info on amplifier damping factor

I am doing research for an amplifier that I hope to eventually build. What I have noticed is something called, "damping factor" in specs of some amps. Is there something somewhere that is written that explains: what it is, what is a good #, bad #, and especially, what in the amp determines damping factors, and how do design this into my amp. Any help would be greatly appreciated. Thanks!
 
nothing to pay any greater notice

Damping factor is something I never
understood either.
A welldesigned amplifier doesn't have to worry
about damp factor.
As most expressions is this a "market slogan"
mostly used to get you into A BUY!

This is the conclusion I, Groman, and Torseten Loesch
agreed upon, when discussing this
uninteresting subject at AudioAsylum,
before the people at AA,
got afraid of me
telling "that the meperor was naked"
and BANNED me PERMANANTLY.

regards
Groman doesn't need to be damped
neither should you need to be
 
Damping factor is a ratio between loudspeaker impedance and amplifier output impedance, ie:

DF = Z loudspeaker/ Z ampli-out

Ideally, DF should be as high as possible, so that Z ampli-out is as low as possible (an ideal voltage source). With a low Z ampli-out, your ampli becomes more independent of your Z loudspeaker (Z variation in loudspeaker has little effect on the voltage across you loudspeaker).

But some say that this is not so important. You could read Douglas Self or Randy Slone book about this jargon, and the explanation on why DF is not so important.

Typical tube amp has low DF, while solid state amp has high DF. Speaking which one is the best, depends on your loudspeaker. Lynn Olson said that Ariel works best with low DF amp, while Linkwitz said his Phoenix speaker works best with high DF amp.

Cheers,
 
Hi dayveshome

Sianturi was a little quicker than me (so I had to erase some part I've already written) but I can generally agree to what he wrote.

An amplifier should ideally represent a voltage source* i.e. it's output voltage should be independant of the load connected to it. IMO one could live with a damping factor of 50 which can be reached easily by almost any carefully designed SS amplifier. I personally don't see any reason to have damping factors up to 10'000 because this is easily reduced by the resistance of speaker cable, contact resistance, crossover network etc. Some might argument that such an amplifier would achieve tighter control over the cone motion (i.e. damping) and would have much punchier bass . The damping argument can easily be destroyed by the fact that the voice-coil DC-resistance is the dominating part when it comes to cone-control (and this one is some orders of magnitude larger than the output impedance of an amp with a damping factor of 10000 !).
To achieve a low output impedance somebody has to use either a circuit that has an inherently low output impedance (e.g. class A) or use a large amount of feedback or any combination of both. When you have two amplifiers with the same damping factor (which is just a static measurement into a resistive load) usually the more generously dimensioned amplifier (i.e. class A, large PSU) will have the better bass control and a more consistent damping factor over it's operational frequency range.
Some tube amplifiers achieve only very low damping factors (often lower than 10) which can cause irregularities in the frequency response since the amplifier's output impedance and the speaker's impedance act as a frequency-dependant voltage divider. But tube fanatics (or me as well who only listens to tubes occasionally) can even live with that since it is perfectly possible to correct the speaker's impedance.

Regards

Charles


* P.S. this is of course different when the speakers are current-driven rather than voltage-driven, but thats another story
 
Re: nothing to pay any greater notice

gromanswe said:
Damping factor is something I never
understood either.
A welldesigned amplifier doesn't have to worry
about damp factor.
As most expressions is this a "market slogan"
mostly used to get you into A BUY!

This is the conclusion I, Groman, and Torseten Loesch
agreed upon, when discussing this
uninteresting subject at AudioAsylum,
before the people at AA,
got afraid of me
telling "that the meperor was naked"
and BANNED me PERMANANTLY.

regards
Groman doesn't need to be damped
neither should you need to be

No offense meant, but you seem to have a strong opinion on something you don't understand, as you state yourself....

Cheers, Jan Didden
 
Groman go read about damping factor!!!!

A loadspeaker with cabinet and anything around it can be showed as a model the same way as an amp.

In this model you will find the output impedance of the amplifier!! Which divided with the speaker impedance gives the damping factor...

Even if you like it or not you will be able to hear the difference on a amp with a high damping factor or low damping factor. Mostly you bass response gets weaker!! This is both Theory and reallife!!
Go try ad a series resistor to you speaker.. Lets say 1 Ohm.. Try it!!
I do not like the sound of a amp with a to low damping factor..

