A clamped drum edge always forms one circular displacement node.

Evidence

Displacement nodes occur in circles and/or diametrically across, and these are shown in the figure. They are identified by the numbers given in brackets as follows: number of diametric modes, number of circular modes. The drum membrane always has at least one circular mode where there is a displacement node, which is the clamped edge. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1290

Categorization

• DEFINE: Explains the mode-numbering convention (diametric, circular) used for membranes.
• QUESTION: How does the fixed clamped edge as a node shape the audible spectrum of a drum versus a free edge?