Birth of public radio broadcasting

The birth of public radio broadcasting is credited to Lee de Forest who transmitted the world’s first public broadcast in New York City on January 13, 1910. This broadcast featured the voices of Enrico Caruso and other Metropolitan Opera stars. Members of the public and the press used earphones to listen to the broadcast in several locations throughout the city. This marked the beginning of what would become nearly universal wireless radio communication. 
First public broadcast.
Date.
A 1907 advertisement placed by Lee de Forest's Radio Telephone Company stated: 
Several years later, on January 13, 1910, the first public radio broadcast was an experimental transmission of a live Metropolitan Opera House performance by several famous opera singers. This transmission was arranged by de Forest. This event is regarded as the birth of public radio broadcasting.
Performers.
The wireless radio broadcast consisted of performances of "Cavalleria Rusticana" and "Pagliacci". Riccardo Martin performed as Turridu, Emmy Destinn as Santuzza, and Enrico Caruso as Canio. The conductor was Egisto Tango. 
The "New York Times" reported on January 14, 1910: 
Equipment.
The few radio receivers able to pick up this first-ever "outside broadcast" were those at the De Forest Radio Laboratory, on board ships in New York Harbor, in large hotels on Times Square and at New York City locations where members of the press were stationed at receiving sets. Public receivers with earphones had been set up in several well-advertised locations throughout New York City. There were members of the press stationed at various receiving sets throughout the city and the public was invited to listen to the broadcast.
The experiment was considered mostly unsuccessful. The microphones of the day were of poor quality and could not pick up most of the singing on stage. Only off-stage singers singing directly into a microphone could be heard clearly. "The New York Times" reported the next day that static and interference "kept the homeless song waves from finding themselves". 
De Forest's Radio Telephone Company manufactured and sold the first commercial radios in the demonstration room at the Metropolitan Life Tower in New York City for this public event. The wireless transmitter had 500 watts of power. It is reported that this broadcast was heard away on a ship at sea. The broadcast was also heard away in Bridgeport, Connecticut.
Significance.
The birth of public radio broadcasting had an immediate impact on radio broadcasting as it stimulated the idea of having additional musical programs. The next month on February 24th the Manhattan Opera Company's new opera singer Mariette Mazarin sang "Love is a rebellious bird" from "Carmen" over a transmitter located in DeForest's laboratory. This radio concert was heard by a group of scientists, diplomats, newspaper reporters and the public within .
The New Jersey Telephone Herald did evening musical shows after their regular daily newscasts starting on March 15, 1911. The various musical programs consisted of instrumental music from a regular orchestra in attendance, individual recitals, and group singers. In addition they had theatrical performances, opera and organ playing at their new location on the second floor of the Essex Building in Newark, New Jersey.
DeForest in 1912 put together an amplifying technology from his 1906 Audion vacuum tube invention. He figured out how to take a weak signal and increase it many times (amplification) through a feedback circuit. He had learned through experimentation that his Audion would increase the strength of a weak signal to some degree if a small wire mesh was placed inside the vacuum tube between the heated electron emitting element at the bottom of the tube and the pick up plate on top that had a high voltage opposite charge. He took this electronic idea one step further by taking part of that amplified electrical signal and sending it back through the Audion again. That increased the signal strength even further. That idea was further developed by Edwin Armstrong and Alexander Meissner and the technology of the vacuum tube feedback oscillator was perfected in 1912 by them. 
This continuous feedback loop idea became a source of continuous waves through repeated feedback and amplification over and over again. The continuous waves of a particular frequency could be altered to a small degree by another signal introduced into it. This is called amplitude modulation. This was further advanced to the idea of having very high frequency continuous waves (tens-of-thousands of cycles-per-second (kHz) modulated (slightly altered) with another signal (e.g. voice, music) from a microphone. From that concept developed the amplitude modulated transmitter, which lead to AM radio broadcast entertainment.