limit when a step is acquired? You simply put in, direction, step and power and the little H drives would figure out that the current limit was achieved so went into 'switch mode'
The ringing caused by that was catastrophic in a paper positioning system! Not a half step over undershoot ringing back and forth, but almost enough to break cog and jump one more step!
Anyway, I confim that a loudspeaker run by current drive sounds terrible!
In this day of solid state and driving with zero impedance the driver is pretty 'stiff'. Is that stiffness too good? I didn't try using resistance to slightly allow a bit of softness. Does that sound better?
Den tirsdag den 1. juli 2014 00.08.24 UTC+2 skrev Robert Macy:
pretty much every stepper driver you can buy is switching constant current and it works very well, but if you don't use micro stepping and just hammer it at max current of cause it'll ring
if you wan any kind of speed out of a stepper you need constant current and many times the rated voltage
speakers should be driven with low impedance because that is what they were designed for
-Lasse
They are the same thing.
I guess some of these current drive scenarios might involve current sense feedback instead of voltage feedback. i.e. a fairly conventional amplifier is used but where feedback is taken from a low value sense resistor in the speaker ground wire instead of output voltage feedback via a divider. The amplifier is then servoing speaker current to faithfully follow the input. Should then still have plenty of muscle to damp speaker resonances when they occur ??
But the amp won't know when there's a resonance. Power = I^2*R, so when the speaker has a hi-z resonance, a constant-current amp will force more power into the speaker, making a boom peak at that frequency.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
They also tried to apply this to very early dynamos by using thin wires. Of course, the dynamo got hot, without any benefits.
On 30/06/14 23.08, Lasse Langwadt Christensen wrote:
Hi Lasse
If your example is a full tone speaker, then it had it's resonances pretty dampened. I assume no attached filter network.
Lower impedance 4 ohm.
It has a resonance at 80Hz, with an impedance at 10 ohm. Pv=R200Hz*I^2 Pi=R80Hz*I^2. Pi/Pv=2.5*1. dB= 10*log10(2.5) ca.= 4dB. That difference is barely audible.
It has a impedance (almost flat) top at 2000Hz, with an impedance at 15 ohm. Pv=R200Hz*I^2 Pi=R2000Hz*I^2. Pi/Pv=3.75*1. dB= 10*log10(3.75) ca.=
6dB. That difference is just audible.That slow power (impedance) change is easily remedied by an active filter in front of the PA, whether digital or not.
Conclusion:
Your example shows that current drive with an electronic filter (whether digital or not) will work fine with your example.
-Please note this:
Speakers er naturelly current driven. I you drive them by voltage, the sound will be amplitude modulated by the coil heating. When the coil heats lower current for same voltage will result. Add a filter nework and you will complicate things further.
Prerequisite/requirements:
A lot of sources have been supplied in earlier posts. Where are yours?
One of my sources is here:
October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:
The author argues that the sound quality of virtually all existing speaker systems has been severely impaired by the manifoldly indefinite electromotive forces induced in the voice coil (arising from both motion and inductance), that corrupt the flow of current; and what's dramatic - the measurable evidence is plain and overwhelming. These inherent EMFs in themselves can never be suppressed by any kind of amplifier, but their detrimental effect on current and hence on sonic performance can be eliminated by adequate source impedance. Thus, the secret of valve amplifiers also becomes apparent. ... According to laws of physics, electric current is that which in a speaker driver effects diaphragm acceleration, which in turn produces sound pressure. Yet all power amplifiers strive, often tooth and nail, to control the voltage at the loudspeaker terminals, which only indirectly affects the current flowing in the voice coil. ... This force, then, determines the acceleration (A) of the diaphragm, which in the main operation area (the mass-controlled region) is got from the Newtonian law F = mA. The radiated pressure, in turn, follows the instantaneous acceleration and not the instantaneous displacement, as many mistakenly imagine. ... There cannot be found any scientifically valid reasons that justify the adoption of voltage as the control quantity - it is only due to the historical legacy originated almost a century ago, most likely by cheapness and simplicity; the quality and physical soundness of operation have not been considerations in this choice. Engineers are also more accustomed to identifying electrical signals as voltages rather than currents. ..."
