The application describes a package for a MEMS transducer. The package has a package substrate having an acoustic port formed in the package substrate. The acoustic port comprises a first acoustic port volume portion and a second acoustic port volume portion, the first acoustic port volume portion being separated from the second acoustic port volume potion by a discontinuity in a sidewall of the substrate. The cross sectional area of the first acoustic port volume portion is greater than the cross sectional area of the second acoustic port volume portion. A barrier may be attached to the upper surface of the package substrate so as to seal or cover the acoustic port.