An acoustic device including a motor disposed in a housing having a non-porous elastomeric membrane disposed across an acoustic path defined by a sound port of the housing is disclosed. The motor may be embodied as MEMS transducer configured to generate an electrical signal responsive to an acoustic signal, or as some other electromechanical device. The membrane has a compliance that is 1 to 100 times a compliance of the acoustic device without the membrane, wherein the membrane prevents ingress of contaminants (e.g., solids, liquids or light) via the sound port while permitting propagation of the acoustic signal along the acoustic path without significant loss.