How to shift the operating range of an amplifier while keeping the speaker volume constant?

[NTK]

These pictures are from Klippel and the graph shows the measured suspension stiffness with displacement. If there is significant stiction, it will show up in the graph as spikes (and the Kms curves will not be smooth). When there is stiction, during the measurement you'd have an increase in the applied force but there is no correspondent displacement, which means stiffness at that point is infinite.

Stiction will also show up in distortion measurements. Its effects are somewhat similar to cross-over distortions in amplifiers.

Picture source: https://www.klippel.de/know-how/mea...rs/transducer-nonlinearities-curve-shape.html

 

[UltraNearFieldJock]

When someone is interested:
I measured the voltage on the mid‑bass with the Hypex module (the same one mentioned earlier in this thread). It’s only 0.5 V.

The power needed for the mid‑bass at my normal listening level is:
P = U² / Z = 0.5² / 8 = 0.03 W (30 mW)
I = U/Z = 0.5/8 = 0.0625 A = 62.5 mA
Surprisingly low, at least for me. That measurement was for a 200 Hz sine wave. The actual power in music is probably much lower. Nevertheless, I can feel the movement of the membrane with my finger, even at such low power.
Should phone amplifier be able to provide this? Perhaps yes, but sometimes I like to listen very loud (live level — and that changes the situation.

And last mesurment of THD: (At normal maximal listening level, perhaps I should make the measurement louder? But in this case, this mesurment would be irrelevant for the whole discussion about driver's extremely quiet levels.)

Do you see any issue here? After all, this is in the range between 80 and 1200 Hz, where the Hypex and the AL170 are operating?
The AL170 must be an excellent driver — does all the THD come from the Hypex?
Or is the driver’s THD at very low levels close to zero?
Does all the mess at –50 dB above 100 Hz come from room noise and the UMIK‑1 itself? If yes, (certainly yes) then all these issues are irrelevant anyway, because everything below normal room‑noise level is meaningless to enjoy recorded music, but it’s still interesting to understand and discuss.

 

[antcollinet]

the point is that the spider and surround is lossy. It takes a minimum current to make the cone overcome frictional effects and start to move. You can very easily show that by pressing your finger on the diaphragm and feeling the resistance to motion. Physically, its not possible for it to be frictionless on earth and thus there is a minimum current that is needed to the voice coil to make it move. This is basic physics and I don’t understand why there is any argument about this. I used the extreme example to make this point, that if there were no losses as others seem think, it would freely move, with a faint force like from your breath. Frictional losses within the materials are the main reason why a microphone has a minimum SPL sensitivity and why there is a minimum SPL floor in a loudspeaker driver.

Lossy doesn't matter. All springs are lossy - but if you apply a force to something at equilibrium on a spring - then it sure as hell is going to move - until the spring force adjusts to match the applied force. Come on - this is high school level physics.

 

[TurtlePaul]

the point is that the spider and surround is lossy. It takes a minimum current to make the cone overcome frictional effects and start to move. You can very easily show that by pressing your finger on the diaphragm and feeling the resistance to motion. Physically, its not possible for it to be frictionless on earth and thus there is a minimum current that is needed to the voice coil to make it move. This is basic physics and I don’t understand why there is any argument about this. I used the extreme example to make this point, that if there were no losses as others seem think, it would freely move, with a faint force like from your breath. Frictional losses within the materials are the main reason why a microphone has a minimum SPL sensitivity and why there is a minimum SPL floor in a loudspeaker driver.

It would move freely if there was zero centering force, not zero friction. A speaker spider and surround is designed to act as a spring under constant tension - which can have force keeping it in place which is not necessarily caused by static friction.

 

[Waveform Fidelity]

Lossy doesn't matter. All springs are lossy - but if you apply a force to something at equilibrium on a spring - then it sure as hell is going to move - until the spring force adjusts to match the applied force. Come on - this is high school level physics.

It sure is. I don’t know what you are arguing about. Go back and read what I said, not what you think I said.

