There is disclosed an improved sheet metal muffler for attenuating the sound of the gas discharged from a hermetic refrigeration compressor, wherein the muffler generally comprises a sheet metal casing having a hollow interior which is divided into two substantially equal chambers by a central baffle, with a restrictor tube extending through the baffle for placing the chambers in communication with one another, the restrictor tube being provided with a flared entrance portion at its upstream end and a venturi-like restriction intermediate its length.