| dayveshome |
| I am doing research for an amplifier that I hope to eventually build. What I have noticed is something called, "damping factor" in specs of some amps. Is there something somewhere that is written that explains: what it is, what is a good #, bad #, and especially, what in the amp determines damping factors, and how do design this into my amp. Any help would be greatly appreciated. Thanks! |
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| gromanswe |
Damping factor is something I never
understood either.
A welldesigned amplifier doesn't have to worry
about damp factor.
As most expressions is this a "market slogan"
mostly used to get you into A BUY!
This is the conclusion I, Groman, and Torseten Loesch
agreed upon, when discussing this
uninteresting subject at AudioAsylum,
before the people at AA,
got afraid of me
telling "that the meperor was naked"
and BANNED me PERMANANTLY.
regards
Groman doesn't need to be damped
neither should you need to be |
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| gromanswe |
Here you can reach Torsten Loesch.
And share the "know how" of a man who
knows about loudspeakers and amplifiers.
http://thunderstoneaudio.nav.to/
Groman selects his associates
someones are not selected |
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| sianturi |
Damping factor is a ratio between loudspeaker impedance and amplifier output impedance, ie:
DF = Z loudspeaker/ Z ampli-out
Ideally, DF should be as high as possible, so that Z ampli-out is as low as possible (an ideal voltage source). With a low Z ampli-out, your ampli becomes more independent of your Z loudspeaker (Z variation in loudspeaker has little effect on the voltage across you loudspeaker).
But some say that this is not so important. You could read Douglas Self or Randy Slone book about this jargon, and the explanation on why DF is not so important.
Typical tube amp has low DF, while solid state amp has high DF. Speaking which one is the best, depends on your loudspeaker. Lynn Olson said that Ariel works best with low DF amp, while Linkwitz said his Phoenix speaker works best with high DF amp.
Cheers, |
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| phase_accurate |
Hi dayveshome
Sianturi was a little quicker than me (so I had to erase some part I've already written) but I can generally agree to what he wrote.
An amplifier should ideally represent a voltage source* i.e. it's output voltage should be independant of the load connected to it. IMO one could live with a damping factor of 50 which can be reached easily by almost any carefully designed SS amplifier. I personally don't see any reason to have damping factors up to 10'000 because this is easily reduced by the resistance of speaker cable, contact resistance, crossover network etc. Some might argument that such an amplifier would achieve tighter control over the cone motion (i.e. damping) and would have much punchier bass . The damping argument can easily be destroyed by the fact that the voice-coil DC-resistance is the dominating part when it comes to cone-control (and this one is some orders of magnitude larger than the output impedance of an amp with a damping factor of 10000 !).
To achieve a low output impedance somebody has to use either a circuit that has an inherently low output impedance (e.g. class A) or use a large amount of feedback or any combination of both. When you have two amplifiers with the same damping factor (which is just a static measurement into a resistive load) usually the more generously dimensioned amplifier (i.e. class A, large PSU) will have the better bass control and a more consistent damping factor over it's operational frequency range.
Some tube amplifiers achieve only very low damping factors (often lower than 10) which can cause irregularities in the frequency response since the amplifier's output impedance and the speaker's impedance act as a frequency-dependant voltage divider. But tube fanatics (or me as well who only listens to tubes occasionally) can even live with that since it is perfectly possible to correct the speaker's impedance.
Regards
Charles
* P.S. this is of course different when the speakers are current-driven rather than voltage-driven, but thats another story |
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| janneman |
| quote: | Originally posted by gromanswe
Damping factor is something I never
understood either.
A welldesigned amplifier doesn't have to worry
about damp factor.
As most expressions is this a "market slogan"
mostly used to get you into A BUY!
This is the conclusion I, Groman, and Torseten Loesch
agreed upon, when discussing this
uninteresting subject at AudioAsylum,
before the people at AA,
got afraid of me
telling "that the meperor was naked"
and BANNED me PERMANANTLY.
regards
Groman doesn't need to be damped
neither should you need to be |
No offense meant, but you seem to have a strong opinion on something you don't understand, as you state yourself....
Cheers, Jan Didden |
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| sonnya |
Groman go read about damping factor!!!!
A loadspeaker with cabinet and anything around it can be showed as a model the same way as an amp.
In this model you will find the output impedance of the amplifier!! Which divided with the speaker impedance gives the damping factor...
Even if you like it or not you will be able to hear the difference on a amp with a high damping factor or low damping factor. Mostly you bass response gets weaker!! This is both Theory and reallife!!
Go try ad a series resistor to you speaker.. Lets say 1 Ohm.. Try it!!
I do not like the sound of a amp with a to low damping factor..
Regarding strong opinion on things you do not know of... In the AudioAsylum .. John Curl ...Should i say more?
Sonny |
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| gromanswe |
Cat Stevens, in song Can't Keep It In:
"Say what you mean, Mean what you think
and Think anything! Why Not?"
I think I have seen others here pointing out
that damping factor of different magnitude
are easily to live with.
There are a lot more important factors
both in Amplifier and Loodspeaker
that call for more attention.
That influence the result more.
A amplifier is just an adaptor
A device between an input and output.
When construction an amplifier you see
'whatinput is, and what is to be driven.
Then you make your adaptor.
If you can not reach a good solution,
then you must modify the source, input.
Or modify the device at output so you can
reach satisfying result.
Maybe put a preamplifier before drive amplifier.
Maybe see to that loudspeaker behavior
is good regarding resistance and impedance.
You cannot build an amplifier suiting all
devices there are.
An adaptor should be adjusted to the environment
it is supposed to serve.
Anything else have to be a compromiss
and a compromiss is only ideal
in a few cases.
In most cases not optimal.
Groman
who says what he means
and think his thoughts
although they cant suit everyone,
else they would have to be compromisses. |
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| sonnya |
Be Carefull with strong opinions and how you express them.... That is what i was trying to say to you...
1)There is all kinds of people in this forum from very yound people to very old people .. Not everyone likes the "here i am" attitude
2)If you have an opinion on a subject which have something to do with design... Then you opinion should be backed up by some good evidence.. A lot of people around here try to designs thing the right way by learning from other peoples knowledge.
I do not say that you have a big knowledge, but you have be carefull on expressing your opinion on things like damping factor... When you are not in the position to answer the question Like :
"Damping factor is something I never
understood either." - Then you should stop your opinion here!
"A welldesigned amplifier doesn't have to worry
about damp factor." - This is nonsense!
"As most expressions is this a "market slogan"
mostly used to get you into A BUY!" - I do not think that a engineer thinks that way when he wrote the spec.sheet.
;O) But if i am to hard on you? tell me!
Sonny |
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| gromanswe |
Sonnya!
some people are
Negativism radiators"
That is not something most people can
be happy about at this forum.
they look for fault in others
Never encurage others statements
with any appreciation.
Just out to make themselves appear
as the perfect way to be.
Can not accept other opinions then their own.
never trying to set themselves into the other man's
thinking.
