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PostPosted: Mon Mar 05, 2018 4:47 am 
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I understand in layman's terms is about woofercontrol. being able to start and stop a woofer. I think. I was told one reason to buy my first Bryson 4b had to do with it's rated 500 at 20 Hz. I see many amps rated at x number at 500 Hz. or x number at 1000hz . My questions are. What number is enough. and shouldn the industry standardize the frequency so all amps are measured at 20 Hz? how do you compare an amp to another amp on this spec when the given number is not at the same frequency. Or. is this rating really not important? thank you.


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PostPosted: Mon Mar 05, 2018 5:12 am 
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Floyd E. Toole sums it up best:

"Choosing an amplifier on the basis of damping factor would be like choosing a high performance car because it is red rather than black. It may result in the right choice, but for the wrong reason."

http://www.roger-russell.com/wire/damptoole.htm

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PostPosted: Mon Mar 05, 2018 5:21 am 
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I would never buy an amp just based on damping. Are you saying it is a meaningless spec?


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PostPosted: Mon Mar 05, 2018 5:22 am 
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Toole may be correct, in some cases, but not always.

Quote:
However I do not doubt that amplifiers with a low damping factor do often exhibit a lesser controlled sounding bass than those with higher ones. In the 70s I temporarily bought a Quad 303 which I substituted for my then in use Nelson Jones 10+10 home built amp., and the results showed a considerably less controlled bass. What was happening is a subject for investigation.

per http://www.harbeth.co.uk/usergroup/foru ... phile-myth

The above re 303 is my experience too; its low DF was causing me issues with 2 different sets of 10 and 12 inch woof/ subwoof drivers. Direct connected, after the active x-over. Flabby, distorted bass. No control of the driver, that you could see.

Whereas a Rotel 980bx with DF over 1000 does the same jobs assigned it very well indeed. Investigation over.


Last edited by natedog on Mon Mar 05, 2018 10:02 am, edited 1 time in total.

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PostPosted: Mon Mar 05, 2018 5:44 am 
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damping factor doesn t mean much for consumer purpose, all McIntosh amp have all low damping factor, and yet are loved by a lot of audiophile , if you have high damping factor , good , it mean the amp as a better control of the woofer,will not affect mid range or high frequencys. will it play better, absolutely nothing to do with the quality of the sound. I even feel many high damping factor amp have too much controle,and many have the bass sound sterile and dry.
high damping factor are good for pa systeme, where you want to use damping for higher power handling without having woofer hiting bottom.
me I love the bass of my krell amp just as much as I like the bass of my McIntosh amp. and both are at opposite sides of the damping factor scale.


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PostPosted: Mon Mar 05, 2018 6:37 am 
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Once you start to parallel output transistors with low value emitter resistors damping factor goes up.
Eliminate the output inductor as the mentioned Rotel does the DF goes even higher.
Increased negative feedback DF goes up.
Is it the stiffer amp or the DF number doing the work?

Gary


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PostPosted: Mon Mar 05, 2018 7:19 am 
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On amplifier damping factors:

1. The OP asked an important question: should manufacturers specify damping factor according to a standardized set of parameters? The answer, of course, is that they don't, but should. Indeed it's very misleading to specify a damping factor measured at 500 Hz or 1 kHz, since damping is all about controlling low frequencies, typically 100 Hz and below. The most informative approach is to specify damping factor at a range of low frequencies, say, 20 to 200 Hz. But few manufacturers do anything like that, so most of the specs on DF we read aren't going to tell us anything reliable or predictable about the amp's "real-world" damping factor.

2. Whatever an amp's damping factor, most of it is dissipated by the large inductors used in passive crossovers. Virtually no manufacturers mention that. So, whether or not a high damping factor might be a good thing in any particular system configuration, the manufacturer's high damping factor—assuming it really is high at low frequencies—will really only be available in an active system that does not use passive crossovers.

