Building the BoilerBall Speakers!

This was a pretty challenging build for me. I had designed these speakers to go along with the SteamAmp II, and I was fairly certain I could pull it off, but there were a bunch of things I was doing for the first time, and I was a bit nervous. In the end, persistence and patience paid off and they came out better than I could have hoped. The sound really good too, honestly better than I’d expected them to. I guess I shouldn’t have been surprised, they were designed using bass box pro to be the correct enclosure and port size for the drivers, but as I’ve found before, what looks good in the speaker modeling software, doesn’t always result in great sounding speakers.

 

The two big uncertainties were the brass ring the speakers mount to, which itself mounts to the copper ball, and the copper ball itself. On a side note, I didn’t build the copper balls, I bought them online from the place where all things copper ball related come from: New England Copperworks. If you’re ever in need, they are super friendly, and their work is the highest quality.

The Base

The base was made from 1×2 inch walnut cut in sequence so the grain wraps around the bases. This was a fun exercise in mitre-saw calibration, as any small variation in the accuracy of the angle compounds by every joint. It took a little doing, but eventually I got it all squared away.

I glued the walnut pieces together with a jerry-rigged jig-thingy (technical term) since I don’t have the proper strap-clamps to do stuff like this, then glued bracing around the inside to attach the brass plate. The Ball Stand for lack of a better word is made up of a 3″ copper pipe cap and a 1″ copper port running through the base to a walnut port flair underneath. The port allows the enclosure to be tuned to a much lower resonant frequency than would be allowed with just a sealed box, resulting in a much larger sound.

The flares were made with a plunge router out of solid walnut. Nothing terribly challenging going on for this part of the build, it just took a lot of time and patience. The salt air from the ocean under my balcony made working with the copper tough, but I learned pretty quick to keep everything covered when I wasn’t working on it.

 

The Ring

Unless I was going to shell out huge bucks for a couple cnc-machined solid brass rings (something I didn’t have the budget for), I was going to have to come up with something a bit more economical. I decided to use cold-cast brass, which is finely ground brass powder mixed in a resin, like epoxy or polyester. I used West Marine epoxy because it’s rock hard and very easy to work with to get consistent results (plus I had some left over from a previous, hellish project repairing my boat).

First I cut the blank from a piece of poplar with my plunge router. I primed and sanded it until it was perfectly smooth and then made a mold of it using silicone rubber with a fiberglass outer mold. When the mold was all set up, it was dusted inside with brass power then filled up with a mixture of brass power and epoxy resin. I put a layer of chopped-strand mat fiberglass cloth in there for good measure; I didn’t want the thing cracking, although I doubt it would have. When the epoxy set up, the ring was de-molded and sanded, then lightly buffed with steel wool and coated with protecta-clear to keep it from tarnishing.

They came out really well, I was very happy with the results from the cold-cast brass. It doesn’t look exactly like solid polished brass, but it was darned close. I think if I build another pair of these in the future I will cast the rings out of resin and then electro-plate them.

 

The Balls

Yep. I said it.

This was all made up as I went along. I needed to have a hole with a flat surface really well attached to the ball so I could bolt the ring and then the speaker to the thing. These little speaker drivers were really heavy, and the weight of them combined with the vibration they would have to put up with made for a tricky design. I originally thought I would solder a thick copper plate to the opening, but the balls were made up of two hemispheres soldered together themselves, and if the heat of soldering the face plate to the ball decoupled the sphere halves I’d be screwed. So I decided to use fiberglass – the cure-all.

I started by making a double ply buildup of biaxial fiberglass matt and epoxy resin. I laid the matt down between two sheets of wax paper and pressed that between two flat boards while the resin set up. Then I cut my round shapes out, and affixed them to the balls from the inside with more fiberglass cloth and resin. Then I coated the entire inside surface of the ball with resin and cloth. These things are rock-solid at this point, very heavy and strong. The copper ball itself isn’t even really structural anymore, it’s just a covering for the fiberglass inside it.

Once that was done, the balls were polished and coated, the rings attached, and the whole thing was bolted to the base with 1/4″ nuts and bolts. I wired up the drivers, bolted the speakers in, and bobs’s yer uncle!

 

All in all this project, like most of my undertakings was a colossal pain in the arse! That being said, I’m very glad that I did it because the results were out of this world. Unfortunately, these were a commission job, so I don’t get to enjoy them, but I’m determined to build myself a pair when I have the time. They’d look great on my computer desk!

Cheers!
Mike

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