 

[Waveform Fidelity]

These pictures are from Klippel and the graph shows the measured suspension stiffness with displacement. If there is significant stiction, it will show up in the graph as spikes (and the Kms curves will not be smooth). When there is stiction, during the measurement you'd have an increase in the applied force but there is no correspondent displacement, which means stiffness at that point is infinite.

Stiction will also show up in distortion measurements. Its effects are somewhat similar to cross-over distortions in amplifiers.

Picture source: https://www.klippel.de/know-how/mea...rs/transducer-nonlinearities-curve-shape.html

Thank you - I agree with your comments.

As to other commenters, there were two points i made and this graph shows both nicely;

A. The minimum force (aka voice coil current) needed to make a cone move - above you see the surround and spider of the suspension system - that should answer the comments that the cone will move with any current no matter how small. I called it stiction, but its really the internal material friction of the cone and spider materials.
How does this affect the ultra low volume use-case of the original OP? If you imagine the fluctuating music signal, then its easy to visualize that the quietest parts of the signal may not be enough to make the cone move, so you have a “hard limiter” effect that clips the low level signal. So you have to drive the speaker at least the dynamic range of the music above this threshold, to avoid low-level clipping.

B. Linearity - the above graph is only depicting the restoring force acting on the voice coil - not the displacement vs. voice coil current so we don't know if the applied force is balanced by an equal and opposite restoring force - for example it a static case of a DC current. That depends a lot on the uniformity of the magnetic field strength inside the pole-piece, which is unlikely to perfectly uniform. In any case one can observe the non-linear restoring force of the suspension. This “might’ go some way to the comments that claim the motor assembly is “linear”

 

[antcollinet]

Thank you - I agree with your comments.

As to other commenters, there were two points i made and this graph shows both nicely;

A. The minimum force (aka voice coil current) needed to make a cone move - above you see the surround and spider of the suspension system - that should answer the comments that the cone will move with any current no matter how small. I called it stiction, but its really the internal material friction of the cone and spider materials.
How does this affect the ultra low volume use-case of the original OP? If you imagine the fluctuating music signal, then its easy to visualize that the quietest parts of the signal may not be enough to make the cone move, so you have a “hard limiter” effect that clips the low level signal. So you have to drive the speaker at least the dynamic range of the music above this threshold, to avoid low-level clipping.

B. Linearity - the above graph is only depicting the restoring force acting on the voice coil - not the displacement vs. voice coil current so we don't know if the applied force is balanced by an equal and opposite restoring force - for example it a static case of a DC current. That depends a lot on the uniformity of the magnetic field strength inside the pole-piece, which is unlikely to perfectly uniform. In any case one can observe the non-linear restoring force of the suspension. This “might’ go some way to the comments that claim the motor assembly is “linear”

It is not telling you what you think it is telling you.

I'm out.

 

[somebodyelse]

the point is that the spider and surround is lossy. It takes a minimum current to make the cone overcome frictional effects and start to move. You can very easily show that by pressing your finger on the diaphragm and feeling the resistance to motion. Physically, its not possible for it to be frictionless on earth and thus there is a minimum current that is needed to the voice coil to make it move. This is basic physics and I don’t understand why there is any argument about this. I used the extreme example to make this point, that if there were no losses as others seem think, it would freely move, with a faint force like from your breath. Frictional losses within the materials are the main reason why a microphone has a minimum SPL sensitivity and why there is a minimum SPL floor in a loudspeaker driver.

I don't know whether this and your previous contributions about stiction are just a loose use of terms or a misunderstanding of the physics. You seem to be mixing up different phenomena and their effects, which is why there's argument about it.

 

[Waveform Fidelity]

I don't know whether this and your previous contributions about stiction are just a loose use of terms or a misunderstanding of the physics. You seem to be mixing up different phenomena and their effects, which is why there's argument about it.

