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Cutting Panels to Size |
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Outdoors, I rough-cut a sheet of 3/4"
thick MDF into smaller pieces
using a circular saw and straightedge. The pieces were cut a little
larger than needed.
After this rough cutting, I took the
pieces to my table saw to cut down to final size. I built a crosscut sled for
my table saw that helps keep cuts square, as well as
providing a handy stop so that sequential cuts are almost identical in
width. Click the picture on the left to enlarge the crosscut sled photo. |
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Joining with Biscuits for
Good Alignment |
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While there are many ways to assemble
cabinets accurately, I prefer using biscuits. A slot is cut on the
mating surfaces of two or more pieces, and a flat, pressed-wood biscuit
is inserted into the slot to key the pieces together. Accurate layout is
needed, and when cutting slots, I always register on the outside surface
of each piece. |
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I've constructed a jig for my
Porter-Cable biscuit cutter that speeds this work. The pieces being cut
rest on a large flat surface instead of the small fence of the biscuit
cutter. Here, I'm holding a piece about to be cut with another piece for
safety. I don't like to have my hands close to the cutter in case
something slips. |
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The faces of some panels are cut with
slots, while the edges of other panels have them. This photo shows slots
being cut into the face of panel. I
deviated a bit from John Krutke's plans for the cabinet - I wanted to
have the sides of the sub continuous (no joints), and to have all the
joints come together on the top and bottom panels. I can then
double-veneer the top to keep the joints from telegraphing. Since the
bottom doesn't really count, having only one surface with all the joints
on it means less work when finishing. |
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To allow for a compressed gasket, I
placed a piece of stout cardboard on a piece of MDF to space the slots
for the baffle mounting frame accurately. I couldn't use my biscuit
cutting jig here, but it's still a big surface on which to rest the
biscuit cutter. |
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Assembling the Amp Box |
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To ensure that the amp box parts are all
exactly the same width (desired for good air sealing), I used a
smoothing plane on them. Clamped together on a flat surface, the plane
shaved them to the same dimension. |
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The sealed space for the amplifier was
created by the poplar boards glued and
screwed into an H frame. |
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When the H-frame was dry, it was glued
to the back panel. I used no biscuits here because I couldn't easily
figure out how to register them. Besides, the long ends of the H frames
would also be glued to the top and bottom anyway, and that's
sufficiently strong. In this
picture, I had already used a Bosch jigsaw to cut out the opening for
the amplifier on the back panel. |
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Once the H-frame was attached, I cut a
piece of 1/2" baltic birch plywood to cover over the space. |
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Marking Amp Box Mounting Holes |
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With the plate amplifier centered and
taped temporarily in position, I used transfer punches to mark the
locations of the mounting screws. Once marked, the amp was removed. |
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Assembling the Baffle Mounting Frame |
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A rectangular frame of poplar wood
recessed into the box provides a mount for the baffle. Small "face frame"
(FF)
biscuits were used to join the frame. Larger #10 biscuits hold the frame to
the inside of the cabinet. That puts them in shear for the baffle
mounting load, which is ideal. |
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The baffle mounting frame was glued
together as a sub-assembly. Five-pound lead weights helped maintain a
level face for the glue-up. I was very careful to maintain squareness
during glue-up. I checked it with a 12" Starrett combination square just
after clamping, and made small adjustments until perfect. |
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Brace Fabrication |
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John's design uses a unique set of
internal braces made from 2x2 lumber. His design information gives an
explanation, and he claims that it is ideally suited for a symmetrical box like
this one. It IS easy to fabricate these braces! |
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After cutting the 45* miters on each end of
the braces, I used a drill press to cut counterbores
for the screw heads and then drill the through-hole. I used a Forstner bit for the
counterbores, and then
used the "dimple" left in the center as a guide for the
through-hole. I used a drill press fence and fence stop to aid this
work. If limited to a simple hand drill, I'd just drill the
through-holes and forget the counterbore. |
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Inserting Baffle Mount T-Nuts |
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I purchased 1/4-20 T-Nuts from a local
hardware store for the baffle mount. The T-nuts have prongs that
penetrate into the wood to keep them from spinning when bolts are
tightened. I press them in using a c-clamp, and use a little Gorilla
glue to ensure that they don't pop out. |
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Baffle Fabrication |
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Every cut is drawn onto the surface
before routing. It reduces the chance for mistakes. I use my old
drafting compass with an extension beam for this work.
