NHT1259 Subwoofer Construction Details

Vital Stats

The final outer measurements for the subwoofer is as follows : It is 38 inches tall and is almost square in cross-section. The top measures 18.75 x 19.125, the middle is 15.375 x 15.75 and the bottom is 16.875 x 17.25. They tip the scale at over 105 pounds each. The internal volume of the enclosure after accounting for the bracing and driver magnet is between 2.7 and 2.8 cubic feet.

Internal Box

Each subwoofer consists of an inner chamber made of medium density fiberboard (MDF) and an outer layer for a finished look. Since the inner box is covered on all sides but the bottom, it need not look clean. The internal size of the box is 11.5 x 12.5 x 35 inches (D x W x H). The external size of the main box is 13.375 x 14 x 36.75 (D x W x H).

Building the box is rather straight forward. I used yellow wood glue on all glued surfaces, and in some instances, I used biscuits to help with alignment. Screws can be used to help hold stock together while waiting for the glue to cure. I used lots of clamps to yield the same results. For the front and bottom, I used 1 inch MDF, while the sides, back and top was made from 3/4 inch MDF. The use of 3/4 inch MDF was strictly a matter of availability, and I would recommend 1 inch if it is available.

Prior to assembly of the box, I cut holes in the bottom and front for a round terminal cup and driver respectively. The front baffle is also reinforced with 3/4 inch birch plywood for a total thickness of 1.75 inches.

Box assembly started with the 4 sides coming together. The front and back piece are 35 x 14; the sides are 35 x 11.5; with the front and back overlapping the sides during assembly. The tops and bottoms are 13.375 x 14 and overlap the other four sides. Since the driver is located a little below the middle of the baffle, ribs were placed above and below the driver as stiffeners. Ribs are 1 x 1 or 3/4 x 3/4 and are glued and screwed to all four sides. All seams are then caulked on the inside. There are many other possible ways of bracing the enclosure, some of which would yield a "deader" box. Nonetheless, I am happy with the results of my efforts.

Next, the terminal cup is mounted to the bottom and the seams are caulked. Wiring is added and the bottom is attached to the box. Lastly, the top is attached.

Exterior Box

The exterior is made from mahogany and 1/4 inch plywood veneered with imbuya. The veneer is glued to the plywood with yellow glue and pressed overnight to cure. Panels are made for the back, sides and top. For the front, I found brown grill cloth at Radio Shack that was almost a perfect match in color to the imbuya. The front grill is treated like the side panel, except that the veneer is replaced with the grill cloth. Since the grill must be placed in front of the driver by some distance, an additional 1 inch extension is added to the box on both the left and right sides of the driver. This squares the original box (measurements are approximate, thus my box is not exactly square). The side and rear veneered panels are glued to the inner box and mahogany trim is added on the corners and around the panel. For the front, the trim is attached to the grill so that it comes off as one. This grill assembly is pressure mounted and has no real fastening mechanism.

The top and bottom trim pieces are just block of mahogany cut with various profiles to create the finished look. Each piece is mitered at the corners so no end grain is visible. At the top, the trim covers the top veneered panel and forms a 1/4 inch lip on all sides. On the bottom, the trim is flush with the bottom of the inner box. Four wooden feet are then added to raise the speaker and allow wiring to reach the terminal cup. On both the top and bottom, trim pieces layered adjacent one another are chamfered with a block plane to provide a V groove at the seam. This not only enhances the look but helps hide any misalignments.

I finished the exterior with Danish Oil (natural) and wax; my wood finish of choice.

Other Possibilities

My subwoofers have achieved and surpassed my expectations both with their sound and their looks. They have added bass detail to the same music I have listened to for years yet never truly appreciated until now.

The pedestal design was a personal necessity. There are others that I have considered but never tried. These include placing the driver into a coffee or end table and hiding one into and under a couch. If anyone decides to try these ideas, let me know how it turns out.

29-September-2000

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