FWIW: Stiction was not the correct descriptor and a one commenter pointed that out early on. However, I explained multiple times I was referring to the internal friction (and used that term) of the materials that make up the surround and spider. Its a shame that some commenters choose to post value-less rude or condensing comments instead of value added constructive comments that advances knowledge and understanding of the topic posted.

 

[NTK]

FWIW: Stiction was not the correct descriptor and a one commenter pointed that out early on. However, I explained multiple times I was referring to the internal friction (and used that term) of the materials that make up the surround and spider. Its a shame that some commenters choose to post value-less rude or condensing comments instead of value added constructive comments that advances knowledge and understanding of the topic posted.

Is that just a hypothesis of yours, or do you have any scientific evidence that you can reference?

BTW, modern technology can measure forces and deflections in atomic scales. From Wikipedia.

 

[somebodyelse]

FWIW: Stiction was not the correct descriptor and a one commenter pointed that out early on. However, I explained multiple times I was referring to the internal friction (and used that term) of the materials that make up the surround and spider. Its a shame that some commenters choose to post value-less rude or condensing comments instead of value added constructive comments that advances knowledge and understanding of the topic posted.

I'm not only talking about stiction - multiple terms seem either loosely used or misunderstood. Take 'internal friction' - I guess you're talking about hysteresis as seen in elastomers rather than viscosity from ferrofluid in a tweeter. Both result in energy loss. Neither result in a minimum force being needed to produce a displacement though, which seems to be what you're proposing. Very small forces just produce very small deflections.

 

[Waveform Fidelity]

I'm not only talking about stiction - multiple terms seem either loosely used or misunderstood. Take 'internal friction' - I guess you're talking about hysteresis as seen in elastomers rather than viscosity from ferrofluid in a tweeter. Both result in energy loss. Neither result in a minimum force being needed to produce a displacement though, which seems to be what you're proposing. Very small forces just produce very small deflections.

It sounds like you have some knowledge worth sharing about elastomers - lets take the spider out of the picture and leave just the surround. Are you saying that any force, not matter how infinitely small, when applied at the voice coil will cause the cone to move? In other words there is NO internal material friction in the surround which opposes motion? I think not. I can take a thin sheet of rubber and flex it back and forth in my fingers and feel resistance. If there was no internal friction, I could create a rubber drive belt, looped over as many pulley’s as you like and it would have no power loss -do you agree?

I am not a material scientist, nor mechanical engineer, but I have been working on satellite designs where in general, and in the absence of gravity, there is always a minimum threshold force need to make “things” move - call it friction, stiction, internal friction, whatever you want to call it.

Please share with us what you know about elastomers.

 

[Waveform Fidelity]

Is that just a hypothesis of yours, or do you have any scientific evidence that you can reference?

BTW, modern technology can measure forces and deflections in atomic scales. From Wikipedia.
View attachment 508479

Let’s here the answer back on the properties of elastomers at the molecular level.

 

[MaxwellsEq]

Let’s here the answer back on the properties of elastomers at the molecular level.

I think you have this whole science thingy back to front.

You have a theory about forces, which is out of alignment with generally accepted wisdom. Fine, that happens in science - it's how progress is made. But as the person bringing this new theory, it's up to you to provide rigorous measurement evidence that you are correct combined with quality mathematical modelling to explain your measurements.

 

[somebodyelse]

It sounds like you have some knowledge worth sharing about elastomers - lets take the spider out of the picture and leave just the surround. Are you saying that any force, not matter how infinitely small, when applied at the voice coil will cause the cone to move? In other words there is NO internal material friction in the surround which opposes motion? I think not. I can take a thin sheet of rubber and flex it back and forth in my fingers and feel resistance. If there was no internal friction, I could create a rubber drive belt, looped over as many pulley’s as you like and it would have no power loss -do you agree?

