Abstract: A sound insulator for a motor vehicle passenger compartment is disclosed. The aim of the invention is to develop a sound insulator which makes it possible to obtain an improved damping effect within a frequency range less than 300 Hz. In that respect, the invention relates to a sound insulator for a motor vehicle passenger compartment, which comprises an air cushion consisting of a dampingly active envelope which is made of an elastic material and disposed between a sound-generating component and the compartment internal space. The invention provides for a sound damping layer (25) which matches the shape of said component (13), acts as a spring material system and is covered on the compartment side by a heavyweight film (26), thereby forming the first shell of the air cushion (29).