Science and Invention, February, 1922, pages 909, 959:

If  President  Harding  Spoke  to  120,000,000  People
As the Average Orator Can be Heard Clearly by an Audience of About 5,000 People a Calculation Shows that if President Harding Desired to Talk to the 120,000,000 Citizens of the United States and its Possessions, He Would Have to Grow to a Height of 173 Feet, Figuring That He Would Grow in Proportion to the Average Man, i. e., in Three Dimensions, Height, Width and Depth. The Dome of the U. S. Capitol at Washington, Here Shown, Rises to a Height of 287 Feet Above the Ground and Owing to the Perspective of the Picture, it Appears Smaller Than the President. It Has Been Seriously Suggested by a Well-Known Telephone Engineer that President Harding, Within His Present Term, Will Undoubtedly Have the Satisfaction of Talking to the Equivalent of 100,000,000 People, Thanks to the Tremendous Intensification of His Voice Made Possible by the Audion Amplifier. On Armistice Day, President Harding Set a New Record for Long Distance Oratory, by Addressing Simultaneously Three Great Audiences, Totaling Over 100,000 People, Thanks to Madame Science and the Audion Amplifier.

ONE hundred and twenty million people, representing the population of the United States, would be a large audience to speak before, wouldn't it? Imagine what power a man's voice would have to possess so as to enable every auditor in such an assemblage to hear his every word. Science now bids fair to enable the President of our country to talk to audiences of 50,000,000 people or even 100,000,000 perhaps before another new president is elected to office. So saith Mr. R. W. King, one of the American Telephone and Telegraph Company engineers, whose work on the loud-speaking device made possible the ushering in of a new epoch in space annihilation at the ceremonies over the bier of America's Unknown Soldier. It is well within the range of possibility that President Harding may see the day in his present term when he can sit at ease in the White House and talk at once to every city, town and hamlet in the United States that is tapt by telephone wires. An audience of 50,000,000 perhaps, or even 100,000,000.
    The accompanying illustration shows in a striking manner the size of man President Harding would have to be if he were physically, and unaided by electrical science, to address an audience of 120,000,000 people, who, by the way, would fill a grandstand having a ground area of 61/3 square miles. It has been computed that President Harding would have to stand 173 feet high, without his high hat, if he were to be proportioned as is the average man, and he would be able to rest his arm easily on the roof of the Capitol building, the dome of which rises 287 feet above the ground. This calculation was carefully computed and based on the fact that the average orator can speak clearly to about 5,000 people. But instead of having to even strain his voice, the orator of today can talk to vast audiences made up of thousands of people, thanks to the telephonic amplifiers which are based on the audion devised in the brain of Dr. Lee de Forest, less than 20 years ago. Amateur radio stations amplify the incoming radio signals with an audion bulb or tube, and they are not very cheap either, but the great resources of the American Telephone and Telegraph Company enables their engineers to utilize vast banks of audion or vacuum tube amplifiers, so as to intensify the spoken word to undreamt-of amplifications.
    President Harding set a record for long-distance oratory on Armistice Day by addressing simultaneously three great throngs of more than 100,000 persons, gathered at Arlington National Cemetery, Washington; in San Francisco, and in New York. The electrical current that carried President Harding's funeral oration to the crowds at Arlington, San Francisco and New York was multiplied 3,000,000,000,000,000,000,000,000,000 times before it rolled out, converted into great sonorous sound waves, over the heads of the three widely separated audiences.
    It took 3,000,000,000,000,000 amplifications to convey the oration and the other ceremonies to San Francisco, so that they could have been heard thru an ordinary telephone receiver. Then they had to be amplified a million million times by the loud-speaking device. A mere ten million billions--10,000,000,000,000,000--of amplifications were necessary to bring the ceremonies out clear and strong in New York. Ten thousand were used to bring the ceremonies here, and a million million to raise them to audibility for the New York audience. The other million million amplifications were used to carry the President's voice to the Arlington crowd. By providing a few more scores of thousands of miles of wire, some thousands of loud-speaking devices and a few foolscap sheets filled with tiny ciphers indicating more amplifications, the entire country might hear future public ceremonies, Mr. King said. It would be relatively simple, he declared, to set up equipment in the capitals of the forty-eight States thru which 150,000 persons in each city--a total of 7,200,000--could hear a ceremony in Washington or elsewhere as distinctly as if they were seated within a few yards of the speaker. A long distance call from New York to San Francisco involves 400,000,000,000,000 amplifications. Similar amplifications occur when the human voice is transmitted by radiophone and amplified sufficiently at the receiving stations to be heard by an audience or audiences of this magnitude.
    Blackwell and Espenchied of the American Telephone and Telegraph Company give the horsepower rating of the human voice as 2 to the 10 minus 8th power (2 X 10-8) in ordinary conversation. This is about 1/50th of a millionth of a horsepower, or 15 millionths of a watt.
    Crandall and Arnold of the Western Electric Company give this figure as about 100 millionths of a horsepower for ordinary conversation. A man (soap-box orator) can talk to about 1,000 people at a time, and even those at the outskirts of the thousand will have difficulty in hearing distinctly. In such oratory the voice is strained from 100 to 1,000 times. In a well designed hall about 5,000 people may hear his speech at one time. Trying to cover a hall seating about 15,000, such as Madison Square Garden, which Crandall characterized as being "an old pot," is impossible, and for this reason amplifiers must be used.