Damping Factor - Interesting article

@kijanki  Interesting!

You are confusing damping factor with dynamic headroom. Damping factor is mainly a factor of feedback, especially at bass frequencies. Dynamic range is a factor of supply rail voltage and capacitor size.
Given the love of tube amplifiers, saying high DF usually sounds better is debatable.

Oh yeah, Thanks for the article. It is a good one.

It is hard to say that a damping factor over 200 is inaudible, because the amps with very high damping factors do usually sound better.  The huge power supplies needed to get a high DF also contribute in other ways.  For example, my old 125 wpc Audire amps use 4 26,000 mf caps per channel (x 4 in my bi-amped system), while the contemporary Bryston with 200 wpc uses 2 4000 mf caps per channel.  Guess which amp starts losing bass at high volume?  Not the 125 wpc per channel one.

@atmasphere  That's how they describe this car amp:

Speakers and subwoofers change their impedances depending on what frequency note is playing. Normally, an amplifier will change its output power according to what impedance it senses. The Constant Power circuitry Rockford Fosgate developed changes all that, allowing the amp to put out exactly the same power no matter what impedance changes happen during play.

The constant power delivery doesn't necessarily mean it is maximum power (maximum power is delivered only when load impedance is the same as the source impedance).

@kijanki  @roberttdid was referring to the idea of an amplifier that operates as a power source rather than a voltage source.

Otherwise how this particular speaker sounds when connected to that particular amp becomes rather unpredictable.

Regarding Bruno's comment from the link above, speakers designed to operate in the Power Paradigm usually have level controls for the midrange and tweeter, as the voltage response of the amplifier is an unknown. If you look on speakers made in the 1950s these controls are fairly common. They are not there to help set up the speaker in a given room!

It is possible to make amplifier like that, but I found only car amp that delivers constant power:

https://www.crutchfield.com/S-W0uT7l6IaIv/learn/amplifier-power-labs.html#:~:text=Constant%20Power&text=Normally%2C%20an%20amplifier%20will%20change,impedance%20changes%20happen%20during%20play.

No offence to Bruno, but he doesn't sound like a very deep expert on transducers, but this is a critical point:

Crossover filters are simply designed with the assumption of a voltage source. It’s a matter of standardisation. Otherwise how this particular speaker sounds when connected to that particular amp becomes rather unpredictable.

It is one of the reasons active speakers have design flexibility that simply don't exist in traditional amp/speaker combinations.

How low? For electrical damping of 8ohm speaker difference between DF=10 and DF=100 will be like 6.8ohm vs 6.08ohm (assuming 6ohm as resistance of 8ohm coil). It is about 12% difference in breaking current.

Not to steal Atmasphere's thunder especially when I stuck my foot in my mouth yesterday, with current drive for speakers, impedance is infinite, but ideally you want a trade-off, so to atmasphere's point, you can use a combination of voltage and current feedback to achieve something close to constant power irrespective of impedance, but for that to work, you need drivers that match that characteristic.

I posted this link on the Class D thread. A few questions into the interview Bruno Putzey talks about DF.

Does the high damping factor of class D amplifiers negatively affect the subjective sound quality of some types of speakers 

https://audiophilestyle.com/ca/bits-and-bytes/purifi-audio-and-the-audiophile-style-readers-qa-with-...

but the low DF will in many cases be better.

How low?  For electrical damping of 8ohm speaker difference between DF=10 and DF=100 will be like 6.8ohm vs 6.08ohm (assuming 6ohm as resistance of 8ohm coil).  It is about 12% difference in breaking current.

I am not saying a huge improvement, but the low DF will in many cases be better.

That's an interesting idea- but I suspect one that has not seen a lot of study.

High damping factor directly into a driver as opposed to electrical dampening, can make high frequency ringing of the cone worse exacerbating some breakup modes. From a high level model, high DF can be like holding the voice coil stiff while the cone flexes. With low DF, the voice coil is not stationary and moves with the flex, and the increased resistance of the lower DF dissipates the energy of the motion. Very high level, almost like adding a resistor to a snubber.

I should clarify, I am not saying a huge improvement, but the low DF will in many cases be better.

What is likely to product worse cone breakup, a high DF or a low DF?

To my understanding, cone breakup has nothing to do with the amplifier.

