Cut a chunk of mirror large enough so that it stretches at least 3/4 the way across the opening, and is a couple of inches wide. We used a Dremel cutting tool to do this, but a small hacksaw would work just as well.
Updated instructions
This will be detailed with V2.0, but for now, we recommend making this mirror much shorter, to reduce angular momentum and improve high-frequency response and the signal-to-noise ratio. In principle, you want the mirror to be a couple of inches wide (the width being the side parallel with the pivot rod) and as short as possible while still allowing the pushrod to be easily attached. If X = the distance from the pivot rod to the pushrod in inches, the making the mirror ( X * 2 ) + 0.5 inches will allow enough material to attach the pushrod.
Lay the pivot rod across the opening for reference. Hold the mirror (upside down) so that the edge is about a quarter inch away from the edge of the opening. Use a marking pen and mark where the pivot rod crosses the mirror. The picture shows the correct position, and you can see the marks we made.
We don't have a picture of this to show you, but you also need to make a second mark. Put the pushrod in place around the voice coil, and the pivot rod in place across the opening. Line the marks you made on the mirror up with the pivot rod, and mark the distance from that point to where the pushrod is poking up. This distance will be roughly equal to the radius of the voice coil.
Drill a hole large enough so the coathanger wire fits through, at the point you marked. The picture above shows the hole, and also reveals our shameful mistake: we had epoxied the bearing (see below) onto the mirror before we drilled the hole. Not that it really matters that much. Just pretend it isn't there.
Take a strip of aluminum foil that is as wide as the mirror and wrap it around a piece of coathanger. Ten wraps or so should do nicely. Slide the aluminum foil tube you've made off the coathanger. Admire your mad skillz. You just made the world's cheapest bearing!
Epoxy the bearing onto the back of the mirror where you made the mark earlier. Be careful that you don't block the openings of the bearing (even partially) with epoxy. If you do, use a stick or something to wipe the offending crap away before it sets. Note: The bearing in the photos turned out to be too short. You want yours to stretch all the way from one side of the mirror to the other.
Next Page: Preparing the Pivot Rod
| Intro | How it Works | Prepping the Speakers | Coathanger Mangling | Preparing the Mirror | Preparing the Pivot Rod | Final Assembly | Setup and Operation | Needed Improvements |