Custom shape for trigger or sound?

I need the sound can only be heard outside the mesh, but is irregular and default trigger shapes are not useful to me.

The problem is that when entering or leaving the Maya, occurs consecutive activation to “BegginOverlap” and “EndOverlap” and not separately. So it does not act like a normal trigger (Only “Begin Overlap” is activated when entering the trigger and “EndOverlap” when leaving).

If you can not what I’m trying, what choice do I have to make the sound matches the geometry?

Other settings: