From Unidyne to Dualdyne – the Dynamic Microphones of Shure

From Shure – the company that created the microphones used on the presidential podium since Lyndon B. Johnson – comes the KSM8 Dualdyne Vocal Microphone, a tremendous advancement in the technology of microphones.

Shure’s microphone engineers understand they’re part of a long lineage of great inventors. One such invention was the “unit phase” principal, which led to the development of the Unidyne I Model 55 microphone, the world’s first directional single-element dynamic microphone, invented at Shure by Ben Bauer; and the Unidyne II, which was introduced in 1951 when television had become important and the original Unidyne was considered too large to be on TV. The Unidyne II element allowed Shure to leverage the technology they’d invented in the original Unidyne, but in a much smaller model (Model 55S).

“It’s you versus physics on a dynamic mic,” says John Born, Shure Product Manager. “There’s no circuitry in there, there’s no electronics. You have to manipulate air to get the response and the level that you want.”

The breakthrough aspect of the Unidyne technology was that it was the first single-element dynamic microphone that responded to sound only from the front. Shure knew that directional pickup patterns feedback less. Their work solved a significant problem that grew when PA systems started to be used for bigger crowds.

Says Born, “On the Unidyne microphone, we allow sound to strike not only the front of the diaphragm, but the back of the diaphragm as well; and we allow sound from behind the microphone to hit the back of the diaphragm first. Just before it hits the back of the diaphragm, we actually delay it a little bit. By time-aligning that delay so that sound from behind the mic strikes the front and the back of the driver at the same time, that diaphragm doesn’t move and they cancel out. That’s how we get rejection.”

Recognizing the innovation of the Unidyne design, Shure patented it and, even today, every directional dynamic microphone in the world is based on that Unidyne patent.

Then, in 1954, engineer Ernie Seeler’s first major development at Shure was the Unidyne 3 which became the SM57 and SM58. “A dynamic mic is a perfect accelerometer. It wants to capture vibrations,” says Born. “That’s what it’s designed to do. It requires a pretty good shock mount to reduce those vibrations that could transmit into the microphone. Ernie Seeler had the foresight to design that into the handle.” The Unidyne 3 element built upon the Unidyne principal of allowing sound to strike the front and back of the diaphragm. Sounds coming from behind the mic travel and hit the back of the diaphragm first, then go down into the handle where the pneumatic shock mount is located. The pneumatic shock mount finally allowed artists and performers to take the microphone off the stand and hold it in their hand.

The timing was perfect. The audio world, particularly at Woodstock, found the Unidyne 3 microphones really worked for large sound reinforcement. They could be turned up loud, they could mic drums, they could mic guitars, they could mic voices, they could just mic everything.  And the same is true today.

“One of the experiences I’ve had in talking to a lot of engineers,” says Scott Sullivan, Shure Global Product Manager, “is they won’t do without having [the Shure SM57 and Shure SM58] in their toolbox. They have to have them.” “A lot of people use the SM58’s,” continues Born. “They know they can put an SM58 up on stage and they know they can make it sound great, no matter who shows up behind it.”

Where Ben Bauer started and Ernie Seeler took over, now Roger Grinnip leads the way for Shure. “The history is what brought me [to Shure],” says Grinnip, Shure Acoustical Engineer. “It makes me very proud to at least be able to say that I’ve made a bit of a difference. The KSM8 Dualdyne project started as an advanced development project which basically meant we didn’t even know if it was possible.”

Grinnip went back through old Shure lab notebooks to truly understand acoustically how the Unidyne 3 worked and what made it special. These were the papers written by Bauer and Seeler – journals kept in storage, filled with hand-written equations. He was able to strip down the Unidyne 3 to its bare bones and build that back up into the KSM8. It’s understood that virtually all directional microphones have what’s known as “proximity effect” which is to say when you’re right on a mic, it sounds muddy and heavy on bass, but when you’re a few inches off it sounds very natural and balanced, and when you get too far it sounds very thin and you’re fighting to get more low end out of the mic.

“Sound engineers intimately know this phenomenon,” says Born. “The challenge was, how to get this second diaphragm in a dynamic mic to control that proximity effect, to give that engineer and the artist a big sweet spot.”

“An omni-directional microphone does not exhibit proximity effects,” adds Grinnip. “The idea is that the second diaphragm effectively makes the microphone behave omni-directionally at low frequencies, but still have some directionality. It’s enough to tame that proximity effect.”

In the KSM8 Dualdyne, Shure reversed the flow of the dynamic mic. Sound coming from behind the microphone passes through the second diaphragm and partially blocks low frequencies from entering, thus controlling the proximity effect. The reversed airflow is what makes the KSM8 Dualdyne special and makes the engineer’s job easier.

“We took a prototype of [the KSM8] which was glued together with tape and rubber bands,” says Born, “and I heard warmth, I heard clarity, which I had never heard in the low end before. When I heard that for the first time, I knew we had to make this mic. I didn’t care what it took. We had to make it.”

September is Mic Month at Full Compass – visit and find special values all month long!


Information provided by Shure

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