Considering there are no speakers flat to 0.5db without equalization, let alone 0.1db, are we certain that a super high DF is going to result in the best on and off axis frequency response?

What is likely to product worse cone breakup, a high DF or a low DF?

According to this article DF=100 produces about 0.5dB variations typically, while DF=200 reduces it to 0.1dB. DF above 200 is inaudible.

BTW:  I really like how Ayre amps, and especially headphone amps sound.

How does damping factor apply to a zero feedback amp like an ayre .

Generally speaking, the output impedance of a solid state amplifier can be so low with respect to most speakers that it can behave as a voltage source, even if it has no feedback. This is why there are zero feedback class D amps that also behave as a voltage source.


One thing I've noticed a lot while working in high end audio is the phenomena known as 'tight bass'. I regard it as a coloration, since in real life tight bass doesn't seem to exist. The head engineer of Electro-Voice wrote an interesting article that pointed to this many years ago but I've failed to find a link to his article. Essentially though, it points out that no speaker made needs a damping factor more than about 20:1 and many need a damping factor much lower, some as low as 1:10 and you read that right (certain kinds of OB speakers).


The sound difference you hear between systems that have much greater damping factors is often related to distortion rather than FR errors, due to how the brain interprets distortion (if often favors such tonality over actual FR errors or the lack thereof).

See my later post where I deleted one of my previous posts ... too much on the brain and wasn't paying enough attention. I was never implying that speaker response is not impacted by amplifier impedance. I was more questioning the "constant power" paradigm, not thinking about specific implementations that incorporate aspects of voltage and current control like the ultralinear tube configuration or mixed output feedback implementations in solid-state.

As a speaker designer I can tell you that the difference between the two amplifier paradigms is significant, whether or not output transformers are involved. The relationship between the impedance curve and the speaker’s output level differs depending on the amplifier type, such that if the speaker’s impedance curve has significant peaks and dips, it will measure and sound different with the two amplifier types.

Duke

I would expect it is not very high output impedance / current output driven, though it may have a relatively low damping factor and may have some current feedback. The issue is most speakers today are designed for an amplifier with high damping factor / low output impedance. Too high of output impedance and your bass response changes, and you screw up the cross-over points.

All that is what I hear with Bakoon amplifiers.Which are class A/B but which are reputed to be zero negative feedback/high output impedance/ current drive/probably low damping factor amplifiers.In simple terms they simply sound incredibly clear and pure.Which I have really only heard elsewhere from expensive SET amps like the

@audiokinesis   Duke, Thank you so much for your detailed response. I'll copy and paste it over on the Nenuphar speaker thread as I believe it is relevant, with respect amplifier pairings with the Nenuphar full range single driver / speaker.

Your answers (and opinion) and real life findings from your experience as a speaker builder were extremely helpful! Thanks!

here is a thought: own better speaker with a smooth impedance modulus,

You know, this can be done artificially for peaky impedance speakers, but it's expensive and wastes a lot of heat.  Low order crossovers (1st) and series crossovers also avoid these issues.

"With low-damping-factor tube amps, I hear more of a sense of ease and liveliness and immersion. I’m hearing more stuff going on, it’s like the voices and instruments have more texture. Music is more engaging at lower sound pressure levels, which I think is related to the low-level details not needing as much SPL in order to be audible. At high sound pressure levels the difference is arguably even more noticeable, as there is an absence of the edginess which often starts to set in as the SPL goes up. I’m hearing more of a difference in soundscape and ambience from one recording to the next, with more of a sense of being "transported into" the recording, especially when it’s a really good one. There is a powerful emotional experience (some might call it spiritual) which some music can convey, but it calls for intensity and density and freedom from distractions. The least expensive amplification I have found which can do this is low-damping-factor tubes... specifically, the Atma-Sphere S-30 and M-60 [dealer disclaimer reminder]."



All that is what I hear with Bakoon amplifiers.Which are class A/B but which are reputed to be zero negative feedback/high output impedance/ current drive/probably low damping factor amplifiers.In simple terms they simply sound incredibly clear and pure.Which I have really only heard elsewhere from expensive SET amps like the Kondo Ongaku.

@david_ten wrote:

"1. Regarding:

My understanding is that low damping factor generally calls for high amounts of global negative feedback, which in turn can obscure low-level detail.

"Is this more of a solid state amp issue?"

In practice probably so.