There is an expression: "See me in my good eye"
That means try to see the good sides of a person,
instead of trying to look in his bad eye.
Surely I have one bad eye,
but the one with no faults may throw first stone...
Groman
avoids trowing stones |
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| gromanswe |
"A welldesigned amplifier doesn't have to worry
about damp factor."
You muust see the ditinction between
worry and care for.
A welldesigned amplifier is built in a way
that required parameters exists.
The behavior can be expressed in many ways,
or using many terms.
It will automatically have the qualities that are needed.
This might be current capability
speed, accuratess in reproducing signal
or dampingfactor, in relation to the load.
So then you do not have to WORRY.
To worry is for me "to be afraid somthing is wrong".
If all is taken well care for in design,
there is no need for worrying.
Is that clear?!
Groman
worries more about sonnya the damp factors |
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| roddyama |
Hi Phase_Accurate and Dayveshome,
| quote: | | The damping argument can easily be destroyed by the fact that the voice-coil DC-resistance is the dominating part when it comes to cone-control (and this one is some orders of magnitude larger than the output impedance of an amp with a damping factor of 10000 !). |
Another part of the "damping argument" is that an amp with a lower output impedance (higher damping factor) will better absorb the inductive reactance of the voice coil thereby exerting greater control over the cones motion. This is particularly true in the resonance range of the driver where most of the cones motion is governed by the mechanical properties of the driver and less by the electrical signal.
Remember that two of the main assumptions made in the T/S calculations of a drivers small signal response are that:
1.) The response is calculated in the low frequency range of the driver being analyzed.
2.) And that the output impedance (Rg) of the source (amp) is negligible (the damping factor is taken to be very high).
If the damping factor starts to exceed 50? (maybe), you have to include Rg in the drivers response analysis. It will alter the total response.
Rodd Yamashita |
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| sonnya |
Okay we stop here!
To add to Rodd Yamashita.
you can see a driver(speaker as a) motor.
When you take a DC motor with nothing connected to its plus minus terminal it is very easy to turn. but when you shorts the input more and more with a smaller and smaller resistor value it will get harder to turn.
The speaker will act the same way. the smaller the driver impedance is the less you can distort the cone movement by external source.
It is the same reason you never add a series resistor to a bassdriver or the inductor in series with such a driver should be have very low DC resistance.... smaller source(generator) impedance => more control of the bass driver.
Sonny |
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| gromanswe |
The loudspeakers are built using too few elements.
2-way speakers are driven at boundry frquencies
where there impedance is far from nominal value.
I give my vote for active systems,
with one power amp for each element.
this might be 3 or 4 woofers/tweeters.
Each amplifier/ADAPTOR is optimized
as far as possible to woofer it is driving.
Also the non-linear crossovers L and C, hysteres and losses,
is to be avoid.
Using R/C of high quality in the active crossover.
This is my way of optimate the sound system.
If one amplifier is to drive 2-4 elements,
with L and C in between, you ask for trouble.
The nonlinearity of the driven components
will hit the feedback point causing
disturbance all the way to the input of amplifier.
Still dreaming of my ultimate
active system with 2x4 LSP-elements/Ampifiers
no LSP cables or Inductors/Capacitors to drive.
The main distortion in todays system is coming
out of what is connected to the Amplifiers!
This is my way
groman's way
with the components available today. |
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| phase_accurate |
sonnya and roddyama
I do of course agree that the amplifier's output resistance affects the damping of the driver. Maybe I was a bit unexact with my description (my mothertongue isn't English).
I just don't like to see how people might be led to the assumption that an amp with a damping factor of 10000 (which is not that easy to achieve when you don't want to sacrifice other parameters) could actually dampen a driver's resonance a hundred times better than one with a damping factor of about 100.
Simply because the source resistance, that our "DC motor" loudspeaker sees, is the sum of amplifier output resistance+speaker cable(s)+connectors+voice coil DC resistance (the latter one usually the largest by far).
I am a strong proponent of active speakers (not just because of the "damping thing"). Here you can either take the output resistance into account and tune the box accordingly. Or you can even control the output impedance of the LF poweramp by current feedback (this has to be done with care because it could lead to instability).
regards
Charles |
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| gromanswe |
The effect produced of an electrically charge coil
is proportional to the CURRENT through to coil.
Todays amplifier Drives loudspeakers
with a VOLTAGE that is propotional to input signal.
As if the coil's impedance was resistance.
There you have the miscalculation!
Groman
makes his own calculations |
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| gromanswe |
Before we ended discussion of so called damping factors.
Todays amplifiers is not optimized to what they should serve.
Groman can't please everybody, so he is pleasing
HIS self |
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| sonnya |
| quote: | Originally posted by dayveshome
I am doing research for an amplifier that I hope to eventually build. What I have noticed is something called, "damping factor" in specs of some amps. Is there something somewhere that is written that explains: what it is, what is a good #, bad #, and especially, what in the amp determines damping factors, and how do design this into my amp. Any help would be greatly appreciated. Thanks! |
We have not answered your question! Sorry!! Really Sorry...
Damping Factor is stated at given load resistance.. Mostly 8Ohm...
But if you see to amps... You need to compare at which load they spec their Damping Factor.
And amp with a damping Factor of 100 @ 8ohm will have a Damping Factor of 50 @ 4Ohm.
So it is a bit blured (Spelled wrong??) what the spec says but you can use it to calculate the ouput impedance of your amp.
DF of 100 @ 8Ohm => 80mOhm output impdance...
The output impedance will raise as the frequency goes up.
If it is a Negative Feedback Amp it will depend on the openloop gain and the closed loop gain at a given frequency...
So the big question is : What should the output impedance be..
<200mOhm... As stated the cable from the amp to the speaker will have an influence on the system.
To high output impedance will alter the frequency response of your speaker....
To design it in i think you should go figure out which kind of output stage you are using and if you will use FB or no FB? Then we could continue the talk.
Sonny |
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| Nelson Pass |
Damping factor is kind of an odd thing. It does correlate
loosely to woofer control, but there are too many examples
which don't support a cause and effect relationship.
The X amps we sell have a wide range of damping factors,
with the cheaper amps having better numbers (due to
feedback around the output stage) and the bigger amps
having lower DF, and yet there is no question that the
bigger amps have more authority and control, even at
modest power levels.
I have seen this elsewhere also, but I don't have a decent
explanation, just hand-waving hypotheses. |
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| Variac |
Gromanswe
No wonder you got thrown off AA. You managed to fill up a simple thread with hundreds of lines of self serving slogans. Try to stay to the point instead of telling us what a cool guy you are. |
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| gromanswe |
And what is your OPINION on damping factor?
Maybe you do not have a clue!
groman
at least have a clue |
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| Variac |
Excellent- a nice concise post,
You don't get thrown off a discussion group for saying the emperor has no clothes, and expressing your opinion, you get thrown off for obnoxious behavior that doesn't respect others. Another opinion: Yes it is important to stand by your beliefs and please yourself, but compromise is sometimes good- it shows you have an open mind and are willing to consider other's opinions and knowledge.
