The Acoustic Impedance at the Surface of the Human Body in Relation to Auscultation

As part of a study of the acoustical properties of the medical stethoscope the acoustic impedance of the body surface at the thorax and at the abdomen was measured through the frequency range 20 Hz to 1 kHz. The most important element of the measuring set-up was a short cavity where the sound pressure amplitudes and phases are determined first when terminated by the body surface and then by an infinite impedance. The acoustic impedance was found to depend on the frequency, the pressure against the body, the application area, and the position on the body.