Damping Factor

[davewantsmoore]

18 hours ago, MLXXX said:

On the other hand many haven't been vague, or wrong.

 

Perhaps it would be instructive to link to one ot two of them ... and then people can point out which bits are "wrong", or "misrepresentations" of a truth.

 

TBC, this isn't about a "hahh, I'm right, you're wrong" .... as opposed to constructive discussion/education.

 

... as opposed to, "ok, let's agree to disagree" ... which helps nobody.

 

[davewantsmoore]

23 hours ago, 125dBmonster said:

Can you clarify this please Dave ?

Yes, I've mentioned it (broadly) a few times already, but I'll do a more detailed post when I have some more spare time.   

[davewantsmoore]

22 hours ago, Zaphod Beeblebrox said:

I have never denied that a current driven speaker system can be built. It's just that no one (statistically speaking) does. Concrete tyres and rubber roads. 

Yeah, of course .... but that's pretty boring and uninformative   (to just say nobody does it, move along people nothing to see). 

 

The thread is (I would have thought anyways) supposed to be about the deep and gritty of "damping factor".

[Joe Rasmussen]

On 29/10/2017 at 10:28 AM, Tranquility Bass said:

There is no simple equivalence of a voltage or current source as such unless there is an external mechanical generator forcing its cone in motion or by an external acoustic disturbance in which case the equivalent source impedance is complex and NOT that of a simple resistance.

 

Hi David.

 

I am only arguing the science, that is all. I am not trying to pick any argument. But when the science here is ultra-clear and unambigious, then you have to stand your ground. To me it is that simple.

 

OK, so....

 

That statement of yours above is not quite correct. Whenever the coil is in motion inside the magnetic gap, any movement there will produce motional back-EMF, even if current is the driving force.

 

I am not sure if you understand that, and I know that it is not easy and takes time to absorb. Please read it again and try to understand.

 

All you need to have is motion and you don't have to wait for some kind of over-shoot, it is already happening way before any so-called over-shoot.

 

I am speaking to engineers about, one of them at the highest level of electricity generation in Australia and the other is my own brother-in-law, who has worked for Siemens as an engineer, for investment banks who needed technical assistance where to invest money, and now is a lecturer in Colleges.

 

These guys knows the science, even better than me, and what I have been stating about motional, whether rotational or piston motors, the same applies. Any motor that is put into motion behaves like this. In a loudspeaker piston motor, if the back-EMF was absorbed, the motor would actually have to stop. But clearly, it is not absorbed. The whole idea of over-shoot and mass needs to be understood. Increased mass decreases damping. This is recognised too in the equation, but you have to understand that equation to see that.

 

I am only arguing the science here, that this audiophile hyped-up idea just doesn't stack up.

 

At the heart is a single equation that was brought abruptly to me attention in 1975 by none other than Richard Small (and I was inclined to believe in DF in those days, to his utter dismay), and this is the equation that you and other have to explain (and I took the time to understand it and likewise agree with Small):

 

 

This equation tells us all we need to know. Understand the equation and you know that the amplifier cannot add damping, for one reason only, the Re value can only increase and not be decreased by the amplifier. That means that Qes will become a higher number, and the higher Qes value means less damping.

 

DO WE THROW OUT WELL ESTABLISHED SCIENCE THAT EXPLAINS THE SOURCE OF REAL ELECTRICAL DAMPING?

 

It is all in the Qes. That defines the electrical damping.

 

The amplifier cannot improve Qes  and it is really that simple. I am the only one here that is quoting the correct science.

 

Thiele and Small were not charlatans.

 

 

Edited October 31, 2017 by Joe Rasmussen
typos

[Joe Rasmussen]

On 30/10/2017 at 7:24 AM, Martykt said:

It's all good Addicted I already have the mathematics to work out Q !!  

.... it's all ahem err part of the Thiele Small Parameters just as @acg correctly pointed out !! 

 

 

 

SPOT ON - KNOW THE EQUATION AND YOU KNOW THE ANSWER!

 

[davewantsmoore]

On 10/30/2017 at 2:49 PM, acg said:

it does not mean anything and does not describe anything

 

Well, it desribes the realtionship of the speaker imepedance to all the other Z in the loop .... and this can be useful to know sometimes.    Eg. when a designer wants to say, "I expect some reasonably low Z in the loop with my speaker".

