Let's start with the more conventional part of the construction-the metal support structure for the spheres. This portion was built from materials that are easily found at your local home improvement and discount stores. The main tubes are ¾" steel conduit, which I bent into the gentle curves by hand. The support for the center channel was built from the same material, but I used a conduit bender to create the tighter curves that I needed.
Attached to the steel supports were small studs made from steel tubing, to which were attached "lighting repair nuts." I'm not sure of the size, thread count, or pitch of these nuts, but they are the size that is very often used in lamps, light fixtures, and ceiling fans. These are readily available in the lamp repair portion of your hardware store. These nuts and their matching hollow rods are what create the "pass-through" for the wire from the inside of the spheres and into the tubes.
The bases of the speakers are built from $2 discount store frying pans with the handles removed. All it took to put everything together was some careful drilling, bending, welding, and bondo-ing.
The construction process of the spheres began with trying to figure out what material to construct them from. I did a great deal of research and investigation on possible materials, and ultimately settled on Tuf-Cal. Tuf-Cal is a type of gypsum plaster designed for slush casting, featuring polymer and fiber additives for high strength and chip resistance. While the material itself is fairly inexpensive, it is not easy to find. Expect to pay around $100 to get a hold of some by the time you include shipping and handling charges.
In order for the plaster to be cast into the spheres, obviously a mold of some sort was needed. I found the molds online, being sold as candle making molds; they are two-part vacuum formed to 5" in diameter. To create the driver recesses on both the woofers and the tweeters, I used the plastic vacuum formed protective covers that come on all Tang Band drivers. I simply attached a hollow sprue to the covers, and then duct-taped them into the molds. It sounds like a haphazard process, but it actually worked quite well!
The plaster is mixed and worked in pretty much the same way as the plaster of paris you may have used in grade school. Mix roughly one part plaster to one and a half parts water, and you're on your way! I used a three-part molding process, involving a pour for the "top", a pour for the "bottom", and a rotational-molded pour for the "sides." I found that after about an hour of setting inside the molds, the objects could be removed, the seams cleaned-up, and then dried.
Once dry, all that was needed was a few finishing touches. First, I gave the spheres a dip in fiberglass resin to create a durable "shell" that would help smooth out any irregularities, provide scratch-resistance, and provide a great base for painting. Then, I drilled the mounting holes in the back of the spheres and attached the threaded studs. I attached the spheres to the supports, painted the whole thing, and then did the usual speaker prep items like stuffing and wiring.
