A Method of Assessing 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 outer 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, it's two-port parameters can be assessed, given the sound pressure level at both sides of the object for two sufficiently diiferent termination impedances