Analog Measurements of Sound Radiation from the Mouth

Abstract

Free-field measurements of the sound radiated from the mouth of a life-size mannequin are described. A transducer installed in the head of the dummy is calibrated to produce a known acoustic volume velocity at the lips. The sound field in vertical and horizontal planes through the head is explored with a pressure microphone. Measurements of pressure magnitude and phase are made for frequencies of 250, 500, 1000, 2000, and 4000 cps. The results are compared with the sound distributions for a simple spherical source, and for a small piston in a sphere of 9-cm radius. Over the frequency range investigated, and within a solid angle of about π sr centered on the mouth axis, the relations for the simple source are found to describe the measured magnitudes within approximately 3 db, and the measured phases within approximately 30 deg. The results are also compared with previously reported pressure distributions for speech. Some brief comment is devoted to approximating the radiation impedance of the mouth.