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Sealed Vifa Bookshelf Speakers
An easy to build, flat frequency response 2-way bookshelf speaker.
Next: Crossover and Testing
Introduction
My parents wanted a pair of speakers, and I was itching to build some, so the time was right. After looking at various drivers on the LDSG at Snippets (a wonderful resouce - thanks Bob!) and modeling them within WinISD and other programs, I finally settled on a design which I found on the web. John K. designed it, and it can be found here. I don't know John personally, but I sure do appreciate his most excellent speaker design efforts, and his web postings describing them - thanks John!
I'm kind of partial to sealed 2-way satelites mated to a sub, since the sats are generally small and easy to position. And the sub can be on the floor near a room boundary where it is radiating into 1/4 or 1/8 space, which increases its efficiency and reduces room modes. I may build a sub for these speakers at some point, but for the time being my parents don't need the copious amounts of bass that we listers do, so EQ may be enough for now. This article describes how I built the cabinets and the crossover.
Cabinet Construction
The cabinets are just 3/4" BC plywood, hand selected for flatness and lack of blemishes. You'll need either two 2' x 4' sheets, or one 4' x 4' sheet. You could also use birch plywood, and I'll probably do that for my next project. MDF or particle board will require some additional type of finishing such as veneer or fancy paint.
Am I the only one who thinks ordinary pine plywood can make a pretty good looking speaker cabinet when varnished? Seems like no one ever uses it, but I like the zebra effect of unstained plywood. Particularly with a true clear finish which won't cause that "amber" effect. I use an acrylic finish here. Many coats are necessary, but they dry fairly quickly, and cleanup is a snap.
Day One
I'm no superman and so will admit that it took me a day just to cut out the wood. And after the cutting I was too worn out to do any glueing. If you use a radial arm saw to make the cuts, try to make all finish cuts with the same setup. Half of the cuts with this method are finished, and half have oversize which will be trimmed after construction. This gives you some leeway during assembly, and makes for very tight joints. I cut the large corner notches with a dado blade set to maximum wobble in one pass (Ooo, scarey!) after the pieces were cut to size.
Day Two
Here you can see how I glued and clamped the sides together using fender washers and drywall screws. This is all I did on the second day since the glue needed to dry for 24 hours. The washers are 1" outer diameter with 1/8" hole, and are zinc plated. The screws are standard issue 1 1/4" drywall types. I pre-drilled the sides 9/64" so that the screw could ealsily go through, and then predrilled the top and bottom pieces 3/32" (through the holes in the sides) so that the screws would start easily and wouldn't splinter. Use some uniform spacing here, as the puttied holes will be somewhat visible on the finished speakers.
Figure 1. Sides, top, and bottom glued and clamped together.
Figure 2. Detail of the corner joint, and the washer-screw clamp. The clamps will be removed when the glue is dry.
Day Three
The fender washer / drywall screw clamps are removed and the sides are flush cut to the top and bottom faces. It helps to relieve the corners so that they don't splinter out when trimming.
I used a laminate trimming 5/8" two flute carbide bit with ball bearing guide (Stanley 85430) here for flush cutting - really works like a champ!
Once the sides are routed flush, take a piece of coarse sandpaper and wrap it around a long stick. Hold the sandpaper tight while you use it to level the gluing surfaces. Keep the non-abrasive end of the stick on the surface so that flatness is preserved.
Glue and clamp the baffles to the sides and top and bottom assemblies, then let dry for 24 hours. Don't forget to pre-drill the holes.
Spread some glue around the joints on the inside to seal them. Another coat will probably be necessary after the first dries and shrinks.
Figure 3. Relieving the corners with a rasp or file makes trimming with the router easier.
Figure 4. Sanding stick to make the joining surface flat, particularly at the corners.
Figure 5. Sanding stick in use - remove saw marks, and level the corners.
Figure 6. Speaker baffle glued and screwed to the top / bottom / sides assembly.
Figure 7. Use the same glue to seal the joins on the inside.
Day Four
Remove the clamps from the baffle, and trim using the flush cut router bit. Again, relieve the corners beforehand to reduce splintering.