3. I've had power amps with damping factors as low as 100 and as high as 20,000 (this latter the Crown Macro Reference)—at least according to manufacturer's specifications—and in no case have I been able to correlate performance with damping factor. Matter of fact, the Crown Macro Reference, while billed as Crown's offering to "no compromise" audiophiles, struck me as (a) powerful, (b) sterile, (c) harmonically bare, and (c) coarse in the upper frequencies.

So, as some other posters have suggested, when choosing an amp, damping factor should be pretty low on your list of technical priorities.

In addition, FWIW, I have encountered more than once over the years the claim that for MF and HF, a high damping factor may actually compromise the sound—see the note on negative feedback below. In fairness, I have not sought to systematically verify or disprove this claim with any of my own experiments.

Finally, the issue of: how does a designer achieve a high damping factor in a power amplifier? The answer usually involves: negative feedback. And many of the participants in this forum will know, there are important engineering and design reasons to avoid negative feedback. Indeed, many audiophile manufacturers make their reduction or elimination of negative feedback—globally, locally, or both—part of their claim to audio excellence.

FWIW, my generalization for all this is that if you are using active bass drivers/subwoofers without passive crossovers, with separate amps for the mids and highs, a high damping factor amplifier may tighten up the bass. Otherwise, when using a single full-range amp to drive speakers with passive crossovers—what most of us do—there are far more important considerations than damping factor as well as important compromises that high damping factors impose on the rest of the frequency range.

I am a huge fan of judiciously using pro audio components in domestic audio systems, but in the case of the damping factor of power amplifiers, I really think the principal application is in sound reinforcement, where you're driving hundreds, even thousands, of watts into big, actively amplified 15 and 18 inch woofers which you don't want jumping out of their frames into the laps of the people in the front row.


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PostPosted: Mon Mar 05, 2018 7:33 am 
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Hi,

drjoe wrote: "I am a huge fan of judiciously using pro audio components in domestic audio systems, but in the case of the damping factor of power amplifiers, I really think the principal application is in sound reinforcement, where you're driving hundreds, even thousands, of watts into big, actively amplified 15 and 18 inch woofers which you don't want jumping out of their frames into the laps of the people in the front row.'

+++++ Amen to that as well as all the other points he makes.

Cheers,
David Neice

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PostPosted: Mon Mar 05, 2018 7:39 am 
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natedog wrote:
Toole may be correct, in some cases, but not always...

I too disagree. The following comment was also stated...
From the 'exact' same URL Link that you cited:

http://www.harbeth.co.uk/usergroup/foru ... phile-myth

"Myth upon myth upon myth - then given a marketing spin.

So-called "Damping Factor" is pure marketing spin - nothing more, nothing less. The implication that Amplifier A can exert a vice-like grip over the loudspeaker cone compared to Amplifier B is clearly highly attractive to the people that write the brochures or reviews, but it tells you nothing about the rest of the system. Damping Factor tells you less about how an amplifier sounds than 0-60 times tell you about the day-to-day driving experience of a car.

Of course, a designer can make the output impedance of an amplifier equal to any value he or she wants. As close to zero as the output connectors allow if you take the negative feedback from the terminals. And including negative - which some active system designers might want (I think that's the essence behind Yamaha's Active Servo Technology, for what that's worth).

Worrying about 0.1 verses 0.01 ohms of output impedance is specious in the extreme when you consider that you have 6 (probably more) ohms in series from the cabling, inductors and voice coil. But it's the difference in DF of 80 and 800. Wow..."

Thank-you!


Last edited by Takira71A on Mon Mar 05, 2018 7:57 am, edited 1 time in total.

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PostPosted: Mon Mar 05, 2018 7:55 am 
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Dr. Joe. Joe here also.

Thanks for noticing my "make a standard frequency used for damping factor rating" comment.

And thanks for pointing out the fact that an amplifier direct driving a speaker, as compared to the signal negotiating it's way through a maze of impeding crossover components, is an ideal situation. On a recent post many argued the point.

Your comment answered all of my questions, thank you.

PS. i asked this question because my mere NAD 100 watt "THX" ? amp drives my Proac Response 3's quite well. I have never seen the clipping indicators come on (maybe they don't work? lol). But. I do notice what appears to be a little sloppiness in the bass. Hence my question re damping factor. Next month I will have about $1500 put away to buy a better amp and my nightmares about getting that Bryston "500@ 20hz" damping factor will no longer keep me up at night.