I apologize to all for this additional self indulgent screed, and won't post on this thread again. |
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| capslock |
I am not sure that the driver impedance per se limits the dampability, as someone stated earlier on. If this were true, a 4R driver would be inherently superior to an 8R driver which does not seem to be the case. At least, I have never heard this to be an empirical truth. Neither would the definition of the damping factor as driver impedance / amp output impedance be meaningful if this were true.
The voicecoil can be regarded as a transformer between the acoustic energy acting on the cone and the electrical signal that is generated by it and should be damped. Twice as many turns may give twice the DC impedance, but also twice the induced voltage. Assuming that external energy is fixed, only half the current needs to be damped, so the doubled resistance would not hurt.
One should also differentiate between LF and HF damping factor, the latter being usually lower. This is partly due to lower loop gain (feedback) at higher frequencies, but usually, most of it is due to the coil that is added at the output of most amps to insure stability with all kinds of loads.
One might argue whether the midrange and tweeter drivers need that much damping, the tweeter having a series resistor in many crossover designs. But the frequency response may become warped if the impedance of the speaker isn't flat. Also, the coils found in many commercial designs are just longish air coils made of woefully thin wire that vibrate with the current applied to them, so their impedance is probably not very linear with the amplitude. First thing one can do is to put some epoxy glue on them....
Eric |
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| alvaius |
Further to Nelson's post....
Back when I had time to actually play around with audio equipment, I was starting to look at how various amplifiers "dealt" with back-emf from the speaker. The sources of back-emf could come from the speaker itself (what starts moving will keep moving....), not to mention from room pressurization, etc. I was as much playing around with the amount of porting, speaker dampening material, etc. I would even go outside to eliminate room effects.
This is a really easy thing to play with though. Get a speaker you don't care about, and then start pushing on the speaker. Take your scope and look at the output of your amplifier.
What I found is that some amplifiers, I am guessing those being on the hairy edge of stable, would exhibit definate ringing on the output independant of just the speaker movement. Those amplifiers being my cheapy, mid-80's Japanese stuff. My lone tube amp (sorry, it has long since died so I can't recreate this), kept a relatively constant output sans a bit of movement. The good transistor amp I had was in the middle.
If I had to list them, the good transistor amp would have the best DF, the tube amp the lowest (probably by a good margin).
... getting to Nelson's comments. In general, the more feedback you have, the less stable your amplifier and the more prone to oscillation. Could this be why the better amps with lower DF have more real control and depth?
Alvaius
... As will always be... sound is the output of a system, not one device... |
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| Nelson Pass |
I suspect it really just comes down to hardware,
all other things being equal. Big hardware seems
to get more control over woofers.
np
(You don't like these ideas? I've got others.) |
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| phase_accurate |
Mr. Pass
I do like your ideas (I actually experienced them) but if you have others as well don't withhold them.
To capslock:
The reason why the resistance-related restriction on damping is still valid, even when drivers of different impedance have the same Qes, is simply because everything is equalled out (I don't know if this is the correct English term for what I mean) by the DESIGN of the drivers, making one to have a certain Qes wit Rdc of 3 Ohms and the other one having the same Qes with an Rdc of 6 Ohms ! But of course half the increase in amp output resistance for the lower impedance driver would have the same detrimental effect as given increase for the higher impedance driver !
Regards
Charles |
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| Pedja |
There is something wrong when speaker’s voice-coil is observed as inductor in series with resistor. Let me be clear, I don’t see problems with this when we investigate what amp sees (though actual equivalent schematic of speaker is more complicated.)
Problem is when we discuss what speaker sees. Speaker does not see its resistance/impedance. In this case speaker is generator with certain output impedance. Its impedance sees amp, not speaker. In this way, speaker is directly connected to amp and damping factor IS important.
But, I cannot see any purpose of DF other than to damp parasitic oscillations of speaker. If speaker is well formed, its parasitic oscillations are out of the range they work (behind the X-over’s cut-off point). Of course, principally it is good, they are damped in the term they don’t work in a region of parasitic oscillations, but this goal can be achieved only partially. Some parasitic oscillations stays, and they should be damped, and here x-over appears as unwelcome impedance. That means it forms the bulk of impedance that speaker sees, amp’s output impedance is negligible in comparison and that means unimportant. In a region the drivers work normally, they have less parasitic oscillations to be damped.
In the bass region, where there are also uncontrolled movements of the speaker’s cone, speaker is (electrically) directly connected. This can explain why amps with better damping factor have better controlled bass, and why everything else is not so clear. Of course, there are exceptions (as always)…
(All these observations assume damping factor only as a possibility of amp to accept energy induced in speakers.)
Pedja |
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| gromanswe |
I found this on "damping factor".
Might clarify some things. might not.
http://classic-audio.com/marantz/mdampingfactor.html
I take the liberty to copy the last paragraph,
and quote it to you.
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Hey, enjoy your music. Don't sweat it. Play with the knobs, and if you like what you're hearing, the specs are probably pretty good. Or your ears don't care. Maybe someday you'll hear something better, or you'll use specs to put something together you know is better. Maybe not. But if you like what you're hearing, you're on the right path. I can guarantee you one thing: There are an awful lot of people out there spending money on specs they will never be able to hear as differences in the music in a million years. Just don't expect them to ever admit it. I have to really work not to laugh my head off when someone tells me they spent several hundred dollars - or even over a thousand - on speaker cables and they "sound better" than a nice heavy gauge twisted pair of stranded copper wires they could have had for about five bucks...
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| phase_accurate |
Hi Pedja
I did not state that DF doesn't matter at all (see my first post in this thread) but that it's impact is sometimes overestimated.
And there is no logical argument that the "generator" loudspeaker doesn't "see" the amplifier (which would theoretically be a voltage source) via the sum of all impedances inbetween ( connector(s) + cable(s) + crossover + voice-coil inductance + VOICE COIL DC RESISTANCE). Because the driver's DC resistance is usually the largest (by far !) of them all, it is also the one that affects damping of the driver's fundamental resonance the most. You can of course eliminate it a little by using an amp with negative output impedance but you'd rather take care !!!
Regards
Charles |
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| janneman |
May I throw another spanner in the works?
What is damping? It is the removal of energy from a system. If no energy is removed, the unwanted movement of the speaker continues. To remove energy, it must be dissipated. You can only dissipate energy in a resistive component, not in a coil or cap. Of course, you can dissipate energy in the resistive part of a coil, but you get the point.
So, back to our amplifier with the very low Rout. If this actually damps the speaker movement, where does the energy go? The amp can only keep its output at zero volts, when the speaker supplies a current, by a counter current from the output stage. Say, as an example, the speaker has a back-EMF that generates a current of 1 A in a short. Our ideal amp needs to "suck" that 1 A from its output in order to keep the output terminal at zero volts. So, the energy goes back into the amps power supply, and some is dissipated in the output stage resistive Rout. But I would think that most of it is dissipated in the speakers resistive elements, notably its voicecoil, because that is the largest part. That means that the output impedance of the amp has no effect on the damping at all, because it plays almost no role in the removal of energy.
