Crowd outside the US 1924 Republican National Convention in Cleveland Ohio listening to the speeches inside the hall by means of a public address system inside the sound truck and the horn loudspeakers on the pole. A loop antenna is visible on top of the truck, so the truck is probably playing radio coverage of the convention from a local radio station. PA systems had only been in use for about 6 years, since World War 1 when amplifying triode vacuum tubes were developed, and they were still somewhat of a novelty. Caption: ""RESIDENTS OF CLEVELAND LISTEN IN ON THE REPUBLICAN CONVENTION - With a company of elephants to sound a genuine Republican keynote, Cleveland crowds found it easy to get into the spirit of the convention that nominated Coolidge and Dawes by means of this "public address system" that connected with the presidential convention hall.""