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Increase (electrical) Damping of a Driver

If a moving coil transducer utilizes an aluminum foil voice coil former, then Rms (lumped mechanical losses) will be increased relative to nonconductive former due the electromagnetic drag created in the gap. Qms and thus Qts will then be reduced.

Doug Button was granted a US Patent, US5828767 (Expired), https://patentimages.storage.googleapis.com/d4/43/0d/d3946a59f4bf99/US5828767.pdf for implementation of this concept in a push-pull motor assembly.

Typically, this concept is demonstrated in physics classes by dropping a magnet into a vertical aluminum or copper pipe and observing the slow motion descent of the magnet inside the pipe.
 
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NTK said:
The problem is that the DC resistance of the voice coil was totally ignored. For "electrical damping", the effects from the amplifier output resistance and the voice coil DC resistance are the same. Once the amplifier output resistance is below about 10% or 20% of the voice coil resistance, reducing it further does nothing (in terms of electrical damping). This has been pointed out by George Augspurger almost 60 years ago (source), 8 years before Dr Toole's article "Damping, Damping Factor, and Damn Nonsense" (source).

View attachment 489290
Click to expand...
To return to the point of this thread, i had AI answer some questions, to help folks like myself on this thread: who have a keen interest, and some limited intellect, but no formal electrical engineering background, just general high school level physics and half a brain to go on.

Most contributors seem to be better informed, but for those suffering from this same dangerous thing called "a little knowledge" i extracted this from a reasonably adequate AI bot:

ME:

Tx, i would prefer if you could explain what the use is of a 5 digit damping factor, if it's effect is limited by the VC resistance. Higher than a certain value it is not gonna damp any better, it just indicates how well the negative feedback is designed. So that raises the question what other factor is the secret to Purifi's incredible cone movement control, if DF is so high it's level is no longer significant.

AI:

You're hitting a very insightful and nuanced point about damping factor (DF) and amplifier control! Let’s explore why very high damping factor numbers (like 5-digit values) are often more about amplifier design quality than practical speaker control, and what else really makes Purifi amps exceptional in controlling speaker cone movement.

1.​

  • As you said, once the damping factor exceeds a few hundred or a few thousand, the incremental improvement in actual speaker cone control becomes negligible.
  • This is because the voice coil resistance (VC resistance)—typically around 4–8 Ω—dominates the series impedance.
  • For example, if the VC resistance is 6 Ω, and the amplifier output impedance is 0.001 Ω (very low), the damping factor is 6000.
  • Reducing the output impedance further to 0.0001 Ω increases DF to 60,000, but the speaker coil resistance still dominates, so the extra control gained is minimal.

2.​

  • A very high damping factor mostly reflects the amplifier’s extremely low output impedance.
  • This low output impedance is a result of very high loop gain and well-implemented negative feedback.
  • So, a 5-digit DF is more a measure of the amplifier’s linearity, stability, and feedback design quality than a direct indicator of speaker control improvement.
  • It shows the amplifier can maintain a nearly ideal voltage source behavior, with minimal voltage drop under varying load conditions.
  • (ME: i think this one is relevant to the topic)

AI:​

3.​

Purifi’s remarkable performance goes beyond just a high damping factor. Here are other key factors:

a)​

  • Purifi amps achieve ultra-low harmonic and intermodulation distortion, even at very low output impedances.
  • This means the amplifier’s output current and voltage are extremely faithful to the input signal, without introducing artifacts that could cause unwanted cone motion or distortion.
  • Cleaner current drive means more precise and predictable cone movement.

b)​

  • The feedback loop bandwidth and speed of response are critical.
  • Purifi’s designs have very wide bandwidth and fast feedback loops, enabling the amplifier to react instantly to changes in speaker current demand or back EMF.
  • This rapid correction means the amplifier can actively “counteract” non-ideal speaker behavior, improving control beyond what damping factor alone predicts.
  • (ME: Ahaa! Interesting..)

