An electronic device may be provided with a microphone in a microphone port. A shield may cover a microelectromechanical systems microphone device on a microphone substrate. An opening in the microphone substrate may form a sound port for the microphone. The microphone port may be formed by perforations in the microphone substrate or other layers such as a flexible printed circuit layer, a sheet metal layer, a layer of adhesive, a flexible polymer carrier layer in an adhesive tape, or an electronic device housing. The perforations may be sufficiently small to help resist the intrusions of foreign material such as liquid and dirt into the sound port of the microphone. Larger openings may be formed in other structures such as an electronic device housing. The larger openings may serve as sound passageways for the microphone port while being sufficiently large to resist clogging.