Milestones:Unidirectional Microphone

From IEEE Milestones Wiki


Single-element Unidirectional Microphone - Shure Unidyne, 1939


In 1939, Shure Incorporated introduced the Unidyne microphone. Using the Uniphase acoustical system, the patented Unidyne was the first microphone to provide directional characteristics using a single dynamic element. This breakthrough offered lower cost, greater reliability and improved performance for communication and public address systems. Shure Unidyne microphones are still manufactured and used worldwide in numerous audio applications.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

42.0126755, -87.7725141, 5800 W. Touhy Ave. Niles, IL 60714-4608

Details of the physical location of the plaque

The plaque will be mounted on a wall in the lobby of Shure's worldwide headquarters in Niles, Illinois.

How the intended plaque site is protected/secured

The building is secure at all times. Visitors can simply enter the lobby entrance to view both the plaque and Shure's display of historical microphones and documents. Additional access to the building would need to be arranged with Shure.

Historical significance of the work

2013 marks the 75th anniversary of Ben Bauer’s invention of the Uniphase principle while working for Shure Brothers Incorporated, a microphone manufacturer in Chicago. As a newly graduated engineer, the 25 year-old Bauer developed an acoustical method that produced a directional microphone using only one microphone element. The Uniphase principle paved the way to the design of the Shure Unidyne microphone. Introduced in 1939, the Shure Unidyne is arguably the most recognized microphone in the world.

Benjamin Bauer (originally Baumzweiger) was born in Odessa Russia in 1913. His family fled Russia after the 1917 revolution and relocated to Cuba. At the age of 17, and speaking little English, Bauer moved to New York City to attend the Pratt Institute. After obtaining an associate Industrial Engineering degree, Bauer matriculated at the University of Cincinnati pursuing an Electrical Engineering degree. Bauer chose a five year work/study program and began working as an intern for Shure. When he graduated in 1937, he joined Shure full time as a transducer development engineer. It was the start of a distinguished career in acoustics and audio that included over one hundred patents. Benjamin B. Bauer became an IEEE Fellow member in 1952 and received his recognition on the Citation: "for his important contributions to the development of microphone and other audio devices." He received other IEEE Awards with the IRE in the Professional Group on Audio in 1955.

Three technologies came of age during the 1930s, and a nascent technology was being nurtured. Radio broadcasting, public address systems, and two-way radio communication became commonplace in the 1930s, and television broadcasting was in development. One common factor required for all was the use of a microphone.

A microphone is a transducer. The function of a transducer is to change one type of energy into another type. A microphone changes acoustical energy (sound waves) into analogous electrical energy. Once the sound waves become electrical waves, they can be amplified, broadcasted, stored on disc, wire, and magnetic tape, or manipulated in other ways. A microphone was the primary audio signal source for radio, public address, and television. Since the 1930s, a microphone has been present at nearly every major or minor event that has shaped the world.

In the early 1930s, the carbon element microphone was in common use. Though not expensive, its audio quality was poor; it required a DC power source to operate; it had no ability to reject unwanted background noise. There were also condenser element microphones – expensive and fragile – and crystal element microphones – adversely affected by heat and humidity.

In 1939, Shure began to manufacture microphones with dynamic elements. This dynamic element microphone was, in essence, a loudspeaker in reverse. Instead of a paper cone, there was a circular diaphragm molded from plastic. Glued to the diaphragm was a voice coil wound from miniature wire. The voice coil was positioned in the middle of a miniature permanent magnet. Sound waves from the talker moved the plastic diaphragm (suspended like a trampoline) which in turn moved the voice coil. A tiny voltage was induced in the voice coil because of the magnetic field. This voltage was the electrical equivalent of the sound wave.

Precision manufacturing techniques were necessary to create a dynamic microphone element, but the underlying design was simple. The result was a reliable, rugged microphone that was inexpensive, required no external power, and could be made by the thousands with repeatable tolerances. Yet the dynamic element microphone did not solve the problem of unwanted background noise.

Unwanted background noise (ambient noise) is often a problem wherever a microphone is needed. In a radio studio, the background noise might originate with the audience whispering or turning program pages. These noises would be distracting to the radio listener at home. In two-way radio communications (fire, police, medical), unwanted background noise would reduce the intelligibility of the messages being sent and that could result in the loss of life. In public address systems, unwanted background noise can be the root cause of acoustic feedback - that annoying squealing and howling that occurs when a public address system is turned up too loud. The unwanted background noise is the amplified sound waves emanating from the loudspeakers. When the loudspeaker sound waves are picked up by the microphone, the waves are re-amplified again and again, and a “feedback” loop is created.