Glenn
Hi Lasse
If your example is a full tone speaker, then it had it's resonances pretty dampened. I assume no attached filter network.
Lower impedance 4 ohm.
It has a resonance at 80Hz, with an impedance at 10 ohm. Pv=R200Hz*I2 Pi=R80Hz*I2. Pi/Pv=2.5*1. dB= 10*log10(2.5) ca.= 4dB. That difference is barely audible.
It has a impedance (almost flat) top at 2000Hz, with an impedance at 15 ohm. Pv=R200Hz*I2 Pi=R2000Hz*I2. Pi/Pv=3.75*1. dB= 10*log10(3.75) ca.=
6dB. That difference is just audible.That slow power (impedance) change is easily remedied by an active filter in front of the PA, whether digital or not.
Conclusion:
Your example shows that current drive with an electronic filter (whether digital or not) will work fine with your example.
-Please note this:
Speakers er naturelly current driven. If you drive them by voltage, the sound will be amplitude modulated by the coil heating. When the coil heats lower current for same voltage will result.
The speakers impedance varies with speaker coil temperature (power history dependent for each speaker...) - up to a impedance factor of two.
Add a filter nework and you will complicate things further.
Prerequisite/requirements:
A lot of sources have been supplied in earlier posts. Where are yours?
One of my sources is here:
October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:
The author argues that the sound quality of virtually all existing speaker systems has been severely impaired by the manifoldly indefinite electromotive forces induced in the voice coil (arising from both motion and inductance), that corrupt the flow of current; and what's dramatic - the measurable evidence is plain and overwhelming. These inherent EMFs in themselves can never be suppressed by any kind of amplifier, but their detrimental effect on current and hence on sonic performance can be eliminated by adequate source impedance. Thus, the secret of valve amplifiers also becomes apparent. ... According to laws of physics, electric current is that which in a speaker driver effects diaphragm acceleration, which in turn produces sound pressure. Yet all power amplifiers strive, often tooth and nail, to control the voltage at the loudspeaker terminals, which only indirectly affects the current flowing in the voice coil. ... This force, then, determines the acceleration (A) of the diaphragm, which in the main operation area (the mass-controlled region) is got from the Newtonian law F = mA. The radiated pressure, in turn, follows the instantaneous acceleration and not the instantaneous displacement, as many mistakenly imagine. ... There cannot be found any scientifically valid reasons that justify the adoption of voltage as the control quantity - it is only due to the historical legacy originated almost a century ago, most likely by cheapness and simplicity; the quality and physical soundness of operation have not been considerations in this choice. Engineers are also more accustomed to identifying electrical signals as voltages rather than currents. ..."
-Of cause the (many-way) speaker(s) has to be adjusted for good (time domain) impulse reponse - and frequency response - after applying current-drive of each speaker individually.
The current driven speaker has lower IM distortion and way better impulse response, which our ears among others uses for directionality of the original music.
Glenn
On 30/06/14 23.08, Lasse Langwadt Christensen wrote:
Hi Lasse
If your example is a full tone speaker, then it had it's resonances pretty dampened. I assume no attached filter network.
Lower impedance 4 ohm.
It has a resonance at 80Hz, with an impedance at 10 ohm. Pv=R200Hz*I^2 Pi=R80Hz*I^2. Pi/Pv=2.5*1. dB= 10*log10(2.5) ca.= 4dB. That difference is barely audible.
It has a impedance (almost flat) top at 2000Hz, with an impedance at 15 ohm. Pv=R200Hz*I^2 Pi=R2000Hz*I^2. Pi/Pv=3.75*1. dB= 10*log10(3.75) ca.=
6dB. That difference is just audible.That slow power (impedance) change is easily remedied by an active filter in front of the PA, whether digital or not.
