The maximum intelligible range of the unamplified human voice

Abstract

The Anglican preacher George Whitefield preached to some of the largest reported crowds in recent history during the Methodist revivals in 18th century London. Benjamin Franklin later performed an auditory experiment in Philadelphia from which he estimated Whitefield could be heard by 30,000 listeners at once. Using the data from Franklin’s experiment and acoustic model of colonial Philadelphia, Whitefield’s on-axis averaged sound pressure level at one meter has been calculated to be about 90 dBA, consistent with the loudest values measured from trained vocalists today. Using period maps and topological data, acoustic models have been constructed of the sites of Whitefield’s largest crowds in London, using a human voice source with the projected SPL for Whitefield’s preaching voice. Based on the total audience area whose speech transmission index value is greater than that at Franklin’s position in the Philadelphia experiment, the total intelligible audience area can be calculated. Using Franklin’s own crowd density calculations, this method allows estimates of the maximum amount of listeners that could hear Whitefield’s voice under different environmental conditions and provides a better maximum estimate for the free-field intelligible range of the unamplified human voice.