On August 30th, 188 1, Clemen Adail obtained the patent of "improving the telephone equipment in the theater". Adail's invention is that two sets of microphones are placed on both sides of the theater stage, and the sound will be relayed to the audience's ears with receivers. This invention was first exhibited at the Paris Expo held in 188 1. There, the performance was "relayed" on the stage of the Paris Theatre, which was a great success. People think this is the first time to hear stereo. At about the same time, an inventor named Ohnsorge used a device similar to Adail's in the palace of the Prince of Prussia.
The outstanding feature of stereo is that it is easier for listeners to find the location of the sound source than mono or mono sound. This phenomenon is the same as that people can judge the distance more accurately with two eyes than with one eye. During World War I, there was a kind of "binaural receiving speaker" used to find enemy planes, which made use of this feature of stereo. In other words, the small ends of the two big speakers are connected to the ears of the operator with rubber pipes, and his auditory directivity will be greatly enhanced.
The development of stereo was initially closely related to the development of telephone system. In the early 1930s, Bell Telephone Dormitory, with Fletcher and others as the guidance and stokowski as the consultant, was the main force in stereo research.
In Bell Laboratories, there is a mute named Oscar, who is the main figure to promote stereo research. Oscar is a tailor's child. Because he is deaf and dumb, he has two microphones in his ears, creating conditions for hearing the sound as much as possible. On April 27th, 1933, Bell TV Lab conducted an open experiment: the concert held in Philadelphia was transmitted to Washington in stereo through the telephone line.
As early as 1925, WPAJ radio station in New Haven, Connecticut, USA broadcast the same program with two different wavelengths, and the audience had a receiver in each ear. At 1930, the earliest stereo record patent was granted by Bluemlein of the Electric and Music Industry Company.