A few days ago I completed the first stage of a long-standing project to create new parts for my BMW M Roadster interior. Two years of design in Autodesk Fusion 360, the procurement of a Prusa i3 mk2s 3d printer, development of at least six physical prototypes and a whole lot of Proto-Pasta HTPLA filament later, I now have two new behind-the-seats speaker housings mounted and loaded for field tests.

Brief history: the previous owner installed a full roll bar behind the seats and in the process, hacked up the plastic bits to the point where they were held together with tape and wire. Although workable, the roadster is now my car and I felt I needed to do something about it.

What prompted the project is the fact that one of the two factory rear speakers is blown and without a garage, I have no way of hoisting the roll bar out of the way to replace the drivers.

Taking an admittedly different approach and inspired by the folks at Car Audio Fabrication, I chose to install new speakers and in the process, design a replacement for the damaged plastics. My initial design centered on 3d printed brackets (printed by Shapeways) to support wakeboard tower cans for 5 1/4″ speaker drivers as shown below:

The aluminum cans were okay, but they were large, heavy, and interfered with the convertible top. That prompted me to move to an all-in-one design, which evolved into the prototype that I installed onto the roll bar itself. Below is version 17 (or so) of the design:

Because I couldn’t print the entire assembly as one component, I broke it up into four pieces and printed each one on my Prusa i3 mk2s:

I designed the components to both be glued and bolted together for added strength. The four pieces that make up each can assembly are shown below:

Once I see how it holds up over time and handles the sun beating down on the HTPLA, I will eventually tweak the design, reprint both cans and have them properly finished. By that time, I should also have a subwoofer box designed and installed too. Anyhow, here’s some photos of the design and installation after gluing, bolting and painting. I’m no automotive finish painter (unlike my cousin, Don), but as a prototype it is good enough for testing in the car.

Because a critical stress component is the clamp to the 1 3/4″ roll bar, I opted to use a machined aluminum bracket that I picked up on eBay instead of relying on the plastic to handle the stress. The bracket is fastened to the plastic assembly with two long bolts with flat and lock washers.

The shot below shows the long bolts to the clamp and the backside of the carriage bolts I used to reinforce the glued together can to the base assembly. I used carriage bolts as I could print a square opening to lock the bolts in place without using a hex wrench. Like the brackets, I used flat and lock washers to hold the chrome nuts in place.

The shot below shows the 3d printed can (left) and the wakeboard can (right). Note the difference in height and depth. The top clipped the back of the wakeboard cans.

Here’s the installed can on the driver’s side. I’m not installing a grill yet – that’s the next part of the project. I wanted to make sure everything fit, cleared the roll bar and was aligned behind each seat first. I may end up printing some wave guide-style grills to spread the sound from behind the seats.

And here’s what they look like installed behind the seats. The plexiglass in the middle is actually a smoked sun visor for a Polaris 4-wheeler. Now that the speaker cans are in place, I can get a custom piece of plexiglass cut and installed as a foldable wind deflector.