My rule-of-thumb is that the DF is of no concern until lower than about 20.
When it is below 20 it begins to change the Q of the driver enough that box tuning needs to be examined. With wide impedance swings it will also affect frequency response. While the later makes a more measureable difference, the former may be more audible (since in general the box size is proportional to the square of the Qts).
When it is below 20 it begins to change the Q of the driver enough that box tuning needs to be examined. With wide impedance swings it will also affect frequency response. While the later makes a more measureable difference, the former may be more audible (since in general the box size is proportional to the square of the Qts).
Originally posted by peranders
Nelson Pass claims that damping factor isn't particular important.Something to think about. I don't say it's true but I'll guess there is a limit surely but where is it?
It is only unimportant if your speakers are designed for that eventuality
In particular, when designing a speaker, you can do it for three general cases of signal source:
1) Idealized pure voltage (Zout -> 0)
2) Idealized pure current (Zout -> infinity)
3) A known Zout
There is only one way to design a speaker to work virtually identically on all of these sources: it's impedance has to be completely compensated to appear as a constant resitance.
This is certainly possible, but with anything but a single driver, it becomes progressively complex. Even for a single driver, this driver has to have an exceptionally linear motor if the reactance is to be compensated properly.
On the other hand, designing a speaker for a voltage source (or reasonably close to a voltage source) puts the 'zero' impedance of the source in aprallel with what would be compensation networks on a fully reactance compensated design, which means they can be omitted, to the tune of a rather hefty amount of $ saved. It also alowes a more relaxed design of the loudspeaker motors (in fact, this is where sometimes inexcuseable attempts at saving money go).
In practise, I would have to agree with the assesment that DF becomes progressively inconsequential as it increases over about 20. I cannot immagine how one would design a speaker which would require DF of say more than 50, and perform drastically different if it was not provided by the amp.
That being said, there are sometimes advantages of having a (relatively' high driving impedance, but if the amp and the speaker are designed as two separate components, without knowing in advance that they are going to work together, given that series crossover components in the speaker already have resistance, it is a better policy to leave any additional correction of amp output impedance inside the speaker - it's mostly as simple as just using thinner wire on the inductors.
The psychological effect of the DF definition deserves a special mention, namely, that DF~~Zload/Zout gives such pleasing large numbers
. In fact, a much better indicator would be something like Zload/(Zload + Zout), preferably expressed as a percentage. Unless the source has negative impedance, you can never electrically damp the speaker cone more than it's own impedance alowes.
Konnichiwa,
Oh NO. NOT THAT OLD CHESTNUT AGAIN.
DAMPING FACTOR.
Boy, does nobody ever actually bother to think things through.
I have, strictly for fun, simulated a highly reactive alignment of subwoofer choosing to vary the damping factor (actually source impedance) from infinite damping factor to a daping fatcor of 2, I then proceeded to simulate strictly boundary effect (that is without room mode effects) of moving the same enclosure in a 1m square within the room.
Here the difference between a damping factor infinite, 6.4, 3.2 and 2:
Worst case variation is a 3db lift at 60Hz which is quite broadband, audible but hardly "horrible", considering the variation between an infinite DF and one of only 2.
And here the difference of golden mean positioning and movement in 20" intervals from 20"-60" wall distance:
We find as much as 7db variation in the 60-100Hz region.
Now which one is worse?
Case closed on damping factor per se.
A VERY DIFFERENT story is if the damping factor is variable with signal (typhical example is the reactive load sending so much current back into the Amp that the SOAR protection briefly activates, completely removing ANY damping).....
Sayonara
peranders said:
Oh NO. NOT THAT OLD CHESTNUT AGAIN.
DAMPING FACTOR.
Boy, does nobody ever actually bother to think things through.
I have, strictly for fun, simulated a highly reactive alignment of subwoofer choosing to vary the damping factor (actually source impedance) from infinite damping factor to a daping fatcor of 2, I then proceeded to simulate strictly boundary effect (that is without room mode effects) of moving the same enclosure in a 1m square within the room.
Here the difference between a damping factor infinite, 6.4, 3.2 and 2:
An externally hosted image should be here but it was not working when we last tested it.
Worst case variation is a 3db lift at 60Hz which is quite broadband, audible but hardly "horrible", considering the variation between an infinite DF and one of only 2.