 

 

... but it just doesn't "mean" all the things the people have co-opted it to mean.     It's a victim of specsmanship....  and in the quest for:  we must have large damping factor .... becuase "control"

 

We've forgotten about all the other things going on...   and the reality of what happens, is very different to what the conventional wisdom says.

 

[davewantsmoore]

On 10/30/2017 at 2:49 PM, acg said:

On the other hand, Joe has pointed to us all the maths that deals with speaker/amplifier reactance...the Thiele Small parameters...which are all you need to know to describe the specific behaviour of a loudspeaker in an electrical circuit.  @MLXXXin a post above seemed to think they are irrelevant to the discussion of loudspeaker behaviour but the fact is is that they are "everything". 

 

I think we need to be careful with "everything" ....  asthey are commonly misused ..... people forget that they are only valid at the system resonance.

 

So they change as soon as you do anything to the speaker (like put it in a box, or a different box) ...  and they do not describe the motion of the cone anywhere but at the system resonance.

[Guest Simonon]

I am afraid that the discussion here may become misinterpreted in the minutia being discussed.
 
1. Damping is very real.
 
2. The damping in a loudspeaker system is defined by its electrical Q and its mechanical Q. 
 
3. Indeed a back-EMF can be absorbed by it being a voltage source if looking back at a resistive load.
 
That last point is important, but now comes the stumbling block:
 
4. Since back-EMF is a voltage source em it cannot be absorbed by another voltage source.
 
This is crucial to understanding the subject.
 
A microphone was given as an example above and it is a good example. So let us run with that:
 
A microphone is indeed an em device, it is a voltage source. Of course, a microphone can also become a mini-speaker (basically a headphone) and then it becomes a current device, because it is current through the Voice Coil that will make motion, not the voltage across the Voice Coil. The VC in motion converts voltage to current function on the fly.
 
But what if we use it as a microphone as well? Now the circumstances are completely different.
 
The microphone looking back is not seeing a voltage source.
 
What it sees in now entirely resistive.
 
Can that resistive load influence damping?
 
ABSOLUTELY!
 
Now the back-EMF can indeed be absorbed. 
 
If you were desperate and needed a microphone, then you could turn a speaker into a microphone, not a good one, but a microphone nevertheless.
 
What do you now connect our 'microphone' into?
 
An *INPUT* on the microphone preamp.
 
Now you are not connecting to another voltage source as if you were using our 'microphone' as a speaker. 
 
So yes. You can indeed apply damping to a voltage source !!!
 
But a misbehaving speaker that that needs 'controlling' become itself em and cannot be damped or controlled by another voltage source.
 
DAMPING IS REAL - YOU JUST NEED TO FIGURE OUT THE MECHANISM AND WHERE THE DAMPING COMES FROM.
 
I think I have just about exhausted myself trying to explain the above and wonder if I should stop here.
 
Or else it is a case of .

I have learned more from this thread in regards to damping factor, amplifier output impedance etc than any text read in the last 20 years.....from what I read amplifier damping factor is largely irrelevant with mechanical factors of speaker design such as alignment having the most effect. It would be good to summarize this excellent and interesting thread.

[Joe Rasmussen]

23 hours ago, davewantsmoore said:

Sure. You mean it will (also) produce a flat frequency response .....  but what of the voice coil operating a dirty quality VI converter?

 

THIS IS THE TOPIC WE SHOULD ACTUALLY BE DISCUSSING!!!

 

Yes, current can easily be corrupted when supplied from a voltage source. But I think this discussion may be beyond many here. I don't mean to sound condescending, but the voltage model is easy and and relatively intuitive. The current model is not intuitive and can get the better of us, because everything seems to be up-side-down and you end up having disorientation problems, "where am I going with this and what for" and give up.

 

Indeed the DF idea hides behind the voltage model, it seems to work so well, until you realise that you are applying a voltage model to a current device. Oops!

 

So corrupted current means the response of the speaker at the cone/air mass interface is also corrupted.

 

What we expected to come out there is not what the voltage model predicted:

 

So if we don't get what we thought we should get, then what DO we get?

 

BAD SOUND?

 

One of the reasons I am over here in Europe is to actually have this discussion and I am meeting up with people - that the V/I conversion not only needs to be understood, but also that it cannot totally be eliminated (motion will always produce back-EMF voltage), but looking at techniques that can suppress V/I errors - that techniques can be developed.

 

I believe I have developed one such technique. Are there others? Maybe mine is simply a starting point. We also need to engage suitable academics, this worked so well with Thiele and Small, but again theirs is still a voltage model.

 

So there is something here that is not yet complete.

