I recently restored an antique rocking chair with the hopes of using it in my living room. It was a greatly satisfying project that I am very happy with. Soon after finishing the chair and testing it out, I decided that to really enjoy sitting in this chair I would need an ottoman. Its just necessary, in my opinion, to have my feet up while I rock. Hmmmm.... Rock.... The idea light went on in my head.
As you might be aware of, if you've seen my last couple of instructables, I've been pulling things out of my basement to repair and restore them. Having been in the basement so often recently, I remembered that I have this massive old sub-woofer down there from my years as a DJ, a 15" sub-woofer. It occurred to me that I could kill two birds with one stone. If I incorporate this woofer into my ottoman, I'd be getting rid of the cheap laminated box in my basement and upgrading my sound system for a better music and movie experience.
Step 1: Tools and Supplies
- table saw or circular saw
- jig saw
- drill and assorted bits
- tape measure
- large clamps
- hobby stapler and staples
- oil brush
- 7 feet of oak, 1"x8"
- 24"x48" pre-made pine plank (found at Home Depot)
- wood glue
- 1 1/2" wood screws
- stain color of your choice
- pre-made wooden couch feet, large dowel, or 2"x2"x48" deck railing support (just something to make feet for it)
- cloth 30"x30", what ever patern you like
- pillow stuffing
- 12" or 15" sub-woofer
- low pass crossover (Radio Shack)
- speaker wire connection plate (or whatever they're called)
- speaker wire
- finish nails
- color wood putty
Step 2: Building the New Box
So mine, for example, is 18" x 22 1/2" x 8" which equals 3,240 cubic inches. Once you have your volume in cubic inches, you divide that by the cubic inches in one cubic foot, 1728. So for mine, I take 3,240 and divide it by 1,728, which equals about 1.9. So my box has about 1.9 cubic feet, about a half a cubic foot less than the original box. In building yours, you can adjust your measurements to fit the specific requirements of your speaker. Oak is kind of expensive which is why my box will be about 1/2 a cubic foot less than the original.
I picked out some oak that would match my rocking chair, seven linear feet of 3/4"x8" oak. This will be the side walls of the box. Cut into four boards, 2- 24" and 2- 18" lengths, I started by gluing them together into a rectangle, using a T-square to make sure the corners were square. A good layer of glue is required in each joint to ensure that the box will beas air tight as possible. Remember that it's important to clamp wood pieces together when joining them with glue. It forces the glue into the pores of both pieces of wood. When the glue was dry, I further reinforced the corners with 6" strips of 1"x1" that I glued and screwed into place.
Now that the side walls are built, I used them as a guide to draw the top and bottom of the box on the two pieces of pine. The pine will be connected to the top and bottom edges of the oak box, instead of fitting it inside the edges of the oak box. This will give the sub-woofer a little more air volume.
After I cut the top and bottom pieces out, I went ahead and glued on the top of the box. When that was dry, I again glued and screwed in some 1"x1" strips to reinforce the connection. A speaker box needs to be very ridged.
Step 3: Cutting the Speaker Hole
The reason the speaker hole is off center was to leave room for the wire connector plate that I took out of the original sub-woofer box. If you are building one of these, a connector plate and speaker can both be bought at Radio Shack or an audio store. I mounted this plate on the bottom next to the woofer. It required a small 3"x5" rectangular hole.
Step 4: Sand and Stain
The reason I stained the wood before I assembled everything, is because I used two different colors. If the box was fully assembled, it would be nearly impossible to keep the oak stain from bleeding into the pine, or vise versa. If you build this and use only one color, you can wait until the box is fully assembled to stain it.
Step 5: Clear Coat
Step 6: Feet
Step 7: Connect the Woofer
When buying a subwoofer, there are a few considerations to make, and a few requirements of a home audio system. The woofer itself needs to be an 8 ohm speaker, home audio components run at 8 ohms . You don't need to use a huge woofer like mine to achieve good low end sound. A 10" or 12" woofer will be very sufficient for most of your music and movie needs, and will require less air space than mine. Another thing to think about is power, how much power does your sound system offer to run your subwoofer? Each speaker you look at will have a specific power rating which you should try to match to power output of your home audio system.
Update: A recent comment by Aeszok, reminded me that I forgot to mention a very important part of building subwoofers. When you send music to them through speaker wire, you are sending the full range of musical frequencies. Subwoofers are designed to pump out the low frequencies that your smaller speakers cannot achieve. To maximize this potential it is important to incorporate a Crossover. Crossovers separate low frequencies from middle and high frequencies, and allow a certain range of frequencies to pass on to your speaker. The idea is to send low frequencies to subwoofers, medium to high frequencies to mid-sized speakers, and high frequencies to tweeters.
There are many kinds of crossovers, each designed for specific uses. Active crossovers are usually a whole component that you incorporate into your sound system and will use power from your house, they plug into the wall or draw power from your car electrical system. Some of these crossovers will allow you to manually set which frequencies go to which speaker, from low all the way to high frequencies.
Passive crossovers use only the power sent through the speaker wire and are designed to allow only a certain set of frequencies through to a speaker. They are usually inside the speaker box. To my knowledge, most pre-built subwoofers that you buy in a store already have a crossover mounted inside its box, which is why I forgot to mention it.
A crossover that allows low frequencies to pass through should be used when building your box and can be bought at Radio Shack or other audio stores when you buy your woofer. Ask for a low frequency 8 ohm Crossover, it should look like a large capacitor. Also ask how to wire it in. It's been so long since I've installed one but i believe they are wired into the positive wire leading to your woofer.
Having one wired in will give you that low rumbling that you're after.
Step 8: Attach the Top and Bottom Board
Step 9: Trim Pieces
When they were dry I glued them to the pine top and bottom boards, with a 1/4" lip above the top board and down from the bottom board. This 1/4" lip on the top holds the cushion in place, and the bottom lip eliminates the speaker from view.
To further support these strips to the box, I put a couple finish nails into them. With a nail set I set them below the surface of the wood and then filled the holes with a little colored wood putty.
Step 10: Top Cushion
When the "cap" is all cut, the pad is the last thing to be made. I just put the pillow stuffing on the cap, stretched my material over it, and stapled that to the underside. Simple as that.
Step 11: Enjoy It
Tomorrow I get to throw out that huge ugly sub box that was taking up room in the basement. I hope you enjoy yours like I know I will enjoy mine.