In-situ acoustic impedance measurement using a free-field transfer function method

A novel method of measuring the normal specific acoustic impedance has been tested in laboratory experiments and applied in-situ. The impedance is used to calculate the corresponding absorption coefficients of the surface. The impedance deduction technique relies on measurements of the transfer function between two points in front of the surface. The sample size required is discussed and different estimates for the area needed are compared. Under laboratory conditions the frequency range between 80 and 4000 Hz can easily be covered. In-situ measurements may meet geometrical restrictions that reduce the frequency range. ©