There are a few microphone shapes, designs, images that could be called icons...that symbolize what many think of when someone says the word microphone. One of those that has become an icon is the Shure model 55 series of mikes. The Shure 55 made its debut in 1939 and its successors are still around today some 70 plus years later. [1,2]
The Shure company was founded by Mr. S.N. Shure back in the 1920s. Later it became a family operation called Shure Brothers. Shure originally made relatively low cost carbon and crystal mikes for use in PA systems and in the communications field as well as phonograph pickup cartridges. The year 1937 was a turning point when a young engineer named Benjamin Baumzweiger (who later changed his name to Bauer) began developing his idea for a unidirectional microphone using a single dynamic element. Prior to this all dynamic mikes were non-directional. As we related in previous articles in this series...RCA and Western Electric had both developed unidirectional pattern mikes using a combination to two different microphone elements in the same housing.
Bauer felt that the best way would be to use just one element...reducing the large and bulky size of the dual element units. He came up with his theory of using a series of front and rear openings in the dynamic element which allowed sound waves to reach both sides of the element's diaphragm. Using acoustic principles that produced a time delay between the sound entering from the rear and sound striking the front of the diaphragm. By varying the amounts of acoustical resistance encountered at the rear openings, Bauer was able to achieve cardioid, supercardioid, or hypercardioid patterns using a single element, and the first true unidirectional dynamic microphone became reality.
Shure called this design the “Unidyne”. The Unidyne model 55 became an instant hit in the audio field. The Unidyne set a new standard of high quality audio pickup combined with discrimination against unwanted sounds. This offered a great new ability to control feedback and reduce ambient noise pickup. The Shure 55 also came in at a much lower price-point than previous directional mikes. Utilizing Shure's proprietary “uniphase” technology, the Unidyne was marketed for PA, recording, and broadcast applications. The streamlined chrome head could be tilted up to 90 degrees. A built-in cable connector and stand mounting were part of the unit.
With the Unidyne Shure was able to crack open the broadcast market against the dominant players RCA and Western Electric. In 1940 Shure introduced a separate broadcast version of the Unidyne which became the model 556.  This unit had closer tolerances and an improved isolation mount of live rubber. An external call letter plate could be purchased separately as an accessory. Many radio stations used the Shure Unidynes in their control rooms and studios.
This being the Modesto Radio Museum site we want to mention that KTRB, Modesto's first commercial radio station, used the Shure broadcast version Unidyne for many years from the time the station moved to the Norwegian Avenue studio site around 1942  and into the 1960s. In the main big studio KTRB utilized the very famous “Starbird” heavy-duty mike booms and hanging on the end of each one was a Shure Unidyne. [8,9,10,20] Many famous performers visiting the KTRB studios had their voice picked up by these iconic microphones. KTRB also used the Unidyne in each of it's two identical control rooms.
The original Unidyne model 55 is sometimes called the “fat boy”...or the “Elvis mike”...of course many, many famous performers used these mikes long before Elvis came along.[12,13,19] In 1952 Shure came out with an updated version of the Unidyne that was quite a bit smaller with a more squarish shape compared to the rounded “fat boy”. This new model was the model 55S...the “S” for small Unidyne.[14,15] Shure made both the large and small models available for about the first year and then the big model was dropped from the catalog.
The new smaller model Unidyne has continued production down to today...yes you can buy a brand new model 55SH Series II from any Shure dealer  The price today is about 3 times what you would have paid for the 1950s era model 55S...about $170 compared to about $48 in the mid-50s! The “broadcast” version...the model 556S was slightly higher in price...but this version was discontinued somewhere in the 80s. The modern version of the 55 has a much improved internal cartridge unit that is on par with any modern unidirectional microphone.
The Shure Unidyne line of mikes included mikes with more modern cylindrical case design units that came into the catalog in the 1960s. These designs gave birth to the famous Shure “ball-top” SM58 model that is one of the most used vocal mikes on stage in the world.  There is also the model SM57 which has been used on the US Presidential podium for more that 30 years as well as being used for musical instrument pickup. All these mikes came from the heritage of the original model 55 developed by Shure engineer Ben Bauer back in 1937. 
Much of the information in this article came from the Shure publication “The Unidyne Story” which can be downloaded from Stan Coutant's Microphone website in PDF format.. I recommend a visit to the Coutant site for some great pictures of the Shure 55 series with a lot of great information for mike buffs on many different microphone manufacturers. The address is: coutant.org/1.html.
(2.) Catalog page showing the PA and broadcast models and the radio station call letter plate accessory. (Coutant)
(1.) Shure's debut of the 55 (Stan Coutant)
(3.) Cutaway drawing of the Unidyne internals. (Coutant)
(4.) The Microphone Man's own original model 55 “Fat Boy” used in the audio file on this page. (Gary Avey)
The Broadcast model 556 which had a live-rubber stand mounting. (Shure)
Actor Bob Crane got his start as a radio DJ at WLEA and used a Shure Unidyne. Later in his career Bob was the morning man at KNX, the CBS station in Los Angeles. (U of Maryland)
Here's KTRB's Andy Anderson showing the station's early use of the Unidyne dynamic.
A KTRB live gospel group program utilizing the unidirectional pickup of the Unidyne.
KTRB announcer Bob Ulrich in the main studio using one of the Unidyne mikes attached to a “Starbird” boom.
Here's KTRB's country music personality, the late Chester Smith, looking over his amazing load of product labels sent in by fans.
The Shure Unidyne was KTRB's standard mike for many years.
Funny man Red Skelton using a Unidyne for a live stage show. (Shure Unidyne Story)
Singer Dinah Shore and many more including Elvis were Unidyne users. (Shure Unidyne Story)
This is the smaller version Unidyne that came out in 1952. (Coutant)
KTRB program director the late Cal Puviance using the newer smaller 55S
You can still buy a brand new model 55SH Series II from any Shure dealer...it has a pickup cartridge inside similar to Shure's modern SM57 or 58.
ABC news commentator Drew Pearson using a Unidyne in the WMAL studios in Washington DC. (U of Maryland)
Chester Smith with country music star Hank Snow in the KTRB main studio in the 1950s
KTRB's large main studio showing three Starbird booms with Unidynes on each and another in the smaller adjacent studio seen through the window.
Shure “ball-top” SM58 model that is one of the most used vocal mikes on stage in the world.
There is also the model SM57 which has been used on the US Presidential podium for more that 30 years as well as being used for musical instrument pickup.