A portable electronic device including an outer case having a wall in which a transducer-associated acoustic hole is formed. An inner case may be positioned inside the outer case. The inner case can include an acoustic port that opens to the transducer-associated acoustic hole and a relief port that opens to the outer case. A transducer having a diaphragm facing the acoustic port of the inner case is mounted within the inner case. A valve is further positioned over the relief port. The valve is configured to reduce an impact of an incoming air burst on the diaphragm.