calculated from 13 with v denoting the cavity volume zpv u03c1 u2062 u2062 c 2 j u03c9 u2062 u2062 v 12 furthermore zpp is the port acoustic impedance consisting of a damping element and a mass element in series connection e g calculated for a narrow slit which typically is introduced for purposes of elevated damping rates 14 the narrow slit impedance may be estimated from its length 1 parallel to the sound propagation direction its width a orthogonal to sound propagation and the least distance between two opposite planes in the slit and the slit height b the constant u03b7 denotes the air viscosity approximately 18 3 10 u2212 6 ns m zpp 12 u2062 u03b7 u2062 u2062 l a 3 u2062 b j u03c9 u2062 6 5 u2062 u03c1 u2062 u2062 l ab 13 the resulting force acting on the sensor diaphragm in system where the rear side diaphragm pressure signal has passed the port volume acoustical filter system then becomes the sum of the contribution from each side a transducer of type iii and with the dimensions and weight given above will perform as shown in fig1 here the variation has been given top to bottom in ah ad mh and cd the latter being the compliance of the diaphragm solid lines indicate the nominal value the dashed lines indicate double the nominal respective values and the dotted lines indicate.