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NHT1259
Subwoofer Construction Details
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.
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.
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.
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
Note: The
contents in these pages are provided without any guarantee,
written or implied. Readers are free to use them at their
own risk, for personal use only. No commercial use is allowed
without prior written consent from the author.
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