And here the difference of golden mean positioning and movement in 20" intervals from 20"-60" wall distance:
An externally hosted image should be here but it was not working when we last tested it.
We find as much as 7db variation in the 60-100Hz region.
Now which one is worse?
Case closed on damping factor per se.
A VERY DIFFERENT story is if the damping factor is variable with signal (typhical example is the reactive load sending so much current back into the Amp that the SOAR protection briefly activates, completely removing ANY damping).....
Sayonara
Konnichiwa,
My point is simple. In terms of FR and "damping of resonance" a quite large amount of output impedance has an impact that is no worse than moving the speaker not all that far (~ 10") in most rooms.
What I think leads to the claims for certain SS Amplifiers having "great bass on difficult speakers because of high damping factor" has in fact more to do with the ability of these amplifiers to retain their damping factor even if the amplifier has to cope with a lot of dynamic & transient current being shoved back up it's tailpipe by the speaker.
Of course, this is not a problem for any amplifier that attains it's output impedance by means of using a device with naturally low internal impedance (triode) instead of attaining it by large amounts of looped inverse feedback, which blows up big time if the amplifier inside of the loop cannot keep up with the combined demands of "damping" the resonant system and the signal.
Sayonara
peranders said:
My point is simple. In terms of FR and "damping of resonance" a quite large amount of output impedance has an impact that is no worse than moving the speaker not all that far (~ 10") in most rooms.
What I think leads to the claims for certain SS Amplifiers having "great bass on difficult speakers because of high damping factor" has in fact more to do with the ability of these amplifiers to retain their damping factor even if the amplifier has to cope with a lot of dynamic & transient current being shoved back up it's tailpipe by the speaker.
Of course, this is not a problem for any amplifier that attains it's output impedance by means of using a device with naturally low internal impedance (triode) instead of attaining it by large amounts of looped inverse feedback, which blows up big time if the amplifier inside of the loop cannot keep up with the combined demands of "damping" the resonant system and the signal.
Sayonara
Konnichiwa,
Even with a "well designed" VI limiting (I prefer the term SOAR protection) you may still get problems, as the SOAR Protection is dependent on the output transistor, not on the speaker.
My point is that a conventionally dimensioned and supposedly "well dimensioned" output stage may still be unable to cope with the back EMF from a highly reactive speaker and the signal, when high levels are present.
The best solution is of course to build the amplifier so that even a dead short to one rail cannot exceeed the output transistors SOAR....
Sayonara
AndrewT said:
Even with a "well designed" VI limiting (I prefer the term SOAR protection) you may still get problems, as the SOAR Protection is dependent on the output transistor, not on the speaker.
My point is that a conventionally dimensioned and supposedly "well dimensioned" output stage may still be unable to cope with the back EMF from a highly reactive speaker and the signal, when high levels are present.
The best solution is of course to build the amplifier so that even a dead short to one rail cannot exceeed the output transistors SOAR....
Sayonara
Konnichiwa,
Something like that. You could add a few small value decoupling resistors between multiple smaller value main filter capacitors as well.
I build many years ago several massive "Borg Cube" PA Amplifiers (basically 19" wide > 20" tall and deep).
I used completely "silly buggers" industrial darlington switching transistor modules (something like 300A @ 380V when switching inductive loads) in a circlotorn arrangement.
No shortcircuit protection was needed when running on around 120V Rails (we DID TRY HARD to blow up the Amp's). The PSU wiring and transformers had enough impedance to stop the currents from rising higher.
Sayonara
jacco vermeulen said:
Something like that. You could add a few small value decoupling resistors between multiple smaller value main filter capacitors as well.
I build many years ago several massive "Borg Cube" PA Amplifiers (basically 19" wide > 20" tall and deep).
I used completely "silly buggers" industrial darlington switching transistor modules (something like 300A @ 380V when switching inductive loads) in a circlotorn arrangement.
No shortcircuit protection was needed when running on around 120V Rails (we DID TRY HARD to blow up the Amp's). The PSU wiring and transformers had enough impedance to stop the currents from rising higher.
Sayonara
Hi Kuei yang wang,
re quote:
the reactive load sending so much current back into the Amp that the SOAR protection briefly activates
Can you explain how this mechanism operates on both a badly designed and a well designed VI limiting circuit?
Can you answer the question and if need be refer to back emf from the speaker or exclude it?