David_ten: "How does it apply to tube amps with zero to very low negative feedback AND corresponding low damping factors?"

I would expect it to have all the low-level detail benefits of any other successful low-damping-factor amplifier.

David_ten: " Regarding:

I’ve had a fair amount of experience in driving the same speakers with both high and low damping factor amplifiers.

"Your generalized findings / results?"

First a bit of background: I design speakers with fairly high and unusually smooth impedance curves so that they have very similar response with both amplifier types across most of the spectrum, and then include user-adjustable bass tuning to adapt to the effects of amplifier damping factor into the bass region impedance peaks. So frequency response differences are minimal, and generally relegated to the region south of 100 Hz, where there can be a "free lunch" to the tune of an extra 1/4 to 1/3 octave extension with a low-damping-factor amp.

The following is my opinion; I can’t "prove" any of this.  Consider these to be generalizations; I’m not a writer of audio prose; and [disclaimer] I'm an Atma-Sphere dealer:

With low-damping-factor tube amps, I hear more of a sense of ease and liveliness and immersion. I’m hearing more stuff going on, it’s like the voices and instruments have more texture. Music is more engaging at lower sound pressure levels, which I think is related to the low-level details not needing as much SPL in order to be audible. At high sound pressure levels the difference is arguably even more noticeable, as there is an absence of the edginess which often starts to set in as the SPL goes up. I’m hearing more of a difference in soundscape and ambience from one recording to the next, with more of a sense of being "transported into" the recording, especially when it’s a really good one. There is a powerful emotional experience (some might call it spiritual) which some music can convey, but it calls for intensity and density and freedom from distractions. The least expensive amplification I have found which can do this is low-damping-factor tubes... specifically, the Atma-Sphere S-30 and M-60 [dealer disclaimer reminder].

Roberttdid wrote: " The example of the constant power amplifier as a tube-amplifier with transformer taps, is in my mind no different from the voltage amplifier paradigm presented... "

As a speaker designer I can tell you that the difference between the two amplifier paradigms is significant, whether or not output transformers are involved. The relationship between the impedance curve and the speaker’s output level differs depending on the amplifier type, such that if the speaker’s impedance curve has significant peaks and dips, it will measure and sound different with the two amplifier types.

Duke

How does damping factor apply to a zero feedback amp like an ayre .

It is not an electrical flaw in the speakers. It is primarily a mechanical design choice. The site you linked is good, but it is easy to draw the wrong conclusions if you don’t read in depth.

A pure current feedback output is not ideal as it will provide a peaky frequency response, and provides no additional electrical damping for the drivers which can be beneficial.

The damping factor the speakers see is never near 0 either due to the crossover impedances.

Neither was is really "wrong", just different and the right answer is probably somewhere in the middle ... though I would say most accurately, the correct answer is speaker specific amplification with an amp per speaker, but that is a tough nut for most companies to crack and not easy to market. Good on SGR tackling it at some level.

Most modern speakers are simply wrong because they have uneven impedance curves and their impedance is too low in the bass region which then means you need amplifiers with low output impedance/high damping factors/negative feedback/high current supply to try to correct these electrical flaws.Two wrongs trying to make a right.When what we should be using is speakers with benign impedance curves in combination with current drive /high output impedance amplifiers because current drive amplifiers sound so much better than voltage drive.http://education.lenardaudio.com/en/12_amps_8.htmland  https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&u...

atmasphere,
I deleted my old post questioning your article as I misinterpreted what your point was and where you were coming from. Put my head into a different mindset and completely agree in principle w.r.t. what you were communicating w.r.t. constant power for a tube output configuration. I don't have a blind attachment to 0 output impedance / infinite damping factor, and I expect most who do don't even know the details of why and why it may not be best from a system standpoint.

Doing 4 things at once including posting here :-) ... sorry for my error. I meant impedance is halfed, but had V-squared/R on the brain :-)

An amplifier that doubles in power as the impedance is squared will keep the most consistent anechoic output.

Buddy, you went the wrong way. I know of no amp that doubles power as impedance goes from 4 to 16 Ohms. That is certainly not an ideal voltage source anymore.

No conflation. It was postulated that ESL sound bright due to higher power output to the speaker as the impedance drops. I claimed that was not true, because though the power goes up, the anechoic response w.r.t. constant voltage over frequency is flat to down at high frequencies.  The postulate w.r.t. bright due to amplifier interaction is not the reason, the reason is different dispersion and how that interacts with the room and creates a room response that will be bright (if not done right).

