Thundering Cacophony

The topmost note, when touched as the quaterstaff impacts the floor, creates a cacophany fo noise, dealing 2d8 thunder damage to those standing in a 15ft perpendicular line to the staff. On failure of a DC15 strength save, a foe of medium size or less is pushed back 10ft and knocked prone. This attack can only be used every other turn. Damage increases by 1d8 at level 7 and again at level 10.