Myths, tricks and hey, that's neat!

[OnAudio]

A video by one of the members here on capacitors. Although I do remember many years ago using different caps on the same chip amp and they sounded different

 

[Fast Eddie D]

I pay up for those Muse capacitors. I like the green NP units as well.

Do they make a difference? Well, people that fancy themselves as audiophiles recognize them on the board. Everything else is maxed out (right down to bling Dale CMF resistors) in my builds so I don't think you can point at one component that makes "the" difference. I still have a lot of them so I guess I'll use them.

 

[rdf]

Another view into damping factor from the Usenet days by Dick Pierce. Columns reformatted for legibility: https://groups.google.com/g/rec.audio.tech/c/5oeu-oCQuaA

Richard D Pierce​

unread,
May 28, 2001, 9:59:57 AM



to
DAMPING FACTOR: EFFECTS ON SYSTEM RESPONSE
A TECHNICAL ANALYSIS
Dick Pierce
Professional Audio Development
1 INTRODUCTION
Much ballyhoo surrounds the concept of "damping factor." it's been
suggested that it accounts for the alleged "dramatic differences" in
sound between tube and solid state amplifiers. The claim is made
(and partially cloaked in some physical reality) that a low source
resistance aids in controlling the motion of the cone at resonance
and elsewhere, for example:
"reducing the output impedance of an amplifier and
thereby increasing its damping factor will draw more
energy from the loudspeaker driver as it is oscillating
under its own inertial power." [1]
This is certainly true, to a point. But many of the claims made,
especially for the need for triple-digit damping factors, are not
based in any reality, be it theoretical, engineering, or acoustical.
This same person even suggested:
"a damping factor of 5, ..., GROSSLY changes the time/
amplitude envelope of bass notes, for instance. ... the
note will start sluggishly and continue to increase in
volume for a considerable amount of time, perhaps a
second and a half."
Instead of unbridled hyperbole, there have been attempts at a
reasoned justification for damping factor. Witness a recent
rec.audio.tech post:
"Since the amplifier source impedance is indeed much
smaller than the speaker impedance, the latter is almost
insignificant. In fact, an amplifier with a damping factor
of 50 will sink twice the current of one with a damping
factor of 25, and therefore dissipate four times the
resonant energy." [2]
As intuitive as this analysis might seem, it is quite flawed since,
as we will see, it simply ignores the one major loss factor in the
entire system, throwing it out the window as if the single most
important controlling element over cone motion had no real
relevance.
2 DAMPING FACTOR: A SUMMARY
What is damping factor? Simply stated, it is the ratio between the
nominal load impedance (typically 8 ohms) and the source impedance
of the amplifier. Note that all modern amplifiers (with some
extremely rare exceptions) are, essentially, voltage sources, whose
output impedance is very low. That means their output voltage is
independent, over a wide range, of load impedance.
Many manufacturers trumpet their high damping factors (some claim
figures in the hundreds or thousands) as a figure of some
importance, hinting strongly that those amplifiers with lower
damping factors are decidedly inferior as a result. Historically,
this started in the late '60's and early '70's with the widespread
availability of solid state output stages in amplifiers, where the
effects of high plate resistance and output transformer windings
traditionally found in tube amplifiers could be avoided.
Is damping factor important? Maybe. We'll set out to do an analysis
of what effect damping factor has on what most proponents claim is
the most significant property: controlling the motion of the speaker
where it is at its highest, resonance.
The subject of damping factor and its effects on loudspeaker
response is not some black art or magic science, or even excessively
complex as to prevent its unserstanding by anyone with a reasonable
grasp of high-school level math. It has been exhaustively dealt with
by Thiele [3], Small [4] and many others decades ago.
3 SYSTEM Q AND DAMPING FACTOR
The definitive measurement of such motion is a concept called Q.
Technically, it is the ratio of the motional impedance to losses at
resonance. Another, completely equivalent view is that Q is the
ratio between the amount of energy stored in the system vs the
energy dissipated by losses.
It is a figure of merit that is intimately connected to the response
of the system in both the frequency and the time domains. A loud-
speaker system's response at cutoff is determined by the system's
total Q, designated Qtc, and represents the total resistive losses
in the system.
Two loss components make up Qtc: the combined mechanical and
acoustical losses, designated by Qmc, and the electrical losses,
designated by Qec. The total Qtc is related to each of these
components as follows:

