How To Make A Sound Bar Fun & Interesting
The house I live in now is considerably smaller than the one I had before this, in particular the living room. And while the speakers I made several years ago are not huge, they are a bit too big for the space I have now, so I decided to replace them with a sound bar mounted directly below the screen.
This will free up some space and also scratches my speaker building itch. It’ll also run cooler (very important in a smaller, well insulated house in the summer) as a small class D amplifier will power it.
I started by cutting out all of the parts from 1/2″ MDF. Not my favourite material to work with, but usually the best for a painted project like this. All of the joints between the sides, front and back are rabbeted, and I cut those on the table saw:
With the sides glued to the front, I put the back in temporarily to provide support while it’s clamped:
After the glue set, I added the end panels and a divider in the middle to separate it into two compartments:
This is, after all, two speakers in one box. The divider also gives the box some bracing in the middle.
I ran a bead of glue along the joints inside the box to help seal it and add some strength:
“I really should have been a bit more selective when I did, since I had to make the enclosure of the sound bar a lot bigger than I originally envisioned…”
While the glue is drying, let’s talk about the box design. I use a spreadsheet called “Unibox” to design the speakers I make and find it to be completely reliable.
When I first had this idea to build the sound bar, I ordered a different woofer (actually a full range driver, but acting as a woofer in these), but it was out of stock and on back order. And after waiting for nearly 3 months for it to come in, I substituted it for another one.
I really should have been a bit more selective when I did, since I had to make the enclosure of the sound bar a lot bigger than I originally envisioned. You can see in the graphic above that the standard design for a box that uses this woofer is over 10 liters, which would be fairly huge for something that it typically much smaller. I managed to whittle that down to 6 liters with the box heavily filled (adds apparent volume, but not the usual approach for a vented box), but that was still quite a bit bigger than the original design.
If you are interested in building this design as is, though, I can recommend a different woofer to use that will give much better base response. That’s the DSA 135-8 from Dayton Audio. The port size would have to be increased to 2″ and made 4-3/4″ long instead of 4″, but that’s the only change.
The woofer I did order and use is the DMA 105-4 and the tweeter was the TD20F-4, both from Dayton Audio. While the 105 is a full range driver, I’m not a big fan of using them for high quality sound reproduction, and the additional tweeter didn’t make the project significantly more expensive.
And speaking of the woofer, here’s how it fits into the recess I cut in the box:
While it is acceptable (in my opinion) to surface mount the drivers, I much prefer to make them flush with the surface of the box.
I had to make templates to route these out and the one for the tweeter was a bit more difficult to dial in exactly. When painting a box, you need to make the recesses slightly oversized to allow for the paint thickness, and I ended up making this template twice:
But the result is a perfect fit for the tiny speaker. Normally for a round speaker I would just use my circle cutting jig, but this one is too small.
The box fully assembled with all of the opening cut for the drivers:
It is 7″ tall, 48-1/2″ wide and 3-1/2″ deep (180 x 1232 x 89mm), which is bigger than I wanted, but not too big.
I used 1-1/2″ ABS drain pipe for the ports and cut the holes in the box with a larger forstner bit first, then finished the cut up to the line with the trim router:
To fasten them, I first filed a shallow groove around the end (see this in the video below) and roughed it up with sandpaper, before gluing it in with epoxy:
The ports face down since the sound bar will be mounted on the wall with nothing below it.
Before painting I had to fill all of the gaps and nail holes and I used automotive body filler to do that:
Then there was a whole lot of sanding, some of which can be seen in the build video. I started with 100 grit to level all the joints, then moved up to 220 grit to make the box as smooth as possible.
I then sprayed on a total of three coats of clear polyurethane to prime the box, sanding between coats. I also sprayed the inside of the box one coat to seal it:
Before spraying on the black paint, I sanded it smooth once again:
All of the finishing products I used are water based and dry quickly, especially on a warm day outside. I put a total of 10 thin coats of black on, then topped that with 3 more coats of polyurethane. You really need to build a thick layer at this point to have something to sand without cutting through to the bare wood:
And you might think this is the end of the painting, but I still have another round. You need to leave this for a few days for the paint and poly to fully dry, then sand the entire box again for the final coats. And some people think painting is easy!
I took a wrong turn on the grilles, originally thinking this design would look good:
But realized I hated it with it placed on the speaker box. And then the additional hassle of covering it with cloth, which is easy enough on one that’s square, but a bit less so on this odd shape.
In the end I went back to a personal favourite of mine – horizontal bars. I made these from some vintage hard pine leftover from renovating my house:
I had to sculpt out the backside where the drivers are and I did that the hard way, on the table saw:
These get basically the same treatment to paint them, multiple coats and let dry for a few days before the final finish:
I first made back panel as a single piece, but thought it would make sense to have a recess for the speaker wires at the back:
I’m mounting this on my wood accent wall and the wires will run down behind the slats, and this gives it some room to position it so they won’t hold the sound bar off the wall.
To attach the grilles, I epoxied magnets into the front baffle:
Should have done this before I started painting. But wasn’t sure how big the grilles would be and wanted to take advantage of a relative rarity this spring to get the painting done – a clear day.
After sanding the box again and putting the magnets in, it back out for the final finish. I say final, but I’m not entirely happy with how it came out and may do it again at some point in the future:
With that done I can start on final assembly. The crossover is simple enough, a single inductor and capacitor:
I hot melt glued the coil to the inside of the box close to the holes and just left the small capacitor flying.
The crossover is at around 2800Hz and is what’s known as a Solen split. This spreads the slopes out to give a roughly 6db dip in the crossover range, effectively lowering the response in the midrange:
Shown parallel connected, this can also be series connected for slightly more effect.
Stuffing is my usual pink fiberglass cut to size so that it doesn’t touch the woofer or port:
Like I said above, the stuffing is not typical for a ported box, but does effectively increase the apparent volume of the box. I don’t think it has much effect on the port resonance, as long as it doesn’t block it.
I sealed around the speaker wires as they come through the back with hot melt glue:
And finally got the drivers connected and installed:
To mount the sound bar, I made these reinforced keyhole slots from 3/8″ fender washers:
Much (MUCH) stronger than just cutting one into the MDF by itself.
With the grilles in place:
I took the time to mount it on the wall in my shop for a clean photo:
And here it is in place under the screen in my living room:
The build video with a brief sample of the sound quality:
As for the sound, I’d judge it to be very good – great midrange and high clarity. The drivers are well matched for sensitivity and work well together at the crossover point.
It’s not as full in the low end, but only in comparison to a the bigger system I had. I may build a small power subwoofer to add to this to boost the bass response even more.