An empty vessel contains more air due to a greater empty area than the filled one. When an empty vessel is struck, the greater mass of air is set into vibration. We know that greater is the intensity of sound if the greater mass of air is set into motion. This means the intensity of sound is more in the empty vessel than in the filled one by the relation
I ∝ a2
Hence, the empty vessel produces a more intense sound than a filled one.