You speak a terrible word of power, setting up potentially lethal vibrations in the chosen target. The target must make a Fortitude saving throw once each round, and the effect grow stronger for each saving throw the creature fails.
On the first round, the target takes 5d6 points of sonic damage and is staggered, for 1 round. A successful save halves the damage and negates the staggered effect.
On the second round, the target takes 5d6 points of damage and is stunned for 1 round. A successful save halves the damage and negates the stunning effect.
On the third round, the target takes 10d6 points of damage and is stunned for 1d4+1 rounds. A successful save halves the damage and negates the stunning effect.
The resonating word has no power after the third round, even if the spell's duration is increased.