This is a lingam bowl, characterized by the raised dome at the center of the bowl floor.
When the bowl vibrates, its walls flex and move in radiating wave patterns. It's a fixed anchor point, and because the vibrational energy has to organize itself around that anchor rather than spreading freely across a flat floor, it concentrates into specific patterns that bring the upper voices out more strongly.
This is why lingam bowls tend to carry richer, more layered overtones.
