arXiv:2611.14016v1 Announce Type: new Abstract: A loudspeaker in a closed box is modeled as a rigid sphere with an axially moving cap. For an axisymmetric cone-velocity profile, its radiation impedance is written as a network. Each spherical-harmonic mode has an impedance rational in frequency, realized exactly as a finite passive ladder of masses and compliances terminated in a resistance. Ideal transformers set by Legendre coefficients couple these ladders; truncated modes reduce to a residual mass. Despite the different geometry, the impedance resembles that of a baffled piston but, at equal volume velocity, has half its low-frequency resistance and about three quarters of its radiation mass.