Regarding strong opinion on things you do not know of... In the AudioAsylum .. John Curl ...Should i say more?

Sonny
 

gromanswe

Disabled Account
2002-07-08 8:42 am
North
www.google.com
Sonnya. Say what you mean.

Cat Stevens, in song Can't Keep It In:
"Say what you mean, Mean what you think
and Think anything! Why Not?"

I think I have seen others here pointing out
that damping factor of different magnitude
are easily to live with.

There are a lot more important factors
both in Amplifier and Loodspeaker
that call for more attention.
That influence the result more.

A amplifier is just an adaptor
A device between an input and output.

When construction an amplifier you see
'whatinput is, and what is to be driven.
Then you make your adaptor.

If you can not reach a good solution,
then you must modify the source, input.
Or modify the device at output so you can
reach satisfying result.

Maybe put a preamplifier before drive amplifier.

Maybe see to that loudspeaker behavior
is good regarding resistance and impedance.

You cannot build an amplifier suiting all
devices there are.
An adaptor should be adjusted to the environment
it is supposed to serve.

Anything else have to be a compromiss
and a compromiss is only ideal
in a few cases.
In most cases not optimal.

Groman
who says what he means
and think his thoughts
although they cant suit everyone,
else they would have to be compromisses.
 
Be Carefull with strong opinions and how you express them.... That is what i was trying to say to you...

1)There is all kinds of people in this forum from very yound people to very old people .. Not everyone likes the "here i am" attitude

2)If you have an opinion on a subject which have something to do with design... Then you opinion should be backed up by some good evidence.. A lot of people around here try to designs thing the right way by learning from other peoples knowledge.
I do not say that you have a big knowledge, but you have be carefull on expressing your opinion on things like damping factor... When you are not in the position to answer the question Like :

"Damping factor is something I never
understood either." - Then you should stop your opinion here!

"A welldesigned amplifier doesn't have to worry
about damp factor." - This is nonsense!

"As most expressions is this a "market slogan"
mostly used to get you into A BUY!" - I do not think that a engineer thinks that way when he wrote the spec.sheet.

;O) But if i am to hard on you? tell me!

Sonny
 
Be care ful about your expressions yourself.

Sonnya!

some people are
Negativism radiators"

That is not something most people can
be happy about at this forum.

they look for fault in others
Never encurage others statements
with any appreciation.

Just out to make themselves appear
as the perfect way to be.

Can not accept other opinions then their own.
never trying to set themselves into the other man's
thinking.

There is an expression: "See me in my good eye"
That means try to see the good sides of a person,
instead of trying to look in his bad eye.
Surely I have one bad eye,
but the one with no faults may throw first stone...

Groman
avoids trowing stones
 
Read me right!

"A welldesigned amplifier doesn't have to worry
about damp factor."

You muust see the ditinction between
worry and care for.
A welldesigned amplifier is built in a way
that required parameters exists.
The behavior can be expressed in many ways,
or using many terms.

It will automatically have the qualities that are needed.
This might be current capability
speed, accuratess in reproducing signal
or dampingfactor, in relation to the load.

So then you do not have to WORRY.
To worry is for me "to be afraid somthing is wrong".
If all is taken well care for in design,
there is no need for worrying.
Is that clear?!

Groman
worries more about sonnya the damp factors
 

roddyama

Ex-Moderator
2002-01-19 9:25 am
Michigan
Hi Phase_Accurate and Dayveshome,

The damping argument can easily be destroyed by the fact that the voice-coil DC-resistance is the dominating part when it comes to cone-control (and this one is some orders of magnitude larger than the output impedance of an amp with a damping factor of 10000 !).

Another part of the "damping argument" is that an amp with a lower output impedance (higher damping factor) will better absorb the inductive reactance of the voice coil thereby exerting greater control over the cones motion. This is particularly true in the resonance range of the driver where most of the cones motion is governed by the mechanical properties of the driver and less by the electrical signal.

Remember that two of the main assumptions made in the T/S calculations of a drivers small signal response are that:

1.) The response is calculated in the low frequency range of the driver being analyzed.

