Sonic: Upon command, a sonic weapon emits a low thrumming hum. The sonic energy does not harm the wielder. The effect remains until another command is given. A sonic weapon deals an extra 1d6 points of sonic damage on a successful hit. Bows, crossbows, and slings so crafted bestow the sonic energy upon their ammunition.

Thundering Burst: A thundering burst weapon functions as a sonic weapon that creates a cacophonous roar like thunder upon striking a successful critical hit. The sonic energy does not harm the wielder. In addition to the extra sonic damage from the sonic ability (see above), a thundering burst weapon deals an extra 1d8 points of sonic damage on a successful critical hit. If the weapon’s critical multiplier is x3, add an extra 2d8 points of sonic damage instead, and if the multiplier is x4, add an extra 3d8 points of sonic damage. Bows, crossbows, and slings so crafted bestow the sonic energy upon their ammunition.
Even if the sonic ability is not active, the weapon still deals its extra sonic damage on a successful critical hit.