How To Make Bookshelf Speakers General Woodworking
I’m making some changes to my office to be a bit more comfortable for me to use. Right now the room is completely cluttered and I’m cooped up in a corner between the computer desk and the wall behind it, and I’d much prefer a bit more space to stretch out.
There will be several projects involved with doing this and probably the one I’d need last is this pair of speakers, so naturally I want to do those first!
To get started, I made a model in SketchUp to work out the construction details and get the approximate proportions:
There are several factors that determine the size of the box and the first is the speakers that will be used. Speaker box design is a fairly involved process that uses the performances specs of the woofer (the Thiele / Small parameters) to calculate the ideal internal volume of the box and whether it should be vented (bass reflex) or sealed.
I’m using woofers (known in the biz as drivers) that I bought more than 10 years ago for a project that never materialized, and they will work in either alignment. I chose to go with sealed mainly because the box could be smaller. And since these are primarily monitor speakers for video editing, they don’t need the stronger bass response that a vented design gives.
“Be warned: it’s a rabbit hole”
If you are interested in more of the nuts and bolts of speaker box design, there are several reliable resources online. Be warned: it’s a rabbit hole and there’s a lot more to it than most people realize. I use an Excel spreadsheet called Unibox to design the ones I’ve made, but you need a good fundamental understanding before you can use it effectively.
Another important factor was that I wanted to make these from a single 8 foot long board of rough cherry. Typically, solid wood should not be used to make speaker boxes because it’s prone to seasonal changes in humidity that cause it to shrink and swell. But there’s a work-around for this, and that is to use it for the top, bottom and sides only, and use plywood for the front and back. This allows the solid wood to expand and contract with the seasons unconstrained (actually making the speakers slightly longer and shorter from front to back), so that no gaps or cracks will form.
So using solid wood presents problems that you don’t have when using sheet stock like plywood (or MDF), and it also adds processing time to the build. Taking rough sawn lumber to a dressed state isn’t trivial and unless you really like working hard with hand tools, does require machines that may not be in the average hobbyist shop. I used my homemade jointer to flatten the stock, and my thickness planer to bring it down to final thickness. I also used my homemade band saw to re-saw the boards to get matching veneer for the front.
Speaking of that veneer, one of the first steps is to glue that to the Baltic birch plywood front baffle. I used polyurethane construction adhesive for its strength and slow dry time:
I spread it out thin, laid on the veneer and then clamped up both of the fronts at the same time:
I used the plywood blanks for the back panels as clamping cauls to help spread the pressure from the clamps evenly. I left those to dry overnight before moving on to the next part of the build.
Where the top and bottom meet the front there’s a miter that needs to be perfect, so I cut a sample on the table saw to check that:
Satisfied with how the sample looked, I made the cuts:
Note the grain orientation from the top (solid cherry) to the front (veneered plywood). The sides, top and bottom must have their grain direction lined up to wrap the box and allow for seasonal expansion and contraction. The veneer glued to the plywood front panel (baffle) is thin enough to be completely constrained by the plywood and won’t expand and contract.
To clamp the miters I’m using strong tape across the seams:
And with the glue in the joints, I used one of my wooden bar clamps to hold them closed with light pressure:
I used regular wood glue for this and let it dry for several hours before removing the clamp and tape. From here on this will be known as the center assembly, made up from the top, front and bottom.
Not a bad fit on the miter joint, considering it was done with a homemade table saw made from a hand-held circular saw:
There were a few different ways I could have put this box together, but I opted for the most practical – simple butt joints between the center assembly and the sides. While I’m pretty sure the glue alone would have held it, I decided that adding some mechanical reinforcement in the form of a long spline wouldn’t hurt. I used my router table to cut the slots:
And made the splines from some scrap 2 x 8 spruce:
The grain orientation of the splines is critical – it has to match the the wood it’s joining, otherwise it will try to constrain the seasonal movement of the wood (and fail):
I used polyurethane construction adhesive to assemble the sides to the center section. The big advantage is the long open time, giving me plenty of time to get the glue spread, the parts aligned and the clamps in place:
Using all seven of my wooden bar clamps to clamp up both boxes at the same time.
The next day I scraped off the excess glue and sanded the boxes smooth on all sides:
Thorough sanding is critical for a piece that will get any kind of stain treatment, since the stain will sink into the scratches left by a poorly done sanding job and be highly visible. I started with 100 grit on my random orbit sander, then hand sanded 100 grit with the grain over the entire box.
