OK, trying to reason with them hasn't worked, calling the cops hasn't worked, you're going to have to get even. The first thing you're going to do is to buy a sound system. Get a reciever with a remote (this remote will be important later,) make sure it's the highest-wattage you can buy. Next, buy some speakers with teh highest RMS rating you can find. Third, Get the biggest Subwoofer you can find. If you need a friend to help lift it, good. If you need a forklift, even better.
Now, the setup. Figure out where their bedroom is. Directly above their bed is the desired location. Put the reciever near a window, where the remote can turn it on from outside. Next, turn all of the speakers so that they face the floor. Once you have it set up, you're off to teh local music store.
Once you arrive at the music store, you'll buy a copy of Dimmu Borgir's "Puritanical Euphoric Misanthropia." You can find samples of the music here:
http://ubl.artistdirect.com/store/ar...117763,00.html
The track you want to focus on is number 6, "Puritania." Listen to the drum rolls in the sample on the Artist Direct website and you'll understand why you wanted a sub so big you need a forklift. It's even louder when you have the CD instead of a digital copy.
At this point, it may be a good idea to alert everyone around you except for the assholes. A few beers may be necessary to convince them that this is the only way to settle it.
Wait until the downstairs neighbors have gone to sleep. Insert what will soon be your favorite CD into the reciever, cue it to track 6, pause it, and turn the volume knob all the way up. Next: remove all cats from the vicinity, and evacuate your apartment. Move a safe distance away from the building, put in earplugs, protect the cats, and hit play.
Here's what should happen
A few seconds of static, followed by a soft drum roll and a demonic voice procliaming, "We will do away with your kind" will radiate from your apartment, after another line and a short countdown, a blast of the heaviest guitar riffs and the loudest drumroll your neighbors have ever heard will shake their apartment violently. If the system you've purchased is good enough car alarms will go off, dogs will bark, and your neighbors will think that the apocalypse is occurring.
Now you may not want to be so extreme, but if you just sit back, relax, and imagine how horrible of a person you would be if you actually did, you might feel a little bit better. Maybe you'll find yourself countering their crap with some evil-sounding music, maybe you will get a big subwoofer to drive them crazy ...
or maybe, just maybe, that forklift will crash through the floor and crush their stereo.