Damping Factor-what is it and is it worthless?

[durwood]

:D Just for Chad. He has been itching for someone to start a thread about this. :p

So what is it and why is it a worthless spec? Or is it?

Discuss.

[fredridge]

Are we talking about Sound deadener?:p :rolleyes:

I have no idea if it is actually worthless or not, I have noticed that it is rated at a number of different freq.

I was blown away at Arc's damping factors, some listed at around 3000. That was until I read that was rated at around 1000hz and some other amps rated damping factor at 200 that are "extreme SQ" amps.

I don't know for sure, but I would think the damping factor would also effect roll off because of it's inability to control the speaker. Not saying that is good or bad, just saying that is what I am thinking.

[a$$hole]

In short, not my words- If you don't understand basic electric current and voltage, let's just say that damping factor is a figure of merit that tells you how good an amplifier is at controlling a speaker system. The larger the number, the better it is. At 100 or above, it's pretty darned good. Below 20 or so, it's pretty poor.
When one amplifier's damping factor is higher than another's, that tells you that the amplifier with the higher damping factor can better control the speaker systems, and all other things being equal (frequency response, phase shift, distortion, etc.) that it is a better amplifier.

READ THIS: http://www.diyspeakers.net/Articles/Richard%20Pierce%20DAMPING%20FACTOR.pdf

[ghart999]

What is the correct way to read an amp's damping factor? Sometimes specs will give the value at a specific frequency, sometimes at a certain ohm load? What is the correct way to read its value?

[MarkZ]

In short If you don't understand basic electric current and voltage, let's just say that damping factor is a figure of merit that tells you how good an amplifier is at controlling a speaker system. The larger the number, the better it is. At 100 or above, it's pretty darned good. Below 20 or so, it's pretty poor.
When one amplifier's damping factor is higher than another's, that tells you that the amplifier with the higher damping factor can better control the speaker systems, and all other things being equal (frequency response, phase shift, distortion, etc.) that it is a better amplifier.

Describe exactly what you mean by "control".

[cvjoint]

Describe exactly what you mean by "control".

ohhh boy.... I'm tuned in!

[Lightninghoof]

BCAE1 has a great section on Damping Factor:

http://www.bcae1.com/dampfact.htm

[Whiterabbit]

I'm glad someone brought up the idea that it's frequency dependant. Is it? I dont know.

But we all understand that amplifier power ratings greatly change depending on how its measured.

Is it unreasonable to suggest that damping factor may also change, and that it may not translate well from amp to amp?

[MiniVanMan]

Simply put, Damping Factor is the load impedance (of the speaker) divided by the output impedance (of the amp).

Why is the number useless. Well, first, show me a speaker that is purely a resistive load, because there aren't any. Then show me a speaker that has an impedance constant throughout it's entire bandwidth. Even loudspeakers with with extremely well designed crossovers have impedances variations of upwards of +/- 2 ohms.

Now, what damping factor is supposed to represent is the ability of the amplifier to maintain a constant voltage throughout the varying impedances that your speaker system will present. Current will change, but voltage should remain as constant as possible. That's why amplifiers with lower output impedances are desirable. They have an easier time maintaining a constant output voltage.

Now, if you know the output impedance of the amplifier, and the damping factor, you can determine the impedance of the load used to get their number.

So, looking up the Arc SE2150, (http://www.arcaudio.com/arc-05/pdf/se_2075_f.pdf) you see a damping factor of >2500. They also state how they test at 4 ohms. So, 4 ohm divided by 2500 equals .0004. So, your output impedance of the Arc SE2150 is around .0004 ohms. If that's accurate, that's really nice amp. At 8 ohms, that's a damping factor of over 5000.

Personally, I'd rather know output impedance than damping factor. Anyway, unfortunately a company will often state a Damping Factor, but no other numbers to validate it. It becomes completely useless at that point.

Hope this helps.

[durwood]

Great post Minivanman.

So mfg's pick some arbitrary frequency to spec it at. What do we think about the frequency they choose? Is it marketing or is it an indication of what they think the amp will be used for?

[MarkZ]

So, your output impedance of the Arc SE2150 is around .0004 ohms. If that's accurate, that's really nice amp. At 8 ohms, that's a damping factor of over 5000.

Depends who you ask. ;) "Audiophiles" often frown upon high amounts of negative feedback, which is how you get output impedance insanely low like that.

Anyway, I think the most comprehensive analysis of the issue came from Richard Pierce.

http://www.diyspeakers.net/Articles/Richard%20Pierce%20DAMPING%20FACTOR.pdf

You know that any article that starts out with the words "Much ballyhoo.." must be the shiznit.

[MarkZ]

Great post Minivanman.

So mfg's pick some arbitrary frequency to spec it at. What do we think about the frequency they choose? Is it marketing or is it an indication of what they think the amp will be used for?

