Method to assess acoustical two-port properties of earplugs

An experimental setup for objective measurements of high impedance objects in ducts, yielding the acoustical Two-Port properties of the object, is presented. The setup has been applied on earplugs. A frequently used experimental setup for measuring objective acoustical properties of earplugs is that of artificial ears. Great effort is spent duplicating the ear of a person. The insertion loss is considered to give the acoustical properties of the object. Such a setup, however, gives a ratio of the 'response of a system' to that of another system. The actual properties of the object are thereby embedded in a complicated artificial response. By instead fitting the test object in a duct, its Two-Port properties can be assessed, given the sound pressure level at both sides of the object for two sufficiently different termination impedances. Furthermore, the Two-Port properties of four earplugs have been numerically coupled to a model of the ear in order to predict the insertion loss.