Suspecting something was lost in translation I went digging, and it seems we have some new terminology to confuse the old school mechanical engineers. 'Internal friction' is now being used (in some circles at least) as a blanket term for almost anything where molecules move and heat is generated. It's not terminology that was used when I was an engineering undergrad. The reason for the hysteresis curve you get when measuring force vs. displacement for a rubber band is 'internal friction' - though I suspect they then talk about relative movements in the tangle of cross-linked molecules that we did. I'd talk about several different sources of power loss in a belt system, but each of those would now have an underlying cause of 'internal friction' despite having different mechanics.

As for 'no matter how infinitely small' I thought we were talking about speakers and microphones for audio, so displacements much larger than the molecular scale. I suppose elastomers might get 'steppy' if you look closely enough, but I doubt we'd be using them where that mattered in audio. Cantilever suspension in a cartridge probably has the smallest movement, and I've not seen it mentioned as a problem there.

I am not a material scientist, nor mechanical engineer, but I have been working on satellite designs where in general, and in the absence of gravity, there is always a minimum threshold force need to make “things” move - call it friction, stiction, internal friction, whatever you want to call it.

It's a good few years since I worked with a former satellite engineer (deployment mechanisms for stuff that had to be folded for launch). As I understood it they had to deal with many effects we don't encounter here on the surface.

 

[Waveform Fidelity]

I think you have this whole science thingy back to front.

You have a theory about forces, which is out of alignment with generally accepted wisdom. Fine, that happens in science - it's how progress is made. But as the person bringing this new theory, it's up to you to provide rigorous measurement evidence that you are correct combined with quality mathematical modelling to explain your measurements.

Well, you are a kind of bossy individual aren’t you? You have not contributed to the post either.

As for your “proof” that you insist is needed a simple google search with AI returned the results below.

2 takeaways

1. Sticky behavior at rest - aka minimum force needed to make the cone move
2. Low-level signal loss - hard limiter effect.

End of discussion.

 

[Waveform Fidelity]

Suspecting something was lost in translation I went digging, and it seems we have some new terminology to confuse the old school mechanical engineers. 'Internal friction' is now being used (in some circles at least) as a blanket term for almost anything where molecules move and heat is generated. It's not terminology that was used when I was an engineering undergrad. The reason for the hysteresis curve you get when measuring force vs. displacement for a rubber band is 'internal friction' - though I suspect they then talk about relative movements in the tangle of cross-linked molecules that we did. I'd talk about several different sources of power loss in a belt system, but each of those would now have an underlying cause of 'internal friction' despite having different mechanics.

As for 'no matter how infinitely small' I thought we were talking about speakers and microphones for audio, so displacements much larger than the molecular scale. I suppose elastomers might get 'steppy' if you look closely enough, but I doubt we'd be using them where that mattered in audio. Cantilever suspension in a cartridge probably has the smallest movement, and I've not seen it mentioned as a problem there.

It's a good few years since I worked with a former satellite engineer (deployment mechanisms for stuff that had to be folded for launch). As I understood it they had to deal with many effects we don't encounter here on the surface.

For me, I was always thinking about the speaker suspension system and imagining the original poster listening with his head close to the diaphragm in what he calls “ultra near field” . Even at these low levels, small cone movements are massive in the molecular scale, but is it true that the basic cause of loss at the macro level are fundamentally linked to the behavior at the molecular level?

There are plenty of practical examples too - rolling resistance of a vehicle tire comes immediately to mind

Thank you for your response.

 

[bmc0]

1. Sticky behavior at rest - aka minimum force needed to make the cone move
2. Low-level signal loss - hard limiter effect.

Check the sources. There is no mention of such phenomena except in an old ASR thread where it is asserted without supporting evidence.

 

[Waveform Fidelity]

Check the sources. There is no mention of such phenomena except in an old ASR thread where it is asserted without supporting evidence.

Audio Engineering Society (AES) and Klippel - I’ll take those references as credible over any ASR thread

 

[bmc0]

Audio Engineering Society (AES) and Klippel - I’ll take those references as credible over any ASR thread

Good. No evidence supporting your claim is given in the AES or Klippel references.