He's right that damping factor will vary considerably based on frequency, even if it's assumed that resistive loads are used. In general, damping factor should decrease with increasing frequency (this is because global negative feedback also decreases with frequency).

Thing is, the spec sheet is kinda worthless because most parameters vary with frequency or output. THD+N is a great example of a quantity that varies a lot as a function of frequency and output. In the world of speakers, we talk about single sensitivity numbers all the time, but neglect the fact that they vary with frequency and with power output. So DF fits right in. :)

[backwoods]

The effects to be aware of, if your damping factor is below 500, it could start affecting your Q.

I've always heard people claim that it makes a difference in IB installations. An amplifier with a low damping factor, will sound "sloppy, and out of control".

What parameters the amps had, I don't know...

I've never found an issue with it though.

[a$$hole]

In a word-"Overshoot", what we are wanting is the ability to brake or rein in the speaker at resonance. If it keeps on going out of control it doesn't sound very good. Sloppy, muddy, these are some terms that spring to mind when a system is out of control for whatever reason. Wrong type of enclosure, choice of drivers, etc.., :)

[MiniVanMan]

Depends who you ask. ;) "Audiophiles" often frown upon high amounts of negative feedback, which is how you get output impedance insanely low like that.


Yeah, but those same audiophiles also rave about tube amps, which to be frank aren't the most accurate amps in the world. ;)

I agree though, that there are always trade offs.

In my opinion, damping factor numbers are another way to sell product. They're meaningless for the most part, but if you can convince the masses that it's important, well, you've just put yourself in a better position to sell your product.

It's just another myth that needs to be debunked.

[MiniVanMan]

In a word-"Overshoot", what we are wanting is the ability to brake or rein in the speaker at resonance. If it keeps on going out of control it doesn't sound very good. Sloppy, muddy, these are some terms that spring to mind when a system is out of control for whatever reason. Wrong type of enclosure, choice of drivers, etc.., :)

That doesn't have much to do with damping factor though. Damping factor is saying that with a rise in impedance, which at resonance there is, the voltage applied to the speaker will remain the same. In a perfect world, at an undesirable state like resonant frequency, power would be shut off, that being a reduction in both current and voltage. Lower damping factors would have a better time of doing that than a high damping factor.

What MarkZ stated is very correct when he mentioned negative feedback. There's a point when all this ultra-engineered componentry can have very negative effects. Ultra high crossover slopes can cause negative feedback, and an ultra low output impedance can do the same. Yet, alone, they are both considered to be the pinnacle of design. Put them together in a system, and you could have problems.

So, my question is, why have an output impedance of .0004 ohms when .01 will do just fine. Why use a 48 db slope on your crossover, when a 12 db slope will work just fine.

These are just things to get caught up on, and nothing more. Take everything with a grain of salt. It's okay to consider all the variables, as long as you don't get hung up on them.

In an IB system, your impedances across the bandwidth of the woofer in question will vary GREATLY. To that end, yes a lower output impedance could be desirable. But, I'm still not sold on damping factor as a whole, though. However, I'm also not an IB fan. I know there are cultists out there that swear by it, but I will never judge a piece of equipment based on it's ability to handle an IB installation.

There is no spec out there that will compensate for a poorly designed system.

Damn, that's a good one. That's probably sig worthy.

[werewolf]

In short, not my words- If you don't understand basic electric current and voltage, let's just say that damping factor is a figure of merit that tells you how good an amplifier is at controlling a speaker system. The larger the number, the better it is. At 100 or above, it's pretty darned good. Below 20 or so, it's pretty poor.
When one amplifier's damping factor is higher than another's, that tells you that the amplifier with the higher damping factor can better control the speaker systems, and all other things being equal (frequency response, phase shift, distortion, etc.) that it is a better amplifier.

READ THIS: http://www.diyspeakers.net/Articles/Richard%20Pierce%20DAMPING%20FACTOR.pdf
That's a VERY good paper :)

Yes ... damping factor tends to be a meaningless spec, for two reasons:

- it really is a "DC" spec ... comparing an amp's output resistance (that is, output impedance at DC) to load resistance (speaker's impedance at DC). And as we know, neither of these resistances are really accurate over 20kHz (the amp's output impedance typically rising with frequency, probably at 6dB/octave, as gain-bandwidth decreases for stability).

- even if the "DC" approximation were valid, numbers greater than about 50 will be indistinguishable.

But the paper quoted above puts things in perspective, by showing what the amp's output impedance (or at least, resistance) must be compared to, to determine significance.

