Amplifier Output Impedance (Damping Factor) and Speakers

[MCH]

Thank you all for your very interesting and educative answers and Don for the article and measurements. Every day one learns something new!

 

[egellings]

Damping factor is important, up to about 20 or so. Beyond that, it makes little difference unless the speakers are nearly impossible to drive and your amp needs a direct connection to a 230Vac line. Ya might need a bit more grunt then. For us chickens, (bedawk!) nope.

 

[watchnerd]

So if I read an amp manufacturer says they increased DF from 240 to 320 between version 1 and version 2 of an amp, does that really matter?

 

[LTig]

So if I read an amp manufacturer says they increased DF from 240 to 320 between version 1 and version 2 of an amp, does that really matter?

No.

 

[pogo]

Damping factor is important, up to about 20 or so. Beyond that, it makes little difference unless the speakers are nearly impossible to drive and your amp needs a direct connection to a 230Vac line. Ya might need a bit more grunt then. For us chickens, (bedawk!) nope.

Is this really true, see also: Link

 

[SIY]

Is this really true, see also: Link

So linking to your own nonsense, with quotes from marketing. Is that actually an improvement over your usual direct linking to advertising material?

Have you bothered to spend a few minutes doing a basic voltage divider calculation as has been suggested repeatedly, or is algebra just too difficult for you?

 

[DSJR]

I was pulled apart once with a 'Douglas Self' article when I tried to defend high damping factor amps, but then Stereophile showed what higher amp output impedances do to a typical two-way passive loudspeaker load, let alone a three or more way one. I still think there seems to be a subjective difference in the bass especially (it still may just be response differences as most speakers have impedance peaks at the box and driver resonances). Lower damping factor amps (or a higher one used in bridged form) do have a very slightly 'warmer' or 'looser' feel I still think and into some speakers I feel it shows. No objective evidence though but just returning to my mid 1970's roots and comparing many amps back then without ego or personal vibes being fully developed.. (the old prosumer power amps I've returned to from that time boasted damping factor figures of up to several hundred in bass and mids).

Interesting thread. Hope it carries on with different findings.

 

[SIY]

I was pulled apart once with a 'Douglas Self' article when I tried to defend high damping factor amps, but then Stereophile showed what higher amp output impedances do to a typical two-way passive loudspeaker load, let alone a three or more way one. I still think there seems to be a subjective difference in the bass especially (it still may just be response differences as most speakers have impedance peaks at the box and driver resonances). Lower damping factor amps (or a higher one used in bridged form) do have a very slightly 'warmer' or 'looser' feel I still think and into some speakers I feel it shows. No objective evidence though but just returning to my mid 1970's roots and comparing many amps back then without ego or personal vibes being fully developed.. (the old prosumer power amps I've returned to from that time boasted damping factor figures of up to several hundred in bass and mids).

Interesting thread. Hope it carries on with different findings.

Again, a short and easy calculation will show how fast you get to diminishing returns.

 

[pogo]

Have you bothered to spend a few minutes doing a basic voltage divider calculation as has been suggested repeatedly, or is algebra just too difficult for you?

The short paragraph on '7.4.3 Damping factor' is sufficient to understand how complex the theory can be and I think this one is closer to reality:
Link

 

[Geert]

The short paragraph on '7.4.3 Damping factor' is sufficient to understand how complex the theory can be and I think this one is closer to reality:
Link

What are we expected to learn from a single paragraph with one simple formula that doesn't even touch the basics of what's already clarified before in this topic? Where does it say you need a DF that goes into the hundreds?

 

[pogo]

Whether hundreds of them are really necessary, let say not reach the final destination at all, is another matter. It is much more important to understand what is influencing the result. In reality, an idealized measured DF could turn out to be 5 to 10 times smaller depending on level, temperature....

 

[Geert]

In reality, an idealized measured DF could turn out to be 5 to 10 times smaller depending on level, temperature....

Where does the article you refer to mentions that? Do you have measurements that demonstrate this behavior?