You are also conflating dispersion with relative differences in amp output
vs. impedance.

Every amplifier has some feedback. Even emitter resistor is a form of local feedback. The problem with global feedback is, that it corrects with a delay (phase shift from input to output). This delay produces overshoot in time domain (odd harmonics in frequency domain). 40dB feedback means, that amplifier has 100x higher gain without feedback. Since amplifier delays signal from input to output, signal fed back and summed at the input is late. It make very little difference for slow sinewaves, but for fast changing input signals amplifier, for a moment, has 100x higher gain and overshoots. Benchmark is trying to time correct it with separate error amplifier (two sets of output transistors).  This overshoot shows in some Stereophile reviews as square wave response.

+1

This is too simplistic a view, and I was thinking specifically just related to the basic output stage which does typically behave much like a voltage source, and is usually configured as a voltage follower, and with a light load (lighter than a speaker), behaves as a voltage source, and with load, as a voltage source with an element of constant and variable impedance.

@roberttdid   I've yet to see a tube output section where on its own without feedback, is able to behave as a voltage source. If you can point me to one I would be very interested. You might want to take a look at this image:https://www.radiomuseum.org/r/fisher_80_az80az.html
This is a Fisher 80-AZ, typical of a number of amps from this period of the mid-late 1950s, prior to when the voltage rules were adapted by the audio industry. It is equipped with a Damping Control, which is a variable voltage and current feedback system.


Note that at 12:Noon the control is marked 'Constant power'. At the extremes the control is allowing the amp to be a voltage source or a current source, as the control operates both forms of feedback. When the two feedbacks means are balanced against each other, that is about the same as zero feedback, hence 'constant power'. Now if you spend time with zero feedback tube amplifiers, and happen to have measured their power response with respect to load, you find that above a certain impedance (depending on the overall output impedance of the circuit) the power decreases quite slowly as impedance is increased, in fact doubling the impedance sees only a small percentage loss of power. Its not perfect of course, but 'constant power' is really not a stretch; a zero feedback tube amp will do pretty well with this as long as the load impedance is high enough. No amplifier is perfect of course and this includes all amps that behave as voltage sources as well.


So my description as not too simplistic. It was simply correct.

Their response w.r.t. voltage, is fairly flat from mids-highs, with usually a bit of a dip at high frequencies. An amplifier that doubles in power as the impedance is squared will keep the most consistent anechoic output.

Huh?? What kind of amp doubles power as impedance is squared? Even a constant current amp only doubles power as impedance is doubled. At any rate this statement is entirely false, as ESLs don't do that. Here's a rather famous ESL impedance curve, the Quad ESL57:
http://www.quadesl.com/quad_main.shtml
You can see that while it does flatten a bit in part of the midrange, its on the decrease all the way from the peak in the bass. We have a lot of customers with Quads and Sound Labs (80% of our MA-2s built over the last 30 years are running on Sound Labs); these speakers don't seem to behave around voltage rules nor should they, as their impedance curve is not that of a driver in a box with its attendant resonance. This is of course not the only example of a modern high end audio loudspeaker that doesn't use the voltage rules; keep in mind that most SETs are zero feedback and so tend to behave more as power sources than voltage sources, and yet there are speakers on which they do quite well as the designer of the loudspeaker intended that it be that way.

Every amplifier has some feedback. Even emitter resistor is a form of local feedback. The problem with global feedback is, that it corrects with a delay (phase shift from input to output). This delay produces overshoot in time domain (odd harmonics in frequency domain). 40dB feedback means, that amplifier has 100x higher gain without feedback. Since amplifier delays signal from input to output, signal fed back and summed at the input is late. It make very little difference for slow sinewaves, but for fast changing input signals amplifier, for a moment, has 100x higher gain and overshoots. Benchmark is trying to time correct it with separate error amplifier (two sets of output transistors). This overshoot shows in some Stereophile reviews at square wave response.

An amplifier that doubles in power as the impedance is squared will keep the most consistent anechoic output.

Buddy, you went the wrong way. I know of no amp that doubles power as impedance goes from 4 to 16 Ohms. That is certainly not an ideal voltage source anymore.