 

And DF being in the domain of a voltage, it needs to be thrown out or else progress could be difficult and stumped.

 

Convincing loudspeaker engineers and designers, I think that is the key, but likely a slow burner.

 

[Martykt]

48 minutes ago, Joe Rasmussen said:

 

SPOT ON - KNOW THE EQUATION AND YOU KNOW THE ANSWER!

 

Thanks to you of course Joe.

I've personally learnt a lot from your posts.

 

Hopefully your posts are not completely in vain, some people at least are actually listening !! 

 

I hope you got a little chuckle from my earlier post studying the mathematics behind 'Damping Factor' too !! 

[MLXXX]

1 hour ago, davewantsmoore said:

Perhaps it would be instructive to link to one ot two of them ... and then people can point out which bits are "wrong", or "misrepresentations" of a truth.

 

TBC, this isn't about a "hahh, I'm right, you're wrong" .... as opposed to constructive discussion/education.

 

... as opposed to, "ok, let's agree to disagree" ... which helps nobody.

That could be a very time consuming exercise, and who knows how many people at large would be likely to read any one such article on Damping Factor and be either reliably informed, or unintentionally misled?

 

I'd suggest, in the first instance at least, examining the Wikipedia webpage on Damping Factor. It would receive, relatively, a lot of traffic. (And of course it is capable of being edited if wrong.)  Here is a link to it again:   https://en.wikipedia.org/wiki/Damping_factor

[davewantsmoore]

23 hours ago, Tranquility Bass said:

It's not better at all. From extensive testing I have found that current drive of woofers increases low frequency distortion

 

 

I'd like to know more, as you would be aware that others have shown data to the contrary.     I've never actually seen any data ever showing a significant increase   (I have seen data showing effectively no change though).

 

I've not any super-reliable data of my own to show .... although I must admit I never tested with a driver in a box either...  only ever a compression driver, and a dipole woofer.

 

 

as the non linear suspension compliance and adiabatic box compression now become dominant sources of distortion.

 

I'm not quite sure I'm with you here....

 

You're saying they "become" the dominant sources of distortion ....   after you remove the distortion from the "voltage drive".

 

If so, then sure ... I agree with that.   You remove one type of distortion from the system... and you are just left with the other types.

 

This seems better than just keeping all the distortion, no?  (?!?!?)  .... If I've misunderstood something, please elaborate.

 

FWIW.   Cms and any air compression effects, are very much dependant on excursion ... the box ... and the driver.     Cms is very non-linear.   Very.    A well designed driver, used at low excursion is a good thing.

 

If you're saying that for a specific excursion... that lack of electrical damping makes Cms more non-linear ... then how?!

 

Quote

 

Also because there is no electrical damping there is a considerable response peak at the resonant frequency depending on the Qms of the driver mounted in an open baffle or Qmc of the driver mounted in a closed or vented box 

 

 

 

Absolutely.... Any fair comparison, requires that this peak is EQed out somehow.   Otherwise this peak dominates everything.   It dominates what you hear ('cos huge peak) ... it dominates any measurement of non-linearities ('cos more excursion, 'cos huge peak)

 

[davewantsmoore]

3 hours ago, davewantsmoore said:

Yes, I've mentioned it (broadly) a few times already, but I'll do a more detailed post when I have some more spare time.   

@125dBmonster  it's where I mentioned right back at the start, that a whiteboard is the ticket here.    My typing out the explanation is almost a comically bad way of conveying it.

 

If we sat in front of a whiteboard for 15 minutes (less time than it would take me to type it and you to read it) ... we could go back and forth, pointing, drawing, scribbling, asking questions .... and going back over the bits which get misunderstood.   Heh.

[Tranquility Bass]

2 hours ago, Joe Rasmussen said:

 

Hi David.

 

I am only arguing the science, that is all. I am not trying to pick any argument. But when the science here is ultra-clear and unambigious, then you have to stand your ground. To me it is that simple.

 

OK, so....

 

That statement of yours above is not quite correct. Whenever the coil is in motion inside the magnetic gap, any movement there will produce motional back-EMF, even if current is the driving force.

 

I am not sure if you understand that, and I know that it is not easy and takes time to absorb. Please read it again and try to understand.

 

All you need to have is motion and you don't have to wait for some kind of over-shoot, it is already happening way before any so-called over-shoot.

