Exploration of Pressure Field Around the Human Head During Speech

A single speaker in a seated position repeated a fifteen-second sample of connected speech, while r.m.s. pressure measurements were made in thirteen frequency bands, and at seventy-six positions, in different directions and distances. The results are applicable to intelligibility and microphone placement problems. They show, in general, the greater variation with direction at higher frequencies. Directivity due to the size of the mouth opening appeared to enter above 5600 cycles per second, the axis at these frequencies being about 45° below the horizontal, in front. Frequencies below 1000 cycles per second were found strongest directly downward from the lips, or nearly so. The power radiated in different directions has been calculated, and a summation gives a spectrum of the total speech power emitted by the mouth. It is proposed that similar spectra for other speakers may be obtained from pressure measurements at a single point, using the relations discovered for this speaker. The necessity for protecting a microphone used close to the mouth, from the puffs of air accompanying the speech, is demonstrated and explained.