Crushing Reverberation

You create a reverberating sound in a 20-foot cylinder centered on a point that forces creatures and objects downward.  Each creature in the area must make a Strength saving throw.  On a failed save, a creature takes 8d6 thunder damage is knocked prone.  If the saving throw fails by 5 or more, the creature is also stunned until the end of its next turn.  On a successful save, the creature takes half as much damage and isn't knocked prone.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d8 for each slot level above 1st.