Sound beams generated by an arbitrary baffled projector are considered. A wave equation which considers thermoviscous effects is derived in terms of nondimensional velocity potential. Then, an improved King integral solution that includes the thermoviscous effect is developed here. The solution shows an interesting phenomenon: that the dissipation effect contributes exponential decay in the propagation spectrum. In addition, the effect also contributes a propagation mode in the evanescent spectrum. The dissipation effects on sound beams are investigated numerically on axis and off axis with propagation spectrum and evanescent spectrum, respectively.