 

It's no more a generator than an inductor or capacitor is. The motional impedance as seen by the amplifier in fact looks like a simple parallel resonant circuit. You will see this in any of Small or Theile's work when they derive the terminal impedance of a speaker. Unless the diaphragm is being driven by an external mechanical source then a loudspeaker is a purely passive device and the only energy source is the amplifier that drives it. To say anything else is completely absurd and alludes to energy being created out of thin air. !

 

I suggest you study Baranek and try and understand eletcro-mechano-acoustical analogous circuits but before that you should have a good grasp and understanding of electrical circuit theory which you seem to have trouble with.

 

cheers

[davewantsmoore]

21 hours ago, MLXXX said:

Dwm, could you tease that out some more, please, in relation to a woofer?

 

 

Damping factor proponents often say that you need to have a high damping factor, in order to stop the cone "flopping around uncontrollably" ..... ie. that you will get "loose and ringing" bass, or on the other hand, a high damping factor will "make the cone stop when it's supposed to".

 

This makes it seem to people like it's a "time" thing.    It makes it sound to people like without this amplifier "brake" that the cone would wobble on forever after the signal finished ... cos the cone it out of control, without the "proper" amplification baking.

 

This is a misnomer.   Largely the confusion comes from a misunderstanding of basic signal theory.

 

 

In this picture... you have examples of a speaker with 3 different levels of electrical damping.   Forget under/critical/over for now... they're just 3 different amounts - it doesn't matter.

 

What does this look like in time?    If we took a signal, and put it through 2 ... and captured that result .... and then put signals through 1 and 3 - we would see that the output went on for longer than it was supposed to for both 1 and 3.

 

Both?!!  1 and 3.     Damping factor proponents would have you believe that only the under-damped result will have sound which "hangs around for longer than it should"

 

So why does 3 sound "tighter" ?  (becuase it does sound that way)    simply becuase the bass energy (and low frequencies last longer) in this one is quieter.

 

So, for #1, you have louder bass energy, and which goes longer than it "should"  (ie. than #2) does.   It sounds "boomier", "woolier", etc, etc..... it sounds just a like a "uncontrolled" cone might be expected to sound like.

 

... but it's just becuase of the different frequency response  (which is also a different time response).

 

 

You can see that this has nothing to do directly with the electrical damping of a woofer..... if you just take #2, and instead of adjusting the amplifier output Z (the DF) .... and instead use EQ, to adjust the frequency responses to be #1 and #3 ... and you will see the identical difference in time (cos it's just another view of the frequency) ..... and you will hear the identical effect.    The bonus with this method (if your EQ supports it), is that you can flick back and forth between them, and listen to the result.    You will hear that taking away bass results in a dry, fast "controlled" sound .... and that adding a peak, sounds wooly (or just like the DF proponents tell you the "out of control cone" should sound).
 

Quote

 

I don't quite understand the distinction you are drawing for a condition of "no signal".

 

 

DF proponents say that electrical damping "stops the cone moving when it should stop" .... but we see above, that this is simply just a way of twisting the view of the frequency response (ie. a response to an input signal) .... and that rather than being due to a lack of electrical braking, the movement which continues longer than it should, is just what a distorted frequency response is  (and can be simply EQed out)

 

 

... but there's one other thing.    What about if we fed the woofer a signal .... and then instantly stopped the signal.    Would the cone "keep on wobbling" then?     

 

It's worth noting this isn't a very 'real-world' test, cos signals just don't instantly stop....  but humouring the test, we see that too much electrical damping makes the cone bounce back to rest too quick (in a distorted motion) ..... that there is a certain amount of damping (which is typically not very much) which makes it come back to rest evenly/nicely .... and that reducing the damping further, doesn't typically do a lot  (ie. the cone doesn't drastically "wobble on forever") .... but this does depend on the driver.

[MLXXX]

1 hour ago, Tranquility Bass said:

Unless the diaphragm is being driven by an external mechanical source then a loudspeaker is a purely passive device and the only energy source is the amplifier that drives it. To say anything else is completely absurd and alludes to energy being created out of thin air. !

That's not tranquil language, Tranquility Bass!  No one is suggesting that energy has been spontaneously created.

The voice coil if the cone for the sake of experimentation were immobilized with a liberal application of araldite(!), would have a measurable inductance, and of course resistance. Ordinarily though, the voice coil of a speaker is free to move in response to signal from a connected amplifier, and that movement results in back EMF proportional to the speed of the movement. The speaker rather than being simply a passive inductor is free to operate as an electric motor (or perhaps electric "solenoid" or "actuator" given that the motion is not rotary).