Qmc * Qec
Qtc = --------- [Eq 1]
Qmc + Qec
Qmc is determined by the losses in the driver suspension, absorption
losses in the enclosure, leakage losses, and so on. Qec is
determined by the combination of the electrical resistance from the
DC resistance of the voice coil winding, lead resistance, crossover
components, and amplifier source resistance. Thus, it is the
electrical Q, Qec, that is affected by the amplifier source
resistance, and thus damping factor.
Qec itself is a measure of, simply, the ratio of the energy stored
in the moving system to the energy dissipated electrically by the
losses in the system, that is, in the resistances in the system. The
energy stored in the moving system, the kinetic energy, is dependent
upon the amount of mass and the velocity.
In the context of a speaker, the Qe is (from Small[4]):
2 2
Qec = 2 pi Fc Mmc Re / B l [Eq 2]
where Fc is the resonant frequency of the system, Mac is the
equivalent moving mass of the system, and Re is the DC resistance of
the voice coil (and this assumes 0 source impedance or "infinite"
damping factor). Further, B represents the magnetic flux density in
the gap and l the length of wire in the magnetic field. (We will
assume that we are using the same driver for all considerations
here, thus, Fc, Mmc B and l remain the same as well.)
The effect of source resistance on Qec is simple and straight-
forward. From Small again [4]:

Re + Rs
Qec' = Qec --------- [Eq 3]
Re
where Qec' is the new electrical Q with the effect of source
resistance, Qec is the electrical Q assuming 0 source resistance
(infinite damping factor), Re is the voice coil DC resistance, and
Rs is the combined source resistance.
The factor
Re + Rs
--------- [Eq 4]
Re
comes from the fact that Re is built into the original derivation
for Qec includes Re in it. The correction simply calculates the
incremental increase in Qe with the incremental increase in the
total electrical resistance. Reconciling [Eq 4] with [Eq 2], we see
that:
2 2
Qec = 2 pi Fc Mmc (Re+Rs) / B l [Eq 6]
Thus it becomes obvious that the electrical Q of the speaker or,
more generally, the electrical damping of the speaker, is NOT
dependent upon the source resistance Rs alone (as the proponents of
damping factor erroneously claim), but on the TOTAL series
resistance seen by the driver, including the DC resistance of the
voice coil, Re. This mistake, as commonly as it is made, the the
fatal flaw in the entire damping factor argument.
It's very important at this juncture to note two points. First, in
nearly every loudspeaker system, and certainly in every loudspeaker
system that has any pretenses of high-fidelity, the majority of the
losses are electrical in nature, usually by a factor of 3 to 1 or
greater. Secondly, of those electrical losses, the largest part, by
far, is the DC resistance of the voice coil.
Now, once we know the new Qec' due to non-zero source resistances,
we can then recalculate the total system Q as needed using [Eq 3],
above.
The effect of the total Q on response at resonance is also fairly
straightforward. Again, from Small [4], we find:
4
Qtc
Gh(max) = sqrt(-------------) [Eq 7]
2
Qtc - 0.25
This is valid for Qtc values greater than 0.707. Below that, the
system response is overdamped and there is no response peak.
We can also calculated how long it takes for the system to damp
itself out under these various conditions. The scope of this article
precludes a detailed description of the method, but the figures
we'll look at later on are based on both simulations and
measurements of real systems, and the resulting decay times are
based on well-established principles of the audibility of
reverberation times at the frequencies of interest.
4 PRACTICAL EFFECTS OF DAMPING FACTOR ON SYSTEM RESPONSE
With this information in hand, we can now set out to examine what
the exact effect of source resistance and damping factor are on real
loudspeaker systems. Let's take an example of a closed-box, acoustic
suspension system, once that has been optimized for an amplifier
with an infinite damping factor. This system, let's say, has a
system resonance of 40 Hz and a system Qtc of 0.707 which leads to a
maximally flat response with no peak at system resonance. The
mechanical Qmc (i.e. the mechanical contributions to system losses
and thus damping) of such a system is typically about 3, we'll take
that for our model.
Rearranging [Eq 1] to derive the electrical Q of the system:
Qtc * Qmc
Qec = --------- [Eq 8]
Qtc - Qmc
we find that the electrical Q of the system, with an infinite
damping factor, is 0.925.
The DC resistance of the voice coil is typical at about 6.5 ohms.
Let's generate a table that shows the effects of progressively lower
damping factors on the system performance:
--------------------------------------------------------
Damping Rs Qec' Qtc' Gh(max) Decay factor time
--------------------------------------------------------
inf. 0 ohms 0.925 0.707 0.0 dB 0.04 sec
2000 0.004 0.926 0.707 0.0 0.04
1000 0.008 0.926 0.708 0.0 0.04
500 0.016 0.927 0.708 0.0001 0.04
200 0.04 0.931 0.71 0.0004 0.04
100 0.08 0.936 0.714 0.0015 0.04
50 0.16 0.948 0.72 0.0058 0.04
20 0.4 0.982 0.74 0.033 0.041
10 0.8 1.04 0.77 0.11 0.043
5 1.6 1.15 0.83 0.35 0.047
2 4 1.49 0.99 1.24 0.056
1 8 2.06 1.22 2.54 0.069
--------------------------------------------------------
Table 1

