The front frame is the more involved of the two, for it is the one that the Kapton is actually adhered to. Made of red oak, it has a 1/4" wide x 1/8" deep dado cut into the innermost edge of the two vertical supports. 1/2" wide foam will be placed here so that it juts out 1/4" along the diaphram. This will serve to help dampen the Kapton.
Outside this, 3/8" of wood will serve to fasten the diaphram to the frame. Just outside this section a 1/8" wide cut runs most of the length of the frame. This groove, delineates between the outer section of the frame (fastened in place) and the inner section (fastened to the diaphram). Tension on the diaphram is adjusted using brass wood screws that pass through the outer section and groove and anchor on the inner section.
The rear frame is basically just a spacer and is made of poplar. The dado for the foam is present here as well.
To impede standing waves, the diaphram is corrugated horizontally. At a local home supply (Builder's Square) I found a "threshold strip" meant to be placed under a door that will work quite well. Once cut up and attached to a piece of wood, I'll have a 3" x 2' or so flat ribbed surface. Since the foil and 0.3 mil Kapton kink easily, this setup will let me corrugate the diaphram slightly.
Normal household foil is about three times this thickness and will add too much mass and produce too little impedance. One idea I'm toying with to use etching to both create the voice coil and thin the conductor. The basic idea is to bond normal household foil to the Kapton, lay resist tape down, and etch the entire conductor from one sheet (much easier to handle and work with). Then, once the resist is removed, the entire conductor can be etched to thin it down to some target thickness. The advantage of this is that the conductor can be any shape (e.g. Apogee's waves) and even change thickness at different places on the diaphram. Kids, don't try this at home yet-- FeCl and Al react violently. I'm experimenting with different diultions and techniques that will give a good etch without making pit marks. The basic process does work, however.
If you use foil from a cap, you won't be able to use the etching process to make the entire conductor. The caps simply aren't wide enough. The cap I'm using is an inch or so wide, so I'll be using one strip for each gap. The strips can be made either by laying down resist tape and etching the space inbetween or by careful cutting with a curved Xacto or a roller razorblade. Note, soldering will kill the conductor so a physical joint must be made. One idea is to press a conductor onto the sheet (such as a copper-clad board) and hold it tightly in place.
The idea is to lay this down on the Kapton, press the foil onto it and then lay the etch-resist lines on top. You'll be able to see where to lay the etch-resist lines based on the additional thickness of the adhesive tape.
UPDATE: Unfortunately, the etch-resist tape seems to be tough to find these days. I'm now using the cutting method. I've trimmed the 1/4" wide tape to 3/16" using a jig for a razor blade and slowly rotating the spool of tape. This was necessary since I must cut the conductor and can't just etch it away (3/16" etch-tape was supposedly findable). Once pressed onto the adhesive tape, the Al foil won't come off (good thing in other circumstances). So, to get this sized conductor, the tape needed to be cut.
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