 

[pogo]

I expect such data from the manufacturers! I still have unanswered questions regarding the AHB2 under normal (real) operating conditions in this area:
Link

The number of 5 to 10 times stuck with me in the 90s, where I was at a seminar and correlates probably also with my referenced single paragraph.

 

[Suffolkhifinut]

I was pulled apart once with a 'Douglas Self' article when I tried to defend high damping factor amps, but then Stereophile showed what higher amp output impedances do to a typical two-way passive loudspeaker load, let alone a three or more way one. I still think there seems to be a subjective difference in the bass especially (it still may just be response differences as most speakers have impedance peaks at the box and driver resonances). Lower damping factor amps (or a higher one used in bridged form) do have a very slightly 'warmer' or 'looser' feel I still think and into some speakers I feel it shows. No objective evidence though but just returning to my mid 1970's roots and comparing many amps back then without ego or personal vibes being fully developed.. (the old prosumer power amps I've returned to from that time boasted damping factor figures of up to several hundred in bass and mids).

Interesting thread. Hope it carries on with different findings.

Think the theory that high damping factor amps are better is due to Lenz’s Law. The amplifier’s low output impedance is seen as a load by the speakers‘ induced EMF. The lower the impedance the less effect the induced EMF will have on unwanted cone movement. Lenz’s Law -e = L x di/dt

 

[DSJR]

I do still think, rightly or wrongly, that severely undamped 8" driver port assisted speakers with 'BBC heritage' (for a warm, 'natural' sound...) or some transmission line models, do or did seem more sensitive to this aspect, but no idea how much back emf such drivers exhibit. O f course, more modern speaker designs may not suffer this issue at all to any great degree...

 

[Suffolkhifinut]

I do still think, rightly or wrongly, that severely undamped 8" driver port assisted speakers with 'BBC heritage' (for a warm, 'natural' sound...) or some transmission line models, do or did seem more sensitive to this aspect, but no idea how much back emf such drivers exhibit. O f course, more modern speaker designs may not suffer this issue at all to any great degree...

Porting allows the drivers to move more freely than infinite baffle designs. While the voice coil inductances and the rate of change of current remains the same, damping of unwanted speaker excursions are likely to need more severe damping.

 

[pogo]

A general question:
Has anyone ever used an amplifier with a switchable DF and what were the different listening impressions?

 

[DonH56]

A general question:
Has anyone ever used an amplifier with a switchable DF and what were the different listening impressions?

Carver had a series of amps that would allow you to emulate a tube amp. A big part of that was switching in a series output resistor. I seem to recall one or two other amps did something similar but the Carver is the only one that comes to mind. And of course tube amps with multiple transformer taps, but their output impedance was already high enough to be readily identifiable from SS amps with many speakers in DBTs.

I have not played with anything like that in many years. The schemes I used were a simple added resistor (or longer cable), which altered the frequency response in measurable and often audible ways, and tweaking the feedback (in DIY designs and sometimes commercial amps I could play with) which changed the output impedance but also other things. I honestly do not remember the transient effects, if any, like additional ringing and such from back-EMF effects and so forth. I mean that literally -- I do not remember. It was long ago. Such things usually show up in the frequency response as well, of course, when connected to a speaker.

The biggest perceived difference was, I think, for woofers and subwoofers where higher impedance would allow the cones to ring a bit after transients stopped (measurably and audibly). In the real world, signals rarely stop (decay) so quickly that the effect was noticeable.

All IME/IMO and based upon old, likely faulty, memories. - Don

 

[pogo]

I find the new T+A A200 (purifis with switchable DF) very interesting, which I already mentioned in post #25.

 

[KSTR]

A general question:
Has anyone ever used an amplifier with a switchable DF and what were the different listening impressions?

As long as you maintain the exact same frequency response at the speaker terminals by proper pre-EQ, no difference when going from DF 1000 to DF 10, and almost no change when going to DF 1. If not EQ'd, you'll hear the frequency response change of course (unless the speaker is fully impedance compensated).
Only when you approach current drive (DF 0) it can sound a little different even when exactly EQ's to the same target. Reason explained here.