The hearing aid, audiometer, artificial larynx, and stereophonic recording: Harvey Fletcher
This installment of Mormons in Technology discusses some of the contributions of Harvey Fletcher to society and technology. Fletcher is known as the father of stereophonic sound and devoted much of his career to studying the production, transmission, and recording of sound.
<table class="mceItemTable" align="left" border="0" width="230"> <tbody> <tr> <td></td> </tr> <tr> <td> University of Utah (Special Collections Department, J. Willard Marriott Library)
</td> </tr> </tbody> </table> Born in 1884 in Provo, Utah, Fletcher graduated from Brigham Young University in 1907. Fletcher then moved his young family to Chicago to pursue a doctoral degree at the University of Chicago. There, Fletcher worked with Dr. Robert Millikan on the famous oil-drop experiments as part of his dissertation work. Millikan won a Nobel Prize for being the first to accurately measure the charge of the electron in these experiments.
After graduating from the University of Chicago in 1911 with a PhD, Fletcher returned to BYU to teach for five years. In 1916, he accepted a job offer from the Western Electric Company, which became Bell Laboratories.
After retirement from Bell Laboratories, Fletcher taught at Columbia University and then returned to BYU to do research. In 1953, Fletcher established the Department of Engineering, which eventually became the College of Physical and Engineering Sciences. Fletcher continued to do research, especially in musical tones, and teach at BYU until his death.
Fletcher is remembered as an innovator in numerous fields. This article discusses some of his most significant contributions.
An audiometer, composed of an oscillator, attenuator, and amplifier, is used to by audiologists to measure hearing. Fletcher is credited with the invention of the audiometer, although he indicated that the device had already been created and in use before his own invention. However, the version Fletcher created, the 2-A, was the most practical and the most used.
The hearing aid
Dr. Fletcher created the first hearing aid using vacuum tubes for Alfred DuPont. DuPont sought a way to improve hearing during meetings. DuPont’s hearing aid consisted of two microphones that led to telephone receivers in a headband. The binaural system improved his hearing and allowed him to sense the direction of the speaker. The components were stored in a cabinet under the conference room table. Fletcher also created a hearing aid for Thomas Edison, a colorful and influential inventor.
The artificial larynx
Some people lose the ability to speak due to medical procedures that require the removal of the larynx, such as is common in cancer treatments. Fletcher developed an artificial larynx using a vibrating reed he had created to study speech sounds.
Fletcher’s work in auditory perspective is now referred to as stereophonic sound or stereo. Stereophonic sound gives a listener the impression that sound is coming from multiple sources instead of just one. This is how natural hearing works. The resulting spatial effect made talking pictures more realistic.
On April 17, 1933, Fletcher worked with Leopold Stokowski (composer and conductor of the Disney film Fantasia and director of the Philadelphia Orchestra) to demonstrate the capacity of stereophonic sound in live performances. Using three speakers (left, right, and center), three microphones, and three transmitting lines, a concert was performed at the Academy of Music in Philadelphia and played at Constitution Hall in Washington D.C. for dignitaries. During the performance sounds of hammering and talking were relayed with perfect depth perception, making it seem as though the activity was happening in Constitution Hall rather than in Philadelphia.
A third experiment involved two trumpeters, one in Washington D.C. and one in Philadelphia. It seemed as if there was a trumpeter on either side of stage in D.C., which was dark. The trumpeters took turns playing alternate selections of a piece. This made it impossible for the audience to tell that one of the trumpeters was not present. Only when the stage was lighted did the audience know that one of the trumpeters was actually in Philadelphia.
Fletcher took his experiments to the next level in 1939 at Carnegie Hall. Instead of transmitting from a different location, the alternate audio came from a previous recording. Fletcher repeated more demonstrations at the Eastman School of Music and in a Hollywood theater which included recordings from the Mormon Tabernacle Choir. It was because of these demonstrations that Fletcher was dubbed the father of stereophonic sound.
To learn more about Harvey Fletcher’s work, watch this interview by Bruce Bogert at Bell Labs.
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