This is a active speaker construction that works on a 12V battery. The speaker gives you the opportunity to throw a party on any given location.
The first part of the instructable consist of making the speaker box. The second part consist of installing the speakers and the amplifiers.
Step 1: Size of the Box
To determine the size of your speaker boxes you got to have the speaker drivers. For the material of the speaker box best use MDF, it's heavy but relatively cheap and it has a high level of density which makes it perfect for speaker boxes.
You also need some screws, nails (optional), glue, a filler to stuff the box with (like polyfill) and silicon to seal the edges.
For tools you need a saw, screwdriver, centimetre, a drill, compasses and a jigsaw.
I split it into two boxes; one for two sub woofer speakers and one for three woofers and two tweeters.
To determine the size of your boxes check the optimal volume and displacement for each driver. For the two 15 inch sub woofers I use a case os 92 by 65 by 40 cm (internal dimensions) For the other case I use 92 by 65 by 30. The MDF I use is 15mm thick.
Step 2: Putting the Pieces Together
Saw the MDF into the right dimensions and put these together using the nails the screws and the glue.
Step 3: Using Braces
Use braces to prevent the box from flexing. A brace is a piece of wood inside of the box. There are different ways a speaker can be braced:
Step 4: Using Battans
Battans is another type of bracing that is used to secure all the edges of the box. It is a thin piece of wood that runs along the joints of the box. It does't need to cover the entire length, about 2/3 should do it.
Step 5: Making the Speaker Holes
For the making of the speaker holes you need a jigsaw. Put the actual speaker on the place where you want the hole to be. Allign these, subtract 1 to 1.5 cm with your compasses. Drill a hole in the middle so you can put the jigsaw in. When you have done this you can start sawing out the hole.
Step 6: Finish the Box
Now you can assemble the parts. I've put the top in a little deeper so and covered the sides with a little piece of wood (same as I've used for the battans). This way, when I put the speakers in it they don't stand out.
Since my mobile sound system is going to be used outdoors I needed something to protect the wood from mother nature. I therefore used not regular paint but tar. This doesn't really look very smooth, but it will protect my speakers better than regular household paint.
So the speaker box is almost ready now, only got to stuff it and silicon the inner edges. With the stuffing I'm going to wait for a while because I'm first going to build in the amplifiers.
(note: when using silicon to seal the edges, wait at least one day to put in the speakers, the fumes can eat away your speakers)
Step 7: The Amplifiers
For the total of 7 speakers I use 3 amplifiers. One for the bass, one for the mids and one for the tweeters. Since the bass uses the most power, it's recommandeble to give the bass the amplifier with the highest output.
I use car amplifiers because they are already set for working on a 12V battery.
Installing the amps:
Put a little strip of rubber between the the amp and the wood, then screw the amp to the speaker box. It's now a little shock proof.
Connection the amps:
You need to drill some holes in the speaker box, for each amp 3 holes for power, and in each box 2 holes for your line input. I also put a "threw" in one of the boxes (2 holes).
The power connection from a 12V amplifier contains three switches, a GND, a RMT and a +12V:
-The GND is the GROUND and is supposed to be connected to the - on the battery.
-The RMT is the REMOTE, this is supposed to be the switch that turns the amp on and off. You can use a actual switch here, I didn't use a switch. I switch it in manual by connecting it on and off the 12V battery. The RMT is supposed to be connected to the + on the battery. (Note: if the RMT doesn't get power, the amp doesn't work, because it's "off")
-The +12V is supposed to be connected to the + on the 12V battery
For the line-in, the amps have a tulp connection. Since I go from one source to three amps I needed to split the signal. I therefore used 2 X "2x tulp female to 2x tulp male / 2x tulp female".
Use the speaker connection from the amp to connect your speakers. If you only connect 1 speaker to each amplifier you can use the bridged connection. If you use more than one speaker try to use equal speakers. Don't connect three or five, always try to equalize the output. Best just don't use more than two speakers directly for each amp. Except when the amp has more outputs.
Step 8: Using a Cross-over
In a 3-way system you split the frequency (hertz) that every amp sends to the speakers. This way the bass gets only the low frequencies, the mid speakers the mid frequencies etc. Therefore you use a cross-over. I was lucky that most amplifiers I used already contained a cross-over. I used one extra passive cross-over.
Step 9: The 12V Battery
The battery that I use is 105Ah. With the use of Ohm's law you can calculate the time the battery should run on your system.
When using such a amount of power from a 12V battery make sure you use thick power cables, else your system simply doesn't get enough power to reach his maximum.
Step 10: Finish the Speaker
Now that everything is installed and the box is stuffed you can screw on the speaker drivers. Make sure that you mount all the screws. To prevent the speaker vibrating on the wood (and making a awful sound) I have placed a piece of carpet in between.
Now you're ready to hook up you're mp3, mic, or whatever you want to connect to the speaker and terrorize your neighbourhood.