After layout, I drill a 1/8" hole at the
center of each circle for the circle jig pin. Usually I do this on the
drill press to ensure a hole square to the surface, but this
baffle was too big for my drill press to "reach" into the center. I use
a hand drill instead with a simple block of wood to aid drilling the
hole straight. See a photo of the wood block on a drill further down the
page. The block of wood has been drilled square on the drill press, and
it works fairly well as a guide. |
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Routing MDF is messy. I try
to do as much routing outdoors as possible. I can use a leaf blower to
clean up afterwards. Shown is the
large Jasper Circle Jig on a Bosch plunge router. A 1/8" pin serves as
the center of rotation for the router with jig attached. One baffle
front is shown in the background of this picture with the driver recess
and through-hole already cut. The inner baffle is shown about to be routed.
I use a 1/4" spiral upcut bit to cut the
through holes. The bits are Bosch brand, purchased from Lowe's. I had
trouble with Freud bits in the past. Each cut is about 1/8" deep, and
they progress until the hole is through. The turret-style depth stop on
the Bosch router is ideal for incrementing these cuts ever deeper. |
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For this job, I used double-stick tape
to hold the pieces to a backing board for cutting. The tape's purpose is
to prevent the center piece from coming adrift when I cut through the
MDF, which may cause an unplanned divot cut into the part. The backing board, of course, prevents the router from cutting into
the work table. |
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To mount the driver, I'll use hurricane
nuts on the back side of the baffle. To mark the holes for their
location, I shimmed the driver to the center of the recess using pieces
of cardboard, then lightly punched dimples into the MDF using a transfer
punch. The punch centers on the driver's screw hole for an accurate
layout. The driver must not move between punches in different holes, and
the shims combined with a 25lb driver were sufficient. |
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To provide sufficient airflow around the
back of the driver, it's customary to cut relief chamfers into the back
of the baffle. Full thickness is needed in the lands where the hurricane
nuts will be pressed in, but the in-between areas need to be chamfered
away. In pencil, I marked the future location of the hurricane nuts so that I
knew where to stop cutting. |
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A router table with a 45 degree chamfer
bit cut the chamfers. A handheld router could be used, but a router
table allows a little more control. I had built this router table last
summer, and I was determined to put it to use. |
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A picture showing the chamfered areas
between the hurricane nut "lands" during cutting. Note the ultra-fine
sawdust from the MDF. I had a shop-vac attached to the router table, but
it's not 100% effective. It helps, though. |
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The chamfers are complete. Especially
needed in thick baffles, chamfering aids the airflow behind the driver. |
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This detail shows how I had
pin-registered the inner baffle to the outer baffle. This was done prior
to routing the holes so that I could work with the pieces separately.
Then, when routing was done, the two baffles lined up perfectly again
when assembled together.
I put two pins in the baffle on opposite
ends of one of the diagonals. Pins locate better than screws, which
serve merely to clamp the two pieces together. Note that the pins were
already in place when I routed the chamfers in the driver cutout, but I
didn't show this detail in an earlier step.
I purchased the 1/8" steel pins in a box
of 100 from
McMaster-Carr online. They also serve double-duty as spare pins for my
Jasper circle guide. |
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I checked the alignment of mounting
holes for three mating items - the baffle mounting frame (shown on top here),
the inner baffle which nestles inside the cabinet, and the outer baffle.
All screws went in fine without serious binding that might be caused by hole location
mismatch. I was a little concerned about matching up three pieces well
enough, but
it turned out OK. |
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Time to press in the hurricane nuts that
hold the driver to the baffle. Again, I used a c-clamp to squeeze them
into their appropriate holes, and I added a couple drops of Gorilla glue
to make sure they don't spin in place when screws are inserted.
