Analysis of noise sources in colonial Philadelphia

Benjamin Franklin famously performed an acoustic experiment while listening to George Whitefield preach in Philadelphia in 1739, in which Franklin calculated that Whitefield could be heard by more than 30,000 listeners. In the course of his experiment, Franklin mentioned Whitefield's voice being disturbed by noise on Front Street, which affected the distance at which Franklin could understand him. In the course of constructing an acoustical simulation of Franklin's experiment, this paper describes research into the noise soundscape of early 18th century Philadelphia. First the attenuation due to diffraction is calculated based on Franklin's position and the frequency of the noise source. Next, historical accounts of noise are considered. The most likely sources of noise on Front Street would have been either a carriage on sand or gravel, or conversations outside the Old London Coffee House. These sources can be measured for approximate sound pressure levels today and inserted into a virtual model of Franklin's experiment to simulate how loud Whitefield's voice would have been and how many people could have heard his unamplified voice.