damping factor

Status
Not open for further replies.

petehall347

the brandy coffee man
what is damping factor and more so what is the major influence for it ?
answers on a postcard please ..or just leave a simple reply :scratch2:
real question is how does one maintain or create the tube sound in a transistor amplifier ?
 
Damping factor is just a calculation, speaker impedance divided by amplifier output impedance.

More than you probably want to read about it...http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

The spoiler is that it's not a big deal about controlling cone motion as often mentioned, but that the effect is predominantly about the frequency response being altered by the impedance swings of the speakers.

With regard to your question, the implication is that if you add resistance to the output of the amp (series resistance factors on the amp side of the equation) the damping factor is lowered, hence taking on a characteristic mostly associated with tube amps. That being the frequency response is no longer mostly immune to swings of speaker impedance, but is more affeced by it. Which also tends to back up what many report....relatively benign loads typically work better on tube amps than speakers with wild impedance swings.
 
what is damping factor and more so what is the major influence for it ?
answers on a postcard please ..or just leave a simple reply :scratch2:
real question is how does one maintain or create the tube sound in a transistor amplifier ?

Many a higher end SS designer lusts after the answer(s)...
 
damping factor is a number, related to output impedence, but it tells you the ability of the amp to control cone motion. Obviously, the higher the damping factor, the better. For example, the new Accuphase A 200 mono Class A amps have 100wpc into 8ohms, but have an insanely high damping factor, 1000 (IIRC). This is unreal and is indicative of a hugh power supply.

To get tube sound with a transistor amp? Go Class A.
 
Damping factor is the inverse of the amplifier's output impedance. So if it has a 1 Ohm output impedance, it has a damping factor of 8 when used with an 8 Ohm speaker. Since a speaker is NOT a constant 8 Ohms, rising much higher at frequencies where is resonant, the frequency response will change with a low damping factor, emphasizing any resonant frequencies. Might sound better, maybe worse, but different for sure. Negative feedback lowers output impedance. Some tube amps in the 50's had adjustable damping factor, a feature that's disappeared, as most (not all!) modern speakers are designed to sound best with a higher damping factor (low impedance source). I think damping factors above 15 are unnecessary - have no further effect. You can create a low damping factor by adding a resistor in series with each speaker - about 0.5 to 1 Ohm.
 
Damping factor is just a calculation, speaker impedance divided by amplifier output impedance.
Damping factor is the inverse of the amplifier's output impedance. So if it has a 1 Ohm output impedance, it has a damping factor of 8 when used with an 8 Ohm speaker. Since a speaker is NOT a constant 8 Ohms, rising much higher at frequencies where is resonant, the frequency response will change with a low damping factor, emphasizing any resonant frequencies. Might sound better, maybe worse, but different for sure. Negative feedback lowers output impedance. Some tube amps in the 50's had adjustable damping factor, a feature that's disappeared, as most (not all!) modern speakers are designed to sound best with a higher damping factor (low impedance source). I think damping factors above 15 are unnecessary - have no further effect. You can create a low damping factor by adding a resistor in series with each speaker - about 0.5 to 1 Ohm.

You guys make it sound so simple!

So why is it my Crown amp makes this claim in its specs?
Damping Factor: >20,000 from 10 Hz to 400 Hz.
:dunno:
 
it means the amp has very low output impedance at low frequencies, where it is most likely to matter. Also, it sounds good doesn't it ? Thats like putting slew rate specs and a bunch of other numbers in a spec sheet. Many people have no idea what it means, but the more data offered must mean that the amplifier is better.
 
I've always thought of this as compared to my automotive hobby.
To me watts are like horsepower, whereas damping factor is akin to torque.


Al. Wise
 
how does one maintain or create the tube sound in a transistor amplifier ?

Many a higher end SS designer lusts after the answer(s)...
They must have failed to perform due diligence with the literature reviews. Bob Carver had this figured out twenty or thirty years ago. Pick a target tube amp, figure out how to impart that transfer function into your SS amp. You can question Carver's ability to achieve the target transfer function in his production SS amps; but it's pretty silly to claim that the concept and the prototypes weren't outstandingly and surprisingly successful.

The real question is whether "tube sound" is actually desirable. Euphonic distortion is still distortion.
 
Last edited:
They must have failed to perform due diligence with the literature reviews. Bob Carver had this figured out twenty or thirty years ago. Pick a target tube amp, figure out how to impart that transfer function into your SS amp. You can question Carver's ability to achieve the target transfer function in his production SS amps; but it's pretty silly to claim that the concept and the prototypes weren't outstandingly and surprisingly successful.

The real question is whether "tube sound" is actually desirable. Euphonic distortion is still distortion.

If only Bob could design a reliable amp.
 
So why is it my Crown amp makes this claim in its specs?
Damping Factor: >20,000 from 10 Hz to 400 Hz.
:dunno:


It means it has very low output impedance. A frequent reason is that high levels of negative feedback contribute to low output impedance. How exactly that works is above my pay grade to explain with technical prowess.
 
I like it when somebody takes the time to put pencil to paper.

Progress!

Let's do some math.

We know that damping factor is a ratio, specifically, it's the load impedance divided by the output impedance of the amplifier. For now, we'll ignore how amplifiers attain low output impedance just for the sake of simplicity.

So, let's say we have an amplifier with a damping factor of 2000 and an impedance of 8 ohms.

DF = Load Impedance / Output Impedance

2000 = 8 / Output Impedance

Output Impedance = .004

All is well in the world, right? We have our staggeringly high damping factor but we've ignored something important.

We forgot to include the series resistance of the speaker wire between the amp and speakers. Let's redo the calculation now.

