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What is meant by damping factor and why is it important

watchnerd

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#2
I see this mentioned and know my amps have very high dampening factor but what is it, how's it achieved and why is it important?
In simplistic terms, it's a measure of the ability of the amplifier to control overshoot, to stop a driver from moving and overcome back EMF.

An amp with low output impedance and high damping factor limits this kind of sloppy driver behavior.

It's sort of like engine-braking in a car.
 

Thomas savage

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#3
It's actually damping factor, not dampening factor.

In simplistic terms, it's a measure of the ability of the amplifier to control overshoot, to stop a driver from moving and overcome back EMF.

An amp with low output impedance and high damping factor limits this kind of sloppy driver behavior.

It's sort of like engine-braking in a car.
Thanks, what's involved in designing a amp to have a high 'damping' factor.. The numbers relate to what precisely?

Thanks for your help, I was under the impression it was to do with controlling the bass drivers well but vague understanding to say the least.
 

watchnerd

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#4
Thanks, what's involved in designing a amp to have a high 'damping' factor.. The numbers relate to what precisely?

Thanks for your help, I was under the impression it was to do with controlling the bass drivers well but vague understanding to say the least.
Damping factor = load impedance / source impedance

Obviously, this will vary by frequency as the speaker load changes with frequency.

But generally what's needed is a small denominator, a low output impedance, which most negative feedback based amps have. ICEPower and Hypex nCore use copious amounts of negative feedback and have huge damping factors.

However, not everyone agrees it's a good thing. Nelson Pass is not a big fan of high damping factor, preferring to let the bass flop around a bit more, which creates more, but tubbier bass.
 

DonH56

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What watchnerd said: damping factor DF = Zload / Zamp

While massive damping factor was the rage in the 70's and 80's studies showed the required factor was much less than thought (by marketing, probably); most people can't tell beyond a factor of 20 or so. Most SS amplifiers these days are probably around 100 or so at lower frequencies, tube amps around 10 or less. For both designs output impedance rises and DF drops as frequency increases due to both feedback and the characteristics of the output devices (gain falls and output impedance rises with frequency).

A low output impedance (high DF) will let the amp look more like an ideal voltage source, the reference for most audio amplifiers. That reduces sensitivity to the load, both its impedance and the reverse EMF speakers can generate that tries to modulate the output. If the amp's impedance is high, then impedance variations by the speaker will change the frequency response. If there is significant back-EMF, essentially the driver acting like a generator instead of a transducer or motor, then an amp with high output impedance (low DF) will let the driver ring more. These affects can be audible and are certainly measurable.

This is part of why some amp/speaker combinations do not work well, and is also at least partly responsible for the difference in sound among amplifiers. I love tubes on panels in the midrange, but most tube amps do not control the panels well in the bass, and the very low impedance (often 2-3 ohms or less for ESL's or ribbons) at high frequencies can make tube amps sound a bit harsh or going the other way a bit soft if they roll off the highs. A speaker with a big dip in impedance at low frequencies can lead to amp stress and muddy sound if the amp has high output impedance. And so forth. Of course, ringing in the bass can sound "richer" or "fuller" and so some people like that sound better, and if the tube amp rolls of the highs again people may appreciate the effect and call the upper end "smoother". The SS amp that provides such solid bass may sound "harsh" even though its distortion is lower; people simply do not like the extended high range it provides.

It gets waaay more complicated than this but hopefully that helps a bit. - Don
 
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watchnerd

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#8
Why the negative stance (some have) on high damping then? Is there a trade off somewhere?
1. Some still object to negative feedback on principle, considering it a cardinal sin.

2. The trade off with high damping factor is you don't know how stiff the speaker driver suspension is, so how much is too much (too much can lead to a speaker sounding subjectively lean, although more accurate)? What kind of damping factor did the speaker designer assume was normal? (one of the benefits of active speakers is that this question goes away)

3. Corollary to #2: Vintage speakers can sound poor with high damping factor amps because they were designed in an era when most amps had less damping factor and thus the voicing between 'too tight' and 'too loose' in the bass was made with a different set of assumptions

4. If you're into tubes, it's not easy to get a high damping factor with tubes
 

Thomas savage

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#9
What watchnerd said: damping factor DF = Zload / Zamp

While massive damping factor was the range in the 70's and 80's studies showed the required factor was much less than thought (by marketing, probably); most people can't tell beyond a factor of 20 or so. Most SS amplifiers these days are probably around 100 or so at lower frequencies, tube amps around 10 or less. For both designs output impedance rises and DF drops as frequency increases due to both feedback and the characteristics of the output devices (gain falls and output impedance rises with frequency).

A low output impedance (high DF) will let the amp look more like an ideal voltage source, the reference for most audio amplifiers. That reduces sensitivity to the load, both its impedance and the reverse EMF speakers can generate that tries to modulate the output. If the amp's impedance is high, then impedance variations by the speaker will change the frequency response. If there is significant back-EMF, essentially the driver acting like a generator instead of a transducer or motor, then an amp with high output impedance (low DF) will let the driver ring more. These affects can be audible and are certainly measurable.