The first column is the damping factor using a nominal 8 ohm load.
The second is the effective amplifier source resistance that yields
that damping factor. The third column is the resulting Qec' caused
by the non-zero source resistance, the fourth is the new total
system Qtc' that results. The fifth column is the resulting peak
that is the direct result of the loss of damping control because of
the non- zero source resistance, and the last column is the decay
time to below audibility in seconds.
5 ANALYSIS
Several things are apparent from this table. First and foremost, any
notion of severe overhang or extended "time amplitude envelopes)
resulting from low damping factors simple does not exist. We see, at
most, a doubling of decay time (this doubling is true no matter WHAT
criteria is selected for decay time). The figure we see here of 70
milliseconds is well over an order of magnitude lower than that
suggested by one person, and this represents what I think we all
agree is an absolute worst-case scenario of a damping factor of 1.
Secondly, the effects of this loss of damping on system frequency
response is non-existent in most cases, and minimal in all but the
worst case scenario. If we select a criteria that 0.1 dB is the
absolute best in terms of the audibility of such a peak (and this is
probably overly optimistic by at least a factor of 2 to 5), then the
data in the table suggests that ANY damping factor over 10 is going
to result in inaudible differences between such a damping factor
and one equal to infinity. It's highly doubtful that a response peak
of 1/3 dB is going to be identifiable reliably, thus extending the
limit another factor of two lower to a damping factor of 5.
Further, we simply do not observe the "factor-of-four" increase in
energy dissipation with a factor of two reduction in source
resistance as claimed in [2]. The statement that it's all about
energy dissipation is quite correct: remember that what damping is
doing is removing energy from a resonant system, and that the
measure of damping is Q, the ratio of energy stored to energy
dissipated. Look, for example, at the difference in Qt between a
damping factor of 50 and 20: the actual difference in the energy
dissipated is less than 3%. According to the theory expounded in
[2], the difference in energy dissipation should be around a factor
of 6!
All this is well and good, but the argument suggesting that these
minute changes may be audible suffers from even more fatal flaws.
The differences that we see in Q figures up to the point where the
damping factor is less than 10 are far less than the variations seen
in normal driver-to-driver parameters in single-lot productions.
Even those manufacturers who deliberately sort and match drivers are
not likely to match a Qt figure to better than 5%, and those numbers
will swamp any differences in damping factor greater than 20.
It is well known that the performance of drivers and systems is
dependent upon temperature, humidity and barometric pressure, and
those environmental variables will introduce performance changes on
the order of those presented by damping factors of 20 or less. And
we have completely ignored the effects presented by the crossover
and lead resistances, which will be a constant in any of these
figures, and further diminish the effects of non-zero source
resistance.
6 CONCLUSIONS
There may be audible differences that are caused by non-zero source
resistance. However, this analysis and any mode of measurement and
listening demonstrates conclusively that it is not due to the
changes in damping the motion of the cone at the point where it's at
it's most uncontrolled: system resonances. We have not looked at the
frequency-dependent attenuative effects of the source resistance,
but that's not what the strident claims are about.
Rather, the people advocating the importance of high damping factors
must look elsewhere for a culprit: motion control at resonance
simply fails utterly to explain the claimed differences.
7 REFERENCES
[1] James Kraft, reply to "Amplifier Damping Factor,
Another Useless Spec," rec.audio.high-end article
2rcccn$u...@introl.introl.com, 24 May 1994.
[2] Steve (aq...@lafn.org), reply to "How can 2 amps
sound so different?," rec.audio.tech article
7go6da$b8q$1...@nnrp1.dejanews.com, 04 May 1999.
[3] A. Neville Thiele, "Loudspeakers in Vented Boxes,"
Proc. IRE Australia, 1961 Aug., reprinted J. Audio
Eng. Soc., 1971 May and June.
[4] Richard H. Small, "Closed-Box Loudspeaker Systems,"
J. Audio Eng. Soc., Part I: "Analysis," 1972 Dec,
Part II, "Synthesis," 1973 Jan/Feb.
Copyright 1994, 1995, 1998-2001 by Dick Pierce.
Permission given for one-time no-charge electronic
distribution with subsequent followups.
All other rights reserved.
--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| DPi...@world.std.com |

Any discussion of the magnitude of damping factor must also include the target speaker. The vast majority of passive multi-way products place an inductor in series with the woofer guaranteeing lower two-digit damping factors on the best days.

