Tim can correct me if I'm wrong, but my understanding of how a speaker gets to be "shielded" is with the use of a second magnet assembly mounted as in polar opposition to the main magnet assembly and then surrounded by a non-ferrous material. The material can vary from manufacturer to manufacturer but is normally an aluminum based material.
That's about it. The second magnet "focuses" the magnetic flux of the primary keeping it from leaking into the surrounding area. This should assist the motor by keeping more of the flux in the gap and in most cases it does so. Many shielded drivers can thus get away with smaller magnets than a non-shielded counter-part. Thankfully, this is needed less often these days due to the increased use of neodymium as a magnet material which possesses the wonderful quality of a inherently focused magnetic field.
Currently, ceramic ferrite magnets are the most common with neodymium gaining ground quickly. Magnets used for shielding (called "bucking" magnets) are typically ceramic ferrite as well. Alnico was common in the past but has a higher potential to become permanently demagnitized than either ceramic ferrite or neo besides being expensive.
How about that! I figured "bucking" wouldn't make it past the forum censors.
It probably should be pointed out that Alnico is still regarded as the Holy Grail of speaker magnets. Alnico full range drivers powered by a 7 watt S.E.T. driven by a passive, autoformer based pre amp and fed by a moving coil cartridge. Some claim it cannot get better than that.
Thank you for the response. I find you both into the '1.21 gigawatt from back to the future' territory for me here, but appreciate the input. I will just lay low a bit..
"It probably should be pointed out that Alnico is still regarded as the Holy Grail of speaker magnets. Alnico full range drivers powered by a 7 watt S.E.T. driven by a passive, autoformer based pre amp and fed by a moving coil cartridge. Some claim it cannot get better than that."
I know some of those. We're fully aware of the subjective nature of audio, however, the basic measurements of magnets are B and H which describe the amount of flux the magnetized material can produce (B)and the materials ability to magnetize/demagnetize (H). Neo combines the best properties of both AlNiCo and ceramic ferrite, exhibiting both high values of B and H. AlNiCo has a high B value, meaning high flux values, but a low H value,meaning it is relatively easy to demagnetize. By contrast, ceramic ferrite has a lower B value than AlNiCo, but ceramic ferrite has a higher H value than AlNiCo, meaning it is harder to demagnetize than AlNiCo. I'm not suggesting a driver should be evaluated solely by it's magnet material, as it is the magnet circuit as a whole that should be considered, however, Neo does seem to hold the high card.
My thoughts were to use a powered field, demagnetized at power off. The eloctrostat can produce a positive field, and can be made to ionize as well, with a field that can be projected, or focused, largely with an aluminun honeycomb. I did not understand the materials content of shielding, imagining a full side(left or right) of the enclosure being physically barriered. If the field provided by an ionized Al could protect from heavy flux externally, could the same field not be focused on the primary field of the driver and create a blanket? A bit over my head, but interesting stuff.
Well, you're stretching my recollection of high school physics class, but my common sense would say it still depends on what you're trying to shield from what.
Given the effectivenss of the current method, I can see no reason to go to such Rube Goldbergish lengths to accomplish the task. However, since you asked, your supposition would appear to suggest an elctrostatic field could negate the effects of the permanent magnet's field on another (I assume) electrostatic field. Because that is what the magnetic field is doing to the CRT in your TV. The electrostatic field which represents the picture is being disrupted by the magnet's flux field. Given the size of the electrostaic field in most TV's vs. the magnetic field of most speakers, I'd say your idea is valid only if the size of the shielding electrostat is quite large in comparison to the flux field of the permanent magnet and the voltage of the electrostat is quite high. Of course, proximity of the shield to the magnet in relation to the TV's electrostatic field would be the most important element of the experiment. And that would mean, basically, moving the speaker magnet far enough away from the TV so that neither it nor the electrostatic field disturbed the other. All in all, the answer would probably come down to, yes, it might work, though the effective sizes and distances would be substantial; and why would you want to try?
Having a McGiver moment is really all. The concept seems fairly adaptable for various applications and I was thinking (probably) a little too loud. But this IS a good place for that.
Absolutel, completely off topic, I have all Looney Tunes collections on dvd, 4 per folder and can recite every line from every cartoon. Now THAT drives my wife nuts. I can see why, in fact