This is part of why some amp/speaker combinations do not work well, and is also at least partly responsible for the difference in sound among amplifiers. I love tubes on panels in the midrange, but most tube amps do not control the panels well in the bass, and the very low impedance (often 2-3 ohms or less for ESL's or ribbons) at high frequencies can make tube amps sound a bit harsh or going the other way a bit soft if they roll off the highs. A speaker with a big dip in impedance at low frequencies can lead to amp stress and muddy sound if the amp has high output impedance. And so forth. Of course, ringing in the bass can sound "richer" or "fuller" and so some people like that sound better, and if the tube amp rolls of the highs again people may appreciate the effect and call the upper end "smoother". The SS amp that provides such solid bass may sound "harsh" even though its distortion is lower; people simply do not like the extended high range it provides.

It gets waaay more complicated than this but hopefully that helps a bit. - Don
That's great don thanks ..
 

RayDunzl

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#10
Dick Pierce looked at Damping factor and his investigation is published at Audioholics.

http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

http://www.audioholics.com/audio-am...ping-factor-effects-on-system-response-page-2

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. Even considering the substantially larger response variations resulting from the non-flat impedance vs. frequency function of most loudspeakers, the magnitude of the problem simply is not what is claimed.

Rather, the people advocating the importance of high damping factors must look elsewhere for a culprit: motion control at resonance, or damping, simply fails to explain the claimed differences."
 

Cosmik

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#15
The reference to active systems concerns the series impedance of a passive crossover, but I don't think anyone has actually mentioned that yet. The passive crossover reduces the damping factor no matter how low the amp's output impedance. Here's an article on it:
A passive XO will always add (usually) undesirable impedance to that seen by the driver(s), the impedance is frequency dependent, and ranges from perhaps an ohm or so to almost infinite. The potential for uncontrolled cone movement, intermodulation distortion and loss of performance is so great that it is impossible to determine in advance, but it is all negated in one fell swoop by using a fully active system.
 
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DonH56

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I did not read the articles linked by RayDunzl; I will try to later but have other things to deal with this week. It's hard to interpret the conclusion in isolation... It appears to say frequency response is modified, but at system resonance high DF does not help. Depending upon the design that can be true since it is a resonance, and it depends upon the cause and type (mode). Given a little energy input a system at resonance can ring (or even oscillate) almost independently of the driving source. That is one reason I like servo subwoofers. As frequency goes up it is harder to make a stable loop due to driver lag and eliminating the crossover makes a big difference as well (since the amplifier directly controls the speaker it can help dampen resonances, to a point).

Cosmik makes a good point and is one of the primary reasons for going to active designs. Other reasons include the ability to provide sharper (higher-order) crossover slopes at finely-tuned and stable frequencies, the ability to compensate phase (and delay) and amplitude across frequency for better performance, isolation of drivers and amplifiers (no more worries about the tweeter signal being modulated by the bass signal, and when the bass clips -- the usual culprit -- the tweeter amp probably does not), and the ability to select amplification appropriate to the driver (e.g. a 1kW woofer amp and 300 W mid/tweeter amp may outperform a 2 kW full-range amp).

On active speakers, I would guess the majority of audiophiles want to get their own amplifiers and will always question any internal amps or manufacturer's choice, so there is market resistance, and then their is the higher cost of active designs if manufacturers include the amplifiers. We have seen a push from the low end for computer speakers and the like, and the high end from Beolab, Harmon, Kii, and so forth, and there have always been active monitors for pro studio and stage work, so I suspect they will gradually become more prevalent. Or not; I suspect the battle will be won by marketing, not engineering. I find it interesting articles that decry active designs for their inability to substitute "higher quality" amplifiers, claiming various ills a different amplifier might cure, and yet fail to cite similar concerns with passive crossovers....

Note passive crossovers do have some benefits: they provide driver isolation from each other and the amplifier, can make the load the amplifier sees easier to drive, and provide a simple solution for the customer. In the past a designer could dial in a crossover to provide better frequency and time response than most consumers, but modern DSP programs have largely given that gift to the consumers at the touch of a button.
 

RayDunzl

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#18
It's hard to interpret the conclusion in isolation...
He explores the problem with some assumptions and formulae, and posts the theoretical results over a broad range of Damping Factors for an example resonance and power loss.

It's a quick read.
 

Cosmik

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#19
He explores the problem with some assumptions and formulae, and posts the theoretical results over a broad range of Damping Factors for an example resonance and power loss.

It's a quick read.
I may not be understanding what he is supposed to be debunking here. Is he denying that amplifier output impedance leads to audible consequences?

If we look at a typical Stereophile review of a valve amp we can see large frequency response variations when driving a (often simulated) speaker load, but a flatter response into a resistor. Different "taps" at the output transformer give different degrees of response variation. A solid state amp is usually flat into any load, the main difference being the amp's low output impedance.


I'm pretty sure the valve amp's frequency response variations are audible.
 

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