A MEMS microphone assembly has an enclosure enclosing a volume of air. A MEMS microphone chip is provided within the enclosure. First and second acoustic ports are formed in the enclosure, defining first and second fluid paths between the volume of air and air outside the enclosure. The MEMS microphone responds to a pre-determined linear interpolative value between two independent pressure signals supplied via first and second ports according to the potentiometic ratio of the acoustic impedances of the first and second ports.