What mechanism causes the limiting to adversely affect the sound quality?
re quote:
the reactive load sending so much current back into the Amp that the SOAR protection briefly activates
Can you explain how this mechanism operates on both a badly designed and a well designed VI limiting circuit?
Can you answer the question and if need be refer to back emf from the speaker or exclude it?
What mechanism causes the limiting to adversely affect the sound quality?
Hi Peranders,
An interesting issue -
..."Is it possible to make a killer amp which is simple?"
I recall jamming a piece of toast in the toaster at 6am one morning with my 1yo daughter sitting in a high chair and running out to pick up the morning paper from the driveway. When I returned the kitchen was full of smoke and the toaster had charred and flamed a jammed piece of toast, searing overhead cupboards. I bought a more expensive safety toaster that day!
While a simple amplifier can be designed to limit excessive currents throughout the stages, many don't, and, in a low cost design without ancilliary measures in place, catastrophe can be serious! However simple designs with limits on each stage are considerably more forgiving.
Take, for example the topic topology. The input stage is differential, desirably using current sources - so currents here are limited to 2 x quiescent. Next stage is running 8-10mA typically and from the emitter resistors = MAX. The drivers actually pull current out! Given gate zeners of Vz just above operating range the output current cannot sensibly be catastrophic, and with fused collectors, inherently safe!
I doubt this amp could go up in flames, no matter what you did at the outputs. Most people expect some problem to result from errors as with most appliances. As long as they're not dramatic or little more than changing a fuse, it comes as a warning/deterrant.
I don't see that a simple amplifier should be expected to incorporate every conceivable protection so it continues to sing during/after prolonged abuse - in a domestic scenerio. A human wouldn't! Different for PA.
My take.
Cheers,
Greg
An interesting issue -
..."Is it possible to make a killer amp which is simple?"
I recall jamming a piece of toast in the toaster at 6am one morning with my 1yo daughter sitting in a high chair and running out to pick up the morning paper from the driveway. When I returned the kitchen was full of smoke and the toaster had charred and flamed a jammed piece of toast, searing overhead cupboards. I bought a more expensive safety toaster that day!
While a simple amplifier can be designed to limit excessive currents throughout the stages, many don't, and, in a low cost design without ancilliary measures in place, catastrophe can be serious! However simple designs with limits on each stage are considerably more forgiving.
Take, for example the topic topology. The input stage is differential, desirably using current sources - so currents here are limited to 2 x quiescent. Next stage is running 8-10mA typically and from the emitter resistors = MAX. The drivers actually pull current out! Given gate zeners of Vz just above operating range the output current cannot sensibly be catastrophic, and with fused collectors, inherently safe!
I doubt this amp could go up in flames, no matter what you did at the outputs. Most people expect some problem to result from errors as with most appliances. As long as they're not dramatic or little more than changing a fuse, it comes as a warning/deterrant.
I don't see that a simple amplifier should be expected to incorporate every conceivable protection so it continues to sing during/after prolonged abuse - in a domestic scenerio. A human wouldn't! Different for PA.
My take.
Cheers,
Greg
By simplicity one can understand many things: low number parts, counting IC as 1 part or not, simple electronic circuits only (CE, EF), some devices in signal path and some not and for some low number of poles and zeros in forward path.
So we all love simplicity, some must only complicate here and there to achieve the expected level of simplicity.
cheers
Konnichiwa,
I did. It so blindingly obvious that I cannot explain any better. It is REALLY, REALLY basic. Read a decent book on how a moving coil speaker works if you don't get it.
Oh come off it. If the protection circuitry engages the amplifier clips. THAT is what adversely affects the sound.
Sayonara
AndrewT said:
I did. It so blindingly obvious that I cannot explain any better. It is REALLY, REALLY basic. Read a decent book on how a moving coil speaker works if you don't get it.
AndrewT said:
Oh come off it. If the protection circuitry engages the amplifier clips. THAT is what adversely affects the sound.
Sayonara
amplifierguru said:
Hi toasterguru,
Any advice on toasters. I'm having trouble getting my raisin toast to brown just right. I either burn it or its underdone. I also find the toast doesn't seem hot enough to melt the butter properly.
Just to keep things on topic, I often eat raisin toast while listening to my AKSA (a "simple killer amp" IMHO).
Thanks
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