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Shure’s Secret, Invisible Shockmount

Friday, November 2nd, 2012 | by


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

  1. How a Dynamic Microphone Works – a tour of the components, from the diaphragm to the transformer
  2. Creating directionality and frequency response through clever engineering
  3. The 50-year old secret behind the SM58’s best-in-class handling noise (YOU ARE HERE)

Transcript

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.

UNIdirectional DYNamic.

JB: Yes. And it used one element instead of two. We designed it in the 1930s, and it was in the Shure 55SH[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.

That’s engineering-speak.

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 –

JB: Absolutely.

– 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.

Posted in Interviews, Microphones, Video | 7 Comments »




7 Responses to “Shure’s Secret, Invisible Shockmount”

  1. Benjamin Isaiah McEntarffer

    November 4th, 2012 at 8:02 am

    Thank you gentlemen for this superb, in-depth look at a device that many take for granted.

    The workings of the dynamic microphone have always fascinated me. It was great to see John Born from Shure Bros. elaborate on the physical properties and how we manipulate using rear entry and air impedance, distance (D), resonance etc

    Thank you Peterson, great interview as always!

    Long live the dynamic microphone!

  2. Yves Van Moerbeke

    November 19th, 2012 at 1:30 am

    Indeed this does bring the old 57 in a different perspective, never thought that it was so well engineered. However, it does bring to mind that removing the transformer in a SM57 to brighten up, and darken the frequency response at the same time, one might suspect that the pneumatic shock mount will not work as it was designed. How would a sm57 react to just bringing the original transformer outside the body, it might change the sound for the better (that’s why we mod anything anyway), without losing the transformer output gain boost?

  3. matthew mcglynn

    November 19th, 2012 at 9:12 am

    @Yves, any change in cavity volume will definitely have an impact on the mic’s frequency response and pattern control. Presumably any such change would also diminish the mic’s mechanical noise suppression. Whether those changes are for the better is for you to decide.

  4. yoav tzfati

    November 27th, 2012 at 11:52 am

    Great videos, i learned a lot.

    I just wanted to respond to the vibration noise graph that appeared in the email you sent to subscribers. Although i don’t have a hard time believing that the 58 really handles noise better than the competition, it might be more useful to compare vibrational noise sensitivity to sound sensitivity instead of 1V of signal. A microphone might be more sensitive to vibrational noise, but if it is also more sensitive to sound by the same amount or more it cancels out and/or gives it a better signal to noise ratio. Therefore the graph is useless to me. It would be a lot more informative if shure compared the voltage created by the defined vibrational noise to the voltage created by a sound pressure of 1 Pa at different frequencies.

    Also, it would have been nice to learn about proximity effect and the electronics involved.

  5. John B

    November 29th, 2012 at 11:33 am

    @yoaz tzfati

    Thanks for enjoying and watching the videos. The graph you’re referring to is created using the output of the mic during a vibration table sweep. They are “Equivalent” dB SPL meaning the graph is adjusted for each mics sensitivity (so a microphone that has say a 6dB hotter output is not penalized). The mic’s response does have an effect on the curve especially if the manufacturer tailors the response to aid in handling noise reduction. There is no acoustic stimulus during this particular test as we’re only interested in acoustic artifacts transferred through the mic during vibration. Hope that helps explain the results.

    Related to proximity effect and using electronics (low cut filtering), we have some videos devoted to those topics in the blog section of our website at shure.com.

    Thanks!
    -John
    Shure Inc.

  6. Big Dave

    November 29th, 2012 at 5:09 pm

    Those were great videos. Thanks for sharing!

  7. David Beneke

    December 4th, 2012 at 2:15 pm

    Wow, great video. I have a couple of old Shure S39 A microphone stands which I cherish and wish Shure still made. Put an SM 57/58 or SM7b on one, and I don’t think a cannon ball hitting the table would cause vibration. Over the years the foam rubber rotted out of mine and I replaced it with several layers of neoprene padding. Also Had to replace the rubber feet with newer silicone pads, good or better than new!

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