Friday, November 2nd, 2012 | by Peterson Goodwyn
This is part III of a 3-part series, in which Shure’s product specialist for wired mics, John Born, talks with Peterson Goodwyn of DIYRecordingEquipment about the innovations — some familiar, some you’ve never imagined — that help make the SM57 and SM58 the most popular dynamic microphones in the world. This video marks the first time Shure has spoken publicly about its proprietary “Pneumatic Shockmount,” an essentially invisible mechanism engineered into these dynamic microphones that gives them the lowest handling noise of any dynamic mics on the market today.
Shure Video Series
- How a Dynamic Microphone Works – a tour of the components, from the diaphragm to the transformer
- Creating directionality and frequency response through clever engineering
- The 50-year old secret behind the SM58’s best-in-class handling noise (YOU ARE HERE)
That brings us to the third real-world problem: these don’t typically site here without any shock and get used. They’re all over the place, in front of the kick drum, they’re on a floor, getting mechanically coupled to the floor —
JB: They’re in your hand, moving around. They’re going inside and out of a stand.
So how do we make it so we hear the sound and not the actual mechanical vibration. What’s going on there?
JB: That’s the beauty of the SM57 and SM58, and the Unidyne III cartridge —
Let’s clarify what that is.
JB: The “Unidyne” was the first single-element, dynamic directional microphone.
JB: Yes. And it used one element instead of two. We designed it in the 1930s, and it was in the [Shure] 55, the “fat boy.” It was the first time you could create a unidirectional microphone using only one microphone element. [Previously] you had to use two, and combine —
and use one to cancel the other.
JB: Yes. We did that through this rear entry and phase-shift network. So that was the Unidyne. And then in the late 1960s we designed the Unidyne III cartridge, which was basically a variation of [the Unidyne] but was a lot smaller, and had what we call a “pneumatic shockmount” in it.
The pneumatic shockmount is an integral part of the success of those microphone and the current microphones today, [meaning] the SM57 and SM58. A dynamic microphone is inherently an accelerometer, and it is excited very easily through vibrations. Especially [for those vibrations] entering on the same plane as the diaphragm moves.
So that means that this kind of movement [motioning side to side] isn’t really affecting the sound too much.
JB: We’re not as much concerned about movement of the diaphragm [side to side], because everything is moving together in this axis. But we are concerned about the diaphragm moving in this axis [along the axis of the mic’s directivity]. A lot of handling noise happens that way, and stand vibrations.
The clever thing about the pneumatic shockmount is, it’s actually designed in conjunction with the acoustic design of the cartridge.
Of course. Because you can’t solo one thing.
JB: You can’t solo anything in a dynamic microphone. You can’t design the shockmount is isolation of designing the acoustics of the microphone.
And just to be clear, we’re not talking about an external shockmount.
JB: Nope. We’re talking about the pumping shockmount inside the mic.
If you open this up here [opening an SM57], this thing [indicating the cartridge] actually pumps inside of this collar. If you move it you can actually see it pump like a piston inside of this collar. Keep in mind there are cavities in here that are changing volumes —
when you pump.
JB: when that microphone [cartridge] moves back and forth. There’s a cavity down here [behind the cartridge], which is also integral to the response of the mic.
But the beautiful part about the pneumatic shockmount, which is unique to Shure products — we’re the only ones who have a pneumatic shockmount — is [that] as vibrations travel up the handle, [they] shrink a cavity inside of this closing ring, inside the collar.
Because the body is moving forward, and the capsule on the mount is moving backward.
JB: Yes. And there’s a cavity in here that’s shrinking, and pushing more air into another cavity which is underneath the diaphragm. And that cavity is putting more pressure underneath the diaphragm and counteracting the mechanical pressure being induced by that vibration on the other side of the diaphragm.
Wow. Ok. Wow.
JB: It’s deep.
It’s deep, but … the basic idea is simple. Obviously the math involved in making that work is something else.
JB: It’s stupid complex.
JB: That’s engineering for “hundreds and hundreds of pages of equations that you can’t even wrap your head around.” And that’s the difficult part of the pumping shockmount, the pneumatic shockmount. You can’t design it outside of just acoustics. You can’t design the acoustics of the microphone and then mount it in a [pneumatic] shockmount. They’re intimately tied together. Because you have to have that connection through those cavities, along with the shockmount compliance parts. So, it’s very complex.
It’s really fascinating. So this entire body [indicating an SM57] design, the entire headbasket, the way that the diaphragm is mounted… it’s easy enough to look at this thing, you know, you can get it for $90 at Guitar Center, you can get it for $50 off of Craigslist. I don’t know if I’m supposed to say that, but that’s the fact of the world. It’s tempting to look at it and say, well, there’s the microphone part here [at the top], here’s the handle…
JB: “I could do this.”
Right. But really, everything about this is finely tuned —
— to make the microphone work in all these real-world situations. And of course the cliche about SM57s is that you can take them to work during the day and hammer nails, then sing with it at night.
JB: And that didn’t happen overnight. And it didn’t get designed overnight, either. It takes years and years to truly develop a good dynamic microphone, and to do it well. And it takes a lot of smart people, a lot smarter than me, to design these microphones. There’s a reason why it works the way it does, because we feel it’s the best that we can make. And it has stood the test of time.
Certainly it has been on a few albums, and been around for a bit.
JB: It’s been around the block a little bit.
So we’ve been talking exclusively about the SM57. But how much of what we’re saying, how much of the basic ideas, applies to any kind of dynamic mic?
JB: Almost all of it does. Aside from the pneumatic shockmount, which is pretty proprietary to Shure, the concept of the phase-shift network and directionality and creating a directional microphone, we designed that in the 1930s, and pretty much every directional dynamic microphone in the world is based on that design. Which is pretty cool.
Interesting. Wild. Well, thank you so much, John. This has been hugely mind-expanding for me. I certainly have a new appreciation for these tools that —
JB: That you use every day.
And maybe I’ll even try singing into one, rather than hammering nails with them.
JB: That would be great.
Thank you so much.
JB: Thanks for coming out.
We appreciate it.
Peterson Goodwyn is a drummer and audio engineer based in Philadelphia, PA. He runs the popular DIY site for audio engineer gear builders, DIYRecordingEquipment.