In part one of this series, I introduced the concept of building DIY speakers. The lowdown is this: it isn't really that hard, and for (say) $300-$800, you can have a pair of speakers that will outperform anything at Best Buy or Circuit City, and will be better than about 75% of the stuff sold in high-end audio stores. And you'll end up paying maybe 20% of what you'd pay if you bought excellent speakers at retail.
So where to begin? Well, there are three main parts to a DIY speaker building project:
- Build the box
- Wire the crossover
- Assemble and enjoy
1. Build the box
The first part is fun if you're into basic woodworking. All you need is a decent table saw, a hand router that plunges, and some basic woodworking supplies (clamps, drill, wood glue, screws, etc.). Your first box might be a little funky if you're a beginner (my first two weren't exactly square), but if you have experience or are willing to learn, it really isn't that hard.
Your DIY plans will probably give you dimensions for your box. If you're lucky, it will have a cut guide and a full schematic. But if it doesn't, never fear - just get a piece of paper and a pencil and do a "3D" drawing to conceptulaize the box. Let's say all you have to go on are a set of exterior dimensions, like 8" wide by 15" high by 10" deep. Factor in the thickness of your wood (typically 3/4") and go from there. As you do your 3D drawings, remember that you can't just cut two pieces of 8x15, two of 15x10, and two of 8x10, because they won't fit together. You have three faces to the box - for one, you will need to reduce both dimensions by 2x the thickness of your wood; for another, you will need to reduce one dimension by 2x the thickness of your wood; and the third face can stay the same. So you could cut two pieces of 15x10 (for your sides), two at 6.5x10 (for your top and bottom), and two at 6.5x13.5 (for your front and back).
There are really only two viable materials for speaker boxes: MDF (medium density fiberboard) or void-free Baltic Birch Plywood (NOT another kind of plywood). MDF is heavy, dense, relatively rigid, gapless, and dead (as in: it doesn't "ring" when you knock on it). It is also toxic, at least when you inhale its sawdust, so cut in a well-ventellated room. You can find 2'x4' and 4'x8' sheets of MDF at most Home Depots or Lowes stores. Baltic Birch is lighter, more rigid, a little less dead, expensive, and harder to find. Either one will work. Most builders use MDF just because it is easier to find.
3/4" material is a good rule of thumb for your box, although double up the material on the front face, because it will be weakened by the large speaker holes. It is always good to add a brace to your box - just cut a piece of material that will fit vertically on the inside of your box (so it touches your top, bottom, and side walls), and cut two large holes in it to allow air flow. (Think of the number 8 on a digital alarm clock.) Bracing is especially important if you're using MDF.
There are a lot of other tips and tricks for making a good box (like lining the walls with damping material and/or acoustic foam), so dig around if you're interested.
After you build your box, it will be ugly. The next step is to veneer it and stain it, but that is beyond the scope of this post.
Of course, there is an easier way. You can buy pre-built boxes from Parts Express that are reasonably priced and really nice. My Dillon Metaphor speakers, for instance, would fit perfectly in their 0.50 cubic foot boxes. If you're not up for (1) some moderately difficult woodworking and (2) having imperfect speaker boxes in your living room, go this route.
2. Wire the crossover
A crossover is a simple network of resistors, capacitors, and inductors, that divides your input signal between the various speaker drivers in your speaker (i.e. between the woofer and the tweeter). Crossovers don't require any AC power from your house, so they aren't dangerous to build, unless you burn yourself with your soldering iron. Crossovers are the heart of any speaker, and a good crossover requires dozens of hours to design and a lot of skill. They are also completely dependent on the other parts of the speaker (woofer, tweeter, and box), so you can't just slap a generic crossover between two speakers and call it a day. (Sorry!)
To build a crossover, you really only need a soldering iron and some solder. You also need something to mount the crossover to, like a thin piece of wood or some cardboard, although pegboard is probably the best choice. Your speaker plan will include a crossover schematic. You will need to buy the parts from an online source - typically Parts Express (http://partsexpress.com), Madisound (http://madisound.com), or Solen (http://solen.ca) if you are in North America. Be sure to buy exact values - don't buy a 1mH inductor when your design calls for 1.2mH. You can combine values if necessary, so if you can't find a 66uf capacitor, buy a 30uf and a 36uf and wire them in parallel. (Inductors and resistors are wired in series to combine.) Be sure to buy decent components designed for crossovers - your computer motherboard has capacitors on it, but they won't work in your crossover. A general rule of thumb is to use:
- 14-18 gauge air core inductor
- polypropeline capacitors (Solen or Dayton are good bets)
- 10w wirewound resistors
Once you have your components and your soldering iron, it's pretty easy. Just look at your schematic and connect the various pieces as shown.
If you've gotten this far, there isn't much more to do. Put the crossover inside the box, connect the speakers to the crossover, connect the crossover to some sort of terminals on your box (to connect the speaker wires from your amp), mount your speakers, and listen!
Of course there is more to the story, and this is just an overview. In my next post, I'll recommend some good DIY speaker designs to build, for a variety of experience levels and price ranges.
If you have any questions or want more info about some aspect of the process, post to this thread and let me know.