AI:​

c)​

  • Purifi uses sophisticated error sensing and correction inside the amplifier.
  • This includes local current feedback, predictive error correction, and optimized compensation.
  • These techniques allow the amplifier to actively shape the current waveform driving the coil, reducing distortion and improving control.

d)​

  • The amplifier’s phase response and stability affect how well the feedback loop can control the speaker.
  • Purifi amps maintain stable, phase-accurate feedback at high frequencies, preventing oscillations or lag that degrade control.

4.​

  • Damping factor beyond a few thousand is mostly a theoretical or marketing number for speaker control.
  • The real secret to Purifi’s exceptional cone control lies in ultra-low distortion, fast and stable feedback, and advanced error correction, not just raw damping factor.
  • These factors translate into more precise current delivery and voltage control, which governs the speaker cone movement with exceptional accuracy.
ME:

Hhhmmm, AI still sounds like someone who's just attempting to please me, but at least SOME valid point were formulated, using terms that can be useful for search prompts on the subject.

Cheers, and sorry if anyone got bored.
 
"To return to the point of this thread, I had AI answer some questions."

Google AI Overview
Damping: Definition, Types, and Formula
Damping is the process where the energy of an oscillating system (like a swing, sound wave, or electrical current) is gradually reduced and dissipated, usually as heat, causing the vibrations or oscillations to die down over time. It's a natural or engineered mechanism that reduces the amplitude of movement, preventing excessive oscillations and controlling vibrations, seen in car shock absorbers, door closers, or skyscrapers.

Key Aspects of Damping:
Energy Dissipation: Damping works by converting kinetic or electrical energy into thermal energy (heat) through friction or other resistive forces.
Amplitude Reduction: The main effect of damping is to decrease the size (amplitude) of vibrations or waves.
Control of Resonance: It's crucial for controlling resonance, a phenomenon where small external forces can cause large, destructive vibrations.

Examples in Action:
Mechanical Systems: Car shock absorbers (dampers) absorb energy from bumps, preventing the car from bouncing excessively.
Buildings: Dampers in skyscrapers minimize swaying from wind or earthquakes.
Music: A musician damping a cymbal or vibraphone to control the note's duration.
Electronics: Damping circuits in radio receivers allow them to pick up a single station by inhibiting other frequencies.

In essence, damping is the "friction" or resistance that makes vibrating things eventually stop, making systems more stable, comfortable, and functional.


Now with respect to Richard Small's moving coil transducer transfer function, electrical damping is related to Qes which goes as 1/Beta and Qms which goes as 1/Rms. Having said that, then how does a power amplifier impact the transducer's transfer function? My claim is that it does not! For example Wolfgang Klippel does not reference the power amplifier in evaluating transducer (driver) performance. What effect does the power amplifier have on high frequency diaphragm bending modes? One cannot even mitigate response peaks and dips with the power amp selection.

Power amplifiers are well understood whereas transducer technology is at least 20 years behind audio electronics. There is little discussion of transducers within this thread but much discussion of amplifiers. There are Patents for but no working product examples of even commutated voice coil transducers and where or where is the digital audio transducer? IBM and Bell Labs gave up on the development of the digital audio transducer decades ago.

For the amplifier to be effective in controlling the moving coil transducer's dynamics, a control system seems to be indicated but history has identified limitations. As a retired transducer engineer, in retrospect my comment concerning amplifier selection is "Don't Care" as an element of transducer (driver) performance evaluation.

A good discussion to aid in understanding moving coil transducer dynamics was published back in 2006; however, in the almost 20 years since the authors' work, there has been only modest improvements in transducer performance (https://www.klippel.de/fileadmin/kl...iterature/Papers/Voice_Coil_ Impedance_04.pdf).
 
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smowry said:
"To return to the point of this thread, I had AI answer some questions."

Google AI Overview
Damping: Definition, Types, and Formula
Damping is the process where the energy of an oscillating system (like a swing, sound wave, or electrical current) is gradually reduced and dissipated, usually as heat, causing the vibrations or oscillations to die down over time. It's a natural or engineered mechanism that reduces the amplitude of movement, preventing excessive oscillations and controlling vibrations, seen in car shock absorbers, door closers, or skyscrapers.