There is another effect of the amp output resistance however that influences the sound quality. If the amp cannot fully null for the speaker generated signal, some of it will stay at the output, and be added to the "normal" signal from the input. That means that the result is a distortion of the signal, probably undistinguisable from other distortion products.
Anybody want to shoot any holes in this? |
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| phase_accurate |
Hi janneman
What you wrote is generally the same as has been written already, just in other words and I can therfore agree with it.
Maybe it is easier to understand than what I have written.:o
Regards
Charles |
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| capslock |
Nelson, I think your observation is not necessarily at odds with the concept of DF if you take into accound that DF can be nonlinear.
I'll argue with a very conventional BJT design in mind. Part of its output resistance is determined by how well the voltage gain stage is buffered from the output. This means it is determined by the current gain and gain linearity of the emitter follower driver and output transistors. In a small amp this gain may be quite high for small signals but the transistors may get into the gain drooping region quite quickly. Conversely, a larger amp might also have larger devices are a greater number of them in parallel so that their gain remains more constant at a given high output level. This particular design might have a lower overall damping factor due to other reasons such as lower feedback, but this damping factor is more constant with output amplitude. I guess the same arguement can be made for the stiffness of the power supply, which is bound to have some nonlinear influence on DF.
I know you use MOSFETS, but I am not that familiar with your topologies, so I am not sure if this argument holds for your amps. I know that MOSFETS suffer from thermal modulation especially at low frequencies. Larger devices would simply see less of a thermal signal.
In my very first design I had 2 or 3 A slow blow fuses in series with the output. Their resistance of roughly 50 mR should have been negligable, and thermal modulation of this resistance at output levels of <1 W should have been absolutely insignificant. Still, I remember that I had the impression of a much tighter and crisper bass when I shunted them.
Regards,
Eric |
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| woneill |
Hi Guys,
My experience is that if the damping factor were simply the result of a finite output resistance on a pure voltage source, then its effects would be consistent and there would be no controversy.
Unfortunately, most amplifiers are not yet close to being a pure voltage source for anything other than DC, or a steady state sine wave into a "real" 8 Ohm load.
As soon as transient signals become involved with complex loudspeaker impedance, limitations in the output driver speed & gain, PSU max current delivery, and feedback topology, cause many amplifiers to exhbit gross limitations in overall current delivery that dramatically reduce the amplifiers instantaneous ability to damp the movement of a voice coil.
Ideally, if the amp were a pure voltage source, the ringing effects of transient speaker voice coil movement would be damped by very high short term currents supplied by the amp through the voice coil, which would literally act as a brake on the voice coil as it moved through the magnetic field.
Unfortunately, while for small, steady state signals, the amp's damping ability is directly related to the damping factor, once the changes become large and dramatic, the amp stops operating as a voltage source, and clips momentarily (limited by either speed, gain, or PSU current capacity) either the curent or voltage supplied to the speaker, and then you get the discrepancies between amps.
The higher instantaneous current capacity offered by most of the higher powered amps is the reason for the general rule of thumb that bigger is generally better in terms of control. However, the best designs I have heard have been lower power (even with a lower damping factor), below 50 Watts, but with a massive, fast, instantaneous peak current capacity.
This is one of the reasons why tube amps with their often poor damping factor figures can offer much better control of the bass frequencies - they are both faster at delivering the higher currents, and the "lever action" of the transformer design allows for much higher instantaneous peak output currents without over-stressing the instantaneous current delivery capability of the drivers/psu.
Interesting stuff, though...
Bill. |
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| phase_accurate |
Hi woneill and capslock
I agree. There's nothing better than a generously designed power amp (the amp itself AND it's PSU) when it comes to LF authority.
One thing that can deteriorate LF authority as well is VI limiting, since the typical load isn't purely resistive. I.e. an output stage should be capable of dissipating a lot of power in order to be able to use pure CURRENT limiting (with a good marging!) only.
Switching amplifiers in general are also quite good (if done properly) in bass control simply due to the fact that they "dont care" into which load they deliver their power, as long as the signal frequency is much lower than the output filter cutoff frequency (but a designer has to cope with the supply pumping effect).
I was able to experience this with the TacT Millennium and the Sharp SM-SX100 amplifiers. A German HiFi magazine recently tested a prototype amp using a class - D output stage (AVM A 6) and made positive remarks about bass control.
Regards
Charles
P.S.:For the lows and mids in active speakers, switching amps would be quite cool (in every sense of this word). Current limiting could even be omitted completely. |
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| janneman |
| quote: | Originally posted by woneill
Hi Guys,
[snip]
Ideally, if the amp were a pure voltage source, the ringing effects of transient speaker voice coil movement would be damped by very high short term currents supplied by the amp through the voice coil, which would literally act as a brake on the voice coil as it moved through the magnetic field.
[snip]
Bill. |
Bill,
No, not at all! There is no braking effect as such. You can only damp if you remove energy, ie change it for instance to heat. If your amp has zero output impedance, the ONLY damping comes through the resistive part of the voicecoil and/or xover filter.
This may sound like hairsplitting, but is significant. The very high short term current you refer to, generates an opposing amount of force that may *temporarely* stop the cone, but as soon as you remove that current (and you have to, sooner or later) the original circulating current will move the cone again. OK, eventually it will stop, because there are resistive losses for instance in friction with the air and the ohmic losses as alluded to earlier.
The ultimate power output stage in this context is a short-circuit. Try shorting the speaker after exitation, and you will see a damped oscillation, that doesnot stop immediately if you short the driver connections, but gets smaller and smaller as energy is slowly removed from the system through all kinds of resistive losses.
Don't think that a high damping ratio amp can stop a cone dead in it's tracks, it cannot. The terminal voltage may be kept at zero by the output stage, especially if it has very low or zero impedance, but the voice coil current and cone movement lead their own lifes. The cone *has* to slowly decay to a standstill, because it will take time for the stored energy to die out.
I know this sounds counter-intuitive for a lot of people, but I think my reasoning is essentially correct.
Cheers, Jan Didden |
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| capslock |
What it boils down to is the question of whether an amp can stop a speaker more effectively than a short circuit.
My gut feeling is yes. I have not done the maths so I may be doing my training as a physicist little credit with this handwaiving argument.
The energy stored in the speaker air volume moves the cone, generating a current in the voice coil. A short circuit would sink the currents. An amp could also inject an opposing current, but that would require its output voltage to move from 0. This is something that won't happen with your everyday voltage controlled voltage source amp which behaves like a short circuit when there is no input signal -- so Jan is right!
One would need to measure the movement of the cone or even better the air pressure by using a microphone in front of the cone to generate the correcting signal.
Acitve sound cancellation through destructive interference works. The point that worries me is: where does the stored energy go?
