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Discussion in 'Amps and Cabs [BG]' started by bottomdweller70, Dec 12, 2006.
Can some please explain what a dampening factor is and how it affects bass amps and sound?
It has to do with how quickly an amp can revover from its input signal I think...in other words an amp with a higher damping factor with appear to sound "tighter" and more controlled, especially in the bottom end. It also helps with speaker cone movement I've heard.
Is a cat slinking through the port and peeing?
That's damping factor, by the way. "Dampening" is sprinkled liberally across bass forums just about as much as the opinion that bass cabs don't follow the inverse square law like other direct radiators, and only form their waves once they are out around 30 feet. I guess that's why we all have 58 foot wide headphones ...oar something ; }
Decent modern power amps arguably don't gain much advantage over each other by touting higher damping factors, as cable runs are now more likely to affect quick damping than amps themselves. But older amps, tube amps included, can affect the sound with "overhang".
Can you elaborate on your last post a bit? How does cable run affect this and what is "overhang?"
In layman's terms damping is the ability of the amp to control the movement of the cone in both a forward and backward motion...Damping Factor is a numerical number given by the manufacturer to rate the effectiveness of this control. The higher the number, the greater the control...typically the number stated refers to a value above or below a fixed frequency range...a rating of 500 at 100hz is nowhere near as good as a rating of 5000 below say the same 100hz. Hope that helps!
Damping factor is the ratio of the effective load impedance to the output impedance of the amplifier. If an amp has a DF of 100 driving an 8-Ohm load, it means the output impedance of the amp is 0.08 Ohms. Such a speaker might have a DC resistance of 6 Ohms, which means that the total DC resistance seen by the amp is 6.08 Ohms, a negligible change.
Point is, with decent modern amps, damping factor is not what determines how well the amp can start and stop the cone. It is determined by the characteristics of the speaker itself.
Thanks fdeck! Nice to have somebody explain it , without the condesending tone to his post.
fdeck is probably one of the smartest and most polite people here.
Not sure of the technical definition but I know how various extremes of damping sound (i.e. the sound of a Thunderfunk amp as compared to a Mesa or SWR amp). Watch for the differences in the speaker cone excursions and listen to difference in the sound.
a nonexistent term for a nonexistent phenomena
Thanks everyone...this helped clear things up!
Is there a difference in damping factors between SS and tube amplifiers? Do I even need to take this into consideration when buying a new amp?
To an extent buy what sounds good to you and don't get bogged down in specifications.
like fdeck said, damping factor is the ratio of the output impedance of the amplifier and speaker cable to that of the speaker.
It's really a measure of how close the amplifier is to an ideal voltage source and by association how well the amp can deal with the voltage generated by the movement of the speaker's voice coil in its magnetic field.
If an amp has a really low damping factor and thus a high output impedance, the load will interact with the amplifier and affect the output voltage of the amp at a particular drive level. This leads to frequency response anomolies, especially at low frequencies where speaker movement is greatest. The most common symptom is a bloated, loose-sounding bottom end. However, in order for this effect to manifest itself in any kind of serious way, the amp's output impedance needs to be quite high, like an Ohm or more. You usually only see this in pure Class A amplifiers. Most bass amps do not have class A power sections and do have adequately high damping factor to provide prefectly good control over speakers. Once you're above a DF in the 10s, increasing it further has no audible effects.
On a final note, damping factor doesn't have any effect on cone excursion. That's a function of the voltage across the speaker (and the power developed) and the frequency of the signal.
Noting that I am posting in the presence of a real tube amp expert (PBG), I think the fact that a tube amp uses an output transformer limits the damping factor that can be achieved by practical means.
Still, the Heathkit W-5M tube power amp (built by my parents as their first hi-fi, retired to the attic, and resurrected as my first bass amp) has a damping factor of 40, which is ample. I think in these times, you can safely ignore damping factor. Design measures to ensure flat frequency response and low distortion (including those employed in tube bass amps) also raise the damping factor, so the latter is somewhat of a gimme in modern design.
If you want to hear what low damping sounds like, add some series resistors. (ignore the power loss and concentrate on the response)
Here's an interview of Bob Carver who is known to add resistors in series with the output of his amplifiers to fool the tube inclined ear.
"... BC: Not entirely, but almost entirely. Ninety per cent of the sound quality that we typically attribute to vacuum tubes comes from the output impedance."
"BC: The forward impedance of the output tubes and the transformer together usually comes out at about 10 ohms. When you use 20 dB of feedback, it reduces it to around one ohm. That's basically what a vacuum-tube amplifier is all about."
And even with older amps.... once the SYSTEM "damping factor" exceeds 10 by a reasonable margin, you will be hard pressed to find a real audible difference.
I say SYSTEM because the speaker cables and connections etc add resistance also, increasing the "effective" amplifier output resistance/impedance.
In some ways, a LOW damping factor might be good. it tends to be an indirect measure of the amount of internal feedback in the amp.
And, amps with very high internal feedback tend not to sound as good on an absolute scale....although for bass it may be less important. But they sure have high damping factors...
As far as ol' Bob...... he has something of an ax to grind, since he has done SS amps in general.
There is nothing actually preventing a tube amp from having an output impedance far lower than 1 ohm.......
But in his HIFI world, there is a lot of effect of "balance"..... if lows vs mids and highs end up treated differently as far as damping, or any other secondary effect, the overall balance of the sound can be changed.
Possibly the somewhat higher output impedance of a tube amp helps equalize the effect on lows and highs.
In any case,. if you don't like the sound, don't buy the amp. And the reverse.....
See the first diagram of:
This amp has low damping, but it shows the effect.
I'd like to see new measurements. And I bet the same happens just adding series resistors.
I still don't think an amp should "sound" like anything. It should just amplify what's it's given. These will be the kind of amps I buy.
..which shows just how little you know about amps. The voltage drop of a series coupled resistor will have a far greater impact on low frequency reproduction than the increase in output impedance. It's not a fair nor even remotely technically accurate test.
...then you'll NEVER buy another amp of any kind. There is no such thing as the perfect amplifer. Even excepting the the distortion induced by different transducers, every amp leaves a sonic imprint on its output for various reasons, be it power supply or output stage topology, input or output impedance and lets not even get into distortion introduced by speaker cables of ANY kind.
The 'superiority' of solid state amps that you purport is fiction.