 

If drive voltage from the amplifier ceases suddenly, the voice coil if it is already in motion will continue in motion for a time for mechanical reasons (e.g. inertia, or resonance inside the speaker enclosure).  At that stage, I don't think it is too much of an exaggeration to say that the speaker is acting as a generator. Three necessary elements for an electric generator exist:

• a magnetic field (established by the speaker's permanent magnet)
• a coil of wire
• motion of the coil of wire perpendicular to the magnetic field.

 

That motion of the voice coil will be a reciprocating motion if the speaker enclosure is producing damped oscillations after cessation of a single test tone (with a very rapid decay) from the amplifier. Such a reciprocating motion would deliver alternating current, albeit only for a short time.

Edited October 31, 2017 by MLXXX

[MLXXX]

9 minutes ago, davewantsmoore said:

but there's one other thing.    What about if we fed the woofer a signal .... and then instantly stopped the signal.    Would the cone "keep on wobbling" then?     

 

It's worth noting this isn't a very 'real-world' test, cos signals just don't instantly stop....  but humouring the test, we see that too much electrical damping makes the cone bounce back to rest too quick (in a distorted motion) ..... that there is a certain amount of damping (which is typically not very much) which makes it come back to rest evenly/nicely .... and that reducing the damping further, doesn't typically do a lot  (ie. the cone doesn't drastically "wobble on forever") .... but this does depend on the driver.

I'm still not sure I fully understand the "no signal condition" being different to a condition of some other arbitrary signal arising after the abrupt cessation of the first signal, but thanks for the explanation!

[Tranquility Bass]

1 hour ago, davewantsmoore said:

 

 

I'd like to know more, as you would be aware that others have shown data to the contrary.     I've never actually seen any data ever showing a significant increase   (I have seen data showing effectively no change though).

 

I've not any super-reliable data of my own to show .... although I must admit I never tested with a driver in a box either...  only ever a compression driver, and a dipole woofer.

 

 

 

I'm not quite sure I'm with you here....

 

You're saying they "become" the dominant sources of distortion ....   after you remove the distortion from the "voltage drive".

 

If so, then sure ... I agree with that.   You remove one type of distortion from the system... and you are just left with the other types.

 

This seems better than just keeping all the distortion, no?  (?!?!?)  .... If I've misunderstood something, please elaborate.

 

FWIW.   Cms and any air compression effects, are very much dependant on excursion ... the box ... and the driver.     Cms is very non-linear.   Very.    A well designed driver, used at low excursion is a good thing.

 

If you're saying that for a specific excursion... that lack of electrical damping makes Cms more non-linear ... then how?!

 

 

 

Absolutely.... Any fair comparison, requires that this peak is EQed out somehow.   Otherwise this peak dominates everything.   It dominates what you hear ('cos huge peak) ... it dominates any measurement of non-linearities ('cos more excursion, 'cos huge peak)

 

 

What others and where are the results ?

 

Just look at the system response function G(s) as in Smalls work. As Qtc->0 (ie a highly damped system) then Cmt drops out of the equation and the system response becomes immune to variations in Cmt. On the other hand for an under damped system ie with Qtc -> Qmc then the system is highly sensitive to changes in Cmt and so any non linearities in the suspension or box compliance will cause more distortion compared to the lower Q case. And this is exactly what I observed when using current drive as part of a servo system. I found that the higher the output impedance of the amp resulted in higher distortion from the speaker and that meant I needed more loop gain to compensate for the increase in Cmt distortion

 

Now for the case where frequency is way above the resonant frequency of the speaker/box etc then things get better for the current drive case simply because the system becomes immune to variations in voice coil inductance as the voice coil moves in and out of the gap the system becomes immune to inductance modulation and one can expect higher frequency distortion to reduce

 

cheers

Edited October 31, 2017 by Tranquility Bass

[Tranquility Bass]

28 minutes ago, MLXXX said:

That's not tranquil language, Tranquility Bass!  No one is suggesting that energy has been spontaneously created.

The voice coil if the cone for the sake of experimentation were immobilized with a liberal application of araldite(!), would have a measurable inductance, and of course resistance. Ordinarily though, the voice coil of a speaker is free to move in response to signal from a connected amplifier, and that movement results in back EMF proportional to the speed of the movement. The speaker rather than being simply a passive inductor is free to operate as an electric motor (or perhaps electric "solenoid" or "actuator" given that the motion is not rotary).