Key Aspects of Damping:
Energy Dissipation: Damping works by converting kinetic or electrical energy into thermal energy (heat) through friction or other resistive forces.
Amplitude Reduction: The main effect of damping is to decrease the size (amplitude) of vibrations or waves.
Control of Resonance: It's crucial for controlling resonance, a phenomenon where small external forces can cause large, destructive vibrations.

Examples in Action:
Mechanical Systems: Car shock absorbers (dampers) absorb energy from bumps, preventing the car from bouncing excessively.
Buildings: Dampers in skyscrapers minimize swaying from wind or earthquakes.
Music: A musician damping a cymbal or vibraphone to control the note's duration.
Electronics: Damping circuits in radio receivers allow them to pick up a single station by inhibiting other frequencies.

In essence, damping is the "friction" or resistance that makes vibrating things eventually stop, making systems more stable, comfortable, and functional.


Now with respect to Richard Small's moving coil transducer transfer function, electrical damping is related to Qes which goes as 1/Beta and Qms which goes as 1/Rms. Having said that, then how does a power amplifier impact the transducer's transfer function? My claim is that it does not! For example Wolfgang Klippel does not reference the power amplifier in evaluating transducer (driver) performance. What effect does the power amplifier have on high frequency diaphragm bending modes? One cannot even mitigate response peaks and dips with the power amp selection.

Power amplifiers are well understood whereas transducer technology is at least 20 years behind audio electronics. There is little discussion of transducers within this thread but much discussion of amplifiers. There are Patents for but no working product examples of even commutated voice coil transducers and where or where is the digital audio transducer? IBM and Bell Labs gave up on the development of the digital audio transducer decades ago.

For the amplifier to be effective in controlling the moving coil transducer's dynamics, a control system seems to be indicated but history has identified limitations. As a retired transducer engineer, in retrospect my comment concerning amplifier selection is "Don't Care" as an element of transducer (driver) performance evaluation.

A good discussion to aid in understanding moving coil transducer dynamics was published back in 2006; however, in the almost 20 years since the authors' work, there has been only modest improvements in transducer performance (https://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Voice_Coil_ Impedance_04.pdf).
Click to expand...
Well, just to chime in with a few observations as a retired 5G/Satellite wireless communications engineer - been building speakers since the late 70’s. …….I agree that there has been very little advancements in the moving coil or electrostatic transducers. KEF have been doing steady incremental meaningful things like phase plugs and coincident drivers and changing the drive point on the diaphragm to get breakup outside of the operating range, but largely its still a cone with a coil at its apex..

It so strange to me how this industry still doesn't take a system approach to the replay chain. Transducer distortion >> semiconductor amp distortion, but you hear people claiming how one amp sounds (Ears) so much better distortion-wise than other. It begs the question what loudspeakers can reveal such effects? My pet topic is preserving the electrical waveform which is input to the amplifier and seen at the output of a perfect microphone (the SPL). The phase distortion of the crossovers causes the waveform to distort horribly! And the nulls in the radiation pattern with non-corindent drivers creates frequency depend level changes too. Few seem to care about these “big” topics… so in a sense there is till much work to be done.
Lastly on the topic of damping comments with lots of knowledge but little understanding
apologies for the long post
 
Waveform Fidelity said:
Transducer distortion >> semiconductor amp distortion, but you hear people claiming how one amp sounds (Ears) so much better distortion-wise than other. It begs the question what loudspeakers can reveal such effects?
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Transducer distortion usually falls with reduced levels, often with a power of level. Amp distortion often rises with reduced level. Speaker distortion is typically just the lowest harmonics whereas amp distortion often spreads out. DACs sometimes have a strong signal-correlated noise floor which is one of the worst kinds of distortion, even when it looks so subtle on the ususal plots/numbers.
Different types of nonlinear distortion don't mask each other, and finally linear distortion is a completely different kind of animal, it is benign and mendable and this practically irrelevant.
All this contributes to the observation that very small amplifier errors still can stick out like a sore thumb even with speakers that show, say, 1% dominant H2/H3 at listening levels, over most of the frequency range (and even more in the bass).
 
The AI "answers" are the typical boatload of incomplete bloated wall of words

All what one needs to know about damping (and the damping "factor" marketing BS) is that the electrical damping is simply defined by the total impedance the voice coil sees, including its own resistance and inductance.