Next, cut the speaker countersinks with a router and circle cutting jig. After the countersinks are done, cut the speaker through holes with the same setup. Practice in a scrap of wood or, I guarantee, you will screw up. For the tweeter, the countersink should be 104 mm diameter by 4 mm deep, with a 83 mm through hole. For the woofer, the countersink should be 171 mm in diameter by 4 mm deep, and the through hole should be 146 mm.
Cut some scrap, plywood or pine or whatever you have handy, in order to brace the rear of the speaker baffle between the woffer and tweeter. I used a 3/4" thick x 2 1/2" ( 1" x 3" nominal) piece of cedar that was laying around. Two 3" drywall screws and some glue fix it to the rear of the baffle.
Glue and clamp the backs on at this point using the same procedure as that used for the baffles. Add some glue to the internal joints in order to seal them.
Figure 8. Clamps removed and trimmed with laminate flush cut router bit - joints don't come much tighter than this!
Figure 9. The countersinks and holes for the drivers were done with a router, 1/4" bit, and circle jig. Practice scrap is shown.
Figure 10. Another view of the driver countersinks, note mirror image for left and right.
Figure 11. 1" x 3" brace glued and screwed to the rear of the front to reinforce this thin area.
Figure 12. The backs are glued and clamped.
Day Five
Remove the clamps from the backs and trim flush, relieving the corners beforehand to reduce splintering. After that, route the countesinks and through holes for the connector cups. I cut diameter 105 mm x 4 mm deep countersinks and 78 mm through holes for the larger "D-cups" from Madisound.
Round over the corners with a 1/4" router bit (carbide with ball bearing guide) then fill all holes and any other obvious indentations with wood dough (Elmer's Professional Carpenter's Wood Filler).
Figure 13. Backs trimmed flush, cup countersinks and holes added, and 1/4" radius cut on all outer edges - all with the router.
Day Six
Second coat of wood dough (the first application will have shrunken).
Day Seven
Sand the boxes first with coarse (80 grit), then with medium (100 grit), and finally with fine (150 grit) sand paper. I recommend that the coarse sanding of the baffles be done by hand with the sanding stick so that they remain flat. Get all of the pits, fissures, and pencil marks off with the coarse paper, then remove the scratches of the coarse with the medium, and so on. If your sander gives you the option of straight line or orbital motion, do the coarse sanding with straight line action with the grainand the medium and fine sanding with orbital. Coarse sanding against the grain tends to rip up the wood.
To keep the box from having the crap vibrated out it during the sanding, and to protect the bottom side in contact with the work surface, place a rag between the box and the work surface. This seems to absorb a lot of the vibration.
Figure 14. Sand on a scrap piece of plywood with a clean rag under the speaker. (Dig the zebra look!)
Use a vacuum to remove the sanding dust from the inside and outside the boxes, and dust them off with a brush, a clean rag, and finally your bare hand. Arrange some way to hang the boxes so that they can be varnished on all sides. I used string through the speaker cutouts and some nails driven into a shelf in my garage.
Apply a coat of acrylic varnish with a cheap foam brush. I had some Minwax Polycrylic clear satin finish left over from building my sub a couple of years ago (getting the top off was a bear!). Start on the back of the box, then do the sides and top and bottom, and finally do the baffle. The first coat went on very thin and dried to the touch in less than an hour. I applied a second coat after an hour or so, and then hung them up to dry overnight.
Figure 15. Speakers hanging up to dry. (The amber cast here is due to the low afternoon sun, and not the varnish.)
Days Eight & Nine
Apply a coat of finish in the morning, then another in the evening. Try not to let the varnish dry for more than 24 hours between coats. If that happens, sand the cabinet lightly before coating (see below).
Day Ten
Sand the boxes lightly with 220 grit or finer sand paper wrapped around a rubber eraser, remove drips, bumps, and specks, and then apply the final coat. You might want to use waterproof silicon carbide paper and water to do the sanding - a little bit of paper will go a long way with this method. If you wet sand, let the sanded finish dry for a couple of hours before applying the final varnish coat.
Next: Crossover and Testing
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