Is it dissipated in the amp's transistors? No, due to the finite speed of sound, the cancellation works only in a certain volume close to the mike. In other areas, we are bound to see constructive interference so the energy goes into the room and gets dissipated there. If the listener does not want to creep to the mike, he will have no benefit... |
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| phase_accurate |
cpaslock wrote
| quote: | | One would need to measure the movement of the cone or even better the air pressure by using a microphone in front of the cone to generate the correcting signal. |
=> http://www.meyersound.com/products/.../x-10/index.htm
Regrads
Charles
P.S :I wasn't able to have a listen to these babies so far but beleieve me I would if I could, though I'd never buy a pair of them.
P.P.S : Feedback is never a cure-all. |
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| janneman |
Ahh, Active Sound cancellation, yes, but that works by setting up an opposing air movement, for example by another transducer, to make the net air movement (as capslock rightly stated, in a very limited volume - works great with headsets though) zero. It does nothing to damp the cone movement.
As for where the current goes, there are two terminals on the driver, right? What comes out must go in - some guys law, I think it was Thevenin. Since the driver is connected to the amp, the current comes out the driver + terminal, into the amp output, through the amp bottom part to the neg supply cap, out again at the ground terminal of the neg supply cap to ground and back to the ground terminal of the driver - loop closed!
Jan Didden |
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| janneman |
| quote: | Originally posted by phase_accurate
cpaslock wrote
=> http://www.meyersound.com/products/.../x-10/index.htm
Regrads
Charles
P.S :I wasn't able to have a listen to these babies so far but beleieve me I would if I could, though I'd never buy a pair of them.
P.P.S : Feedback is never a cure-all. |
Right! They have the sensor 1 inch in front of the cone. Lessee, that takes the sound about 1msec to get from the cone to the sensor, so all corrections come 1msec late. No wonder it only works for the woofer.
Jan Didden |
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| woneill |
Hi Janneman and Capslock,
Sorry for my vague terminology. I agree with what you are saying. My vague use of the word braking was referring to the energy transformation from mechanical (kinetic) to electrical when a coil moves through a magnetic field: the electrical energy that is generated as the current flows through the coil, is directly transformed from the kinetic energy of the cone.
It is dissipated primarily as heat in the coil windings, and in the output stages of the amplifier. This process is not braking in its true sense, but is, the topic we are concerned with here: damping.
Many of the transient current demands on the amp are related to its ability to source/sink appropriate current to maximise this damping effect and to reduce the time taken for the kinetic energy due to the cone's/coil's movement to be dissipated such that the cone assumes the appropriate displacement based on the voltage applied by the amp.
Thinking about the physics of damping, it is quite possible to overdamp as well as underdamp - I wonder how many amps are matched to the damping requirements of the speakers they are driving such that the drivers are critically damped?
It IS a fascinating topic!
Bill. |
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| phase_accurate |
Hi janneman
This is not supposed to be Active Sound Cancellation but active control of the generated sound versus the input signal !!
Regards
Charles
At 40 k$ a pair they are quite a bargain compared to some highend speaker/amp combinations ;) |
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| roddyama |
Hey Guys,
"Damping Factor" is a way of putting a number on a very dynamic characteristic of an amplifier. The output impedance of an amp is not purely resistive. It is a complex function that has a phase angle and amplitude that varies from instant to instant. The inductive reactance of the drivers voice coil moving through the magnetic gap is also a complex function with phase and amplitude. Energy from the driver will be disipated in the the resistive component of this complex impedance, this is true. But, this is not the only way that the amp will damp the motion of the drivers cone. The amp will absorb and store energy from the driver and use it in the next instant of time depending on the phase and amplitude (which can be negative) relationship between the Rg and the back EMF of the driver.
Rodd Yamashita
P.S. Sound travels 1in. in ~0.1ms, not 1ms. |
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| janneman |
| quote: | Originally posted by roddyama
Hey Guys,
[snip]
" The amp will absorb and store energy from the driver and use it in the next instant of time depending on the phase and amplitude (which can be negative) relationship between the Rg and the back EMF of the driver.
Rodd Yamashita
P.S. Sound travels 1in. in ~0.1ms, not 1ms. |
Yes, I stand corrected.
Hey Rodd, this is an interesting concept. Have to think about that one. I can see that the energy could be stored, but I'm not sure about the re-use bit.
Cheers, Jan Didden |
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| roddyama |
Jan,
The output impedance (Rg) is the Thevenin equivlent impedance of the amp looking back into the speaker terminals. What your seeing at any point in time is the sum of all the components (active or passive) that in some way affect the VI and phase at those output terminals.
In the same way, you can take any two points in the amp and the VI and phase across those two points will be dynamic, changing from instant to instant. As an example, the PS caps are constantly being charged and discharged changing the DC buss voltage. Depending on the topology of the amp, the current produced by the back EMF of the driver can go to bring the PS cap voltage back toward the DC supply value. This extra voltage can be used in the next instant because the out of phase feedback loop has just caught up with the VI conditions at the output terminals and are changing the voltage at the bases of the output devices.
Because Rg is so complex, and depends on the design of the amp in question, the damping presented to the driver is not just a function of "Damping Factor", as Mr. Pass points out in his post.
Hope that helps clear thing up.
Rodd Yamashita |
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| Nelson Pass |
ZZZZZZZZ.....
Huh? What? Somebody mention my name?
I refer you to my patent for acoustic cancellation circuit
# 4,899,387, also known as the Phantom Acoustics Shadow.
On the original topic, there are some fairly easy techniques
for creating a negative impedance on the output of
an amplifier, so that the "damping factor" exceeds
infinity. This amounts to motional feedback, where the
amplifier actively mounts opposition to back EMF, reducing
the apparent series impedance of the amp/cable/speaker
loop.
This seems to help, but as before, doesn't quite deliver
without the heavier hardware resources. |
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| setmenu |
Interesting read.
As I have been developing different coils for my planar headphone
transducers I have observed the bass control increasing as the
amount of turns increases.[thus far]
These things are very sensitive to lf signals at present but the
control is Ok.
Also regarding the need for brakes on big cones I note one approach is to use dual coils,one as a pure generator into a load,
or even an active control.
Seems this damping factor issue has many people quite unsure about its real effect.
This whole business is fairly new to me an quite facinating.
Setmenu:) |
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| ALW |
I'm firmly of the opinion that damping factor, as normally quoted is almost irrelevant to the sound.
I've heard many amps with theoretically massive damping factors that sound flabby and soft in the bass, and others that have series resistors in their output (after the feedback tap point) that sound fast, tight and infinitely more musical and punchy.
Constant dynamic output impedance is what I'd aim for, across the widest BW possible.
Andy. |
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| Pedja |
| quote: | Originally posted by ALW
I've heard many amps with theoretically massive damping factors that sound flabby and soft in the bass, and others that have series resistors in their output (after the feedback tap point) that sound fast, tight and infinitely more musical and punchy.
Andy. |
Can you name them?
Thanks.
Pedja |
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| ALW |
For Flabby and unmusical listen to just about any far-eastern amp from the 80's and 90's.
Many of these claimed damping factors of 1000 or so and sounded execrable.