A directional microphone is a desirable tool to reduce the pickup of unwanted background noise. It is more sensitive to sound waves that originate at the front; less sensitive to sounds that originate to the sides; and far less sensitive to sounds that originate to the rear. The most common and useful microphone directional pattern is shaped like a heart, and is aptly named “cardioid,” as in cardiac. Be it a radio studio, a police station, or an auditorium, a directional microphone will attenuate unwanted background noise and that will improve the quality of the audio signal being heard by the listeners. The Shure Unidyne was the world’s first directional, dynamic, single element microphone. Manufacturing of the Unidyne began in 1939 and it has been in production ever since.

The industrial design of the Unidyne is firmly grounded in the Art Deco movement. Sleek in design with a futuristic appearance, the Unidyne pays homage to the grilles of late 30s automobiles, such as the Cadillac roadster. The appearance of the Unidyne has come to mean “microphone” worldwide. A Google image search on “microphone” presents the Unidyne as the first result. The Unidyne has appeared on postage stamps in many countries. It has been a graphic icon on countless TV shows and innumerable Web sites. It has public recognition rarely attained by any product except perhaps the Coca-Cola bottle. The reason is that the Unidyne has stood in front of celebrities, politicians, and entertainers for over seven decades…and has been photographed with these people during celebrations, performances, and historical events. Examples include: Martin Luther King Junior’s “I Have A Dream” speech, “Dewey Defeats Truman”, Elvis Presley, President Roosevelt addressing the nation during World War II, Frank Sinatra during the Big Band Era, Indira Gandhi, the Japanese surrender on the battleship Missouri, Groucho Marx radio programs, Star Wars movies, Battlestar Galactica TV series, MTV music videos, Robin Williams in “Good Morning Vietnam,” President Kennedy press conferences, and singer Taylor Swift at the Grammy Awards.

It is not hyperbole to state that since 1939 a Shure Unidyne has been the chosen microphone model at more important historical and entertainment events than any other microphone.

Features that set this work apart from similar achievements

The Unidyne microphone was the first directional microphone that used a single dynamic mic element. Using a single element reduced the size, weight, and manufactured cost, increased reliability, and significantly improved the acoustical performance. The Unidyne spawned even more popular models. The Unidyne II, a smaller version of the Unidyne, was introduced in 1951. The Unidyne III, grandchild of the Unidyne, was introduced in 1959. It is the most widely used professional microphone in the world and has been the microphone of choice for every U.S. President since Lyndon Johnson. And in 2013, a Unidyne III microphone is used on the International Space Station for live TV and Internet interviews with the crew.

Significant references

To fully understand the design details of the unidirectional microphone, you only need to read patent 2,237,298 which was filed by Benjamin Baumzweiger on September 29, 1938 and granted on April 8, 1941. To those in the sound industry, he authored the article “A New Unidirectional Microphone” in the February, 1939 issue of Electronics. Just before the IRE merger with the IEEE he contributed an article entitled “A Century of Microphones” to a commemorative issue of Proceedings of the IRE in May, 1962. However, the best endorsements about the significance of unidirectional microphone come from the sound industry. In the second edition of The Microphone Handbook by Jon Eargle (2012), the author says on page 350 in regard to Shure’s unidirectional microphone that “the M-55 has been in the Shure catalog in one form or another since its inception in the late 1930s. It is truly one of the icons of the industry and has been documented in press and news activities over the years.” In the Twelve Microphones that Made History by Jim Webb, ( the author says this about the Shure Unidyne Model 55. “It is hard to imagine another microphone based on its original concept and styling that has remained in production as long as some version of the Unidyne.”

The invention of the single-element unidirectional microphone is truly a milestone.

Supporting materials

The following references were submitted in pdf format:

Bauer-Century of Mics AES, A Century of Microphones, J. Audio Eng. Soc., Vol. 35, No. 4, 1987 April

Electronics Feb 1939 Article, A New Unidirectional Microphone, Electronics, February 1939

Patent 2237298(A1), Conversion of Wave Motion Into Electrical Energy, Patent 2,237,298, April 8, 1941

The Microphone Book, The Microphone Book Second Edition, John Eargle, Focal Press

Bauer Tribute-1, Bauer Obit by Cyril M. Harris, National Academy of Engineering, Volume 2 (1984) p.1

Bauer Tribute-2, Bauer Obit by Cyril M. Harris, National Academy of Engineering, Volume 2 (1984) p.2

Bauer Tribute-3, Bauer Obit by Cyril M. Harris, National Academy of Engineering, Volume 2 (1984) p.3

The following reference was submitted in jpg format:

Shure Ad in 1950, Shure Advertisement, 1950 Directory of the I. R. E. Chicago Section

Shure Ad in 1950, Shure Advertisement, 1950 Directory of the I. R. E. Chicago Section






Media:Bauer Tribute-2.pdf