You are also conflating dispersion with relative differences in amp output
vs. impedance.


The feedback loop of Class D amps looks so different from linear amps I’m not at all sure we should be judging by the same criteria, assuming 35db is even correct. Last I looked there were at least 3 different ways in which Class D amps used feedback.


It is not unreasonable to imagine an amp with a 300 DF at 20 Hz but 50 at 20 kHz. At 20 Hz the amp’s output Z is ~ 0.03 Ohms, but at 20 kHz ~ 0.16 Ohms. With a normal dynamic speaker, these are not really significant, but ~ 0.16 Ohms is significant when compared to the 0.5 or less an ESL may present. Some quick math, and you’ll see about 1/4 of the amp’s output voltage is gone.


Of course, this is all hypothetical and math-y. Listening alone will tell you if you’d like it.


Best,
E

Not sure the justification for this statement. Their response w.r.t. voltage, is fairly flat from mids-highs, with usually a bit of a dip at high frequencies. An amplifier that doubles in power as the impedance is squared will keep the most consistent anechoic output.


The brightness is more a factor of their emission shape and how they will interact with most room, and the resultant room response, which will differ from a "point source" dynamic driver.

The problem with ESLs is that they typically vary by about 9 or 10:1 in impedance from bass to treble, but their efficiency doesn't vary in lockstep as it is supposed to like you see with box speakers. So an amp that doubles power as impedance is halved is typically way too bright on most ESLs. Martin Logan got around this (sort of) by making their ESLs very low impedance in the bass (4 ohms) so they are only 0.5ohms at 20Khz. Even most solid state amps have troubles into that impedance, thus reducing the brightness that would otherwise manifest.

This is too simplistic a view, and I was thinking specifically just related to the basic output stage which does typically behave much like a voltage source, and is usually configured as a voltage follower, and with a light load (lighter than a speaker), behaves as a voltage source, and with load, as a voltage source with an element of constant and variable impedance.

One thing you are not getting has to do with the application of feedback. What I have said in that paper is true if the amp has none- what you say above is true if the amp has enough feedback to allow it to behave as a voltage source.

Again, I find this is too simplistic of a view. Simply saying 35db is too little feedback without taking into account the frequency response of the feed-forward and feedback paths, not to mention what the inherent feedback is in the output stage if you are considering that separately makes any hard number in the sand questionable. The statement makes assumptions about the linearity of the feedback network as well. Ditto for Gain-Bandwidth, which is one number, but gain at frequency is far more relevant. Instrumentation op-amps may have very high gain-bandwidth, but are useless at 20KHz.

This is a bigger deal that it would seem to appear; if the amplifier has too little feedback (less than about 35dB) the consequence is that the feedback itself will introduce distortion, mostly composed of higher ordered harmonics (and some IM). Somewhere in the area of 35dB and north the amp finally has enough feedback such that is can actually compensate for the distortion introduced by the feedback itself.

The bottom line is this is all about Gain Bandwidth Product and the resulting loop gain- both of which have been insufficient in the prior art. The Benchmark amplifier is one of the very few non-class D designs that actually gets the feedback into the ballpark. So if you want really natural sound, you either go with an amp like that or go with an amp that uses no feedback at all- and deal with the simple fact that it won't work on all speakers, which is also true of an amplifier that is a perfect voltage source! So you'll have to audition the speaker and amp combination in any event.

Another dimension of DF not often discussed is having high DF, and high current through the treble. While conventional speakers tend to have their low points in the mid-bass, where most amps have the highest DF, ESL's are essentially capacitors, and have their lowest impedance in the peak frequency.

If an amp has 'high current' (which is a bit of a myth; current can't exist without voltage) then it will at all frequencies.


The problem with ESLs is that they typically vary by about 9 or 10:1 in impedance from bass to treble, but their efficiency doesn't vary in lockstep as it is supposed to like you see with box speakers. So an amp that doubles power as impedance is halved is typically way too bright on most ESLs. Martin Logan got around this (sort of) by making their ESLs very low impedance in the bass (4 ohms) so they are only 0.5ohms at 20Khz. Even most solid state amps have troubles into that impedance, thus reducing the brightness that would otherwise manifest.


Generally speaking most ESLs don't follow the voltage rules; IOW their impedance curve does not match their sensitivity through their frequency range!