Edit : to first order, one can model the amp's output impedance as a resistor in series with an inductor ... the inductance representing the impedance rise as frequency increases, due to decreasing feedback. Let's say we represent the loudspeaker load as a coil resistance in series with coil inductance (a gross oversimplification, as any driver impedance chart will show, because it ignores resonance). So, to first order, we could say that frequency effects of "damping factor" can be comprehended by comparing amp output resistance with coil resistance (as explained in the above paper) ... and comparing amp output inductance with coil inductance :) After all, these elements are all in series ;) Just a thought ...

[chad]

This is the tirade I had a while back on Damping Factor.

I guess what I was trying to convey is that regardless of DF at the amp terminals (if that's where it's measured, you never know, could be at the emitter resistors on the test jig) After the output gets to the speaker this figure is drastically changed and the playing field gets evened out. It's like saying i don't like amp X because it has a lower DF but in reality the amp IS BETTER because it has proper output filtering, etc.

I still don't see a use in this figure, it is NOT used outside the car world, like in the pro world where people use these things to convey their message to millions and make their money off of it. I have never seen or looked into a DF figure for a sub amp in pro use... I know that the 50' of 12/4 that I'm sending the signal down to subwoofers will change the figure drastically.

What is the unit of measure for damping factor? They haven't come up with one, That doesn't happen very often in scientific measure. I still vote for Whipsnades (or we could call it UD, for useless drivel)

But since we know it's the speaker's impedance divided by the amp's output impedance. What the fuck? How the hell do you pull this off when the speaker's impedance is all over the place like a shit sandwich? The DF will never be even CLOSE to the published spec while driving a nice Dale non inductive resistor.

Now. We all know that most of the solid state amp world is an unmatched place. Low output to high input impedances. In a matched system like in tube amps or transformer coupled SS amps there needs to be a match, which would make your DF..... ONE! As stated before my monoblock KT88's sound just like my big Crowns, when run in linear mode.

So do a little math. Lets say the amp has an UBER low output impedance Like .001 ohm contributing to a very high damping factor of 4000UD. And we have another amp with a .05 Ohm output Impedance which gives us a blazing damping factor of 80UD. So that’s a BIG difference there eh? Sure, if you never plan to hook up a speaker! Let’s add a conservative figure of .1 Ohm for speaker cable, tinsel leads and connector resistance and calculate DF.

Amp A would have a total output impedance of .101 Ohm giving us a DF of 39.603UD

Amp B Would have a total output impedance of .15 Ohm giving us a DF of 26.667UD

So a difference of 3920 Useless Drivels turned into a difference of 12.936 useless drivels once the amps in question are put into their application.

See my point?

Chad

[durwood]

ahahaha

I like this one

I still vote for Whipsnades (or we could call it UD, for useless drivel)

[durwood]

I'm taking this one too.

There is no spec out there that will compensate for a poorly designed system.


Thanks minivanman. :)

[MiniVanMan]

This is the tirade I had a while back on Damping Factor.

Damn, tell us how you feel. :D

[chad]

Damn, tell us how you feel. :D

I Think there were several disputes going on at once that day... that one got some attention :blush:

[MiniVanMan]

I Think there were several disputes going on at once that day... that one got some attention :blush:

I was talking with bobditts last night about personal crusades. It seems we all have a particular set of buttons that just set us off. Collectively, we're a wealth of knowledge that can debunk just about any myth. It's quite humorous though to see who comes out of the woodwork on any given topic.

/Edit

Just notice this got moved to "Tutorials". Looks like we might be on to something here.

[MiniVanMan]

I would like to play Devil's Advocate here though.

Based on yesterday's thread that came up with "motivated watts", I would like to come at this from the "extreme SQ" perspective.

We all know people that may be motivated while doing a job, but they may need a little prodding to get started, or have a hard time finishing up with the final details, i.e. station clean up, paperwork, etc. They may be great at actually accomplishing the job at task, but just can't quite get the little stuff finished up.

Now if we correlate that to Damping Factor, we can see that a high damping factor is indeed a product of a "motivated" watt. It's a watt that gives you 100% start to finish, as opposed to some watts that, while they get the job done, leave a little bit of residual mess when they're done, or just don't give that 100% out of the starting gate.

Hopefully, this clears up any more myths about damping factor, and Extreme SQ amps.

That and my post count is "1" higher now.

[MarkZ]

I was talking with bobditts last night about personal crusades. It seems we all have a particular set of buttons that just set us off. Collectively, we're a wealth of knowledge that can debunk just about any myth. It's quite humorous though to see who comes out of the woodwork on any given topic.

When DS-21 makes it to the party, you know it's serious stuff.

[MiniVanMan]

When DS-21 makes it to the party, you know it's serious stuff.

Let's try this...

Truly motivated watts are like republicans. While pretend motivated watts, that just talk about getting things done are like democrats.

/Runs for cover now. :p :D ;)

[pikers]

DF ratings are the same as wattage ratings: Guideposts for non-EEs--which is most of the buying public (and many competitors). Like anything else on a consumer-targeted white paper, it's there to help, not explain.

