Meeting Report: Historical Development of the Unidyne

Meeting Topic: Historical Development of the Unidyne I, II, III

Moderator Name: Jay Dill & Nate Sparks

Speaker Name: Gino Sigismondi & Michael Pettersen, Shure Inc.

Meeting Location: virtual (YouTube:

Date: January 21, 2021


Shure’s Michael Pettersen and Gino Sigismondi joined the Central Indiana Section to dive into the storied history of the Unidyne dynamic microphone motor/capsule and the subsequent evolution that have shaped our industry.
Michael began the program by taking us back to the original electrical equivalent diagrams written in Benjamin Bauer’s notebook in 1937, describing what would become the “Uniphase Network” to create a single-capsule, directional dynamic microphone. The design was complimented by the work of designer Wesley Sharer, along with a little inspiration from the grill of the ’37 Oldsmobile Coupe Six, and was released as the Unidyne Model 55 in 1939.
The Unidyne II was first released within the Model 55S in 1951. The Unidyne II features the same performance with a size some 30% smaller than the original Unidyne capsule, thus the “S” nomenclature for small. The new design was oriented towards the television medium, which considered the original Model 55 to be somewhat obtrusive.
The Unidyne III Model 545 was released in 1959, touted as the “smallest cardioid dynamic microphone” ever. The Model 545 was end-addressed, and therefore had a more consistent polar pattern than similar and competing models of the era. This led to popularity with the burgeoning sound reinforcement industry, as the pattern’s consistency allowed for more gain before feedback. The Beatles were marquis users of the Model 545 with the A25B swivel mount.
As the Model 545 gained popularity on stage, Bob Carr worked on a line of Unidyne III-based microphones to appeal specifically to studios. This line, dubbed “Studio Microphones” (SM) consisted of microphones using the same capsules as existing mics, but with less reflective finishes, no switches, and included XLR connectors. The venerable Unydine III SM56 was released in 1964, with the SM58 released just two short years later. While not instant sales successes, the use of the SM56 at the Monterey Pop Festival by McCune Sound in 1967 yet again raised their profile in the live sound arena. The push as a live sound microphone line occurred more in the 1970s with their introduction to the performers and sound companies in Las Vegas, with artist such as Frank Sinatra becoming devoted users. Also of note was the introduction of the now-famed SM7 in 1972.
Following the history of the Unidyne series, Gino and Michael took audience questions, as well as providing a little “audio mythbusters” surrounding the Unidyne family.

Written By: Brett Leonard