Abstract
Several problems on the phonocardiographic microphones are investigated. A tentatively made condenser microphone used for phonocardiography is discussed briefly at first. Then, the characteristics of several types of air cavity of phonocardiographic microphone are discussed rather in detail by calculating their acoustic fields and measuring them with a probe tube microphone. Two sorts of microphones, condenser and moving coil, are considered in these calculations.
Next, the vibration sensitivity of the phonocardiographic microphone is discussed. Its measured values are compared with theoretical ones. A few dBs of differences appear in some frequencies, but the tendencies of two curves are in good agreement. The sensitivity of the microphone to the room noise is investigated finally. The ways how the room noise reaches the microphone are also discussed.
