Re: Modelling loudspeaker magnets..

["davehyre" <davehyre@xxxxxxxxx>]

--- In femm@xxxx, "emacoustics" wrote:
> The model is just to show that the coil affects 
> the permanent field when a current runs through it, 
> and by adding a seconc coil in antiphase this can 
> reduce this problem.

Hi Mike,

This is an interesting effect; I've looked at it some, too. The 
idea of the counter-coil goes back to the 1920's or earlier, 
described in Thomas' U.S. patent, granted ~1935. Hall & Velodyne, US 
#5,832,096 (~1996) is a recent take on the same idea. I don't know 
which of their subwoofer models employ this approach, if any. You 
can dig up US patents at www.uspto.gov ; the recent ones are fully 
available.

I'd be curious to hear what you find!

David