Dissatisfied with the current stand of the boom box world, I set about to see if I could do better on my own. The end result is a boombox so loud, so RUDE, it's like nothing you've ever seen or heard before, and it wasn't particularly difficult.
Step zero: Speakers
I believe that if speakers are the heart of a boom box, you should build your boom box around the speakers you have. In my case I found a set of old pyle 10" drivers and some mid-70s RadioShack 4" tweets. All in all about 25$ at the thrift store.
Step one: Find a case
This is actually one of the easiest steps, I picked up a metal looking briefcase from a thrift store for 5$. Measure you where you want your speakers to go.
Step two: Find an amp
I picked up a cheap Chinese 200W monoblock amp for about 20$ on amazon.
Step three: Power supply
When you're looking for 12V power supplies, there's nothing easier, cheaper, or more readily available at thrift stores than an xbox 360 power supply. The good ones will put out 230W at 12V, more than enough to power our amp.
Step four: Cut the holes.
You're going to find out some interesting things when you do this. In my case, I found out my cheap metal looking briefcase was actually metal, covering bamboo, covering foam. Not what I expected to find, but it gives the boom box a punchy sound that I like.
Step five: Screw in the Speakers and Start Wiring
Screw in the speakers and start wiring! We soldered up the speakers to the amp and the power supply, and arranged them inside the case with epoxy.
Step six: Test it out
This is the loudest boom box I've ever heard. It tops out all of the sound meters I have. My nearest best guess is about 110-115 decibels. It's ridiculous.
Step seven: Make some noise
Seriously, it's ridiculous how much sound you can put out from a briefcase.