There is a class of waveguides problems in which energy is provided by a source distribution of finite extent on the surface of the guide and for which usually the behavior of the acoustic field created is not analytically correlated with the source strength. The present paper aims at providing an analytical model describing the field which can be obtained from such nonuniformly distributed, time-periodic source creating either pressure waves in fluid-filled waveguides or Shear Horizontal waves in isotropic solid plates. This model involves convolution products between appropriate Green’s functions and the source stress. A relevant example is finally displayed.