 

[jan.didden]

Dick Pierce always made sense, although he was not infallible.
I enjoyed his posts at rec.audio for instance.

Jan

 

[MarcelvdG]

The loudspeaker designer can account for the voice coil resistance and crossover inductor wire resistance.

 

[jan.didden]

As, I have mentioned, Morgan Jones did with his Arpeggio speaker.
It's worth a read, especially in the current context.

https://www.diyaudio.com/community/threads/arpeggio-loudspeaker.158899/

Jan

 

[jan.didden]

The article is being praised by those who already understand. Perfectly fine if that's the target audience but don't kid yourself that you have reached any musicians , trades people, doctors, history teachers and other diyers without a career investment in math who will continue to ignore your forum conversations in favour of those threads rehashing the supremacy of zero feedback, non-oversampling and fatter speaker cables.

True. But those people you describe do not ignore it because they can't understand it,
Not because the math is over their head; there isn't any, it's just some junior algebra.
They ignore it because they're just not interested; they have no ambition to move beyond 'solder resistor 4 between points 6 and 7. The order does not matter'. Paint by numbers. You can lead a horse to water and all that.

Jan

 

[ItsAllInMyHead]

^

I've learned a great deal from you. I have no formal background in acoustics, audiology, psychoacoustics, electronics, or any other 'relevant' field. However, you and others are always kind to help narrow the search for some level of truth in the vast sea of information (and some misinformation).

I've loved assembling kits (and I still do). When I heard differences in some various pieces of gear, I wanted to learn some bare essentials measurements. Then, I wanted to try in my own very odd way to determine if there is anything I can determine that correlates from measurements to what I perceive (I'm not really worried all that much about others' perceptions). Maybe some day, I can learn to lay out a circuit and make some PCBs. Then... maybe I can even learn to tweak some circuits. We all start somewhere in this wonderful hobby.

The curious will always wonder, "why". These articles are wonderful, IMO.

 

[cabirio]

Dick Pierce always made sense, although he was not infallible.
I enjoyed his posts at rec.audio for instance.

Jan

Good times! I always appreciated his very clear and detailed explanations, though politeness wasn't quite his forte... I incurred his wrath a few times and I remember his back and forths with Ethan Winer, as entertaining as they were informative.

 

[b_force]

They ignore it because they're just not interested

They ignore it because their believes are so rock solid and stuck in concrete and seek opportunities to strengthen that believe.
Some people just find it hard to face reality, probably because they don't want to admit that they are wrong.
(ironic idea as a human being)
With a bit of "just follow the herd"/parroting mentality. (if a lot of people say it's good, it MUST be good 🤦‍♂️ )

I had conversations with people who literally think they are smarter than Einstein (etc), yet don't even know how to do extremely basic junior algebra as well as basic rational/logic problem solving.

Go figure .........

Because those believes are so solid, you'll also never be able to convince them.

The curious will always wonder, "why". These articles are wonderful, IMO.

And that is also immediately the best attitude anyone can have! 👍
Be curious, investigate all possibilities, change your mind once in a while, rethink your own believes etc etc! 🙂

 

[egellings]

Knowledge can be edited when necessary. Belief is read only.

 

[ItsAllInMyHead]

^ Stealing that...

 

[egellings]

It's free. Just help yourself to it!

 

[Hearinspace]

True. But those people you describe do not ignore it because they can't understand it,
Not because the math is over their head; there isn't any, it's just some junior algebra.
They ignore it because they're just not interested; they have no ambition to move beyond 'solder resistor 4 between points 6 and 7. The order does not matter'. Paint by numbers. You can lead a horse to water and all that.

Jan

Well, your description will certainly apply to some , but . . . . . I forget exactly who it was, I just remember it was somebody whose opinion is something I'm supposed to regard as a benchmark delivered from an arbiter of truth , that the solution should be as simple as possible but no simpler , or words to that effect. You may have covered the way it really is for a number of people with that sort of shotgun approach, but you certainly haven't covered it for me, and experience is that where one person in the class asks a question , there are a few others who had the same question but for whatever reason didn't put their hand up.

My difficulties with the common way of explaining the various forms of feedback still stand . That typically, explanations for concepts are given that contain terms only understandable to those who already understand the concept being explained.

In my case , the constant reposting of Crowhurst's block diagrams for series and parallel forms of feedback do nothing to help somebody like me , who sees "in series" as "inline" and "parallel" as "running alongside". This is a physical/ visual sort of perceptual problem, and I can't tell you how bewildered I get when it is further moved into sub-types of " Series derived , Shunt applied " etc.

