A method for determining the sensitivity of a microphone in an acoustic unit (1, 34), the method comprising: providing an acoustic unit (1, 34) comprising said microphone and a sound source; providing an acoustic coupler having at least one internal cavity configured such that a sound field can be generated within the cavity, the cavity being further in acoustic communication with a reference microphone, said reference microphone being configured to measure a reference sound pressure at a given position in said cavity, establishing acoustic communication between said acoustic coupler and said acoustic unit (1, 34), in that said cavity is further provided with an opening configured to establish acoustic communication with said acoustic unit (1, 34), of which said microphone sensitivity is to be determined, characterized in that the method comprises the steps of: - determining the sensitivity of the microphone of the acoustic unit (1, 34), wherein the sensitivity is determined as the ratio between an output voltage of the acoustic unit (1, 34) and said reference sound pressure generated in said cavity by said sound source and measured by the reference microphone of the acoustic coupler multiplied by a frequency dependent transfer function, where the transfer function is a function of an input impedance Z in at said opening of the acoustic coupler and a transfer impedance Z trans between the opening of the acoustic coupler and the position at which said reference sound pressure is being measured by the reference microphone. providing an acoustic unit (1, 34) comprising said microphone and a sound source; providing an acoustic coupler having at least one internal cavity configured such that a sound field can be generated within the cavity, the cavity being further in acoustic communication with a reference microphone, said reference microphone being configured to measure a reference sound pressure at a given position in said cavity, establishing acoustic communication between said acoustic coupler and said acoustic unit (1, 34), in that said cavity is further provided with an opening configured to establish acoustic communication with said acoustic unit (1, 34), of which said microphone sensitivity is to be determined, characterized in that the method comprises the steps of: - determining the sensitivity of the microphone of the acoustic unit (1, 34), wherein the sensitivity is determined as the ratio between an output voltage of the acoustic unit (1, 34) and said reference sound pressure generated in said cavity by said sound source and measured by the reference microphone of the acoustic coupler multiplied by a frequency dependent transfer function, where the transfer function is a function of an input impedance Z in at said opening of the acoustic coupler and a transfer impedance Z trans between the opening of the acoustic coupler and the position at which said reference sound pressure is being measured by the reference microphone. - determining the sensitivity of the microphone of the acoustic unit (1, 34), wherein the sensitivity is determined as the ratio between an output voltage of the acoustic unit (1, 34) and said reference sound pressure generated in said cavity by said sound source and measured by the reference microphone of the acoustic coupler multiplied by a frequency dependent transfer function, where the transfer function is a function of an input impedance Z in at said opening of the acoustic coupler and a transfer impedance Z trans between the opening of the acoustic coupler and the position at which said reference sound pressure is being measured by the reference microphone.