For the other case listen to a Naim power amp. There is a series resistor in the o/p of these that limits the maximum achievable damping factor. I've never heard a tighter, punchier power amp, from any manufacturer.
There's an argument that damping of the loudspeaker is something that should be accomplished within the loudspeaker design itself. If your speakers sound woolly, maybe they are at fault, rather than the amp?
It's always best to sort problems out at source, not later on.
Andy. |
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| gromanswe |
I have listened to the different speakers on Damping Factors.
As this is for me a secondary issue,
I can not say I have more than very fast read over the texts.
I have however not found reason to change my first
Opening Statement. Not the basic message expressed.
So I quote this:
Damping Factor;
nothing to pay any greater notice
Damping factor is something I never
understood either.
A welldesigned amplifier doesn't have to worry
about damp factor.
As most expressions is this a "market slogan"
mostly used to get you into A BUY!
gro |
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| gromanswe |
for my view on other things that can relate
to similar subjects,
see my views presented in my posts
in this thread
and in all my posting
might be WORTH
while to study
humbly
gro
* is written in a simple language
*I do not care aboot them yankees
so i agromaan from the icecold north
WELCOME, REALLY welcome :p
japanese indians(red or black) argentinians
israelis chinese scandinavians
English Gentlemen ........
not to mention my african friends
living in africa
or elsewhere
Do not care aboot tham yankeemaan, Jamaicans!
serbians
run out of space |
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| gromanswe |
Sorry, abobut the bad function, at geocities,
but it is a free webspace.
Limited bandwidth--
So you have to be patient--
wait some hours
or days
And things will have calmed down.
Thanks again! people
groman
webmaster at gromanaudio@swipnet.se |
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| Variac |
| What he hell does this blather have to do with damping factor? |
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| capslock |
Well, IF a super high damping factor is not that important, bridge tied lead (BTL) class A deserves another consideration.
One could stay differential all the way from the DAC to the speaker terminals.
Advantages:+ EMI rejection
+ partial distortion cancellation
+ doubled efficiency in class A mode!!!
+ halved supply voltages for same power
Disadvanges:
- halved damping factor
- higher parts count |
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| gromanswe |
be good.
Haven't tried it.
Have my ways.
Get it working.
Cheers
gro |
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| promitheus |
Damping factor is a secondary issue like THD or maximum watts and so on.
Its all numbers used to sell.
Who ever has the biggest numbers (or smallest in some cases) sells more.
Don´t even believe the numbers at all, they are usually measured in totaly different ways anyway.
What you have to see is the design and hear the quality of the sound it reproduces. |
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| mrfeedback |
| quote: | Originally posted by Variac
What he hell does this blather have to do with damping factor? |
Yeah, can someone send Groman some Prozac or something.
Eric. |
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| capslock |
| I find myself wishing for the first time here on DIYaudio that there was an "ingnore(member)" command... |
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| AudioFreak |
| quote: | Originally posted by capslock
I find myself wishing for the first time here on DIYaudio that there was an "ignore (member)" command... |
For what it is worth, there is an ignore function...
Goto the profile for the person whose posts you wish not to see, then at the bottom click the link 'Add xxxxx to Your Ignore List' |
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| Variac |
| Thank You so much for the ignore info. My blood pressure might return to normal. I don't know who you might be referring to :rolleyes: but by his own admission he has been banned from other sites. When will he learn that an opinion isn't a very high level contribution to a thread if it doesn't add a useful concept or technical back-up! |
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| gromanswe |
I might suggest it to the authorities.
On this place.
gromanswe |
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| promitheus |
| He IS getting on my nerves. |
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| sonnya |
Groman ... Maybe you should listen a bit to what we say...
No one in this forum would have any bad negative feellings about you if you listen a bit to what we say...
Serious!! You will get a lot of friends here... I think that is what makes people happy...
Sonny |
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| mrfeedback |
Hi Groman,
we have had some overley manic people here and they get told, and politely, so don't take it personally.
Perhaps you should work on your english a little (some of your translations don't make a whole lot of sense), and post stuff that is friendly and relevant to the discussion concerned, such as interesting observations, knowledge, experience or advice - that is how you get respect round here.
Variac - chill.
Regards, Eric. |
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| janneman |
..and, I may add, be honest. You (gromanswe) posted on another
thread that you had a *local* volume control working, but you ignored requests for specific details. Unless you come up with those, I can only conclude that gromanswe lied. That is unforgiveable on a board like this. People may spend money or go in a specific direction based on your info. If you talk nonsense or outright lies, that resets your trustworthiness to zero. I myself will ignore gromanswe's posts because so far I don't know if he is joking, lies or has something worthwhile to offer.
Jan Didden |
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| Variac |
The irony is that I thought the local volume control was a really good idea and I had never heard of it or thought of it before.
I told him this. Maybe he just got a little carried away.
Clearly Gromanswe has some things to contribute to the forums,
but as I was putting him on my ignore list I noted his posts averaged 13.5 per DAY. I don't think anyone here could come up with over 13 useful posts a day. Hey Gromanswe, just cut down the posts a bit to the ones that you can really contribute to and keep 'em short, and you will be very appreciated here;) |
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| gromanswe |
so I will not do it
as it would'nt be me
and groman is who I want to be!
what do you want.... |
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| Geoff |
Groman
By all means be yourself, but please do it elsewhere. |
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| gromanswe |
| quote: | Originally posted by Geoff
Groman
By all means be yourself, but please do it elsewhere. |
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| Electro |
To me dampening factor has very little or no effect. Like Douglas Self said, "the dampening factor will contribute to 0.67% of the sound." If anybody did an experiment on dampening factor verses frequency. They will see an inconsistant dampening factor spec.
Look up http://www.trueaudio.com/post_013.htm
| quote: | Originally posted by promitheus
Damping factor is a secondary issue like THD or maximum watts and so on.
Its all numbers used to sell.
Who ever has the biggest numbers (or smallest in some cases) sells more.
Don´t even believe the numbers at all, they are usually measured in totaly different ways anyway.
What you have to see is the design and hear the quality of the sound it reproduces. |
Trying to hear an exotic amplifier before buying is like seeing a pig fly. |
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| promitheus |
| Groman if you have nothing else better to say in this Forum you should go somewhere else. If you just want to make a lot of posts, make your own thread and talk to yourself. Nobody is very interested in what you say. |
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| capslock |
Well, I am humbled! I have measured the components in the bass crossover of my highly respected (were second highest class in the German Stereoplay magazine in their time) T+A T160E speakers. Turns out the woofers (2x5R6 DC resistance, connected in parallel) are driven trough two series connected inductors with a total series resistance of 0.43R. There is a dubious optional bass boost circuit which puts 800 uF in series. I suspect the two paralleled capacitors to add another 0.2-0.5 R.
So on this speaker, which is probably better than 95% of the speakers around, it really won't matter whether amp and cable add a few mR...
If I knew what influence the speaker reactance has on the total frequency response, I'd probably do away with the passive filter and go active for the bass section...
