Bwaslo posted a passive crossover design over at the DIY Sound Group forum:
... which is excellent because I want a passive crossover for various reasons, including simplicity. Thank you Bill!
So I got my shipment of crossover parts from PE today and I built a crossover tonight. If you are building the same crossover, you can use my layout. Or if you are building a totally different crossover, you might pic up some tips here. I'm not an expert in crossover design, but I know enough to lay one out on a board. Here's my process:
To start, lay the parts out on a table, roughly according to the layout from the schematic. It's a good way to double-check that you have all the parts you need, and it helps familiarize you with the circuit details and the parts themselves (size, where the wires are, how long the wires are, etc.)
The next step is to come up with a layout, while still just placing them on a table. Don't worry about actually putting them on a board yet. Assuming that you have limited room, you'll want to come up with a compact layout. And for the sake of simplicity, you'll want to minimize the number of crossed (but not connected) wires, too. A circuit board is a nice convenience, but it absolutely is not needed, and many fancy speakers and audio gear use "point to point" wiring with no circuit board. Generally you can layout the whole circuit by just connecting the existing leads on the components, but you can add wire to complete the circuit if you need to.
So, for this circuit, I started with the big inductor from the woofer circuit, and then just added the rest of the parts around it. One of the few "rules" about crossover layout is that you want to minimize the interaction between inductors. The first way to do that is simply to maximize the distance between two inductors. But if you are going for a compact layout, you will need to put them pretty close together. The other way to minimize the interaction is with the orientation of the inductors relative to each other. The basic idea is to orient them so that the current flows perpendicular relative to any nearby inductors. If you think of inductors as car tires, the three interaction-minimizing orientations are 1) flat on the ground, 2) upright facing the side, and 3) upright facing the tread. Some inductors, such as the iron core one in this crossover, don't look much like tires, but the part that matters is the orientation of the coiled wire. You can see how I used all three of these orientations for the inductors in my initial layout:
A useful guiding principle is that you probably want to get all the "ground" connections to end up near each other so you can connect them. Alternately, you can create a "bus" wire for ground and/or positive, if it isn't possible to gather those connections into a single location. You will probably end up needing to re-do the layout a couple of times until you find one that works well.
I like to use terminal blocks like the one in the link below to connect the crossover to the inputs and to the drivers. I like this style because they connect to the solid component leads without having to wrap them around screws or anything like that. You just insert the wire into the terminal block, and capture it with the screw. You can cut these into parts with a knife or saw, since you often only need a few connections in a block. You can buy these kinds of strips in the electrical department at Home Depot, too, but they are much cheaper online:
Once you get a layout on the table, take a rough measurement to see how big of a board you need. This one looked to be about 6x9", so that's how big I cut the board. My enclosure is pretty large, so I didn't bother to test fit the board through a driver hole, and find a mounting location inside the enclosure. However, it is a good idea to do that for most speakers. I tend to use scrap 1/2" plywood for the board. Plywood is nice because it is pretty sturdy. I screwed the big inductor and the terminal blocks to the plywood board for this crossover. I also drilled two holes and used a zip tie to secure an air core inductor on end. However, first things first -- do another test layout on the board before you screw or glue anything down. In this case, I was able to compress the layout a little more, and cut the board down to ~5.75x7.75".
Then just start building the crossover onto the board, one component at a time. I started by screwing the iron core inductor to the board. I generally hot glue all the components to the board, to ensure that they won't vibrate and rattle against the board. You don't want the components to rattle against each other, or the wires to rattle against the components, so generally avoid having anything touching each other, or nearly touching each other. The wires are generally all bare, so you must ensure that they don't touch each other or anything conductive. The wires vibrating in the air isn't so great, either, so try to avoid "floppy" stretches of wire. Don't be afraid to cut the leads down if they are too long. Sometimes it is unavoidable, so in those cases just add a little hot glue. I'm probably too paranoid about that -- I end up gluing the wires to the board in many cases.
I've read a lot of posts where people are trepidatious about soldering, but it really isn't very hard and a crossover like this is as easy as it gets. I'm sure that even a first timer with just a few Youtube videos under their belt could do this. In most cases, you can twist the wires together, which makes it very easy to solder. You do need a high-wattage soldering iron or gun, since the wires are pretty thick. I use a Weller 100/140W soldering gun.
On this build, I ended up needing to join the IN-, WOOFER-, and TWEETER+ terminals, so I made a little mini-bus of bare solid wire, to join all the grounds.
So here's how it turned out: