In the summer of 1999, I built my first speakers: a subwoofer/satellite speaker system based on designs discussed on the internet. Originally I was only going to build a subwoofer based on the NHT 1259 12-inch woofer. However, after reading about a Linaeum-based satellite designed by William Eckle I decided to give it a shot.
My subwoofer is based on the popular (at least in the DIY world) NHT 1259 12-inch woofer, which is used in the NHT SW3 subwoofer. The enclosure is made of 1-inch-thick medium density fiberboard (MDF) and measures 21-inch square externally (19-inch x 19-inch x 18-inch internally) for a total volume of approximately 3 cubic feet. The enclosure is braced with 12 1-inch by 1-inch pieces of MDF in the corners, and joined between parallel walls (not shown on the drawing). All of the joints are butt joints secured with yellow carpenters' glue. I used 1/4-inch wood dowels, mainly to help me line up the pieces during assembly, although they do add strength to the joints.
I used pillow-stuffing-type polyester fiberfill for damping, which I later found to be the wrong type of stuffing to use. However since the performance of the sub is still quite good (IMHO, see measurements) I'm just going to leave it for now. I used 1/4-inch hex bolts and t-nuts to fasten the woofer to the baffle. I didn't caulk any of the enclosure joints because I figured between the glue, the wood putty, and the multiple layers of paint and primer, all of the joints are probably air-tight. I didn't use any gaskets other then the rubber already on the woofer basket.
I didn't build a crossover for the sub, my intention being to use the sub with an active crossover. The primary reason for this was I wanted a steep crossover slop with minimal phase penalties, and it gets difficult to do that passively (especially if you are a MechE by training).
The cabinet is made of 3/4" inch thick mdf, and measures 6.5-inch x 7-inch x 8.5-inch. Originally I tried to made the cabinet dimensions conform to one of the golden ratios, but I couldn't design a cabinet shape that I found pleasing. I eventually settled upon the current measurements, based on the statement in the Loudspeaker Design Cookbook which suggests that the effects of enclosure dimensions on standing waves would be secondary to the effects of properly damping the enclosure with an appropriate stuffing material.
The crossover is a first-order passive type, consisting of a 6.0 μF capacitor and .3 mH inductor as suggested by Bill Eckle, resulting in a crossover frequency of about 4kHz. I had designed a rather complex 2nd-order Linkwitz-Riley crossover, but decided at the last moment to keep it simple. I later had to add some resistors to bring down the tweeter level (relative to the woofer output) but I am extremely happy with the results.
As with the subwoofer, the satellite enclosures utilize butt joints, aided by wood dowels. I chose not to add extra bracing to the cabinets, figuring the MDF was thick enough that flexing would not be a problem. The woofer is counter-sunk 1/8-inch into the baffle, and the tweeter is mounted directly on top of the enclosure.
For the finish, I chose to go for the black-lacquer look rather than veneer mainly because I was not comfortable with the veneering process. I've since talked with several woodworkers who are experienced with veneering, so I'll likely attempt to add veneer to my next speaker project.
After assembling my speakers I used wood putty to try to hide the butt joints. I applied three layers of gray primer, sanding with 100 grit sandpiper between coats. I then applied three layers of gloss black spray paint, sanding with 220 grit sandpaper before the first two applications, then wet sanding with 300 grit sandpaper before the final application. I really should have applied at least 3 or 4 more coats of black paint, but my roommates were getting sick of coming home to a house full of toxic fumes. Finally I applied two coats of gloss varnish. Overall the finish came out fairly well.
I later added speaker grills to the speakers. The grill frames are made up of 1/2-inch quarter-round molding that I picked up at a hardware store. I bought loudspeaker fabric from a local JoAnn Fabrics store, and attached them to the frame using hot-melt glue. The grills are attached to the speakers using neodymium magnets. One set of magnets is glued to the grill frames. Another set is counter-sunk into the speakers. I have pictures of the satellite grills here.
You can also read about my DIY speaker stands
Click here to see the measurement results of my speaker system
If you want to try making your own speakers, here are some resources that will help:
Warning: contains relatively large jpegs: