Alex
You can’t use the boards and most of the crossover parts that came with the kit.
You’ll need this stuff:
- Soldering iron – pencil type – at least 25 watts
- Electrical solder with rosin core (don’t use acid core solder, that’s for plumbers)
- Cable ties roughly 8” long
- Closed end crimp caps – Parts Express #095-340 and #095-330
- PE Connector wire (PE #100-074 red and 100-072 black) or any 18 or 16 gauge zip cord from any hardware store works as well. I like the color coded stuff as it is much easier to see when I’m assembling stuff in poor light. Don’t fall into the trap of using fatter 14 or 12 gauge wire. It will be a genuine pain to solder it to the much thinner leads of the various crossover parts.
- ¼" thick or thinner plywood or masonite for crossover boards.
I don’t use those aluminum disconnects anymore (part #095-282 in the kit). They are a pain to get them to fit tight so they don’t come loose. To connect the wires that run to the woofer, tweeter, or the terminal cup, I solder them directly. I attach the wires together with a cable tie, twist wires and leads together, solder, and then cap the connection with one of those closed end crimp caps. They never come loose even if I ship a speaker UPS.
The parts for the Murphy-designed crossover are listed lower on down in his web page
http://murphyblaster.com/content.php?f=pe_br1.html . Each part is linked to the right page to order it from Parts Express. Be sure to order two of each. Buy all the parts first. You’ll need to know how big they are when you layout the crossover board.
How big should the board be?
- It has to hold all the parts.
- It has to pass through the woofer hole in the cabinet (about 5¾") with the parts mounted.
- And it has to sit flat on the floor of the cabinet.
After doing it wrong several different ways, I now measure the diameter of the woofer hole and cut a piece of paper or cardboard a bit smaller than that diameter. The other dimension should be short enough to lie flat on the floor inside the cabinet.
There are 3 inductor coils in this design – the 1 mH inductor will be the largest. Plan on lying that one flat. The next biggest is 0.56 mH. Hold it on your cardboard standing on edge like a wheel. Try to pass the cardboard and the inductor through the woofer hole. Trim the width of the cardboard until it does go through. This will be the size of your crossover board.
Dennis Murphy shows his in two separate circuits, one for the woofer and one for the tweeter. You can easily put both on one board. I redrew the schematics to make it easier to read. See the attached file. In the original diagram, the resistors shown in-line with the inductors with values less than 1 ohm aren’t separate resistors. They are the inherent resistance of the wire in the inductor coil. I took them out, and labeled things so they are easier to read.
If electrical units and abbreviations bug you because you don’t understand them, here is Crossover Parts 101.
Inductor coils are variable electrical filters measured in Henries, or more often milli Henries mH. They are used in crossovers as low-pass electrical filters. The higher their mH value, the lower the audio frequency they start filtering. Inductor coils also come in different size wire, so if the Murphy design calls for a 1.0 mH 18 ga inductor, don’t get one that’s 16 or 20 gauge.
Capacitors are variable high-pass electrical filters. They are measured in Farads or more often micro Farads µF. Sometimes people use the letter u, as in uF, because they don’t know how to type µ the Greek letter mu. The higher their µF value, the lower the audio frequency they start filtering.
Resistors measured in ohms, Ω (Greek uppercase letter omega). They reduce current flow at all frequencies.
As long as you wire the parts as shown in the schematic diagrams, it doesn’t matter where you place the capacitors and resistors. The inductor coils, those doughnut shaped coils of wire, can interact with each other, so you should watch out how you locate them. This link has an easy to follow guide
http://www.troelsgravesen.dk/coils.htm. Scroll all the way to the bottom to see the diagram. I keep a printed copy at my workbench.
I'll work on a drawing for the layout tonight and post it tomorrow.
