| Electronics > Projects, Designs, and Technical Stuff |
| Do we have any magnet/magnetism gurus here? |
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| Marco:
This seems to be about ribbon speakers ... but ribbon speakers don't have a planar field coming from below the ribbon, it wouldn't work. Ribbon speakers need the magnetic field lines to be parallel to the ribbon, Lorentz force and right hand rule and all. I know the Apogee ribbon speaker has a massive "ribbon" which makes it impossible to achieve that with magnets just on the side of the ribbon (like ribbon tweeters have) but they can't cheat physics ... if the force has to move the ribbon front to back, then the magnetic field lines have to come from the side (on average). What you could do is have the ribbon metallized in sections, and run the current up and down on alternating sections. Then have alternating strips of N/S magnets below, along the insulated parts of the ribbon. It won't be an even field, but on average the magnetic field will have a component running parallel to the ribbon and at a right angle to the current and thus create a force front to back. The forces on all the sections will point the same way too. |
| T3sl4co1l:
OP refuses to answer about their application, so I guess we should assume they don't know what it is; and therefore the answer is trivial (it doesn't matter). Or if they are unable to tell, but the same conclusion applies, at least as far as public discussion is concerned. :( Tim |
| CatalinaWOW:
This breaks the bank for all but the mega rich, but you could cheat a bit given your ill defined requirements. Build a large C shape magnet with dimensions of the pole pieces on the scale you describe and spacing between them as you need. Then a flat sheet of virtually any soft magnetic material placed between the poles would assume the configuration you are looking for. This approach does illustrate in a different way the difficulty of achieving what you want. |
| Marco:
Well he was talking about ribbon speakers in another thread, so it's a safe guess that's what this was for. Ribbon tweeters have the magnets as in pic, but that doesn't work with a full range speaker ... the magnets would have to be way too big. Apogee segments the ribbon into zigzag pieces. So I assume they work just as I suggested, with the bar magnets below the ribbon not all being the same polarity, but alternating such that they create field lines which run somewhat parallel with the ribbon. Alternating in polarity as the direction of the current alternates so the force stays pointing the same way. The field will also have large components perpendicular to the ribbon, but those are mostly irrelevant, they will create forces in plane with the ribbon. The magnet cvanc wanted to create would create forces only in plane with the ribbon ... that's not going to be a very good speaker. |
| ejeffrey:
Yeah, that should work and would be a good application of a halbach array :) |
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