There are several ways to secure the back, but only two that I think are practical: one is to cut a rabbet, and the other is to install cleats:
The cleats are just pinned in place and basically stop the back panel from going all the way in. I spread glue around the sides and pushed the tight fitting panel in, and that carried the glue onto the cleats as well:
The clamps lightly tightened to keep the panel flush on the back until the glue sets. Note the two holes – these are for the banana jacks that are the electrical connection for the speaker.
Time to layout the divers to get the best placement. A 5″ sanding disk stands in for the tweeter:
To cut the flange recess, I used my simple circle cutting jig on the cordless router:
I made a sample on a scrap piece of plywood first to dial in the fit. There needs to be some space for the thickness of the finish used on the box, so it can’t be too tight.
I also used the same router setup to cut the hole, but didn’t go all the way through. I left a thin sliver at the bottom to prevent the center from coming loose and messing up the cut:
A nice fit – flush with the surface and just the right diameter:
Now on to a significant problem with the tweeters I have for this – they are in rough shape. One has had a thin layer of foam torn off its face, while the other has been resized smaller:
Again, I’ve had these forever and I think I got them from a pair of homemade speakers I bought at Goodwill. The tweeters are good, they just look bad.
I decided the best way to fix them was to make new face plates from 1/8″ aluminum. I drew a 5″ diameter circle using my new compact compass:
Then roughly (very…) drilled out the center with a hole saw:
I didn’t think it would be that rough, but that will be cleaned up later.
I then cut it out with the jigsaw as close to the line as possible:
To clean up that hole, I drilled a 1-1/2″ hole in a piece of plywood and used double sided tape to hold the aluminum in place:
A round over bit in the router does a respectable job:
Worth noting the the aluminum finishes better when you do a reverse pass with the router bit, also know as a climb cut.
On my belt / disk sander, I ground off part of the flange on each tweeter so that they would be the same outside diameter:
The random orbit sander cleans up the surface of the face plate nicely:
So much so that I considered leaving it natural:
But went with the classic flat black instead:
I used polyurethane construction adhesive to glue the new plate to the old face of the tweeter and left that to dry overnight.
With those done, I could cut the recesses and holes for the tweeters:
Note the towel on the workbench collecting dust. I have this mainly as a pad while sanding the speakers.
Before the first coat of linseed oil was applied, I rounded over the front edges of the sides and again sanded the box thoroughly using 220 grit this time:
Rounding the corners is traditionally done to reduce diffraction, but the audibility of this effect is questionable. Certainly given the state of my hearing at present, I wouldn’t be able to detect a difference. Instead, I did it more for the way it looks – it makes the box look less boxy.
I let the linseed oil dry overnight and gave it a light sanding with 400 grit before applying the first of several thin coats of a danish oil blend. The oil has a small amount of cherry stain mixed in that will get into the open grain of wood and accentuate it. And since cherry will naturally darken over time, this gives it a head start on that:
I wound up putting four coats of the tinted oil to get the colour that I was looking for, and then finished up by spraying on two coats of clear polyurethane:
I used a spray because it’s fast drying and I needed to get the speakers “ready” for the video and this build article in time for my self imposed deadline of Sunday morning.
To install the drivers, I had to paint some #8 flat head screws black:
Of course I’ll have to take them out again to wire them up and install the crossover that I haven’t made yet, but they look finished and that’s what’s important:
The somewhat wild grain variation of this particular piece of cherry really makes these interesting, and the tinted oil did a lot to bring that out:
I’m very happy with the work done on the tweeters – time well spent to resurrect these and the size seems to be just about perfect:
The dome on one of the woofers had a dent that I pulled out by using my small shop vac. The trick is to hold the hose tight to the dome then brifly switch the vac on and off again.
For those of you who are curious, the woofer I used is the Vifa PL18WO09. Vifa no longer makes these, or any other individual speaker drivers anymore. The tweeters were made by The Canadian Loudspeaker Corporation under the brand Max Fidelity, which now seems to be out of business. However, both woofer and tweeter are well above the average as far as build quality and frequency response is concerned.
And on the topic of frequency response, I need to make a crossover for these, and that project is next.
Here’s the build from start to finish: