A system comprising: a body and a MEMS microphone assembly, wherein the MEMS microphone assembly is provided in the body, the MEMS microphone assembly comprising: an enclosure enclosing a first volume of air; a MEMS microphone chip provided within said enclosure; a first acoustic port formed in said enclosure, the first acoustic port defining a first fluid path between the first volume of air and a first body of ambient air outside the enclosure adjacent the first acoustic port, said first port having a first acoustic impedance; and a second acoustic port formed in said enclosure spaced apart from the first acoustic port, the second acoustic port defining a second fluid path between the first volume of air and a second body of ambient air outside the enclosure adjacent the second acoustic port, said second port having a second acoustic impedance; wherein the ratio of the first and second acoustic impedances is at least 5:1; wherein the first and second acoustic ports (1004, 1005) are formed in opposite surfaces of the enclosure such that the first and second bodies of ambient air are on opposite sides of the body; an acoustic vent provided in the body and having a third acoustic impedance, wherein the third acoustic impedance in parallel with the sum of the first and second acoustic resistances provides an acoustic resistance through the body; wherein the MEMS microphone assembly generates a signal that is proportional to a pre-determined linear interpolative value between the sound pressure level at each of the two ports (1004, 1005) according to the ratio of the first and second acoustic impedances. a body and a MEMS microphone assembly, wherein the MEMS microphone assembly is provided in the body, the MEMS microphone assembly comprising: an enclosure enclosing a first volume of air; a MEMS microphone chip provided within said enclosure; a first acoustic port formed in said enclosure, the first acoustic port defining a first fluid path between the first volume of air and a first body of ambient air outside the enclosure adjacent the first acoustic port, said first port having a first acoustic impedance; and a second acoustic port formed in said enclosure spaced apart from the first acoustic port, the second acoustic port defining a second fluid path between the first volume of air and a second body of ambient air outside the enclosure adjacent the second acoustic port, said second port having a second acoustic impedance; wherein the ratio of the first and second acoustic impedances is at least 5:1; an enclosure enclosing a first volume of air; a MEMS microphone chip provided within said enclosure; a first acoustic port formed in said enclosure, the first acoustic port defining a first fluid path between the first volume of air and a first body of ambient air outside the enclosure adjacent the first acoustic port, said first port having a first acoustic impedance; and a second acoustic port formed in said enclosure spaced apart from the first acoustic port, the second acoustic port defining a second fluid path between the first volume of air and a second body of ambient air outside the enclosure adjacent the second acoustic port, said second port having a second acoustic impedance; wherein the ratio of the first and second acoustic impedances is at least 5:1; wherein the first and second acoustic ports (1004, 1005) are formed in opposite surfaces of the enclosure such that the first and second bodies of ambient air are on opposite sides of the body; an acoustic vent provided in the body and having a third acoustic impedance, wherein the third acoustic impedance in parallel with the sum of the first and second acoustic resistances provides an acoustic resistance through the body; wherein the MEMS microphone assembly generates a signal that is proportional to a pre-determined linear interpolative value between the sound pressure level at each of the two ports (1004, 1005) according to the ratio of the first and second acoustic impedances.