This, I feel, is the hardest part of the project, invest a big amount of money
on a bunch of ceramic rectangles, for a project you still aren't completely
sure will work... On top of it all, the project gives you very little help with
respect to the real life specifications they need to have. I had the "luck"
that a Physics Instrumentalist friend of mine had casually 500 magnets of more
or less the specs I needed lying around unused.... and was willing to give them
to me...! That they were a bit weak in magnetic force was no impediment for me
I just planned to put the membrane closer to the magnets, 2mm instead of the
projects 5 mm distance. I had two different types of magnets, one type was
plastic, sort of the type you use for your refrigerator, 5.0 x 1.2 x 0.6 cm, of
those I used 38 per loudspeaker (76 in total) for the tweeter section. And for
the woofer section I used aprox. 150 magnets per speaker, of a ceramic type,
2.5 x 1.9 x 0.4 cm, of a much lower magnetic strength than the others. I
recommend you find long and thin rectangular magnets, that follow the
diagrammes specs with respect to the plane of magnetization, they have a
special name I will include later. I have not been able to find magnet
distributors in Chile.... but I have not tried too hard either. I hope you do
find them where you live. The original project recommends rare earth magnets
due to their strength and due to the fact that their magnetic fields are not
strongly affected by the presence of other magnets close by. I will in the near
future include more info on this subject.Here is a diagramme showing how to place the magnets on the perforated metal plate, notice the fact that the first row on one plate is the contrary of the other plate, this relates to the tweeter magnets too.
A diagramme showing the magnets with respect to the membrane conductors