I don’t get your point. Do you suggest some kind of acoustical feedback system? Motor forces or coil movements don’t change the spring/damping qualities of the connection to the cone, except for the thermal changes in the coil due to the currents applied.
The connection to the cone is usually rigid (I'm assuming), and I'm also assuming a powerful motor - so that the cone is tightly held at the driving end.
This isn't what you want if a cone contains reflected energy from the surround. What you actually need is a means of absorbing the reflected energy - and resistive termination does just that.
The idea is that a midrange driver cone should be resistively terminated at both the voice-coil and surround. This offers the best possibility of reducing (if not eliminating) cone resonances and breakups.
At the voice-coil, the termination can be mechanical and/or electrical (in which case the driver needs to be fed from a resistive source).
I have a feeling that the concept of the transmission line isn't necessarily well understood.
In electrical terms, at high frequencies (or fast risetimes) and relatively long lengths, it's necessary to take into account the nature of the line, that it has a characteristic impedance, and that it needs to be correctly terminated in order to avoid reflections.
Even if it's correctly terminated at the "receiving" end, all may not be well if the line isn't perfectly continuous, or if there's a termination mismatch.
If there are discontinuities/mismatches, reflections will be sent back to the sending end. In order to avoid further reflections, the sending end should be "back-matched" - i.e. have a source resistance matching the line impedance. Thus, "ringing" is avoided.
All I'm saying is that the speaker cone is in effect a transmission line, and needs resistive matching at both sending (voice-coil) and receiving (surround) ends.
Bass/mid drivers will generally have neither, and can be expected to exhibit cone resonances and breakups.
In electrical terms, at high frequencies (or fast risetimes) and relatively long lengths, it's necessary to take into account the nature of the line, that it has a characteristic impedance, and that it needs to be correctly terminated in order to avoid reflections.
Even if it's correctly terminated at the "receiving" end, all may not be well if the line isn't perfectly continuous, or if there's a termination mismatch.
If there are discontinuities/mismatches, reflections will be sent back to the sending end. In order to avoid further reflections, the sending end should be "back-matched" - i.e. have a source resistance matching the line impedance. Thus, "ringing" is avoided.
All I'm saying is that the speaker cone is in effect a transmission line, and needs resistive matching at both sending (voice-coil) and receiving (surround) ends.
Bass/mid drivers will generally have neither, and can be expected to exhibit cone resonances and breakups.
Variation in B is the same problem voltage or current drive doesn't mater.
I use current drive for many years. What to experiment there?
Variation in B is the same problem voltage or current drive doesn't mater.
I use current drive for many years. What to experiment there?
Well, if B varies, back-emf varies, and voltage drive will counteract it by causing current to vary to compensate - thus counteracting the B variation, and reducing any resulting distortion. So, from that viewpoint, voltage drive is superior.
Current drive can have higher THD around Fs, but it is not the rule. It depends on the driver and how hard you drive it.If you go full xmax than voltage drive better. Back EMF acts like negative feedback linearizing a bit Kms and Cms large nonlinearity. Like electric motor if you load it, it will put more current to resist it. With current drive you don't get this. But this is important for large excursions (for very non linear Kms Cms part) I have measured better THD with current drive once down to Fs then comparing visaton BG20 vs Seas FA22RCZ. Just don't remember which driver looked better there. Of course it was not large SPL measurement.
So i think there is no one answer. Depends on conditions and driver. But usually around Fs makes sense to use voltage drive as Kms Cms nonlinearities should dominate there IMHO.
But lately i measured lowest THD around Fs with moderate output impedance about the same to driver impedance. So voltage has benefits and current has benefits, but where they meet is dependant on application , driver and use case. This is what i think around Fs up to Fs*2.
I think i will do some measurements and document better to show the results. But it will not happen soon. Busy busy
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An amp with an output impedance that is increasing with frequency may be beneficial.This could be achieved with frequency dependant current feedback. This will most probably give a rising response which would have to be compensated beforehand. This isn't too difficult either.
Regards
Charles
Regards
Charles
Maybe we can stick to the subject please?
I see all kinds of things popping up now that don't have much to do with the original subject at all.
I am with Mark on this, I don't see how the example is even related on the systems we talked about.
Once again, any kind of feedback system, current driver or whatever will only have an effect on the part were the speaker act as a piston.
Any local resonances in the cone itself or other local disturbances won't be effected by it.
The only exception would be when this disturbance is more like a constant over the whole range.
For further information I would like to refer to books like Loudspeaker Handbook by Eargle, Loudspeaker en Headphone handbook by Borwick or Acoustics: Sound Fields and Transducers by Mellow and Beranek.
I see all kinds of things popping up now that don't have much to do with the original subject at all.
I am with Mark on this, I don't see how the example is even related on the systems we talked about.
Once again, any kind of feedback system, current driver or whatever will only have an effect on the part were the speaker act as a piston.
Any local resonances in the cone itself or other local disturbances won't be effected by it.
The only exception would be when this disturbance is more like a constant over the whole range.
For further information I would like to refer to books like Loudspeaker Handbook by Eargle, Loudspeaker en Headphone handbook by Borwick or Acoustics: Sound Fields and Transducers by Mellow and Beranek.
I hope you appreciate now that cone local resonances can be ameliorated by correct terminations at the voice-coil and surround.
Where I was going with my replies is that the effects of f as we are discussing it, are the same basic characteristics we in other resonances that are related to harmonics...this will result in an expression of oscillations that diminish as we move away from the root mode.
Attachments
Resonances further down the line are never correlated to the Fs
But are a result of resonances in de cone it self, effects of air cavities/pockets -> compression of air (although not really an issue with higher frequencies), rocking modes, overall quality of the symmetry and above all and most important, resonances of the surround and break-up modes (Which can reflect in lower order frequencies, mostly higher order)
But are a result of resonances in de cone it self, effects of air cavities/pockets -> compression of air (although not really an issue with higher frequencies), rocking modes, overall quality of the symmetry and above all and most important, resonances of the surround and break-up modes (Which can reflect in lower order frequencies, mostly higher order)
..yeah, Keith sort of "derailed" the discussion when he started talking about cone-breakup in post 52:https://www.diyaudio.com/forums/multi-way/376164-importance-kms-bl-mid-ranges-6.html#post6769616
https://www.diyaudio.com/forums/multi-way/376164-importance-kms-bl-mid-ranges-6.html#post6769616
Yes, sorry about that - got sidetracked by mentions of current-drive. Interesting threads often do get sidetracked, as various avenues are explored...