Eric |
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| phase_accurate |
Hi Eric
Below you see, in a simplified form what an amplifier basically
"sees", when a bare driver or a driver in a closed box (to keep things simple) is connected to it.
The mechanical resonance is elecromagnetically transformed into an electrical resonant circuit prensent at the driver's terminals. The damping of this resonance is mainly achieved by the diver's "motor" connected to the amp via the winding resistance (Re) which is the dominant part when it comes to adding together all series resistances.
A good designer is taking the series impedances of x-over components into account when determining the tuning of the box (any positive series resistance increases Qes).
If you now go active and drive your woofer directly from a power amp this will have some influence on the tunig/damping. If better or worse or to your like/dislike -- you will have to try out and judge by yourself, but I am positive about that, beeing a fan of active solutions.
The trick with the series capacitance is one of the favourite tricks of Mr. Timmermanns, the editor of the German magazine "Hobby HiFi". It is adding another order into the bass system's transfer function and is trading off a little more bass at the lower end - against a steeper rolloff.
In an active system this behaviour could be achieved electronically without the need of large and expensive capacitors.
Regards
Charles
P.S. The values shown would be for a typical driver in a box with a Qtc of 0.6 approx and an fsb of 50 Hz approx. |
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| JensRasmussen |
I just had a nice cup of coffey with my girlfriend, and while we were talking about something else I had an idear.
How about taking the NFB from the fpeaker terminals (The live one) insted of keaping it inside the box.
Has it wver been done ? and could it be stable ???
Has anyone tried this ?
\Jens |
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| phase_accurate |
Hi Jens
The ones that just crossed my mind are the Spectron amplifiers and the Dutch company Stage Accompany (SA). They supply speaker cables with integrated feedback lines. That is they don't go into the Speaker (at least to my knowledge - maybe SA does this for actively driven P.A. Speakers) but take feedback at the end of the cable.
This is indeed a solution to eliminate the cable resistance's detrimental effect on damping factor.
But you can do it only before the crossover or else use active solutions - AND as you seem already beeing alert of: it may deteriorate stability.
SA once stated a damping factor in the range of several thousand using this technique (or even 10 000 ?!).
But as already mentioned before: There is little sonic difference between a DF of several hundred and several thousand (if the ONLY differenc is DF).
Another solution is the use of amplifiers with negative output resistance which would even allow lowering of the Qtc, but such things have to be done with great care or "things might get interesting"*.
Or you can do the contrary and use current-drive instead of voltage drive which eliminates the effect of any series resistance (even heat related efficiency decrease !) and voice-coil inductance completely, but then special action has to be taken around the driver's fundamental resonance.
Regards
Charles
* the originator of this ingenious phrase is Nelson Pass although not in the context of damping factor. |
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| JensRasmussen |
Since the passive crossover for a LP - filter often includes an inductor, does damping change throu the freq span, or is i just a definition that includes the nominal impeedence of the speaker ?
If the same driver is driven with an active system, does the damping factor become the same ? I would prefer active cross overs anyday (It's what I was brought up with when i did my apprenticeship at B&O) Since active filters give one the option of "helping" a driver when it needs it.
Is damping generelly better in active systems, or is it just because of better filtering that they sound more precise ?
\Jens |
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| mrfeedback |
Questions/Pondering.
Assume that a typical bass driver has a DC resistance of say 6 ohms.
In the overshoot condition (after application of a pulse) such a driver acts as a generator.
When the driver is in the generator condition (overshoot) it has an output impedence of, say 6 ohms.
Radio and transmission line theory would indicate that this generator needs to be coupled with a line of same characteristic impedence, and the line loaded with the same characteristic impedence so as to eliminate signal reflections.
So is back loading (damping) a driver with an amplifier with near zero output impedence actually the wrong approach ?.
Should the damping factor be 1 ?.
There have been observations that low damping factor amplifiers can sound more pleasing, and that high DF amplifiers can be displeasing.
I use 25 pair telephone cable that gives a characteristic impedence of around 8 ohms I think.
I find this cable to give a typically more pleasing result on most systems.
Are we listening to high frequency ringing conditions causing intermod distortion in high DF (high loop NFB) amplifiers ?.
Eric. |
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| phase_accurate |
Hi Jens
The control of the amp over the driver does indeed change over frequency influenced by any component between speaker and amp.
The direct connection of amp and speaker is actually one of the reasons that make them sond more clean. The German magazine
"Klang & Ton" (a mag about speaker building) went active with one of their flagship designs and they measured a distinctive decrease in DRIVER related THD !
But this does not per se mean that every amp would like driving every bare driver.
Another reason is that you can theoretically correct for whatever warped frequency response of your driver you like to (although rationality sets limits here).
You don't even have to live with the TS-parameters your driver is delivered with, i.e. you can artificially alter them if you like !!!
You can use analog computing techniques to achieve flat frequency response AND perfect transient response (i.e. subtractive crossovers).
You can use MFB (motional **************) techniques to have even more control over a cone's motion. Although I am not a fan of this.
Regards
Charles
I am wondering when the automatic parser will be going to scan for "OP-AMP", "ceramic capacitor", "electrolytic" and Bose as well !! ;) :D |
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| phase_accurate |
Hi Eric
On the one hand somebody can assume that the wavelengts of audio frequencies are that immensly large that only a small fraction of a wavelength can be placed into a speaker cable, so cable impedance wouldn't matter.
If one takes a really high "audio frequency" of 100kHz approx. then it's wavelength is around 3 km.
1 kHz' wavelength is a hundred times that much.
So voltage drive of a speaker would be quite fine from cost-value ratio.
On the other hand the really overwhelming dynamic range of 120 dBs of our hearing system can cause little errors being audible, that some measurements or simple considerations wouldn't expose. There have been lots of discussions on cables in audio magazines and also EW+WW and there are as many opinions as there are "experts".
I think the damping factor should be as low as possible but not at the cost of any other parameter. One has to consider that the usual DF measurement is made with a steady-state sinusoidal frequency and a PURELY RESISTIVE load (maybe there is a need for a new standard ?!). But how will an amp react when loaded with a real life speaker ? I think that's the reason why usually really beefy amps have more control over the load, simply because they are left virtually unimpressed by what is connected to them.
Regards
Charles
P.S. regarding the advantages of active speakers I forgot to mention "short cables" !! |
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| JensRasmussen |
Hello,
Is it possible to adjust the outputresitance of an amp to try different sounds ? I'm working on a design, and haven't really though differently than to get as low an outpusresistance as possible.
\Jens |
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| mrfeedback |
Hi Charles,
I understand that characteristic impedence ought to be irrelevant in the audio band, but modern digital audio causes RF throughput.
Yes, Self I think referred to Interface Intermodulation Distortion.
Also other articles referring to loop inductance causing distortion.
Yes, I am discounting the steady state sine wave condition.
Rather the pulse condition.
And yes stout amplifiers are typically less load dependant.
Is this a case of a big supply quencing the return pulse without significantly modulating the power rails and causing PSRR consequent artifacts ?.
