Amplifier Output Impedance (Damping Factor) and Speakers

[SIY]

Is there any progress on this to be able to bring the simulations closer to reality?
But also a dynamic amplifier model would be helpful here.

You haven’t even bothered doing the simple calculation.

 

[pogo]

The simple calculation has already been made in many cases, but it does not match my and those of others perceptions, i.e. at least one component/effect is still missing.

 

[SIY]

The simple calculation has already been made in many cases, but it does not match my and those of others perceptions, i.e. at least one component is still missing.

Yes, you doing an actual experiment instead of asking other people to try to justify your evidence-free crackpot claims.

 

[DonH56]

Is there any progress on this to be able to bring the simulations closer to reality?
But also a dynamic amplifier model would be helpful here.

Not my area and I have a full-time (plus) day job unrelated to audio. They are close enough to illustrate that output impedance can influence frequency response; IME that is by far the biggest impact. The frequency response reflects the effects that things like back-EMF will have, and things like the Stereophile speaker model will generate such effects.

I am not sure what you mean by "dynamic amplifier model". The stuff I do here uses very simple models to illustrate general principles that hopefully interested non-engineers/scientists can follow. I did not think dynamic output impedance varied enough to matter and would require a big step beyond my small-signal steady-state models. Actual amplifier simulations are well beyond the scope of what I would post on ASR (though some have done so), followed by measurements and correlation to the simulations. That is normal good design practice.

Output impedance, and its relative damping factor (which means something different in the audio world, not sure why they use it except for marketing), are well-covered on older literature and touched upon in a number of more modern'ish white papers as well as a body of knowledge at organizations like the AES. You can join and access the papers -- that is likely the best place to start for more rigorous research papers.

That is all well beyond the scope of this thread, which was simply to introduce the concept to interested audiophiles. If you are familiar with basic amplifier design (at the device level) and feedback theory you can do a fairly simple calculation to show how the impedance varies over frequency, and pick a few bias points to see how it varies dynamically. I am disinclined to try to chase that in this thread, it is far beyond what is needful IMO.

It would be a good idea for you to open another thread to explain your calculation, what you perceive is missing and why, and try to measure and quantify it.

 

[pogo]

Still output impedance does never dominate the damping the drivers sees as long as it remains low in comparision to the driver impedance. Below 1/10th (DF > 10) it has zero effect on damping...

Here's a good counterexample that there's more to it:
Link

 

[SIY]

Here's a good unsubstantiated, unlikely, evidence-free claim that there's more to it:
Link

FTFY.

 

[BDWoody]

Here's a good counterexample that there's more to it:
Link

Seriously...haven't you been here long enough to realize that kind of anecdotal 'evidence' is meaningless in this context?

 

[pogo]

Seriously...haven't you been here long enough to realize that kind of anecdotal 'evidence' is meaningless?

It shows just by a single keypress in the same setup, how the audible impression changes with different DF. I have the same experience for 30 years, but with different amplifiers. This is not meaningless to me and others.

 

[BDWoody]

It shows just by a single keypress in the same setup, how the audible impression changes with different DF. I have the same experience for 30 years, but with different amplifiers. This is not meaningless to me and others.

When not set up with proper controls, that's to be expected.

 

[NTK]

Who knows what that switch really does. T+A claims it toggles between damping factors of 800 and >70, whatever that means. Without measurements/investigations by competent independent parties, I wouldn't take their words that that's all it does.

 

[Suffolkhifinut]

Who knows what that switch really does. T+A claims it toggles between damping factors of 800 and >70, whatever that means. Without measurements/investigations by competent independent parties, I wouldn't take their words that that's all it does.

Why would T + A lie over this?

 

[pogo]

Why would T + A lie over this?

They don't.
According to a german test review (DF LO):
DF at 4 Ohm (63Hz/1kHz/14kHz): 150/147/88

 

[sergeauckland]

Why would T + A lie over this?

