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RE: magnets

Magnets are weird things

Alnico drivers basically use slugs, and the Alnico elements are located where the pole pieces are normally located. The Outer shell of the magnet structure forms a sort of "keeper" like what you are making pulling the magnetic field closer to the slug and thus increasing the magnetic intensity.

Funny budget alnicos like in TV sets use a u shaped keeper with two ends open. Still work but not very efficient Just slapping on a couple pieces of steel to the open sides helps a lot. The good drivers, Altec, Bozak, etc. use rings ( looks like steel pipe to me), and afford better shielding ans well as stronger magnets.

Less emf is correct, you don't want direct contact with the magnetic material as the "lines " of force can cross over and muddle the field intensity. In pulling the lines closer together, you are reducing the overall magnetic field extension, and increasing the intensity at the same time, at least at the magnet core.


There's a paragraph in the Lessemf catalog which states you should be directing magnetic fields not necessarily trying to eliminate them. That fact took me many years to sink in. so now I work on redirecting the magnetic fields and achieve much better results


YMMV

and FWIW
Too bad Radio Shack closed down. About 15 years ago they had a number of raw drivers, cheap and fairly good. RS 1354, IIRC a 5 inch full range with whizzer with tight voice coil spacing. Bought a dozen to play around with. They actually sounded pretty good. I cut off the dust caps, drilled the pole pieces, built phase plugs since at $7 each they were pretty much expendable. It was a great learning experience, since what I heard often contradicted standard wisdom and advice

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