Shure Model 55 Unidyne microphone

Classic Projects: Shure Model 55 Unidyne microphone

Image credit: Holger Ellgaard

The Shure 55 microphone is an American design classic that has been in continuous production since 1939, but its initial success was based less on its looks than its ability to filter out background noise.

With its Art Deco automobile grille line and chrome-plated die-cast case, the Shure Model 55 Unidyne microphone ranks not only as one of the most identifiable microphones in the history of pro-audio, but also as one of the highlights of 1930s industrial product design.

The Model 55, which was superseded in 1951 by the similarly styled but smaller 55s, has become fixed in the public imagination as the ‘Elvis mic’. The association is largely due to the US Post Office in 1993 issuing a 29-cent stamp bearing an illustration of the King performing with a stylised version of the 55 mic (other singers in the stamp series include Billie Holiday and Patsy Cline). The stamp broke all records, becoming the most collected ever in the USA, and, despite the illustration not being particularly accurate, there is conclusive photographic evidence that Elvis used a 55 mic on many an occasion. As indeed did Fidel Castro, Eva Peron, Martin Luther King and US President Harry S Truman.

The reason the Shure 55 was so popular had little to do with its aesthetic design and more to do with the new unidirectional dynamic (‘Unidyne’) technology, which was delivering huge improvements in broadcast and public address audio amplification. As Shure’s literature explains, a microphone is essentially a transducer, the main purpose of which is to change one energy type into another. Until the Shure 55 came along, microphones tended to be either of the carbon or condenser element variety. The former was inexpensive, needing a DC power source, while lacking the ability to filter unwanted noise. The latter, because of the crystal technology, tended to be fragile and expensive.

The beauty of Benjamin Baumzweiger’s design for Shure was that it overcame all of these issues, as it incorporated ‘dynamic elements’, which meant it was essentially a loudspeaker in reverse. Shure’s technical paper goes on to explain, “instead of a paper cone, there was a circular aluminium diaphragm”. This in turn was connected to a voice coil positioned in the centre of a miniature permanent magnet. “Soundwaves from the talker moved the diaphragm (suspended like a trampoline), which, in turn moved the voice coil.” From here, a tiny voltage was induced in the magnetic coil, becoming the electrical equivalent of a soundwave. Baumzweiger also knew that directionality is crucial in microphones for reducing both unwanted background noise and feedback, the most common field-shape being heart-shaped, which is why we have ‘cardioid’ mics. With the launch of the 55 Unidyne model, the world was introduced to the first ever directional, cardioid, single element microphone. It has been in production ever since. With the possible exception of early Neumann condenser microphones, there are no other mics with such a long history.

Such was the technol­ogical importance of the Shure 55 that in January 2014 it was awarded the IEEE’s Milestone in Electrical Engineering and Computing award. The citation says that the technical “breakthrough offered lower cost, greater reliability and improved performance for communication and public address systems”. While this is beyond dispute, what is also true is that when the microphone burst onto the scene, it was a design that captured the zeitgeist like no other. Shure’s Tim Vear says it was down to the fact that “they have become cultural icons and a visual cue that can transport us to a different era. Viewed from a design perspective, they exude all the coolness of a 57 T-Bird, Stratocaster guitar, or a James Dean movie”. 

Shure Model 55 Unidyne microphone facts and figures

Date: 1937

Architect: Benjamin Baumzweiger (later ‘Bauer’)

Unit cost: Still in production, £200 plus (depending on model)

The Shure 55 appeared on a 1993 commemorative US postal stamp along with Elvis Presley

First single-element unidirectional dynamic microphone

The 55 Series mics were awarded the ‘IEEE Milestone’ award in 2014

Used by Martin Luther King for his ‘I have a dream’ speech

Pictured with Fidel Castro on the cover of Life magazine, 19 January 1959

Today, Shure produces the 55SH II ‘Elvis mic’ replica with modern technology

Overall appearance has remained constant since 1939

Original catalogue price: $42.50

Early advertisements marketed ‘The Microphone That Needs No Name’

Eva Peron made speeches using the Shure 55


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