Energy absorption of a conical cavity truncated by a spherical cap subject to a focused beam is systematically and quantitatively investigated. The incident flux on any transverse cross-section has a Gaussian distribution, which is specified by the convergence angle, energy distribution parameter at the focal spot, and focal spot location relative to the workpiece surface. Absorption and scattering within the plasma in the cavity are assumed to be negligible. By accounting for specular and diffuse reflections the results show the effects of the spherical cap and cone angles of the cavity, locations and sizes of the focal spot, and convergence angles of the energy-beam on absorption. Asymptotic results agree with available solutions of simple models. An explanation for the occurrence of spiking in welding is also proposed.