It is obvious to see that the only way to significantly increase the damping is reducing this total impedance and a negative output impedance of the amp -- directly driving the driver -- is the only technical way to achieve this, increasing the inherent corrective feedback in the driver (besides true motional feedback with an external sensor).
 
KSTR said:
The AI "answers" are the typical boatload of incomplete bloated wall of words

All what one needs to know about damping (and the damping "factor" marketing BS) is that the electrical damping is simply defined by the total impedance the voice coil sees, including its own resistance and inductance.

It is obvious to see that the only way to significantly increase the damping is reducing this total impedance and a negative output impedance of the amp -- directly driving the driver -- is the only technical way to achieve this, increasing the inherent corrective feedback in the driver (besides true motional feedback with an external sensor).
Click to expand...
So to my understanding that is what Putzeys's negative feedback and loop gain use seems to achieve, to a better extent than ever before.

So de DF is not so much a quality of the amp as it is an indication measure of how well feedback and loop gain are implemented.

Don't get me wrong, i am of the equal conviction that all well designed electronic components (should) sound equal into magnitudes way behind the dot, while transducer behavior still is an issue that remains fully before the dot.

So let's concentrate all efforts on transducer R&D, and acoustical properties of loudspeakers (perhaps in rooms).

That does not mean i'm not interested (and indeed somewhat fascinated) by Putzeys' unprecendented approach to class-D circuitry in general and negative feedback application as a control tool in particular. He seems to approach sensing-coil-like results without using an actual sensing coil in the conventional sense (pun intended).

OK everybody, back to loudspeaker R&D now!
 
Y~BNA said:
He seems to approach sensing-coil-like results without using an actual sensing coil in the conventional sense
Click to expand...
Not really. The AI response is largely plausible-sounding (to a layman) nonsense trying to confirm the belief you expressed in your prompt. This is one of the problems with these LLMs: they are clearly designed to please, so giving any hint of the conclusion you seek will tend to cause it to concoct a defense of your existing belief instead of a balanced answer.
 
A key element to a system approach could be active loudspeakers with the elimination of reactive (L/C) components in the signal path. Note that Genelec does this.

I once asked Amir to comment on Active vs. Passive Loudspeakers. His reply was that Active is always better and I agree. Then why are there so few Active Loudspeakers? Admittedly, most subwoofers are Active; however, most Loudspeakers are Passive for what most likely are cost and/or complexity considerations but not performance.

In an interview, Andrew Jones claimed that he does loudspeaker system development in an Active Format and then maps the system into a Passive Version. In that interview, he claimed that Active Loudspeakers are not popular and do not sell well. In addition, he implied within the interview that Active Loudspeakers were his preference.

I claim that the Audiophiles' claim that Passive Loudspeakers "sound better" is heresy and cannot be without some sort of prejudice.
 
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A few thoughts on topic.

One can design amplifier with negative output resistance. It can reduce total resistance of speaker circuit and increase electrical damping. That design include positive feedback, which can lead to instability. Practically negative resistance is limited to low frequency and its value can only be a fraction of speaker resistance. That's kind of limited solution.

Speaker design is based on resonance. You shouldn't damp it, because you will damage frequency response. Speaker at lowest frequency works kind of like instrument. Adding a negative resistance would be similar to putting wool inside a violin. Unreasonable, unless you design a set consisting of amplifier and speaker.

Damping factor is a relic from tube era. Modern amplifiers have DF in range 40-100, which makes this parameter irrelevant. If a manufacturer claim DF in range of thousands, then it is marketing only. You probably can find some small print with explanation, that DF is not measured at terminals, but somewhere inside amplifier circuit.
 
KSTR said:
Transducer distortion usually falls with reduced levels, often with a power of level. Amp distortion often rises with reduced level. Speaker distortion is typically just the lowest harmonics whereas amp distortion often spreads out. DACs sometimes have a strong signal-correlated noise floor which is one of the worst kinds of distortion, even when it looks so subtle on the ususal plots/numbers.
Different types of nonlinear distortion don't mask each other, and finally linear distortion is a completely different kind of animal, it is benign and mendable and this practically irrelevant.
All this contributes to the observation that very small amplifier errors still can stick out like a sore thumb even with speakers that show, say, 1% dominant H2/H3 at listening levels, over most of the frequency range (and even more in the bass).
Click to expand...
Do you think the hearing system is capable of identifying even or odd harmonic distortion?
 
smowry said:
A key element to a system approach could be active loudspeakers with the elimination of reactive (L/C) components in the signal path. Note that Genelec does this.