I don't think 'lying' has anything to do with it. However, changing Damping Factor between 800 and 70 won't in itself change anything sonically, so if people are reporting 'night & day' differences, then they're either imagining it, (perfectly possible) or T&A are doing something else like adding audible distortion or changing the frequency response, both easily measurable. The sort of people liable to ascribe N&D differences are not the sort to impose strict controls on listening, so could be easily taken in.

It's all marketing bollocks!

My summing up of pretty much anything in today's world....

S

 

[Suffolkhifinut]

I don't think 'lying' has anything to do with it. However, changing Damping Factor between 800 and 70 won't in itself change anything sonically, so if people are reporting 'night & day' differences, then they're either imagining it, (perfectly possible) or T&A are doing something else like adding audible distortion or changing the frequency response, both easily measurable. The sort of people liable to ascribe N&D differences are not the sort to impose strict controls on listening, so could be easily taken in.

It's all marketing bollocks!

My summing up of pretty much anything in today's world....

S

With an increase in frequency you would get an increase in load inductive reactance (Xl). Due to this the damping factor isn’t constant.

 

[sergeauckland]

With an increase in frequency you would get an increase in load inductive reactance (Xl). Due to this the damping factor isn’t constant.

So what? As long as the DF doesn't drop below 10, it matters nowt. Especially so at HF where on a passive loudspeaker, the damping factor measured at the tweeter will be a lot lower. On an active loudspeaker it matters even less.

S

 

[Suffolkhifinut]

So what? As long as the DF doesn't drop below 10, it matters nowt. Especially so at HF where on a passive loudspeaker, the damping factor measured at the tweeter will be a lot lower. On an active loudspeaker it matters even less.

S

Active or passive makes no difference, because the amplifier’s output impedance is fixed, the speaker drivers changing impedance is the one that alters with frequency. . Why would it matter if the power amplifiers are on board or not? We’re did you get the figure of 10 from?

 

[KSTR]

Going from DF 800 to DF 40 (@ 8Ohm) is equivalent to adding 0.1 Ohm of series resistance in the DF 800 setting. And that's the way this must be tested -- and with level-matching as the series-R decreases volume ever so slightly. Level matching is not trivial because of the speaker impedance curve where the volume decrease will be frequency-dependant, not constant. Actually it is impossible to level-match if the variation of FR is more that 0.1dB.

At any rate we must factor out the FR (and level) change to isolate the effect of different DF alone. When we do so, it turns out there are no audible differences unless when going into the extreme of DF way smaller than 10 or so.
---> Different reasonable DF has no different sound character by itself.

But if we don't undo the tiny level and FR changes we are just hearing those side-effects of reduced damping factor, not damping factor itself. The volume loss and its frequency-dependance is dominating what we are hearing and that is easily shown when testing these factors alone.

 

[sergeauckland]

Active or passive makes no difference, because the amplifier’s output impedance is fixed, the speaker drivers changing impedance is the one that alters with frequency. . Why would it matter if the power amplifiers are on board or not? We’re did you get the figure of 10 from?

The amplifier's output impedance isn't fixed, but doesn't vary by enough to make a difference, but the output impedance seen by the tweeter includes that of the crossover, which can be enormous relatively if there's a level matching resistor in series. Even without, there will be the series resistance of the inductors, so the output impedance of the amplifier is largely irrelevant.
As to the 10, just do the sums as to how much level variation an output impedance of one 10th of the loudspeaker's minimum impedance makes. Bear in mind also the series impedance of the cables and crossover in passives, those also appear in series with the amplifier's output impedance. 10 is enough. More doesn't do any harm, but isn't necessary.

S

 

[DonH56]

Amplifier output impedance (and thus damping factor) changes significantly over frequency, largely due to reduced feedback factor at high frequency. My models assume that.

 

[sergeauckland]

Amplifier output impedance (and thus damping factor) chances significantly over frequency, largely due to reduced feedback factor at high frequency. My models assume that.

Indeed. Do you have any figures for this with a 'typical' amp? I knew how it varied with valve amps due to very limited open loop bandwidth, but always assumed with SS amps that even if the variation was 'large', it was still sufficient even at HF and low LF or it not to have an audible effect.

S