Step 1: Getting the Parts
a pair of computer speakers
a pair of nice speakers you wish to upgrade to
spare speaker wire
If you want them to be battery powered, you also need:
an 8 AA battery holder
an extra power supply (it needs to fit in the power input, but doesn't have to be the same voltage)
a 12 volt regulator (or whatever voltage yours are)
Here are some things to look out for when you're buying stuff:
Look for a set that comes with a power supply, unless you know you have a spare power supply at home. For some reason Goodwill has a habit of separating the speakers from the power supplies. I don't know why. But you may need to look through the bin of tangled cords for a power supply with the same voltage as your speakers. Also if you want to power them on batteries, you MUST get speakers that are rated for DC power, preferably ones that run at 9 or 12 volts. You may be able to work with other voltages, like 15, but that might get tricky. They really don't need to be nice speakers. Mine are stock Dell speakers that probably came with a computer. The only control is a volume knob. They cost me $3.
You may need to check Goodwill a couple of times before you find an appropriate pair. Look for speakers with a name brand like Sony or Panasonic. These are usually nicer. You should also check the power rating. A pair of 50 watt speakers usually sound a lot better than a 5 watt pair of speakers, even if you aren't going to power them at anything higher than 5 watts.
Step 2: Opening the Speakers
Basically all you are going to use out of the computer speakers is the amplifier. Disassemble the speaker with the amp in it (the one with the volume control on it). You may only need to unscrew the actual speaker itself. There will be two wires connected to the speaker. Connect the two wires to a piece of speaker wire. My speakers had a bass reflex port, which is just a hole in the speaker that allows air in and out. I ran my wires through there.
Step 3: Close Them Up
Step 4: The Battery
Make sure you find the polarity of the input on the speakers before you make any permanent connections. POLARITY MAKES A DIFFERENCE. If you get the positive and negative backwards, you can fry your amp, so make sure you do it right. There is a way to tell by the symbols on your power supply or on the back of the speakers, but I don't know how to interpret those, so I just tested it first.
You should have found a spare power supply that fits the input on your speakers but isn't necessarily the same voltage. For instance, I found a 3 volt transformer that plugged into my speakers. The reason it doesnt matter, is because we are only using it for the input jack. You may be able to buy these somewhere, but I've never seen them. They are usually pretty standard size. Cut the wire on this, and connect the jack to the output on the voltage regulator.
Step 5: You're Done!
But I have a question, and I'm hoping some of you more experienced people can help me. When designing the battery system, I originally planned on using 10 AA batteries. This is because I planned on using rechargeables, which are only 1.2 volts. 10 x 1.2 = 12 volts. Then I wasn't going to use a voltage regulator, because i was going to have the exact amount of voltage. But when I connected 10 batteries I realized that they actually had a voltage much higher than 12. In fact, when I connected 8 batteries it exceeded 12 volts.
That's when I decided I would need a regulator. So I ended up testing it with 8 batteries, but I assumed the voltage was high because they were fully charged, and once they lost some power, the voltage would drop too low. But that wasn't the case! The amp ran for hours off 8 batteries! I am confused as to why this setup works. The batteries should only be producing 9.6 volts. I would appreciate it if anyone could explain why this works.
By the way, you may not even need a voltage regulator because after testing the original power supply, I discovered it actually provides something around 25 volts. Clearly the amp is fine with a little extra juice.
Step 6: Future Modifications
I thought about removing the amplifier and putting it in a separate container. Getting the amp out of the case is really easy. The problem is finding a case that will still allow you to control the volume and plug in your power without opening it. I once had an amp like this, and I just took the circuit board out and stuck it in an insulated tin. In order to change the volume, you had to open the tin and turn the potentiometer that's connected to the circuit board. Needless to say, this amp didn't last long. For my next project, I decided it would be easier and safer to just leave the amp in the case it came in and make a few modifications. So that's what I did. And this is the result.