Abstract: By using plane wave integral representation for the spherical wave,the sound insulation performance of an infinite partition subject to a point source incidence in a free field is investigated with theoretical analysis and computer simulations.The numerical simulations show that the sound insulation based on a point source incidence doesn't follow the mass law which is obtained based on plane wave incidence.The transmission loss increases by about 3 dB and the insert loss increases by about 6 dB as the frequency or the surface density doubles for a thin partition at low frequencies.