2. amps-preamps
  3. 124407-80260

... how important is Damping factor in determining what amp to buy

Hi there...

Just how important is damping factor in determining what amp to buy?

In literature and specs - I find this is an often left-out bit of info...


justvintagestuff
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Gs5556
It is not important at all....
... a general rule of thumb is that an amp with a DF of 20 or below has sonic consequences. Doing the math, the speaker in this case is 95% of the load -- a considerable change that results in sonic degradation from dynamic load variation since the amplifer is no longer a perfect voltage source .
Gs5556, I think you may have worded your post a little more broadly than you intended to.  In addition to these two statements being contradictory, you seem to be saying that any amplifier having DF<20 would cause "sonic degradation," and you seem to be saying that for good results all speakers should be driven by amplifiers that act as voltage sources (i.e., amplifiers whose output voltage is not sensitive to load impedance variations, as long as the amp is operated within its capabilities).

As I'm sure you realize, almost all tube amps have DF<20.  And as I indicated in my earlier comment, differences in damping factor and consequently output impedance within that range can certainly be sonically significant, if speaker impedance varies significantly over the frequency range (as it does with most speakers).  And certainly differences in damping factor/output impedance can contribute to sonic differences between tube amps and solid state amps.

And certainly some speakers are tube amp friendly (meaning they don't necessarily have to be driven by voltage source amps, and in some cases shouldn't be driven by voltage source amps), some speakers are solid state amp friendly, and some speakers (especially those having relatively flat impedance curves, highish impedance, and highish sensitivity) are friendly to both. 

As Mapman alluded to just above, at the low end of the range damping factor does matter.  Statements that it is of no importance are simply incorrect.

Regards,
-- Al 

atmasphere's avatar
atmasphere
11,993 posts
 
I seriously doubt that 0.45% change is audible. However, a general rule of thumb is that an amp with a DF of 20 or below has sonic consequences. Doing the math, the speaker in this case is 95% of the load -- a considerable change that results in sonic degradation from dynamic load variation since the amplifer is no longer a perfect voltage source .
The 'traditional' thinking here is that frequency response is the last word on tonality.

It isn't.

It turns out that the human ear/brain system assigns a value to distortions; they are translated to tonality. In fact it now appears that there is a tipping point wherein colorations created by distortion can be favored over actual frequency response errors.

In addition, the use of global negative feedback is well-known to contribute to higher ordered harmonics (see Norman Crowhurst). The higher ordered harmonics are used by the ear/brain system to detect volume levels (rather than the fundamental tones). The result of trace amounts of higher ordered harmonics is called brightness and harshness because of human sensitivity to these harmonics.

This is why many designers don't use feedback and frequently favor tubes- to avoid that particularly annoying coloration. This often results in a high output impedance/low damping factor but this can be easily dealt with giving careful speaker selection. 
mapman's avatar
mapman
22,549 posts
 

With most of the speakers in my house, including the OHMs and Dynaudios which are not inherently tube amp friendly speakers, moving from the lower Damping higher output impedance amps I mentioned to others with damping much grater than 50 produced perhaps the biggest sonic benefits of any change I recall in recent years.

Those same amps played very nice with my more tube amp friendly Triangle Titus XS speakers for which I would like to find a nice small easy to maintain tube amp. I use the Triangles also with my highly damped Bel Canto ref1000m Class D amps and the sound is quite good still in many ways (crystal clear especially at lower volumes) though somewhat sterile at higher volumes in comparison to the others that are a better match to that amp in regards to impedance and damping.

So I have found that damping/output impedance matters VERY VERY MUCH, perhaps as much or more than many other also important things. Understanding this has been a key for me to getting to a good place faster with fewer stumbles along the way.

Beats playing with fuse directions by a light year IMHE of course that is a much easier thing to do right being there are only two choices, more like answering a true false question that has no right answer other than what you think and/or hear.

atmasphere's avatar
atmasphere
11,993 posts
 
@mapman, if I recall, your speakers are 4 ohms. Damping factor as a spec is usually stated with respect to 8 ohms. So in reality your speakers seem to need an amp with a damping factor of about 25, once you correct for the impedance. As I stated elsewhere, no speaker needs a damping factor of more than about 20:1 or so; your speakers seem to be within that ballpark.

kijanki's avatar
kijanki
4,432 posts
 
Vibration of the speaker membrane, without signal, causes back EMF producing current that flows in opposite direction working against membrane motion, hence damping vibration. This current (damping effect) depends on the total resistance in the circuit including amp’s output, wires resistance, woofer’s choke resistance and speaker’s impedance (source impedance) itself, that is mostly resistive. All this will limit maximum possible "DF" to about 1. As long a amplifier doesn’t add to this limitation, there should be no difference in sound. AMP with DF =10 will affect overall damping only by 10%. Very high DF (my amp has 4000), come either from the output configuration or negative feedback used to reduce distortions, widen the bandwidth etc. Even shallow 20dB negative feedback will reduce output impedance ten times.

Damping Factor plays one very important role - it can be used to impress customers.

As for NGF - it is a wonderful tool when it is used wisely. It improves pretty much everything (bandwidth, distortions, output impedance etc). It might produce TIM distortions (higher odd harmonics, overshoot in time domain) for faster changing signals, because of increased amps gain caused by late summing of delayed output signal (phase shift). Reducing bandwidth at the input, perhaps to one that amp had without feedback, should prevent TIM. That would require designing a stable wide bandwidth amp with low distortions to start with. The main problem is that designers use cheap parts and poor circuits trying to fix it with deep feedback. For instance, very popular output transitors 2N3055 have very nonlinear h21e (Beta) - a current gain vs current. There are much better choices but they cost more money (2N3055 cost less than $1). NGF is pretty much free.
More to discover