Conclusion:
Your example shows that current drive with an electronic filter (whether digital or not) will work fine with your example.
Thanks.
-Please note this:
Speakers er naturelly current driven. If you drive them by voltage, the sound will be amplitude modulated by the coil heating. When the coil heats lower current for same voltage will result.
The speakers impedance varies with speaker coil temperature (power history dependent for each speaker...) - up to a impedance factor of two.
Add a filter nework and you will complicate things further.
Prerequisite/requirements:
A lot of sources have been supplied in earlier posts. Where are yours?
One of my sources is here:
October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:
The author argues that the sound quality of virtually all existing speaker systems has been severely impaired by the manifoldly indefinite electromotive forces induced in the voice coil (arising from both motion and inductance), that corrupt the flow of current; and what's dramatic - the measurable evidence is plain and overwhelming. These inherent EMFs in themselves can never be suppressed by any kind of amplifier, but their detrimental effect on current and hence on sonic performance can be eliminated by adequate source impedance. Thus, the secret of valve amplifiers also becomes apparent. ... According to laws of physics, electric current is that which in a speaker driver effects diaphragm acceleration, which in turn produces sound pressure. Yet all power amplifiers strive, often tooth and nail, to control the voltage at the loudspeaker terminals, which only indirectly affects the current flowing in the voice coil. ... This force, then, determines the acceleration (A) of the diaphragm, which in the main operation area (the mass-controlled region) is got from the Newtonian law F = mA. The radiated pressure, in turn, follows the instantaneous acceleration and not the instantaneous displacement, as many mistakenly imagine. ... There cannot be found any scientifically valid reasons that justify the adoption of voltage as the control quantity - it is only due to the historical legacy originated almost a century ago, most likely by cheapness and simplicity; the quality and physical soundness of operation have not been considerations in this choice. Engineers are also more accustomed to identifying electrical signals as voltages rather than currents. ..."
-Of cause the (many-way) speaker(s) has to be adjusted for good (time domain) impulse reponse - and frequency response - after applying current-drive of each speaker individually.
The current driven speaker has lower IM distortion and way better impulse response, which our ears among others uses for directionality of the original music.
Glenn
Early electrical folks didn't use much theory, so did a lot of expensive experiments, like almost-useless transatlantic telegraph cables. Edison was bad that way. Lee DeForest never understood how his triode worked.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Sorry, I haven't read the whole thread yet, but I suggested such a circuit to someone regarding the inoput to a sound card to use for instrumentation. Not a USB scope, a scope running off the linbe input of a PC soundcard.
They generally have a single ended supply so DC coupling was pretty much ou t. However a depletion mode FET does the trick quite nicely.
What beats me about this is why anything after the FET ? Just stick the sou rce to the input of the scope. It should be a megohm.
When I did TV service, DC was importanyt to me. Came a time when they almos t put more in TV to make them not work (shutdown) than to work. I needed a scope to measure DC, for one, to see how fast it dropped. If it drops like a rock it is shorted or whatever,m or bad filtewrs. If the HV stops and it floats down taking its good old time, the problem is not a direct or nearly direct short. I wanted it to synch fast, to the pulse on the HOT or HVOT s o I could see if it is distorted. Those old Tek with the tunnel diode trigg ering were the best for that.
Of course any offset can be compensated. I could easily make that circuit d o that, and adjust itself. It's already got + and - supplies, why didn't he do it ?
I have just went flicking around the thread here and someone said cascode. That is NOT a cascode circuit. It is actually a common drain stage feeding two common collector stages.
Cascode, from what I thinik I tremember is a common emitter feeding a commo n base, or a common source feeding a common gate, or some such combination.
It has medium input impedance, extremely high voltage gain and output imped ance. Mainly used for small signal, RF, shit like that. Used rarely in inst rumentation for obvious reasons. (stability) You CAN, but it can be a bitch . Shit would oscillate if you looked at it crooked.