Thank you to all for commenting, All of your comments are helpful and much appreciated.

---------------------------------------------

"Just because you can doesn't mean you should". Like eating McDonalds crap, stepping on ants, and purchasing an amp for damping factor bragging rights.

Back in the late seventies when I was an audio genius, when I brought people over to hear my Tangent RS 6's, I alway made sure they knew the 4B was 500@ 20hz. Like me, they pretended to know how cool that was.


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PostPosted: Mon Mar 05, 2018 8:56 am 
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PostPosted: Mon Mar 05, 2018 9:47 am 
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An amplifier's damping factor matters. But it is not terribly important and it only applies to woofers.

So, what it is about a woofer that is noteworthy? When a woofer is moving, its voice coil (VC) is traveling though a stationary magnetic field. Anytime magnetic lines of force ("flux") cut through a conductor, current will flow through the conductor. This causes a woofer's voice coil to become an electric generator.

If the output of a generator sees infinitely high impedance (ie an open circuit), it will not have to do any work. So the woofer's VC will move freely if there is nothing connected to the speaker terminals. This is not desireable for it means the woofer will have a tendency to overshoot and ring and the result will be a sloppy and muddy bass.

An amplifier with a high damping factor solves this by essentially being a dead short (circuit) across the speaker terminals. This causes the woofer to stop very quickly because the energy produced by the motion of the woofer will quickly be used up doing work driving current through the short circuit. So, sloppiness and muddiness is mitigated and the result is a cleaner bass with better transient response.

In addition to the impedance ratio, the damping factor is also affected by the amount of global negative feedback in the amplifier. The net effect is that the amplifier counters the bad behavior of the speaker as though it had motional feedback. So the damping factor will be improved by a modest amount of global feedback.

Note that the above discussion assumes that the amplifier is connected directly to the woofer. In most speakers, this will not be true because most speakers use passive crossovers.

In a passive crossover, there will be one or more inductors in series between the woofer and its amplifier. Inductors have significant resistance and, so therefore, they will tend to isolate the amplifier from its woofer, which effectively reduces the ratio of the impedances which, in turn, reduces the effective damping factor. Note that the increased impedance caused by passive crossovers is not included in an amplifier's damping factor specification. The calculation is made using a known resistance, like the load resistor you will use when testing amplifier power.

As an aside, this is why many people choose to use active crossovers (among many other reasons) for they eliminate this problem because they allow the amplifier to be connected directly to its woofer.

EDIT:

BTW, it is easy to check (feel for?) the impact of damping factor.

Take the grille off your speaker and disconnect its speaker cables from your amp. Now push the woofer quickly with your fingers …. you will feel it move freely and quickly and it will stay in contact with your fingers at all times.

Now short out the speaker binding posts with a piece of wire. Push the woofer quickly again …. it will now feel like there is a tiny shock absorber attached to the woofer. It will not move freely or quickly nor will it stay in contact with your fingers as you pull them away from the woofer. In other words, the woofer's motion is well damped.

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Last edited by Pneumonic on Mon Mar 05, 2018 10:13 am, edited 2 times in total.

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PostPosted: Mon Mar 05, 2018 10:06 am 
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Quote:
An amplifier's damping factor matters. But it is not terribly important and it only applies to woofers.

Thanks Pneumonic.

@ Takira71A
It's a bit more complex than you think, than the dismissive Harbeth bod opines.


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PostPosted: Mon Mar 05, 2018 10:09 am 
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natedog wrote:
Quote:
An amplifier's damping factor matters. But it is not terribly important and it only applies to woofers.

Thanks Pneumonic.

@ Takira71A
It's a bit more complex than you think, than the dismissive Harbeth bod opines.

Wait till we get into slew rate ;-)

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PostPosted: Mon Mar 05, 2018 11:28 am 
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Glad you asked, and its been a good response. Thanks to the posters, I have learned something new today.

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