Note the use of an old plywood 90 degree jig to hold
the baffle upright for this operation. It seems that I never throw anything away, and
some unused things come in handy even after years of gathering dust. |
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Gluing the Cabinet Together |
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Dry Fit: The first task before gluing
everything together is to do a test fit without glue - a "dry fit". The
biscuits make this a "snap-together" test. They hold things in position
well enough so that I don't have to juggle a pile of loose parts. |
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Here's a chance to assess the fit of
mating parts before gluing. A tight-fitting joint is desired, and all
joints in this project looked fine like the picture shows. After the
check, everything is taken apart again for gluing in steps. I usually
glue up subassemblies in larger projects like this one. |
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In this photo, the rear panel and the
bottom panel are being glued together. I used the right side panel, with
biscuits in it, to align the bottom and rear panels correctly. A piece
of waxed paper placed at the joint prevented the bottom/rear subassembly
from gluing itself to the right side at this time. Not shown in the
photo is that I also snapped on the other side panel (would be located
on the top at this orientation) to also locate the glued panels for
assembly. |
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After the two panels shown above had
dried, I then glued and clamped the baffle mount frame to the bottom
panel. The other panels pictured are there merely to have their biscuits
align the assembly in the proper location for drying. Slips of wax paper
keep squeezed-out glue from sticking to the panels used to register the
assembly. After the glue dries on the other panels, they were
removed, and glued together later in separate steps. |
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When the baffle mount frame glue had
dried from the previous step, the top panel was then glued to the
subassembly. I am getting ready to glue in this step, and the panel
partially shown on the left of the photo would be used to register the glued
pieces to keep things square. The panels themselves become part of an
assembly jig. |
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Because one side was still detached, I
had ample room to start adding some of the internal 2x2 bracing with screws and glue. It was
easier at this point because there was room to work, but I could
have waited until the end. There are
still more braces to attach, but that can't be done until after final
panel is glued on. |
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Regardless of the care taken beforehand,
there are always slight mismatches between adjacent surfaces after
gluing. I used a small block plane here to quickly level a small
mismatch between two adjoining panels. It's faster than sandpaper, and
likely more accurate because of the dead-flat bottom on the plane. |
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The final panel is glued on. Not all clamps are shown
in position yet. I still had to attach several small 6" clamps to the
interior baffle mounting frame to secure it against the inside of the panel
shown at the picture's left. |
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Final Assembly Details |
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Attaching the plate amplifier to the
back: drilling pilot holes square into stock without a drill
press is challenging. To provide a "portable guide", I pre-drill a clearance
hole in a small block of wood with my drill press. To use it, I put it
on the hand drill with bit, position the point of the drill in a
punched "dimple", slide down the wood block until it's flat against the
surface to be drilled, and that guides the drill in straight.
I prefer to use German-made Colt drills (when
possible) with wood or MDF. The brad point of the drill reduces bit wander when
drilling deep holes, and they are very well made. Unfortunately, they have
only 1/32" increments between sizes. I'd prefer to have 1/64"
increments. They still got the job done nicely for these pilot holes though. |
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Installing gasket material onto the
driver. I used Parts Express #260-542 speaker gasket tape. It comes
in a 1/8" thick x 1/2" x 50 ft. roll. Tip for first-time
users: it won't bend around curves until you remove the paper backing. |
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I used #10-32 flat head socket screws
(1-1/2" long) to mount the driver to the baffle. The driver mounting
ring counterbore for the screw head measured 0.390", and the #10 FH
screws have a 0.385 diameter head. That provided a nice, tight fit. [I
don't remember if I had to enlarge the hole in the driver rim to clear
the #10-32 threads.] |
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First Sound |
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First impressions: It is a BIG box. It
weighs about 70 lbs, and I
wrenched my back moving it into position. The sound is impressive though. It digs deep enough to make my pant
legs flap in the breeze when playing bass-heavy material like
Herby Hancock's Dis is Da Drum or Virgil Fox's The Bach Gamut
organ music. There's some rolling, deep bass in Beats Antique's
Tribal Derivations (track #6 - Derivation) that becomes very
audible with this employed. It's not just audible, it's tactile enough
to feel. In some cases, it makes your head feel funny.
I haven't trimmed the baffle edge flush with the
sides of the cabinet yet, so it's very ugly right now. I won't trim it
until I know whether I will paint or veneer the cabinet. Veneering adds
thickness to the box, so a flush trim of the baffle at this point would not be flush after veneering. Paint
is cheaper, but requires a lot of prep time. Decisions... |
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My big problem now is where to put it in
my room. It commands attention out in the open. One option I'm
considering is to make it into an end table, with the driver firing
downward. I'd likely have to move the amp to an external location on the
equipment rack and probably build separate box for it. If I chose this
route, I'd fabricate a table top from solid wood
and attach it to the subs' current back side. The back would then become the top. I've seen very nice, furniture-quality examples of
this approach on the internet, but it would be a lot of work to do.
Finishing always takes longer than building! |
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