Another dimension of DF not often discussed is having high DF, and high current through the treble.  While conventional speakers tend to have their low points in the mid-bass, where most amps have the highest DF, ESL's are essentially capacitors, and have their lowest impedance in the peak frequency.

Having an amp that can do high current and low output impedance at 20 kHz can restore the treble.  This is a reason why a lot of tube amps can sound dull with ESLs.

Of course, no one cares more about this than Roger Sanders, and his Coda based amps are optimized for low DF and high current across the spectrum.

https://www.sanderssoundsystems.com/

My understanding is that low damping factor generally calls for high amounts of global negative feedbac

Doesn’t have to be global.  Local feedback can also be used to lower distortion and increase DF.  Also, a high output impedance (low DF) can be offset by having more output devices.

Still, yes, it is easy and cheap to achieve low damping factors with high amounts of global feedback.

Let's assume for a moment that wire is perfect.

The only problem with that is wire isn't, so the math can't be realized.

The example of the constant power amplifier as a tube-amplifier with transformer taps, is in my mind no different from the voltage amplifier paradigm presented, the only difference is the taps on the transformer impedance match the output to what is still essentially a voltage amplifier. The output power of those amplifiers will still change as the load impedance changes, perhaps not as much as if there was more feedback to compensate for the low output impedance of the amplifier, but it will still change as it is inherently a voltage amplifier.

@roberttdid

One thing you are not getting has to do with the application of feedback. What I have said in that paper is true if the amp has none- what you say above is true if the amp has enough feedback to allow it to behave as a voltage source.

Now Duke touched on something of high importance, that relates to @douglas_schroeder 's comments quoted from his review. Loop negative feedback is not a trivial matter in any amplifier, and the amount used can have profound consequence on the sound that derives from the amplifier. I am immediately asking- in an amplifier which has variable damping the easiest way to set that up is by the use of variable feedback- so what is the minimum and what is the maximum feedback?

This is a bigger deal that it would seem to appear; if the amplifier has too little feedback (less than about 35dB) the consequence is that the feedback itself will introduce distortion, mostly composed of higher ordered harmonics (and some IM). Somewhere in the area of 35dB and north the amp finally has enough feedback such that is can actually compensate for the distortion introduced by the feedback itself.

Now the ear converts all forms of distortion into tonality and can favor that tonality over actual FR errors. The ear is particularly sensitive to the higher ordered harmonics and IMD; the former are used by the ear to calculate sound pressure. If they show up, the amplifier will sound brighter and harsher and louder than real life, even if in 'tiny' amounts that we are used to seeing on spec sheets.


This simple fact is at the root of the tubes vs solid state debate! Tubes don't make the higher ordered harmonics in the same way as solid state and so sound 'smoother' as real music does not have these harmonics enhanced either.


So its understandable that an amplifier with variable feedback would sound quite different, and not because of damping factor, even though that is being varied. When an amplifier has insufficient feedback it will have colorations and those colorations will overshadow frequency response errors on account of how the brain perceives distortion. This is why two amps can measure flat on the bench but one can sound bright and the other doesn't!

Now some of you may have noticed something- that most amplifiers made in the last 70 years don't have enough feedback. This is why solid state amps have been bright and harsh all this time- its only been recently that newer semiconductors have been available to allow amplifiers to be made with enough loop gain. But it appears that you can count those amps on one hand at this point.

So the alternative is to simply use no feedback at all- and thus avoid the highly audible distortion caused by the feedback itself. This results in an amplifier with a high output impedance and thus low damping, but many speakers don't need much damping to sound quite realistic. This is why things like SETs exist- put them on the right speaker and the result is excellent.


The bottom line is this is all about Gain Bandwidth Product and the resulting loop gain- both of which have been insufficient in the prior art. The Benchmark amplifier is one of the very few non-class D designs that actually gets the feedback into the ballpark. So if you want really natural sound, you either go with an amp like that or go with an amp that uses no feedback at all- and deal with the simple fact that it won't work on all speakers, which is also true of an amplifier that is a perfect voltage source! So you'll have to audition the speaker and amp combination in any event.

I can't really buy into Ralph's paper at least the terminology defined. The example of the constant power amplifier as a tube-amplifier with transformer taps, is in my mind no different from the voltage amplifier paradigm presented, the only difference is the taps on the transformer impedance match the output to what is still essentially a voltage amplifier. The output power of those amplifiers will still change as the load impedance changes, perhaps not as much as if there was more feedback to compensate for the low output impedance of the amplifier, but it will still change as it is inherently a voltage amplifier.

