Sound radiation from point-excited structures: Comparison of plate and sphere

Acoustic radiation from a structure can be expressed in terms of “modal radiation” and “modal coefficients”. This paper investigates the contributions of these two modal properties to radiation excited by a point force. Sound radiation from two basic structures is considered: a baffled rectangular plate and a closed spherical shell. The plate behaviour is familiar, and governed by the relation between the natural frequency of a mode and its coincidence frequency. For a closed spherical shell, there are either zero or two “critical frequencies”, depending on the radius and thickness. When there are two the shell radiates well both above and below the two frequencies, and poorly in the frequency range between them.

► Radiation from a plate and a spherical shell was studied via modal analysis. ► Flat average response in plate radiation results from the first mode. ► A spherical shell has either zero or two critical frequencies. ► Dip in radiation efficiency is shown between the two critical frequencies. ► General radiating structures were discussed in terms of plate and sphere radiation.