High loop NFB amp implies high number of gain stages which implies FB propagation delay and opportunity for ringing condition.
Any such ringing would cause sonic masking of the original impulse (not silence after an impulse) and loss of real clarity.
I find this to be a sonic effect in high NFB amps imo, and fatigueing.
What happens to the cone during the overshoot condition.
Ie - does putting a sudden brake on the cone cause mechanical ringing in the cone, and is a gentle braking more sonically correct ?.
Nelson gives musing about air being non symmetrical, so should the braking rate of the cone be matched to the characteristics of air ?.
Eric. |
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| phase_accurate |
Hi Jens
Of course can you make your amps output resistance positive or negative or even a complex impedance. But if you don't take care "it might get interesting".
I will put together what might be useful to you and may be post it here (is anybody else interested ?) or mail it to you.
But I have to close now.
Regards
Charles |
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| capslock |
Charles,
the schematic of my bass XO is posted in the loudspeaker forum. If you forget about the bass enhancement, it is a simple 3rd order low pass.
Instead of worrying which kind of core for the inductors will give me the best peformance, it itches me to place the LCLR filter (rescaled for nice small air coils) before the amp and drive the speakers directly.
Is the interaction of the speaker with the XO purely resistive? In order not to change damping and tonality, it would then suffice to place 0R43 in series with the power amp. Doesn't do anything for the damping factor but gets rid of the distortion in the ferrite coils and electrolytic.
If not, could I place L1 and C1 before the amp and keep L2, maybe in series with 0R19?
Eric |
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| peranders |
Wow, what a debate! Lots of opinoins, few who really knows.
To be short: Most amps have decently low output impedance (high damping factor). Some tube amps and non-feedback amps with MOSFET's may have rather high output impedance.
As Nelson says, speakers (some of them) may get influenced by different kinds of damping factor and therefore sounds different (not necessarily bad) with different amps. |
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| phase_accurate |
Hi Eric
Uh, that bass enhancement circuit is even 2nd order ..... !
But apart from that, the load a driver presents to a crossover is never purely resistive. If you want to have a resistive load on the crossover you will have to correct the driver's impedance. If you don't want to do this then you have to account for the frequency dependant load when designing the crossover.
In other words: This lowpass will have a different amplitude response when driving a resistor than a loudspeaker driver.
Just try to measure the response at the driver's terminals.
If you want to use a passive filter in front of your amp then you would also have to design it for higher impedance !
Your resistor problem:
If it were a closed box then I would say, just try it, the bass will sound tighter and more precise if the tuning wasn't already of very low Qtc. In the latter case (quite seldom) the bass response would drop too early and sound too weak.
But I think your speaker is a TML (a favourite with T+A), isn't it ?
I don't know what will happen then, although I have a simulation program for TMLs. But I don't know how accurate this is (some people say TMLs couldn't be calculated at all).
As far as I remember TMLs don't like drivers with too low a Qts.
Maybe you should ask planet10, he is aTML expert.
Regards
Charles
P.S. In the meantime I did the maths again for the simulated output resistance. If anybody is interested I will post it. |
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| capslock |
Sure, go ahead and post. Do you have a brief explanation of how the second order bass enhancement works (maybe in teply to my other thread in the speaker forum)?
Eric |
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| capslock |
Seems to be complicated to activate the woofers. Still seems to me I could save money on quality caps and baked air coils by activating mid and high range. I could measure amplitude and phase at the drivers and tailor a passive low power filter with the same resonse that sits in front of the amp. I am not sure whether I need to include the series resistance.
Would the midrange (2x approx 3 inch cones) and tweeter (i inch dome) also be sensitive to the resistance they see? Would they profit at all from being damped by the amp?
Eric |
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| phase_accurate |
Hi Eric
Though this is a little off-topic in this DF thread I will try to answer it.
The series resistances have influence on the tuning of the tweeter and midrange as well (damping and amplitude response).
In the latest "Klang und Ton" they mentioned that their flagship speaker has a less smooth (but still excellent) amplitude response in it's active version but that the overall improvment achieved by activatin would well be worth the effort.
I have never done an activation of a passive loudspeaker. All speakers I used in active configuration were active from the beginning so I don't see any reason for not going active.
Is there any chance that you can borrow the additional amps and a (maybe adjustable) crossover to make a try (at least the crossover wouldn't be that difficult and expensive to build just for this trial)?
Many "activists" are using adjustable Linkwitz Riley crossovers and achive excellent results even thogh they are not exactly tailored to the speakers used.
Regarding the simulation of output impedances you seem to be the only person interested in. Since it is a lot of work I may probably fax my hand notes to you because it would give me some work to put it in a neat electronic form.
The passive equalization circuits work as complex frequency-selective transformation like the ones that are common for matching purposes in RF-circuits.
Regards
Charles
P.S. You still owe me the answer if your speaker is a TML. |
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| capslock |
Dear Charles,
I put your response and my answers in the T+A thread in the speaker forum.
The only thing that is relevant here is the question whether a mid or high range speaker would profit from high damping. Well, frequency response may show more jagged features as you said. How about transient behavior etc.?
Just for clarity: low output resistance = low Q? Looks strange at first sight but made sense once I realized that a low output resistance will actually dampen the oszillation of speaker cone & air and hence lower its Q.
But a damped oscillator has flatter and broader resonances. Why would damping then cause a more jagged frequency response?
Eric |
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| phase_accurate |
Hi Eric
Unless the driver's Q is already very low, things will most likely be better with better damping.
The response issue is simply because a good designer will arrange the COMBINATION of driver AND crossover network to perform as wanted.
If you now go and connect maybe a third-order butterworth or 4th order LR crossover in front of your amplifiers the original tweaked response doesn't apply anymore.
In other words: the optimal active crossover would be the one that is tailored to the drivers in use, but you can still achieve good results with tuneable universal crossovers.
Regards
Charles
P.S. Have you got enough amplifiers to make a test-run ? I might probaly have a simple crossover you could use (i.e. I would want it back afterwards) and tweak but this is depending on the current filter functions of your speaker (my crossover is 3rd order butterworth). |
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| capslock |
Hi Charles,
sorry, wasn't around this weekend and didn't get to post anything in the loudspeaker forum.
Yes, the T160E seems to be a transmission line.
I can build an active filter and a sufficient number of power amp boards very quickly, but thanks for the offer.
I am very firm in digital and analog audio electronics but did not get too much into speaker design until I realized what kind of junk can be inside even top of the line speakers. Therefore I am currently reading up on speaker and crossover design.
As a quick fix, I am still wondering whether I should redo my passive crossover with decent components (which will cost several 100 €) or go (partially) active without too much tweaking.
From what I have gathered so far from your posts and some reading, measuring voltage vs. frequency at the speaker terminals and tailoring an active filter with the same resonse should work well for mid and high range. The benefit would be mainly in lower distortion, the benefit of high damping on mid and hi not being so evident. Correct?
For the bass, the same approach but with added series resistance should work, foregoing for the time being the positive effect of higher damping until I can work out a more intricate filter.
Eric |
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