This, I feel, is the hardest part of the project (ON YOUR POCKET :-)), invest a large 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 casually had 500 magnets of more or less the specs I needed lying around unused… after having callibrated some special astronomical CCD camera and was willing to give them to me for free…!
That they were a bit weak in magnetic force was no problem for me. I just planned to put the membrane closer to the magnets, 2mm instead of the project’s original 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 (Fig. 1).
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.
Fig. 2 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.
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