The trigger for this trap can be whatever you want it to be, usually passing by the trap or opening something. Then comes the sonic blast:
No page in history baby- that, I don't need
I just want to make some eardrums bleed
— Spın̈al Tap
Remember, in the case of Sonic Attack, Survival means every man for himself.
Detect: Per-based Thaumatology, or Perception + Magery for mages, at -6.
Circumvent: Automatic (don't trigger).
Effects: 2d corrosive to everyone within a 2-hex radius of the trap. The attack is Hearing-based.