I may have some volume to my voice, but I don't think I can hold a candle to George Whitefield, the eighteenth-century revival preacher best known for leading the eighteenth-century religious movement known by historians as the "First Great Awakening." (Mandatory Jon Butler scare quotes included. Sorry, but only my early American historian friends will get that one, though I am happy to explain).
Whitefield appears several times in Benjamin Franklin's Autobiography (which I teach every year). My favorite reference to Whitefield is the passage in which Franklin tries to calculate the number of people that can hear Whitefield's booming voice. Here is Franklin describing Whitefield:
He had a loud and clear voice, and articulated his words and sentences so perfectly, that he might be heard and understood at a great distance, especially as his auditories, however numerous, observ’d the most exact silence. He preach’d one evening from the top of the Court-house steps, which are in the middle of Market-street, and on the west side of Second-street, which crosses it at right angles. Both streets were fill’d with his hearers to a considerable distance. Being among the hindmost in Market-street, I had the curiosity to learn how far he could be heard, by retiring backwards down the street towards the river; and I found his voice distinct till I came near Front-street, when some noise in that street obscur’d it. Imagining then a semi-circle, of which my distance should be the radius, and that it were fill’d with auditors, to each of whom I allow’d two square feet, I computed that he might well be heard by more than thirty thousand. This reconcil’d me to the newspaper accounts of his having preach’d to twenty-five thousand people in the fields, and to the antient histories of generals haranguing whole armies, of which I had sometimes doubted.
As this passage indicates, Franklin estimated that Whitefield could be heard, without a microphone, by 30,000 people.
It turns out his estimation was correct. Recently two researchers at New York University's Music and Audio Research lab reproduced Franklin's experiment and generally confirmed his conclusions.
Here is a small taste of this fascinating report:
As can be seen from the results, in the Moorfields and Mayfair areas, the largest reported crowd sizes would not have been able to hear Whitefield's voice even under optimistic acoustic conditions, and if the crowd was noisy or Whitefield was feeling hoarse, the maximum number of listeners would decrease sharply. However, at Kennington Common, the most wide-open of the three sites, it is projected that the largest reported crowd of 50,000 could have heard Whitefield's voice under optimal conditions.
It will be noted that if Franklin's more generous density figure is used, these crowd size estimates will be more than doubled. However, Franklin's maximum intelligible area calculation yields about 23,000 square meters, which is close to the values simulated here for some of the sites. This shows that Franklin's overall method of estimating the acoustic range of the voice was actually fairly accurate. His primary error was his overly large density calculation, which would have predicted a crowd size of about 125,000 listeners. A crowd of that size packed so densely would probably find it difficult to be silent and might even run the risk of a stampede.
However, Franklin reported a more modest figure of 30,000 listeners, possibly because he believed that the higher estimate was far-fetched, and also because the majority of Whitefield's crowds were reported as 30,000 or fewer. The largest crowds were only reported during the summer of 1739 in London, after which Whitefield's celebrity waned somewhat. Similarly, these computer simulations are also useful for evaluating the more modest crowd sizes that were reported: most of his large crowds in Britain and America were estimated at 20,000 to 30,000, and based on these simulations those numbers seem acoustically reasonable. Without a time machine, we will never know these crowd sizes exactly, but by applying scientific techniques to historical data we can still discover new pieces of the past that had previously been lost.