We like to see people building things that are a little unusual, and we really like it when said unusual thing uses salvaged parts. This project from [JGJMatt] ticks all our boxes — the build creates a planar speaker that uses salvaged magnets from a hard drive.
A planar speaker, according to the post, uses wires and magnets to manipulate a flat film that acts as the transducer. The speaker housing is 3D printed and looks great but is otherwise unremarkable. The fun starts when a Dremel with a diamond disk cuts the magnets in half. Cutting neodymium poses several challenges. For example, if you heat the material up too much while cutting, it can lose its magnetism.
With the proper magnets, you can move to the tedious method of creating the coils. The post shows three different methods. But the part we really liked was using a resin 3D printer as a UV source to expose a resist mask which transfers to a copper or aluminum foil that will be the sound-generating film. [JGJMatt] used a similar technique to put resist on PC board blanks, too. Unfortunately, there were some issues so the finished speakers didn’t use the foil prepared using this method. Instead, a quick modification to the resin printer allowed a thin film of resin to rest on the foil, which was then exposed.
Once you have the pieces, there isn’t much left to do but put them together. Honestly, this is one of those things you probably won’t do yourself unless you are obsessed with speakers. But there were a lot of interesting techniques here that might come in handy, even if you don’t care about audio reproduction.