Assembling the main structure
Here are some ideas for the final construction of the enclosures. First, dry fit everything before beginning assembly. Finding an 1/8" gap or overlap beforehand will save a lot of time when it comes time to sand and fill the joints. Also, I find it beneficial to have all of the wood for all of the enclosures cut ahead of time. If each cabinet is assembled right away, it is easier to figure out tricks to ease the construction. Building one at a time leaves more time to forget the difficulties of the construction, leaving the builder "reinventing the wheel". If all of the pieces are cut well enough, and if some thought has been put into the design of the cabinet, it may be possible to do some of the edge rounding before construction.
I like to use polyurethane glue to hold the whole thing together. I've used regular yellow glue and construction adhesive, all of which seem to work fine. Construction adhesive is better suited to an enclosure that will be heavily covered. Because it remains slighly flexible after it dries, the panels are allowed to move slightly, which can cause cracks in at the joints, through the filler and paint. Standard wood glue works quite well, but is a little difficult to remove after it dries. Poly glue has a couple of things going for it. First, it "foams" when it activates. This helps fill in any irregularities in the joints to provide a better bond, and to help seal the enclosure. Second, it is supposed to be several times stronger than wood glue, which has obvious benefits. The other nice thing is that it cleans up fairly easily. The foam scrapes almost completely off with a putty knife or large screw driver. The residue that remains sands off quite easily.
Along with the poly glue, use a liberal amount of wood screws to hold everything together. I like to use the coarse threaded screws. The fine threaded ones seem to strip out a little easier. I also predrill and countersink the screw holes so I am guaranteed the heads are below the surface. Predrilling also avoids the possibility of the screw "bulging" the adjacent panel, which takes a lot of time and effort to reflatten. It also keeps the screws going in at the proper angle and not shooting out the side! Sometimes it's handy to glue the panels and temporarily hold them in place using a brad nailer. Of course, those little things don't have much structural value, but to quickly hold a piece in place, it can be real handy. It's also nice because is won't throw the panel off from where you intended to fasten it. I find that when I screw two pieces together, I'm quite luck if they stay in the same position after the screwing is done. Brad nailing can help avoid that problem.
I use mainly butt joints in constructing my cabinets. I've built some using solid wood where I mitered the corners and installed the front and back panels in dado'd slots, but when using something like particle board or plywood that will be painted in the end anyway, butt joints are the simplest way to go. Another great option is a half-lap type joint. I've built a couple of enclosures using this method, and they have turned out by far the best. If all of the cuts are made accurately, the enclosure is mostly self aligning, which is a really nice feature. I doubt there is inherently any added structural strength with the half-lap joint. For a rectangular enclosure, I would highly recommend this type of a joint. For the slanted enclosures, I'm figuring it would be more work than it's worth.
Here's another tip that most people don't think about, but could save some headaches 6 months down the road - finish the inside of the cabinet! It sounds kind of odd, and maybe unnecessary, but believe me, you'll be glad you did (or sorry if you didn't). After building a few cabinets, I noticed that over the course of a few months, the joints were starting to show. After another 4 or 5 months, they didn't seem quite so bad. I was baffled as to why this was happening. I thought I could rule out himidity/climate changes because the enclosures were well painted. I couldn't see how the joints could have moved, after being glued and screwed like crazy. If finally dawned on me that the inside of the cabinet wasn't sealed, so the humidity changes could affect the wood from the inside. MDF, particle board and plywood are just as subject to environmental changes as solid wood. If not completely sealed, they will expand and contract with humidity changes. It's generally a very small shift (maybe 1/64" or less) but that can be enough to crack paint or filler. The result isn't very pleasing to the eye. A quick coat of paint, varnish, sealer or even oil can help prevent this. Sealed enclosures may be less susceptable to this kind of joint expansion, but it still couldn't hurt. It only takes a few extra minutes and at probably almost not cost. Trust me, it's worth it!
In a vented enclosure, it is very important that every joint is sealed well. This means sealing the joints from the inside with silicone or some other type of flexible sealer. Another necessity is sealing between the speaker frames and the baffle. Little gaps will result in whistling at higher volumes, which is definitely not desireable. Also seal around the speaker terminal, and any other joint like variable l-pads and ports.
The main part of the speaker cabinets are going to be painted. I've used many different types of paint in the past. Simple latex or enamel paints work quite well. I would recommend investing the $1.29 (or whatever) in a small 3" trim roller. This will give a much more even finish. The result is slightly textured and will cover irregularities pretty well. It's a lot more attractive than brush streaks. (I've had plenty of those in my days) Gloss paints show up irregularities to a greater extent than flatter paints. Darker colors will also tend to show up imperfections. Of course, the color and level of gloss is completely up to the builder, but the glossier and darker, the more work will need to go into filling, sanding and priming. For this project, I'm using a matte finish black paint. I have access to an air compressor and spray gun, which is probably the best route to go. This will be easier to keep clean than the ultra-high gloss piano finish. Fingerprints and dust don't show as bad on a flatter surface.
The last step in the construction of the cabinet is to mount the cherry side panels. Before installing, I took the time to finish them using a urethane based varnish. It is also a flatter finish, which will blend nicely with the matte paint of the rest of the enclosure. The panels are attached by applying a small amount of glue to the back and screwing from the inside of the cabinet. This is a rather difficult task as there is a rather small hole for access, and the internal dimensions are fairly small. I predrilled holes through the enclosure, lined the cherry panel up, and then marked the hole locations. That made it possible to drill some pilot holes in the cherry to make the assembly easier. Having a right angle drill would be real handy here!
All that's left now is to hook up the crossovers and install the drivers and terminals. Mounting the woofers (and maybe even the tweeters) using t-nuts is another good idea. If the drivers are removed a few times, standard screws will begin to lose their grip as the holes become enlarged. The t-nuts provide a solid mechanical anchor that won't ever strip. Before we finish installing the drivers, we want to line the enclosure with some sort of sound deadening material to keep reflected waves from exiting through the port. I've used fiberglass insulation in the past, and it works fine, but isn't much fun to play with. That type of material is better suited for sealed enclosures, anyway. Many people will opt for "egg crate foam", which may be one of the better options. I've had good luck with high density carpet foam, which is what I'm using here. It's relatively thin, easy to install and does a good job of deadening sound. This is installed on all sides but the front baffle.
With the drivers installed and everything hooked up inside, we're ready to kick back and enjoy the results.