So provided it's honest, it certainly isn't "worthless" simply because it isn't explained over 45 pages in a manual.

[DaleCarter]

Please don't kill the Noob with his first post. I find the posts on this forum to be some of the more reasonable, logical and technically sound that I have seen on the web so far. Just getting into mobile audio after a loooong time in pro sound.

I am not sure what the term "pro audio" means here, but to me it means the concert production and recording stuidos where I learned about audio. Damping factor is indeed a widely quoted spec by the most respected amp manufacturers in the buisiness. Some specify it over a given freq range, often suggesting the amps best application.

For example see - http://www.crestaudio.com/media/pdf/Pro200_specs.pdf

My understanding of damping factor (in lay terms) is the amplifiers ability to control cone movement. The ability to push the cone out, stop it and then reverse the motion. The higher the damping factor, with all other factors constant, the greater a given amps ability to accomplish the task.

Like most specs, it receives more attention than it deserves.

Good design is key. I giggle at some installs I see around town (NOT on this board) where guys kvetch about all sorts of esoteric stuff and don't fix the rattling tag or leaking weatherstripping.

[DaleCarter]

Please don't kill the Noob with his first post. I find the posts on this forum to be some of the more reasonable, logical and technically sound that I have seen on the web so far. Just getting into mobile audio after a loooong time in pro sound.

I am not sure what the term "pro audio" means here, but to me it means the concert production and recording stuidos where I learned about audio. Damping factor is indeed a widely quoted spec by the most respected amp manufacturers in the buisiness. Some specify it over a given freq range, often suggesting the amps best application.


My understanding of damping factor (in lay terms) is the amplifiers ability to control cone movement. The ability to push the cone out, stop it and then reverse the motion. The higher the damping factor, with all other factors constant, the greater a given amps ability to accomplish the task.

Like most specs, it receives more attention than it deserves.

Good design is key. I giggle at some installs I see around town (NOT on this board) where guys kvetch about all sorts of esoteric stuff and don't fix the rattling tag or leaking weatherstripping.

[foosman]

Nothing to kill you over, and welcome to the forum.

[tjamz]

pulled this from the Zapco DC Reference Owners Manual (http://www.zapco.com/prod/DC_Ref/documents/2005_Digital_%20Reference_%20Manual_Rev_A.pdf)...I 'm not saying that it is 100% gospel, but I can say that they are right when they say that their 100 watt amp is perceived to be more powerful than it is, and I'd like to think that a high damping factor plays a part in that:

Damping Factor:
The most common misconception about ZAPCO amplifiers is that
we drastically under-rate our power output. Not true, it just sounds that way.
Today’s music, of all genres, has a great deal of bass content. Damping
describes the amps ability to control a woofer. An amp with poor damping
will leave bass notes sounding soft and undefined, regardless of its power.
In most amp lines, the largest units have damping factors between 100 and
200. Since rock solid bass is perceived as a function of power, our 100-watt
amp sounds like other brands 300-watt amps.

Slew Rate:
A similar situation exists in the higher frequencies. Ever turn up the
volume and hear cymbals sounding like fingernails on a blackboard? That’s
because the amplifier simply wasn’t fast enough to accurately reproduce the
high frequency tonality of the cymbals. A higher slew rate means a faster
amplifier, which means crystal clear high frequency reproduction. ZAPCO
amps have the highest slew rates in the industry. Once again, clear defined,
sound is perceived as a function of power.

[tjamz]

pulled this from the Zapco DC Reference Owners Manual...I'm not saying that it is 100% gospel, but I can say that they are right when they say that their 100 watt amp is perceived to be more powerful than it is, and I'd like to think that a high damping factor plays a part in that:

Damping Factor:
The most common misconception about ZAPCO amplifiers is that
we drastically under-rate our power output. Not true, it just sounds that way.
Today’s music, of all genres, has a great deal of bass content. Damping
describes the amps ability to control a woofer. An amp with poor damping
will leave bass notes sounding soft and undefined, regardless of its power.
In most amp lines, the largest units have damping factors between 100 and
200. Since rock solid bass is perceived as a function of power, our 100-watt
amp sounds like other brands 300-watt amps.

Slew Rate:
A similar situation exists in the higher frequencies. Ever turn up the
volume and hear cymbals sounding like fingernails on a blackboard? That’s
because the amplifier simply wasn’t fast enough to accurately reproduce the
high frequency tonality of the cymbals. A higher slew rate means a faster
amplifier, which means crystal clear high frequency reproduction. ZAPCO
amps have the highest slew rates in the industry. Once again, clear defined,
sound is perceived as a function of power.

[MarkZ]

Hasn't this issue already been beaten to death? Why are you guys still insisting that it's a meaningful parameter?

[And slew rate is an even bigger BS spec than DF...]