John Curl's Blowtorch preamplifier part II

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#70,186
snup said:
bcarso
I think it would be nice to know, where the center of the coil is located, when it is trying to do additional freqencies at a specific point of excursion. Everybody knows, that relieving a midrange from large excursions improves clarity. The springloading of the spider and surround, will be easy to account for.
Having an extra stationary coil in the gap will give a possibility of feedback for applying some servo.
A built in miniature light-distancesensor should give info enough to run signal through DSP for correction.
I know it sounds too simple, but I will try playing with it.
Another thing to try is to use magnetic fluid as the motor.
Inverse fieldcoil if there is such a thing.
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Go for it. I've either been too busy or too lazy for many years now. Small signal design has a few squeezes left in the toothpaste tube and is a lot easier and cheaper to do.
 
#70,190
fas42 said:
Brad, so you're saying that that the motion of the cone is always significantly non-linear, otherwise we wouldn't be getting IMD?
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Seems so, and what's more the speaker driver is typically outside any feedback loop so this is typically not correctable. It is possible to significantly linearise voice coil motion via additional (feedback) windings on the former, or within the magnetic gap - there are very impressive speakers based on this.

But cone flex remains outside the loop, though reflections from the outer rim can be controlled via voice coil or mag gap feedback, and that seems to help a lot.

Don't know if these are the drivers you refer to, can't see most drivers meeting a -60dB (0.1%) THD figure otherwise........
 
#70,193
snup said:
you might be able to reduce conebreakup with the control of unwanted excessive excursion at subfrequencees.
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I generally doubt that, because at low frequencies the cone behaves pretty much as a rigid body anyway, the incremental effect of slew rates at which the cone behaves flexibly then shouldn't depend on it's absolute position or velocity as a rigid body, in principle............probably at silly excursions the rim suspension might impart some cone flex I suppose, but that's not the same as the travelling waves within the cone.

Large excursions test the uniformity of magnetic gap field though.
 
#70,195
Cone resonances are induced by movement of the voice coil. The only way to prevent this from happening is to not feed the vc with frequencies which would set off such resonances. I can't imagine any kind of feedback being able to control such resonances, since they are chaotic by nature and the cone is only loosely coupled to the voice coil at the frequencies they occur.
 
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