What is the optimum amount of amplifier “damping factor”? The consumer grade amplifiers appear to range from about 15 -70 (If even mentioned in the specification sheets) The large “tractor” amplifiers range from 200 – 1000 The class “D” amps are rated higher again I have no information regarding how valve amps perform in this area. I have been advised; “More is better” Class “D” have too much damping
There are many variables to making good sound, but as a general rule between an amp with a low damping factor and one with a high damping factor you would want the one with the higher damping factor to better control the woofer. By the way, I believe I have read that damping factor is HIGHLY influenced by the speaker cable length and gauge.
I believe that to be true as well, it offers infinitesimally small advantage in most cases so it should not be given much weight after a certain point. For large drivers and solid state amps I am inclined to believe it can have some impact, but again this is only if the numbers are very far apart and if one of them was pretty low (like below 50).
Damping factor can be used to determine how prone the amplifier is to be affected by speaker (this includes cable) specs and "reactions" during playback. The higher the DF, the more stable the amplifier can operate and in optimum conditions, regardless of what the speakers are "sending back".
Disagree Some of the consumer grade audio suppliers exaggerate (In our market anyway) the wattage of their amps (perhaps indicating a doubling the real wattage) These guys do list a damping factor (example 30) – when tested this amp could not hang onto the speakers at all – Flew off into distortion when either volume was required or a complicated track was played.
That would be because the amp ran out of steam (clipping) and has nothing to do with the damping factor. I have a tube amp with a damping factor of 10. I also have a monster SS amp with a damping factor of >200. Both have absolutely no problem controlling the drivers before clipping. Actually, I've never been able to make the SS amp clip, but that's another story.
DF is simply 8 (based on the impedance of a typical speaker) divided by the output impedance of the amp. Because solid state devices have an inherently low output impedance, it is easier to achieve a high DF. Higher DF for tube amps would require paralleling a lot of output devices and/or using a transformer with very high turn ratio, both of which, have significant drawbacks. Single-ended triode amps and output transformerless amps tend to have the lowest DF. What does this mean in terms of sound quality? Not that much beyond a certain DF, provided some sensible matching of amps and speakers is adhered to by the buyer. Speakers with extremely wide swings in impedance (particularly to really low impedances) may not be suited to amps with low DF. My own guess is that an amp with a DF of 8 can be used with almost any speaker and DF will not be an issue. Most amps with even lower DF can be used with most speakers, assuming other factors, such as efficiency, is in the right range. Super high DF (measuring in the hundreds) is meaningless. If it has been achieved through the use of a lot of negative feedback, there is a likelihood that the amp will sound very cold, brittle and analytical (my personal impression of high negative feedback designs). Atmasphere, a maker of output transformerless amps has an interesting paper on their website. Of course, as an OTL design, their amps have very low DF, so the paper is arguably self-serving, but, it does make a good argument, For the record, I don't own any of their products, but I really do like the sound of their amps.: http://www.atma-sphere.com/papers/paradigm_paper2.html
I think of damping factor as a sort of dynamic brake. It's fairly easy to get a speaker into motion. Damping factor is the ability to quickly stop that motion when the signal demands dictate.
Based on my own experience, I agree with Doug. I once owned a class D amp with a high damping factor that I used to drive a nice pair of JBL L-90s. It was obvious from the sound that the amp was exerting complete control over the drivers which yielded some of the best sound quality I've ever owned. I truly regret letting that gear go. Also, a lot of Magnepan owners swear by high damping factor amps to drive their panels.
The lower impedance, lower efficiency speakers, particularly the dynamic types, benefit the most. I have had those and a very high current, SS amp was best suited and that is essentially a high DF design. I have also owned a curious design by Fisher, which had a variable damping control on it! I never could find much use for it unless it was full max or full min settings with the relatively easy 8 ohm speaker that I was using to test it with. They called the circuit the ZMatic! -Bill
Exactly, and in cases of speakers with wild impedance curves (going very low, usually the ones with large drivers), it certainly does keep it in check. Perhaps it should be an indication of the ability of the amp to operate low impedance, high current, speakers well.
While I'm not a fan of this site in general, this article's explanation on damping is spot on. http://www.audioholics.com/education/amplifier-technology/damping-factor-effects-on-system-response
Interesting article, F1nut. It shows that, at least on a theoretical level, there is no practical effect of DF over 5. On a practical level, high DF and low DF are pretty much linked to particular amp designs which do have substantially different sounds and different abilities to handle the requirements of particular speakers so that it appears that DF is the differentiating factor when it is not necessarily so. KT88, I wonder if the DF control on the Fisher is some kind of variable feedback control.
