Subwoofer Box Construction

The construction of the subwoofer started late in 2010, delayed by several weeks of illness, Christmas, etc.  Many of the techniques I used are unique, some worked out, others did not. For me it is as important to create the methods and learn from the process as having the final project.  I will use these techniques to build future speakers, much more easily now that they are worked out.

The first step was to purchase a sheet of 3/4 inch maple plywood, and 2 sheets of 3/4 inch MDF. I cut the plywood to size, and the MDF slightly oversize.

Each of the walls is made up of a sandwich of 3/4 inch plywood on the outside, a 1/4 inch layer of foamed urethane glue, and a 3/4 inch layer of MDF on the inside.

Why the 1/4 inch layer of urethane glue? Well… the idea was to try to isolate the inner and outer layers, and provide some dampening of the walls.  This was an experiment, it seemed to work for smaller panels I glued up, but I do not think it worked for large panels as the glue is quite rigid when cured.  I do not think this  is worth doing, and I do not recommend it. (It is also expensive and time consuming  – I used 5 large bottles of Gorilla glue…)

Here I am gluing one of the panels.  You can see the glue foam bubbling up from a relief hole I drilled:

Next I milled each panel to size, and rabbited the edges so they would have a lot of glue surface.  Here you can see the dado for the divider (between the main box and the amp section).

Next I cut the hole for the driver in the front baffle using this circle cutter I made for my router:

There is a shallow cut so the driver will be flush with the surface, and deeper cut for the driver to fit through.  I cut quite a bit deeper so I could place the driver face down over this to test the fit, without hitting the surround.  I needed to do this before cutting the center of the circle away.  It turns out the driver was not perfectly rounds, so I’m glad I checked.

I finished the cutout from the back using a smaller diameter, as you must leave room for the t-nuts.  Then the inside was rounded over.

And the t-nuts are installed.  I did later add some epoxy so the t-nuts would never fall out, and inserted some 1/4 inch strips of wood at and between each location so the foam core would not crush when the driver was bolted in.

Then I assembled the box, one panel at a time with urethane glue:

Box glue-up finished including the divider.  The top will be left off till the end:

Next: Building the Corner Coving


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