Again, we know that DF = Load Impedance / Output Impedance, but now we are going to add in the effects of the speaker wire into our equation to figure out what the "real" or "effective" damping factor is of the real world situation. For simplicity sake, we'll err on the side of caution and say that it's very low resistance wire and only presents a .1 ohm load.

DF = 8 ohm / (.004 ohm + .100 ohm)
DF= 8 ohm / .104
DF= 76.9

The advertised damping factor of 2000 is now only 77 at the terminals of the speakers.

Now, let's look at what is going on at the terminals of the woofer in a speaker system with a passive crossover.

It's not unusual to have a series resistance of 1 ohm in a passive crossover, but just for a best case scenario, let's say that it's only .25 ohm.

DF = 8 / (.004 + .100 + .250)
DF = 8 / (.354)
DF = 22.6 at the woofer.

Now, let's say the damping factor of the amp is 20000! Surely that must make a huge difference being an order of magnitude higher than 2000!

Unfortunately, the reality is:

DF = 8 / (.0004 + .25 + .1)
DF = 22.8

It's essentially the same.

Now, let's say that the amplifier in the same scenario is only at 50.

DF = 8 / Output impedance

50 = 8 / Output Impedance

Output Impedance = .16

Now that we have the output impedance of the amp with a DF of 50, let's subsitute into our scenario to see the DF at the woofer:

DF = 8 / (.16 + 1 + .25)
DF = 8 / (.51)
DF = 15.7



Do you see how most people just don't find DF that important? In the real world, the difference between a low DF amp and a ridiculously high DF amp is essentially moot at the woofer.
 
Very nice. The article I linked in earlier suggests why DF of 1000, 100, or 10 (or whatever) may or may not have any material significance. It's sorta interesting, suggested reading (perhaps statement of the obvious since it's linked in).
 
If only Bob could design a reliable amp.
Carver amps have some...difficulties...due less to circuit design than to circuit layout and parts selection.

Like so many other products, a competent serviceman and careful aftermarket parts selection can remedy most all the faults. There's also the idea that the electrolytic caps used in any "Carver" product from the Bob Carver era are beyond their expected service life, and I think we're closing on that time for the Carver/Sunfire era.

None of which is important to the idea I was trying to get across: The technology/methodology exists for making a SS amplifier implementation sound like a tube amplifier implementation, and it has existed for decades. If any of the "higher end SS designers" truly wanted a "tube" sound, they know how to do it.
 
Last edited:
real question is how does one maintain or create the tube sound in a transistor amplifier ?
Some folks have had success by simply adding a bit of series resistance between amplifier and load.

I think a few early SS amplifier manufacturers even added circuits allowing the user to add series resistance via a damping factor switch. I have an early JVC power amp with switchable damping factor. But, i've not torn deeply enough into the thing to determine if the selector just switches in series resistance to the output or performs some other function.
 
Last edited:
It is rumoured on the Carver amps having "voltage" and "current" outputs that the current output is just the voltage output plus 1 ohm series resistance. Said to give a slighly warmer, slightly more laid back sound. The voltage output is just a name for the normal amp output. Since the overwhelming majority of audio amplifiers are designed as voltage source/voltage amplifier I guess it makes some sense.
 
Last edited:
Here's an easy, layman's method to get a sense of DF:

- Take a larger woofer - 12" to 15".

- Raise it to your ear (sometimes difficult due to weight)

- Now, with your finger, tap on the woofer cone and note the sound of the cone as it vibrates until it goes silent. Note how long that takes.

- Now, jumper the terminals - a dead short.

- Raise the woofer to your ear again and tap on the cone.

- Note how the cone now sounds and how long it takes to go silent.

You have just tested the 2 extremes of damping factor:

- Dead Short: Extremely high DF
- Completely open: Extremely low DF

Hope that adds some perspective. In practical application, I consider it a minor merit of amplifier performance. For tube amps, its even less of a consideration since you're matching impedances for maximum power transfer anyway with the output transformer.

Cheers,

David
 
... For tube amps, its even less of a consideration since you're matching impedances for maximum power transfer anyway with the output transformer.

Cheers,

David

I think I know what you mean but to further expound, the matching you speak of is not that the 8 ohm tap has 8 ohm impedance thus "matches" an 8 ohm speaker.

It's that the 8 ohm tap has the correct turns ratio to put the as-designed plate load on tubes through the reflected load of an 8 ohm speaker. The 8 ohm tap winding itself likely has much lower impedance than 8 ohms (but considerably higher than typical SS amp output impedance).
 
Damping factor, as others have stated, is nothing more than another way of describing the output impedance of an amplifier. As previously stated, it tends to affect frequency response more than "damping", due to the fact that the impedance of a speaker varies with frequency.

My point is more specific to the tubes vs. transistors thing. I don't believe that the good qualities of "tube sound" come from having a low damping factor. In fact, many good tube amplifiers both vintage and modern have a pretty good damping factor, definitely good enough to not cause any perceptible frequency response anomalies.

I would go so far as to say that a tube amplifier which has a very poor damping factor, is poorly designed, and it's unfair to judge all tube amplifiers by this standard of bad performance, and especially it is a bad idea to consider a poor damping factor as ever being desierable.
 
Depends on how one likes his Bass.
A full range driver usually has constrained lo freq output. (Small drivers are best at attempting full range sounds)
Especially so with a SS amp, which typically features at least some to a lot of 'damping factor'.
Use a tube or SE type (typically devoid of any damping factor) and the bass output increases.. notably.
Counterintuitive ain't it ?
The lack of 'damping' allows the cone to bounce around more.. adding to the bass effects.
 
Status
Not open for further replies.
Back
Top Bottom