Bookshelf Speakers

After much debate with the powers to be (the wife) about upgrading the audio for our television, I knew the time had come to build something. The built-in tv speakers just don't cut it for me, so the battle of performance vs aesthetics was on!

Bulkiness was my main enemy here so towers, arrays, and large enclosures were a no go. (Inclusion of a subwoofer will be an Instructable for another day... maybe). So I got my hands on a 2.1 a/v receiver to connect and power my soon to be speakers.

After scrapping all of my overly excessive ideas and researching a ton of designs and speaker combinations I decided on a simple set of ported cubes, pairing a nice mid-woofer with a tweeter. Basically the smallest feasible enclosure with the most output that can play as low as possible with the chosen speakers... Easy as it gets, right?

Although I will be using them for my tv, they are perfectly capable for playing music and can easily be matched with a record player, computer, or even just a bluetooth amplifier.

Let the building begin!

Speakers:

Dayton Audio 4-1/2" Woven Carbon Fiber Midwoofer 4 Ohms

Dayton Audio 3/4" Soft Dome Neodymium Tweeter

* I'm a big fan of Dayton Audio products. They usually have the best performance/quality in the budget range. Plus the carbon fiber cone looks amazing!

Enclosure:

3/4" MDF

• 8x - 7" x 7"
• 2x - 6.25" x 6.25"

1/2" MDF (for back plate)

• 2x - 6.25 x 6.25"

Other parts:

PVC pipe 1.033" ID for ports (Just happened to find this in my garage)

Pressfit Speaker Terminal Cup 2-1/4" Gold Banana Binding Post

Crossover components (proto boards, caps, inductors, resistors, wire)

Tools and stuff used:

Table saw

Router (plunge and table) w/circle jig

Router bits (spiral cut, roundovers, rabbet, flush trim, chamfer)

Drill with hole saw bits

Dremel

Wood glue, CA glue, silicone caulk, Bondo

Chalk paint (black and smoke colors) & brushes

I decided to try and make the box as seamless as possible. No screws or nails (besides the removable back plate)

First I cut all the pieces on the table saw (7" squares), ran them through again to add the 45 deg edge to 2 sides, and then used the router to put in a 1/2" rabbet the other sides. (Putting the rabbet in allows the front and back plates to be dropped-in while keeping a border around all 4 sides)

After doing a quick test fit to see how things lined up, it was time to get gluing! I saw this masking tape technique online a while back and thought I'd give it a shot and it worked out really well.

I laid the four pieces side-by-side (outside facing up) against a straight edge and put 2 strips of masking tape on top.

Then I flipped them all over and spread a generous amount of glue on all the joints.

By folding each side into the next I assembled the box, tightly taping it to itself once it was all lined up. I wiped any excess dripping glue and spread it into the joints as much as possible.

Easy as can be, no clamps (unless it's off a bit like my 2nd) or brad nails needed. Just verified everything was lined up and square.

Once dried, I removed the tape and used some bondo to fill in any gaps and to cover the seams/edges to create a smoother surface to paint. Sand and repeat until happy.

I rabbeted the back plates a tad so they would sit slightly recessed instead of flush with the edges since its only 1/2" mdf.

Since the hole cutouts for the port and terminal plate were smaller than my circle jig could handle, I used hole saws with my drill. This resulted in some rough holes that took some sanding and my dremel to get just right.

Ports (My first ever attempt):

• Mounted the tube flush to the outside using CA glue to secure it.
• I flared out both inside ends of the tube with a roundover bit.
• Filled in any gaps with Bondo and sanded smooth.

For the terminal plate I cut out a small rabbet to flush mount in the hole, it will be glued and caulked later.

Finally I drilled 4 holes for screws as this plate will be removable.

By far the most difficult and time consuming portion of this entire build, it's basically all router work. I changed bits and bearings on bits so many times to get things just right.

I marked the center of the speaker locations with the intent on getting them as close as possible to each other while avoiding any overlap.

First I cut out the holes for both speakers, circle jig (3-7/8") for the mid and hole saw (1") for the tweeter.

For the mid hole, I rounded over the outside edge and then flipped it over and rabbeted to make room for the speaker to sit closer to the front. This was tricky because the mounting of the mid was not a perfect circle, and my rabbet bit wouldn't cut deep enough. So I had to freehand a bit with a spiral cutting bit to fit the corners in.

For the tweeter, my nearest hole saw size was quite a bit too small. So I had to rabbet a tiny bit, flip and flush trim it, then check if it fit. It took 3 rounds, each requiring a bit change (blah). When I finally got it perfect, I used a small roundover bit to flare out the edge.

Although I forgot to take pics before painting, I also put a tiny chamfer on the outside front edge and rabbeted the back side so the chamfer meets up with the edge of the box.

I then sanded any rough spots to make it as smooth as possible.

For the finish, I decided to use a chalk based paint and just brushed it on.

I did two coats for the black with no sanding to give it a bit of texture. Sealed with a finishing wax.

I did the same for the front plates, but lightly sanded in between coats (1200 grit) to make it super smooth and remove any brush marks.

Prior, I also spray painted the inside of the ports a bit to cover up the white inside of the tube.

For the mid, I centered the speaker and used some CA glue to keep it in place while I put 4 screws in to secure it.

The tweeter was a pretty tight fit, so I just glued and pressed it in.

I then did a final fitting and was more than pleased with how it looks!

Crossovers can be made as simple or as complicated as one would desire, what sounds good to one person may sound like crap to another.

After trying many, many variations, I finally settled on a 2nd-order Linkwitz–Riley @ 5 kHz. I made this decision based on the only important factor... I liked how it sounded.

Perks of a 2nd order filter... has a 12 dB/octave roll-off and does not have any gain increase at the crossover frequency, in other words the speakers blend well and avoid any volume variance near 5 kHz. However, this type of crossover does inherently introduce a 180 deg phase shift between the tweeter and mid. To compensate and get both speakers in phase, I reversed the pos and neg of the mid speaker (shown on schematic).

Since the tweeter I chose has a higher sensitivity than the mid (90 dB vs 85.5 dB 1W/1m), it played much louder to the point of being distracting. So I added a L-Pad to drop it ~4.5 dB. It blended and sounded much better eliminating the harshness, although it does also waste some of the power to achieve this (not a concern in my build). I also added a Zobel impedance equalization circuit to the mid... because why not?

In the end, its just a matter of how much money you wanna spend on components and if you're happy with the result. Just make sure to use properly rated components for your design in terms of wattage. I'm also a big fan of using twisted pairs for wiring instead of side-by-side speaker wire. I had 16 gauge available so that's what I used.

I included a schematic of the circuit along with some internal enclosure dimensions and port details.

After soldering all the wires, I just hot glued the crossover boards inside... nothing fancy.

It's finally time to put things together for good!

I went through and made sure any potential leak points were caulked and sealed. I also used a foam strip to help seal the back plate once assembled and added some felt pads on the bottoms to prevent any rattling.

Once the back plate is on tight its time to give them a try and enjoy!