And don't even think I'm not interested. If I can persuade you to send me phone shots of Erno's article and then bully JC Prescott into very kindly putting it up on the audioXpress website because I need a printed copy I can do searches on, annotate and also direct members here too when I have studied it enough to ask a few good questions , I'd say that would denote a certain amount of interest.

From Einstein: His Life and Times by Ronald W. Clark:

"To de Broglie, Einstein revealed an instinctive reason for his inability to accept the purely statistical interpretation of wave mechanics. It was a reason which linked him with Rutherford, who used to state that "it should be possible to explain the laws of physics to a barmaid."
Einstein, having a final discussion with de Broglie on the platform of the Gare du Nord in Paris, whence they had traveled from Brussels to attend the Fresnel centenary celebrations, said "that all physical theories, their mathematical expressions apart, ought to lend themselves to so simple a description 'that even a child could understand them.' " "

 

[jan.didden]

In my case , the constant reposting of Crowhurst's block diagrams for series and parallel forms of feedback do nothing to help somebody like me , who sees "in series" as "inline" and "parallel" as "running alongside". This is a physical/ visual sort of perceptual problem, and I can't tell you how bewildered I get when it is further moved into sub-types o" Series derived , Shunt applied " etc.

If it is any consolation, these are also often bewildering to me.
It appears that things that are sort of intuitively to some are totally incomprehensible to others. And vice versa.

Related topic is my interest in quantum physics, the fact that two particles can be entangled over vast distances so that when you measure the position of one, it instantly fixes the position of the other. Then I stumbled on a book about evolution where the author argues that evolution depends on quantum effects in the living cell. One chapter was dedicated to explaining quantum mechanics, and I suddenly grasped it. In a biology book. You never know.

Quantum Evolution - Life in the Multiverse, JohnJoe McFadden, Flamingo/HarperCollins, 2000.

Jan

 

[rayma]

Maybe this is a little better, see pages 8 and 9. There are some actual circuit realizations on following pages as well.
It doesn't matter whether the devices are tubes or transistors. They are both three pin devices and similar for this purpose.

https://in.ncu.edu.tw/~ncume_ee/harvard-es154/lect_18_feedback.pdf

 

[Hearinspace]

If it is any consolation

Nice of you to say that but I somehow don't think it 's representative of your overall knowledge, where in my case it probably is.

It appears that things that are sort of intuitively to some are totally incomprehensible to others. And vice versa.

I tend to see the problem as linguistic. We most often communicate as though the words convey meanings, but they don't . They only signal them.
So, if your signals code book is by a different author it means calibration has to happen first. Most of us are too impatient for that.

Related topic is my interest in quantum physics, the fact that two particles can be entangled over vast distances so that when you measure the position of one, it instantly fixes the position of the other. Then I stumbled on a book about evolution where the author argues that evolution depends on quantum effects in the living cell. One chapter was dedicated to explaining quantum mechanics, and I suddenly grasped it. In a biology book. You never know.

Interesting stuff. I've read explanations approaching it from the point of view that it's only our (science based) intervention that does the entangling. I find it a little difficult to believe we're the only way it can happen, and if it does occur naturally, then some things 'til now considered superstition start to look like they need another look.

Back to Feedback :

While it's easy enough to see where feedback is being applied , I would still like to see explanations that make sense of the series or shunt derived, series or shunt applied designations , starting with tube circuits. Anybody got one?

Thanks

 

[Hearinspace]

Thanks for posting that.

see pages 8 and 9.

The block diagrams are to me like the Crowhurst ones I mentioned and as the feedback block in particular appears as a black box I have no idea what to do with it. . The following pages look promising however . . . . . . . . . . . . . but to understand them requires starting at the top.

I'll ask a question about it if I may, In the statement : A➡️Xo = A*Xi. on page 3, what's the reading for the right arrow ?

Thanks Rayma

 

[rayma]

The arrow is part of the label for the transfer function A->
Its implicit meaning is that signal flow through the gain block A-> is unilateral,
that there is no reverse transmission through it.

It may occur to you that this is only approximately true for A-> in a real circuit,
and is not at all true for β-> in a real circuit, since β-> is normally a passive network.

 

[rayma]

Feedback circuit analysis is best learned with a few very simple examples,
since the mathematics quickly gets out of hand.

Starting with a simple op amp circuit is a good special case,
since the math is about as minimal as possible, and normally
the A-> forward gain can be considered to be very large,
which makes the error signal Xi very small.