For determining acoustic impedances the direct methods are now often used, based on measuring the sound pressure excited on a measured object by the known volume velocity. With the sine sweep technique it is easily possible to maintain, with sufficient accuracy, the generated volume velocity constant. When using direct methods at higher frequencies gross errors can arise from the sound field inhomogenities in the coupling space among the sound source, the measuring microphone, and the measured object. For some coupling configurations it is, however, possible to find acceptable relations between the measured and the sought values.