2.) And that the output impedance (Rg) of the source (amp) is negligible (the damping factor is taken to be very high).

If the damping factor starts to exceed 50? (maybe), you have to include Rg in the drivers response analysis. It will alter the total response.

Rodd Yamashita
 
Okay we stop here!

To add to Rodd Yamashita.

you can see a driver(speaker as a) motor.

When you take a DC motor with nothing connected to its plus minus terminal it is very easy to turn. but when you shorts the input more and more with a smaller and smaller resistor value it will get harder to turn.
The speaker will act the same way. the smaller the driver impedance is the less you can distort the cone movement by external source.

It is the same reason you never add a series resistor to a bassdriver or the inductor in series with such a driver should be have very low DC resistance.... smaller source(generator) impedance => more control of the bass driver.

Sonny
 
One problem is the Loudspeaker

The loudspeakers are built using too few elements.
2-way speakers are driven at boundry frquencies
where there impedance is far from nominal value.

I give my vote for active systems,
with one power amp for each element.
this might be 3 or 4 woofers/tweeters.

Each amplifier/ADAPTOR is optimized
as far as possible to woofer it is driving.
Also the non-linear crossovers L and C, hysteres and losses,
is to be avoid.
Using R/C of high quality in the active crossover.

This is my way of optimate the sound system.

If one amplifier is to drive 2-4 elements,
with L and C in between, you ask for trouble.

The nonlinearity of the driven components
will hit the feedback point causing
disturbance all the way to the input of amplifier.

Still dreaming of my ultimate
active system with 2x4 LSP-elements/Ampifiers
no LSP cables or Inductors/Capacitors to drive.

The main distortion in todays system is coming
out of what is connected to the Amplifiers!

This is my way
groman's way
with the components available today.
 
sonnya and roddyama

I do of course agree that the amplifier's output resistance affects the damping of the driver. Maybe I was a bit unexact with my description (my mothertongue isn't English).
I just don't like to see how people might be led to the assumption that an amp with a damping factor of 10000 (which is not that easy to achieve when you don't want to sacrifice other parameters) could actually dampen a driver's resonance a hundred times better than one with a damping factor of about 100.
Simply because the source resistance, that our "DC motor" loudspeaker sees, is the sum of amplifier output resistance+speaker cable(s)+connectors+voice coil DC resistance (the latter one usually the largest by far).
I am a strong proponent of active speakers (not just because of the "damping thing"). Here you can either take the output resistance into account and tune the box accordingly. Or you can even control the output impedance of the LF poweramp by current feedback (this has to be done with care because it could lead to instability).

regards

Charles
 
dayveshome said:
I am doing research for an amplifier that I hope to eventually build. What I have noticed is something called, "damping factor" in specs of some amps. Is there something somewhere that is written that explains: what it is, what is a good #, bad #, and especially, what in the amp determines damping factors, and how do design this into my amp. Any help would be greatly appreciated. Thanks!

We have not answered your question! Sorry!! Really Sorry...

Damping Factor is stated at given load resistance.. Mostly 8Ohm...

But if you see to amps... You need to compare at which load they spec their Damping Factor.

And amp with a damping Factor of 100 @ 8ohm will have a Damping Factor of 50 @ 4Ohm.

So it is a bit blured (Spelled wrong??) what the spec says but you can use it to calculate the ouput impedance of your amp.
DF of 100 @ 8Ohm => 80mOhm output impdance...

The output impedance will raise as the frequency goes up.
If it is a Negative Feedback Amp it will depend on the openloop gain and the closed loop gain at a given frequency...

So the big question is : What should the output impedance be..

<200mOhm... As stated the cable from the amp to the speaker will have an influence on the system.

To high output impedance will alter the frequency response of your speaker....

To design it in i think you should go figure out which kind of output stage you are using and if you will use FB or no FB? Then we could continue the talk.

Sonny
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Damping factor is kind of an odd thing. It does correlate
loosely to woofer control, but there are too many examples
which don't support a cause and effect relationship.

The X amps we sell have a wide range of damping factors,
with the cheaper amps having better numbers (due to
feedback around the output stage) and the bigger amps
having lower DF, and yet there is no question that the
bigger amps have more authority and control, even at
modest power levels.

I have seen this elsewhere also, but I don't have a decent
explanation, just hand-waving hypotheses.