 

If drive voltage from the amplifier ceases suddenly, the voice coil if it is already in motion will continue in motion for a time for mechanical reasons (e.g. inertia, or resonance inside the speaker enclosure).  At that stage, I don't think it is too much of an exaggeration to say that the speaker is acting as a generator. Three necessary elements for an electric generator exist:

• a magnetic field (established by the speaker's permanent magnet)
• a coil of wire
• motion of the coil of wire perpendicular to the magnetic field.

 

That motion of the voice coil will be a reciprocating motion if the speaker enclosure is producing damped oscillations after cessation of a single test tone (with a very rapid decay) from the amplifier. Such a reciprocating motion would deliver alternating current, albeit only for a short time.

 

Yes it is a motor and is always modelled as a transformer with electrical signals (voltage and current) on one side and mechanical signals (force and velocity) on the other side. The motional impedance as seen on the electrical side of the transformer is that of a simple RLC parallel resonant circuit with a resonant frequency of fs and a Q-factor of Qms. Of course things get a bit more complex once it is installed in a box but there is nothing more to it.

 

If you araldite the speaker diaphragm so it can't move then the mechanical impedance becomes infinite and the motional impedance drops to zero ie a short circuit as one would expect and all you would see if you measured the loudspeaker impedance is the voice coil resistance in series with voice coil inductance 

 

cheers

Edited October 31, 2017 by Tranquility Bass

[MLXXX]

1 minute ago, Tranquility Bass said:

The motional impedance of a loudpseaker in free air is that of a simple RLC parallel resonant circuit with a resonant frequency of fs and a Q-factor of Qms.

It can be so modelled, for the purpose of computations, but unlike an electronic circuit the voice coil moves.  It becomes possible to describe it as a motor (or actuator), or even generator, words that are obviously not apt for a tuned electronic circuit.

[Addicted to music]

Speakers are microphonic and can be used as a microphone.  

 

[Tranquility Bass]

4 minutes ago, MLXXX said:

It can be so modelled, for the purpose of computations, but unlike an electronic circuit the voice coil moves.  It becomes possible to describe it as a motor (or actuator), or even generator, words that are obviously not apt for a tuned electronic circuit.

No this is a misconception. The voice coil in the magnetic gap behaves like a transformer and as such is modelled like that in any analysis of loudspeaker systems. The so called 'back emf' that is talked about so often is a characteristic of other mechanical mechanical elements in the system such as diaphragm mass, suspension and box compliance and suspension resistance etc. 

 

cheers

[davewantsmoore]

 

11 minutes ago, Tranquility Bass said:

 

What others and where are the results ?

 

Just look at the system response function G(s) as in Smalls work. As Qtc->0 (ie a highly damped system) then Cmt drops out of the equation and the system response becomes immune to variations in Cmt. On the other hand for an under damped system ie with Qtc -> Qmc then the system is highly sensitive to changes in Cmt and so any non linearities in the suspension or box compliance will cause more distortion compared to the lower Q case.

 

Yes, of course, they're the equations   .... but in practise, Qtc never gets close to zero ... and definitely never due to electrical damping .... and even if you did (eg. super box stuffing), then you have losses and << less SPL.

 

For the system to become "immune" to change in mechanical compliance  ("drops out of the equation") .... the system damping needs to approach infinity.   This doesn't happen by using a low output impedance amplifier.

 

It's just not an argument for significant electrical damping being helpful.

[Tranquility Bass]

5 minutes ago, Addicted to music said:

Speakers are microphonic and can be used as a microphone.  

 

Yes it can be but like a microphone it is still a transducer just obeying the laws of reciprocity  

 

cheers

[Tranquility Bass]

12 minutes ago, davewantsmoore said:

 

 

Yes, of course, they're the equations   .... but in practise, Qtc never gets close to zero ... and definitely never due to electrical damping .... and even if you did (eg. super box stuffing), then you have losses and << less SPL.

 

For the system to become "immune" to change in mechanical compliance  ("drops out of the equation") .... the system damping needs to approach infinity.   This doesn't happen by using a low output impedance amplifier.

 

It's just not an argument for significant electrical damping being helpful.

 

Yes but the important trend is that as Qtc is lowered there is less sensitivity to Cmt variations and hence lower distortion 

 

If you use an amplifier with a negative output resistance which cancels out the voice coil resistance (ie Rg=-Re) then you can force Q to zero and then the distortion performance becomes independent of Cmt variations and exclusively dependent on BL linearity

 

cheers

Edited October 31, 2017 by Tranquility Bass