Where to begin.... I suppose a disclaimer. Yeah yeah,
I'm tired of those too, but they're important for contextualization. Ultimate
Bass Cabinets is something of a misnomer, as there are bigger,
stronger, higher output cabinets out there. And not just a few but many, both in
DIY and in commercial products. There are exotic materials, brute force
approaches with 6" thick walls, cabs the size of Volvos (and larger) and horns
big enough to park a Volvo inside. Most of these are extremely expensive , time
consuming, and difficult to produce. This article focuses on the build process
of some very well-done cabinets that work with a wide variety of bass drivers,
and effectively address many of the problems that exist in a typical enclosure.
These problems include panel resonance, internal reflections, and external
diffraction. This cabinet design is carefully balanced between cost,
performance, and practicality. Ultimate practical bass cabinets just doesn't
have the ring of Ultimate Bass Cabinets.
Time is money, so if you are interested in cost savings look
elsewhere. These will take some significant time to do properly. You must enjoy
the process for this project to be worthwhile.
In my case, I wanted to create a rounded external shape for both performance and cosmetic reasons, and do it in solid wood material (well, plywood) without the hassles of a laminate construction. This meant the use of mass-produced round wood materials, specifically, a half-cylinder shell of plywood, and millwork joinery that creates a large-diameter round-over. The combination of these components resulted in the requirement of a complex shape of a joined semicircle and trapezoid for the shelf bracing, and a little extra effort in terms of filling, joining, and finishing compared to a "normal" box speaker with the internal baffles, but is otherwise not terribly difficult. The result is that we have the longest diffractive surfaces properly dealt with to avoid response ripple, and only have 1 set of parallel walls in the enclosure- top and bottom. Multiple shelf braces and other structural components contribute to the rigidity, and help create a well-optimized acoustic environment. The shelf braces in particular are designed with large windows to allow free airflow without significantly compromising rigidity, and also provide a method of breaking up any top-bottom standing waves.
1. Plywood Half Cylinders as
seen at this link.
2. MDF millwork L-columns: as
seen at this link.
3. Baltic Birch or other high-quality
plywood (Appleply, full-hardwood ply)
4 Gorilla Glue (or other expanding
5. Shellac based primer
6. Veneer or paint
7. Removable mounting hardware
(T-nuts, screw inserts, or other fixed socket materials for screws)
8. Gasketing material for driver
1. Tablesaw or circular saw
2. Misc. Grit sandpaper (a random
orbit sander would be helpful here)
3. Router with roundover and/or bevel
4. Others will be needed
First step is to trim the millwork to appropriate size. The
cylinders are 31" high, and their form will not be modified in any way.
Accordingly, all heights are 31" to match. You'll want to use some sort of
chopsaw/mitresaw to do this, a normal tablesaw will be difficult to do
effectively due to the thickness of the material. MDF is NASTY stuff, and the
dust is extremely fine and will get into your lungs and/or sinuses any way they
can. Wear a good mask.
Now that you have this, you're going to test fit the pieces, and get a precise measure of the front panel as it will be once mounted. There's only 1 way to fit these pieces together, so this is self-explanatory. Following this, you'll trim some 31 1/8" x Gapwidth panels. You want a tiny bit of wiggle room left on the width to ensure that when you clamp it up you can get it aligned well.
Now you have a pair of front panels, a quad of front MDF
millwork roundover posts, and two shells. Assembled, these would make two
misshapen tubes. The next piece is the top and bottom panels and shelf braces. A
top and bottom can be applied on top of these tubes, but a well-done inset panel
makes the rest of the assembly easier, and you need the oddball shape anyway for
You can see the ribs, the shelves, and the white paint there
for your viewing pleasure (actually it's shellac-based primer, great sealant).
To get the braces as described to fit in, as well as for attaching the
edge-round, strap clamps are used.
I used recycled denim "Ultratouch" damping material, held in place by the ribs and vertical struts, with a slight airgap between the shell and the damping (spaced away by the ribs). Depending on the woofer and alignment you choose, you'll want to tweak your stuffing to match.
From there, the requirements get much easier- you can do driver cutouts, stuff and vent to taste on the flat front baffle. I allowed the baffle to remain proud of the "squashed cylinder" form, with beveled edges, as this was the most convenient for iterative testing. For some of you, this won't be necessary. I leave it to you. For me, this meant I needed a panel that would accept the removable baffles for the driver and venting arrangements.
As you can see, there are gaps for both the driver and for a panel allowing me to swap out venting/sealing options ad nausea. If it matters, 37 Hz tuning or thereabouts is my favored point with pro woofers like those in my woofer testing article. Vents have a bevel around their output. The termination helps keep vent noise low.
Paper backed self-adhesive cherry veneer was used for the horns and the main cabinet bodies. Self-adhesive applied with a scraper is the preferred option here due to the curvature. Below you can see that the veneer follows the curved edge nicely, and you can also see the mounting ring initially used (since eliminated) for driver mounting. Cherry darkens up quite a bit with exposure to sunlight and oil.