Advice for DIY ribbon tweeter construction.

[Puggie]

Couple of questions for those more knowledgable. I have some N40 neo magnets for building my ribbon tweets:

How important is it to 'complete the magnetic circuit', can I just mount the magnets 10mm apart with an acrylic frame or would it be considerably better to make a steel frame to go round and over the top of the structure connecting the N pole of one magnet to the S pole of the other?

If I wanted to make steel plates to go over the magnets and 'focus' the magnetic field (change the shape of the surface of the magnet), what grade of steel should I be looking at using?

Anyone got a nice guide to winding your own transformers using ferrite toroids and enammeled copper wire?

thanks guys and girls,

[Paul W]

I highly recommend the use of FEMM because magnetic circuits don't always follow logic (at least my logic).

In simulations, there was not a substantial difference between common 1018 and, say, 1006.

The strongest circuits I tried had the magnet surface facing the gap directly. Steel between the magnet and the ribbon always weakened field strength...increasing cost for a given field strength in the gap.

On the other hand, steel on the magnet surface away from the gap helps minimize a magnetic "short circuit" between magnetic poles. Completing the circuit above, below, and behind the gap improves strength but not always as much as you would think.

YMMV so download FEMM
Have fun!

[ABJensen]

I have used this magnetsystem for my 150 cm ribbons, ok i had to use 12 meter neomagnets for a pair.

http://v3.espacenet.com/textdoc?DB=E...=US4317966&F=0

[LineSource]

The "Lister Ribbon" topology in the mentioned patent has the potential to deliver the best sound, and can be adequately efficient for a narrow tweeter ribbon. The efficiency is marginal for wide bandwidth ribbons, where a complete iron magnetic circuit can provide much higher flux.

http://v3.espacenet.com/textdoc?DB=...X=US4317966&F=0


The Lister Ribbon topology allow very precise machining of the iron pole pieces, and this allows very narrow gaps between the ribbon edge and pole pieces which reduces distortion.

The Lister Ribbon topology reduces deep side magnet cavities and their resonances by putting the magnets on the side pole pieces.

The Lister Ribbon topology reduces rear reflections by not having any rear iron, or minimal rear iron. Always extensively stuff the rear cavity to absorb all of the rear wave.

The Lister Ribbon topology has very high stray magnetic fields and may affect CRTs.