On 01/07/14 00.08, RobertMacy wrote: ...
...
Hi Robert
Do you have an articles reference?
Or should I trust:
-
PS: There is no need to mention electrodynamically position systems. It has nothing to do with the purpose to make acoustic sounds.
Source:
October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:
Glenn
On 01/07/14 00.33, Lasse Langwadt Christensen wrote: ...
Hi Lasse
There is no need to mention electrodynamically position systems. It has nothing to do with the purpose to make acoustic sounds.
Source:
October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:
Glenn
Just wondering, why feedback from the actual cone has not been more used during the years.
The only one I know of was the Philips MFB series, which used a piezo accelerometer on the cone. By integrating you got the cone speed and integrating again you got the cone position. Other measurement methods would certainly be possible.
Every basic electrical engineering textbook contains the necessary information, all you have to do is read it and understand it.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On 01/07/14 09.34, Adrian Tuddenham wrote:
Hi Adrian and others
Please read this:
Current-Driven Switch-Mode Audio Power Amplifiers. Research - peer-review ? Article in proceedings ? Annual report year: 2012:
Proceedings of 132nd AES Convention Current-Driven Switch-Mode Audio Power Amplifiers:
Comparative Analysis of Moving-Coil Loudspeakers Driven by Voltage and Current Sources:
How is that possible you ask? It is well known that most of the power delivered to a speaker is dissipated as heat in the voice coil. Speakers are poor transducers of electrical energy into acoustical energy. A typical conversion efficiency for a domestic speaker is about one to two percent. That means that up to 99 percent of the signal is spent heating up the voice coil. Voice coil hearing has been estimated as being on the order of 0.4 percent per degree centigrade for copper wire. It is not uncommon for voice coil temperatures to spike up to 200 degrees centigrade, at which point a 6-ohm nominal voice coil resistance increases to 10.3 ohms. As the voice coil heats up, the power delivered by a voltage-controlled amplifier decreases. This leads to loss of sensitivity with increasing drive signal, also known as power compression. Since the loss of sensitivity would be most prominent in regions of minimum impedance, shifts in frequency response would also occur with drive signal level. For a woofer, the impedance minimum corresponds to the lower midrange, which implies tonal balance shifts as the vice coil heats up and cools down. In addition, the increased resistance reduces driver damping and leads to misalignment of crossover networks. ... Current drive offers the potential for dramatic reduction in moving-coil speaker distortion due to power compression and other voice-coil non-linearities. ... On the speaker design side, things are also different. For example, the ploy of reducing a driver's rated impedance from 8 ohms to 4 ohms in order to gain 3dB in sensitivity does not work with a current source amplifier. Instead of doubling the current draw, as would be the case with a voltage-controlled amplifier, the current draw remains the same, which means that sensitivity is actually lost. On the other hand, increasing impedance leads to increased sensitivity with current drive. Consider that a woofer's resonance region is no longer current limited and sinks the same current as the frequency band above resonance. That makes for a huge boost in bass response around the resonance region. The bottom line is that using drivers of differing nominal impedance but identical sensitivity ratings will result in output mismatches. Finally, conventional parallel type crossover networks do not work well with current sources. I spent a weekend convincing myself of that. Instead, series type networks are necessary for optimal performance. No wonder then that current source amplifiers require matching loudspeakers, designed for a current drive interface, and capable of taking full advantage of their distortion reducing potential. ... The green curve gives the system response when driven by the F1. The purple curve illustrates the frequency response when driven by the Pass Aleph 30 ? a conventional voltage controlled amplifier. The bass extension under current drive conditions is obvious, resulting in an F3 of 45Hz. The fine tuning of the overall Q was done by ear to obtain the most satisfying in-room bass quality. ..."
-Transconductance Power Amplifier Systems for Current-Driven Loudspeakers:
Who have access and can read this?:
Effects of Acoustic Damping on Current-Driven Loudspeakers:
Glenn
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