@audiokinesis   Duke, Thank You. I'll reference the paper. 

1. Regarding:

My understanding is that low damping factor generally calls for high amounts of global negative feedback, which in turn can obscure low-level detail.

Is this more of a solid state amp issue?

How does it apply to tube amps with zero to very low negative feedback AND corresponding low damping factors?


2. Regarding:

I've had a fair amount of experience in driving the same speakers with both high and low damping factor amplifiers.

Your generalized findings / results?

Thanks. - David.

@david_ten asked: " Reaching out to those that know this stuff: does damping factor play a role with (influencing) perceived scale (image size)? If so, how? Thanks. " 

Not directly, to the best of my knowledge, but imo it can indirectly. 

My understanding is that low damping factor generally calls for high amounts of global negative feedback, which in turn can obscure low-level detail.  And soundstage size and depth, along with a sense of immersion or envelopment, benefit from preserving low-level detail. 

That being said I'm not an amplifier guy, but as a dealer for both types and as a speaker manufacturer and dealer, I've had a fair amount of experience in driving the same speakers with both high and low damping factor amplifiers. 

Here's another paper which examines the two paradigms of amplifier design, the constant-voltage paradigm (most solid state, generally high damping factor) and constant-power paradigm (mostly tubes, generally low damping factor).  This paper was particularly useful to me as a speaker designer: 

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php  

Duke

@djones51  Thank you!

According to Pass the SIT-1 damping factor doesn’t change with frequency. The Cube is a single driver speaker, looking at the standard vertical scale at 50dB there’s a lot of axial variation from 20 -300 hz, below 100hz it looks a little strange. It’s probably bumping the bass below 100hz and above 10khz with distortion and then rolling off at about 15khz. Looks like it would sound good paired with the SIT-1 not sure DF would have anything to do with it.

The frequency and phase response is flat, distortion
harmonics are consistent in amplitude and phase relationship, and the damping factor remains the same.

Reaching out to those that know this stuff: does damping factor play a role with (influencing) perceived scale (image size)? If so, how? Thanks.

Member @stephendunn from the Cube Audio Nenuphar thread:

one area in which the SIT-1 excelled that I believe might be related to damping factor is scale

the SIT-1 bring[s] a noticeably increased sense of largeness through a sound stage that opens more in every direction

Does this have something to do with damping factor?

 

One last thing:

Damping factor theory is basically series network analysis. There’s nothing here very complicated. You just string up your amp’s output impedance and put it in series with the load, then analyze the difference in output vs. F.

Amp (+) --> Output Z --> Load Z --> Amp (-)

A little work with a spreadsheet and a speaker impedance graph and you too could model this at home! Any EE learns to do this probably in the first semester of electronics. If you want to learn more search for "AC Circuit Analysis"

There is one thing I’d like to say though: While network analysis like this is straightforward, the effects I’ve heard from speaker cables has led me to believe that amps are more susceptible to cable and speaker impedance than we would model this way. I don’t think the model as outlined above fully accounts for what I’ve heard in all instances. This does not mean speaker cables are worth $30,000. It just means I think there’s untapped research to be done there.

Best,

E

Here is an older paper I found  that explains the DF relationship between amp and speaker. It was a little easier for me to understand some of the numbers. 

https://butleraudio.com/damping2.php

General observation:  much of the discussion above focuses on high DFs of 20, 200 or 2000.  I surmise that most amps that fall into those DF categories are solid state amps that are constant (or near constant) voltage sources.  

I was hoping Atmosphere (Ralph) would have chimed in because he manufacturers very fine tube amps that probably have output impedances in the single digits. 

Anyone have any thoughts about the db spread on tube amps, even those that use NF??

BIF

In the Benchmark paper it says most amplifier specs assume 8 Ohm whether that's true for Hegel and marantz I have no idea. What's interesting to me about the article is they are saying low DF of 10 or high as 10,000 is not an issue damping of driver motion but a low DF can affect the sound of speakers because of variations in impedance of the speaker. I notice the Hegel integrateds show a DF of 4000, I can't imagine a speaker bad enough to for the DF to matter at 4000.