I once asked Amir to comment on Active vs. Passive Loudspeakers. His reply was that Active is always better and I agree. Then why are there so few Active Loudspeakers? Admittedly, most subwoofers are Active; however, most Loudspeakers are Passive for what most likely are cost and/or complexity considerations but not performance.

In an interview, Andrew Jones claimed that he does loudspeaker system development in an Active Format and then maps the system into a Passive Version. In that interview, he claimed that Active Loudspeakers are not popular and do not sell well. In addition, he implied within the interview that Active Loudspeakers were his preference.

I claim that the Audiophiles' claim that Passive Loudspeakers "sound better" is heresy and cannot be without some sort of prejudice.
Click to expand...

One reason, in my opinion on why active systems are not popular is that it would destroy the market for power amplifiers and possibly pre-amplifiers too, so there is big financial motivation not to do that. On the consumer side, customers might want to maintain the idea of “separates” so they can discuss/debate/review, for example distortion figures and how they perceive the change the in sound. So its all good for business!
 
The transducer is inherently "Damped" with the Quality Factor, Qts. Qts is a result of Electrical Damping (Qes) and Mechanical Damping (Qms) and is related to the transducer's 2nd order transfer function. The Transducer Engineer sets Qts with Beta = [Bl(x)]^2/Re(T) with motor design and/or Rms(f,v) by material and geometry selections. Qts is a typical system requirement with respect to enclosure and/or mounting et al. My point is that obviously every moving coil transducer has Damping with the question being of how to increase it. It should be noted that in general, most new transducer designs seek to maximize Beta while minimizing Rms.
 
bmc0 said:
Not really. The AI response is largely plausible-sounding (to a layman) nonsense trying to confirm the belief you expressed in your prompt. This is one of the problems with these LLMs: they are clearly designed to please, so giving any hint of the conclusion you seek will tend to cause it to concoct a defense of your existing belief instead of a balanced answer.
Click to expand...
I am very aware of that of course, but my comment on Putzeys amp properties are not based on the AI story.
I see some more posts downplaying claims about Putzeys' circuits. Those are based on assumptions of marketing babble. For Hypex it may be with marketing in mind, but it remains based on claims Bruno himself publishes, in peer reviewed white papers and review confirmed measurents.
So if anyone has anything to disprove it, show it, if not, let's keep to the argumented content and not make it a yes-no contest.
 
With regards to Amir's reviews, Topping "tops" Hypex by 7 dB!

screenshot.596.jpg
 
smowry said:
A key element to a system approach could be active loudspeakers with the elimination of reactive (L/C) components in the signal path. Note that Genelec does this.

I once asked Amir to comment on Active vs. Passive Loudspeakers. His reply was that Active is always better and I agree. Then why are there so few Active Loudspeakers? Admittedly, most subwoofers are Active; however, most Loudspeakers are Passive for what most likely are cost and/or complexity considerations but not performance.

In an interview, Andrew Jones claimed that he does loudspeaker system development in an Active Format and then maps the system into a Passive Version. In that interview, he claimed that Active Loudspeakers are not popular and do not sell well. In addition, he implied within the interview that Active Loudspeakers were his preference.

I claim that the Audiophiles' claim that Passive Loudspeakers "sound better" is heresy and cannot be without some sort of prejudice.
Click to expand...
I am always only talking active. Sonically speaking it really only has advantages, many of 'em, so i will never waste time on passive except for the most basic applications (like amplitude shading multiple HF drivers on a single --active-- amp or so).
 
What we all NEEEED is Constant Directivity anyway, preferably independent of listening rooms, so let's quit talking amps, and start chasimg those final frontiers of speaker design. Unless some amp can really change something about speaker behavior..
 
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