On September 11, 1884, US-american physicist Harvey Fletcher was born. Considered as the “father of stereophonic sound” he is credited with the invention of hearing aids and is well known for his contributions in acoustics, electrical engineering, speech, medicine, music, atomic physics, sound pictures, and education.
Harvey Fletcher – Early Years
Harvey Fletcher was raised in Utah in a religious community. He received his early education at he Brigham Young University where he graduated in 1907. The young engineer then moved to Chicago in order to continue his studies. There, he worked together with Rober A. Millikan measuring the charge of the electron. Their findings in this period highly contributed to the development of radio and television. After successfully performing the oil drop experiment along with Millikan, Fletcher graduated with the first summa cum laude Ph.D. ever awarded by the Physics Department at Chicago. [1,2]
Audiometer and Hearing Aid
As promised by Fletcher, the scientist returned to Brigham as the chair of the university’s physics department. However, he accepted an offer made by the Western Electric Company, and moved to New York in 1916. The engineer had always shown interest in sound and was then responsible to study the fundamentals of human speech-produced sound. He managed to develop the 2-A Audiometer and continued broadly contributing to Bell’s work on sound technologies. It was Fletcher, who guided the development of the Western Electric Hearing Aid, the first device of this kind to use vacuum tubes. 
The History of Stereophonic Sound
The earliest precursors of stereo technology can be traced back to the French aviation pioneer and inventor Clément Ader. During the International Electricity Exhibition in 1881, he had opera performances transmitted electrically in multiple channels to a remote room, where these signals could be listened to via telephone receivers. Ader called his system “Théatrophone”. In 1925, the engineer Heinrich Kluth-Nauen developed a device that created a spatial impression from a mono signal by means of a 180° phase difference. He called it “Stereophone“. From 1930 onwards, the first sound recordings were made in the USA, in which the same performance was recorded by two microphones at different positions, and which could later be combined into stereo recordings. However, it is not known whether stereophonic reproduction was intended with these recordings or whether the intention was merely to try out different microphone positions. Alan Dower Blumlein, an electrical engineer and inventor in the research department at EMI, began experimenting in 1931 with what he called “binaural” recording techniques, initially with speech. The coincident system of two angularly offset microphones with figure-of-eight characteristics known today as the “Blumlein method” is named in his honor, but does not appear to have been invented by him. Blumlein was also instrumental in developing the cutting stylus to record binaural signals on shellac record. By early 1934, EMI’s “Abbey Road Studios” were operational with the “binaural” technology, and the first experiments with music were conducted on January 11 and 12, 1934. A few days later, on January 19, 1934, the recording of a rehearsal conducted by Sir Thomas Beecham with the London Philharmonic Orchestra was also made there on a total of nine discs.
Harvey Fletcher’s “three dimensional Sound”
In 1928, Fletcher was appointed director of the director of acoustical research at Bell Labs and was even promoted Director of all Physical Research about seven years later. His first demonstration of stereophonic transmission and stereophonic recording also took place in the 1930s. One of the techniques investigated was the “wall of sound“, which used an enormous array of microphones hung in a line across the front of an orchestra. Up to 80 microphones were used, and each fed a corresponding loudspeaker, placed in an identical position, in a separate listening room. Several stereophonic test recordings, using two microphones connected to two styli cutting two separate grooves on the same wax disc, were made with Leopold Stokowski and the Philadelphia Orchestra at Philadelphia’s Academy of Music in March 1932. The first (made on March 12, 1932), of Scriabin‘s Prometheus: Poem of Fire, is the earliest known surviving intentional stereo recording.
Reporting on the first presentation of “three dimensional” sound in 1934, the New York Times said that the audience was quite “mystified” and “terrified”. Also, it was stated that “Had it not been for the knowledge they were witnessing a practical scientific demonstration, the audience might have believed they were attending a spiritualist seance. Some women in the audience, admitting a feeling of ‘spookiness’ left the auditorium in fright“. Back then, his system used three separate sound channels, in contrast to the two used in modern stereo. [2,3]
Fletcher left Bell Labs at the age of 65 in order to help Columbia University develop a department on acoustics. The engineer also helped found the American Acoustical Society and became its first president. He was elected an honorary member of this Society, an honor which is only shared by Thomas A. Edison. And by the way, Edison was also one of the first to be equipped with Fletcher‘s innovative hearing aids. However, his experience differed from most of Fletcher‘s patients. Edison states that “When I used to attend these dinners I sat in silence wondering what the after-dinner speaker was saying and wishing I could hear him, but I was content to turn my thoughts toward some of my inventions. But now with the hearing aid I can hear and understand the speaker but usually find it so dull I turn it off and turn my thought to my inventions.” 
Harvey Fletcher died on July 23, 1981, after a stroke.
Toby Mountain, “The Birth of Stereophonic Recording” excerpt” 
References and Further Reading:
-  Harvey Fletcher at the National Academy of Sciences [PDF]
-  Harvey Fletcher at IEEE Global History Network
-  Harvey Fletcher at the New York Times
-  Harvey Fletcher Papers, MSS 1233 at L. Tom Perry Special Collections, Brigham Young University
-  Fletcher Interview, 1963
-  Toby Mountain, “The Birth of Stereophonic Recording” excerpt” , (2014), Toby Mountain @ youtube
-  Harvey Fletcher at Wikidata
-  Timeline of Speech Perception Researchers, via Wikidata and DBpedia