For normal
audio retaliation systems, nothing beats
monster wattage with a pair of slot-loaded dual 18-inch
EV bass speakers playing
Gravity Kills.
In the situation detailed in the node above, however, one has to be more creative. Get a small speaker, something about an inch in diameter. You're looking for mid- to high-range sound, so don't worry about the bass response. Drill a small hole in the ceiling and poke the speaker into the portal, pushing aside any insulation (ha ha ha!) that you may find.
When they folks are annoying, just crank up some grating nails-on-chalkboard loops. You can also hook a microphone and act like a poltergeist, letting the little rugrats know that they're bothering the crazy headless ghost and he is about to start going berserk with a chain saw just like he did with the last people who lived there. That'll shut them up.