Dampening factor

[Tom Adams]

Of the many subjects with regards to power amps I've read here, it occured to me (after some threads about Crown amps) that one of the specs I don't see too many folks talk about is dampening factor.

In college, when I bought my Heresy's, I had little left over for great equipment. In fact, all I could afford was a Sherwood reciever that had a whopping 12W/channel output (which BTW, would get the Heresy's so loud my dorm roommates swore I was lying to them about the power. Had to teach them about efficiency donchaknow). One day I had the grills off and at elevated volume, the woofer cone was doing the wha-toosie. Later, when hooked to my friends' Pioneer SX-something and listening at Bud induced listening levels, I noticed that the woofer cone was a-jiggling, but not quite as much. Not long after this, my Heresy's had the opportunity of being fed by a Crown DC300A. At ridiculous volume levels, the Heresy's woofers hardly looked like they were moving. Back at the audio store where I was part-timing (and bought my Heresy's) I asked Dr. Sheppard about my observations. It was then that I got my lesson in dampening factors.

So.....my question is, what is the forum's perspective/opinion as to the importance of an amp's dampening factor?

Tom

[Born2RockU]

I am curious too...

[sfogg]

Tom,

"So.....my question is, what is the forum's perspective/opinion as to the importance of an amp's dampening factor?"

Usually it is very important to keep an amp from getting wet.

Damping factor is just another way of expressing the output impedance

of an amplifier. Damping factor is just the ratio between the presumed

load (8ohm) and the output impedance of the amp. An amp with an

output impedance of 1 ohm would have a damping factor of 8 for example.

Output impedance on an amp can effect the FR of the speaker/amp system

as the two can form a voltage divider between them if the amp has a

relatively high output impedance and the impedance of the speaker

varies.... which most do. It also can have an effect on the apparent

bass response of the speaker as well. A low damping factor (high output

impedance) can't as easily absorb the back EMF generated by the woofers

motion and that back EMF can contribute to more motion by the woofer

(the EMF resists the surround/spider trying to stop/center the cone)

then there should be. It can exagerate the bass response of the system

compared to an amp with a high damping factor (low output impedance)

which absorbs the back EMF.

Shawn

[colterphoto1]

Mssr Fogg has it right. I usually describe the damping factor as the amps 'back pressure' on the speaker. It's the amps ability to control the ringing of the woofer cone after an excursion. That's what you were witnessing with the lesser powered receivers.

Although damping factor is not directly related to power, a massive unit like the Crown, which is designed for very high output PA type cabinets, will usually have a high damping factor. I think 100 or better is generally considered good. Lots of modern receivers have 240 or so.

I have read here on the Forum that many members don't consider an especially high damping factor being as critical with the highly efficient Klipsch speakers as with other designs. Still, given the choice, I'll go for a high factor any time.

Michael

[Deang]

http://www.classic-audio.com/marantz/mdampingfactor.html

A bit deeper:

http://www.audioholics.com/techtips/audioprinciples/amplifiers/dampingfactor.php

[jacksonbart]

Wasn't it a big number often quoted in 70s amp/receiver specs? Don't see it much anymore.

[dragonfyr]

This is a topic that I enjoy, as it pits two diametrically opposed groups directly at each other here![]

There are those who i am sure will arrive any moment now to quote PWK and decry damping factor as a superfluous 'measure'...that any damping factor >=20 is sufficient.

And there are those who ascribe almost mystical significance to it.

The funny thing is that most do not realize the relative strengths and limitations of their respective positions.

Nor do many have a comprehensive understanding of the complex impedance of the system (and if I can ever find sufficient time, I will finish assembling ALLOT of pretty amazing info regarding this that I suspect few have seen, and even fewer have seen all in one place! And I suspect that it will have more then a few asking quite a few more questions and challenging allot of preconceived notions.)

The total damping component of a driver is comprised of the sum of two major components: the acoustical loading and the electro-motive 'loading'. (Note, the 'loading' referred to is the ability to oppose or restore the transducer voice coil motion. In other words, as the speaker cone is accelerated in one direction, its motion is both contributed to by the loading as well as opposed by the loading. You might think of it as the abitlity to accelerate and to brake the motion, and then to accelerate and brake the motion in the opposite direction. And the two components are the electro-magnetic field and the air pressure exerted upon the surface area of the transducer cone.)

To radically simplify this discussion, at higher frequencies well above the free air resonance of the transducer, the acoustic loading of the driver is typically large compared to that of the electro-motive component. And it is also why the acoustical tuning of the cabinet becomes an important element. At this point the amplifier damping is not critical. And this is the environment to which PWK refers. (And we will also conveniently neglect the effect of the passive crossover here!![] BTW, here is where the proponents of active crossovers should want to jump in!!!)

BUT, when the response of a tuned vented cabinet approaches the free air resonance of a driver where the acoustical damping of the driver approaches zero and it becomes 'un-damped' (such as in a bass reflex cabinet tuned near the free air resonance of the driver), the electro-motive damping component becomes large relative to the acoustical damping component, and here the EM component becomes very important! (It is also a reason to question the use of bass-reflex loading for subwoofers where the LF extension extends down into the lower two octaves - even with the use of extreme slope/brick wall filtering!)

So both positions are correct and both are wrong! It depends upon how the question is framed.

And all of this is stated without entering the realm of potential and kinetic energy within the realm of electronic and acoustical impedance - an issue that must be breached, but this is left for a later time when we delve into Nyquist! It will then become quickly apparent that to simply know the nominal impedance (resistance!) is anything but sufficient regarding the behavior of the system!

Oh, and if Michael or Duke haven't already mentioned it, the Crown Macrotech amps have a damping factor of > 1000! I wonder if this might be useful for use with reflex loaded LF units?** []

(**Note: I would still focus on a more effective cabinet design exhibitng a greater appropriate acoustic load rather then simply depending upon the EM damping for a more complete solution!)

[colterphoto1]

my brains hurts, can I go home now?

In 10 words or less, what DF should we look for as Klipsch owners?

[dragonfyr]

Michael, for you Cornwall/Scala folks, I would be looking for an amp that exhibits (among other things!) a high damping factor for the reflex loaded LFs. For LaScalas and KHorns with LF horns whose drivers are loaded in a sealed 'acoustic suspension' environment, you can get away with an amp with a lower damping factor, as other characteristics take precedence.

I don't have a magic number, but most amps nowadays exhibit a sufficient damping factor for most applications. Personally I like a damping factor >100 for any reflex/ported LF enclosure - and since I typically have used the large Crowns for heavy duty LF the point is moot for me!

And since most MF & HF transducers are operated well above their free air resonance where the acoustic loading is large compared to the EM factor, the issue is less critical and SS or tube amps each become more of an option. Especially as I am looking for additional characteristics here as damping factor recedes in relative importance.

How's that for avoiding the issue!?[]

[colterphoto1]

you went way over your 10 word limit, but I understood it! LOL

I go for the 100+ in most cases. Noted that my modern 2ch Yamaha receiver has 240, whereas the HT unit is only rated 100.

Wonder what my little HK430 is rated?

Michael

[djk]

"the woofer cone was doing the wha-toosie. "

The jerking cone movement has NOTHING to do with the DF of the amplifier.

The Sherwood would have been capacitor coupled, the Pioneer direct coupled outputs, and the Crown DC coupled all the way through.

This behavior is called dynamic off-set, and is largely a function of resistor-capacitor time constants (even in the Crown DC 300A), feedback, and clipping (in the small amplifier).

There is an article on line at ESP that touches on this, and Fred Ireson, Jon Risch (of Peavey) and I have discussed this elsewhere.

Crown builds a special circuit into some of their larger amps to try and control this.

[dragonfyr]

That's nice.

But driver offset is not what we were speaking of with regards to damping factor.

But it is related to the relationship of potential to kinetic energy and the information contained within the Nyquist & Heyser spiral models!

[djk]

His original point was the jerking motion of the driver and the subsequent mis-identification as a DF problem by his Dr. Sheppard.

DF has little or nothing to do with 'tight' bass, and absolutely nothing to do with the observed cone behavior.

[dragonfyr]

Of the many subjects with regards to power amps I've read here, it occured to me (after some threads about Crown amps) that one of the specs I don't see too many folks talk about is dampening factor.

........

So.....my question is, what is the forum's perspective/opinion as to the importance of an amp's dampening factor?

Tom

Regardless of who Dr. Sheppard is/was or whatever the cone motion was, the question is as stated above.

You respond to whatever you desire, this is that to which the rest of us have responded!

[Speedball]

The words Dampening Factor is something I've been looking for lately while browsing the many available S.S. amps on the market. Reason for that I 'read' a higher DF really makes the cones jump and do their thing...which to me couldn't be a bad thing at all. Now whether it plays a big difference in sound quality I do not know.

Average middle of the road amps from these companies is what I've found and even the biggest names in the industry sometimes do not have a that high DF...sorry, not all model numbers listed.

B&K - 450

Sim I-5 - 200

Crown - 3000

Threshold 8.0 - 160

PS Audio 100w - 1000

Accuphase P-300 - 150

Musical Fidelity A-5 - 140

Rotel 1080 & 1090 - 1000

Channel Island Monoblocks - 1000

[Tom Adams]

Just wanna jump in at this point and give a big thanks to all of you who've responded.[H]

I appreciate the input/opinion/discussion/debate/perspective/etc.

(man I love threads like these where I actually understand what folks are saying and I actually learn something).

Tom

[Duke Spinner]

the Crown Macrotech amps have a damping factor of > 1000! I wonder

if this might be useful for use with reflex loaded LF

units?** []

hey, my K-2 ... has a Damping factor of 20,000 ......[]

[sfogg]

Duke,

"my K-2 ... has a Damping factor of 20,000 ......"

I thought it was 10,000... and that was below 300hz or so. As the frequency rises in the K2s the output impedance goes up. Higher up I think it is 'only' around 1000.

Either way though obviously the K2 has an extremely low output impedance.

Shawn

[j-malotky]

Before you guys start looking for amps with the highest DF to drive

your horn loaded gems, check out the numbers on my favorite all time

sweetest sounding SS amp, IMHO, the McIntosh 250. Its dampening

factor is 10, thats right TEN.

JM

[colterphoto1]

Why would it be called 'damping factor'? What is the origin of that name and does it or does it not relate to the amps controlling the motion of the speaker?

Michael