Review: Shure KSM8
Shure has torn apart its dynamic microphone concept to add in another diaphragm; and two is definitely better than one.
By Mark Woods
3 May 2016
Whether it’s in ALL CAPS, longwinded technical jargon truncated into an acronym, or simply a made up, authoritatively-stamped name like ‘TransMotik™’, marketing phraseology is mostly designed to disguise the fact that Company A’s product does exactly the same thing as Company B, C and D’s.
Shure’s new epithet, Dualdyne, actually means something. Firstly, it comes from a distinguished lineage of corporate milestones that started with the first Unidyne directional microphone in 1939 and evolved into the Unidyne III; identifying the dynamic diaphragm assembly inside your bog standard SM58. Secondly, it’s not just a description slapped on one small piece of a product to give it a bit of leverage in the marketplace; Dualdyne is the core reason Shure’s new KSM8 — the first handheld dual diaphragm dynamic microphone — is a product.
Everyone loves simple, strong dynamic mics but there’s always been a few areas ripe for improvement: they’re boomy up close, thin at a distance and nasty off-axis for starters. I’ve been winding the bottom end off SM58s for around 40 years and the prospect of a Shure-made dynamic handheld with controlled proximity effect and a decent off-axis response is, well, exciting. Shure’s KSM8 is a new type of microphone designed to address those issues, and live sound will never be the same again.
OLD YET NEW
Shure has put a lot of effort into the KSM8, inside and out. It’s an old look that comes off new; shiny (black version withstanding) yet practical. The aluminium body is finished in brushed nickel reminiscent of the old Unidyne models, but it looks flashy and modern on stage, especially under lights. The slotted collar and Shure insignias are similarly retro but the silver grille is too finely machined for the 1950s. It’s too nice to substitute in as a hammer, like one might an SM58, but it feels strong and the hardened grille, lined with a layer of spit-blocking hydrophobic foam, has no give in it at all. The silver version I was reviewing had started to develop fade marks where the mic clip grips the body and a couple of little scratches from use, so they may develop some patina over time.
The attention to aesthetics continues under the grille too. The capsule housing the diaphragms looks like a little rocket and even though you’d never see it in use, the disc sitting above the diaphragm proudly sports the shiny Shure logo. The shape of the KSM8 body flairs towards the top, similar to family-mate KSM9, and even though its slightly wider it still conveniently fits in a regular Shure clip. At 330gm it’s 10 percent heavier than a 58 but it’s well balanced and feels just right in the hand.
CONTROLLED DYNAMICS
The dual-diaphragm is not there for its looks however, it’s there to solve problems. Proximity effect is probably the biggest one and it affects all directional mics. I love my SM58s and keep coming back to them, but when singers are right up on the mic the low frequencies overload and you have to filter them out. The high-mid presence peak is built-in, partly to try and cut through the mush but it adds harshness and colouration. The physical layout of the two diaphragms in the KSM8 allows it to behave like an omni (no proximity effect) at very low frequencies and gradually become cardioid around 100Hz. In use there’s still some added lows right on the mic but it’s well controlled and sounds natural rather than boomy. The low-frequency response is also extended and while some LF filtering may still be needed for vocals it will only be a touch, compared to what you’re used to. Like all mics, it will pop if provoked, but not unduly and according to Shure, the dual-diaphragm design delivers a lower level plosive than single-diaphragm designs.
The other benefit of controlling the polar pattern to limit proximity effect is its effect on the source as it moves away from the mic. Rather than disappearing up the frequency spectrum into thin air, the KSM8 retains clean and strong low-mids. This extra clarity has allowed Shure to remove the familiar presence peak built into most dynamic vocal mics. The net effect is a mic that is essentially flat, has an extended frequency response, maintains its response over a greater range of distances, and dramatically reduces proximity effect up close. Basically, an entirely better microphone.
There’s more. Microphones turn three-dimensional sounds into two-dimensional outputs and the accuracy of the sound arriving from the rear and sides is a big part of why some mics sound more natural than others. I mentioned that I love my 58s, but not for drum vocals because the kit sounds trashy in the drum vocal mic. If I use a mic with a more accurate off-axis response the kit can sound pretty good in the mic. Reinforcing acoustic music requires mics with good off-axis response to sound natural, but this hasn’t been as important for louder music, where everything’s close miked. Yet, as sound reinforcement systems have improved and IEMs have become popular the focus has turned towards higher quality microphones. The KSM8 has a pleasing SDC condenser like neutrality to its off-axis response but it has a sharper cardioid pick-up pattern and much greater rejection. The pick-up pattern stretches evenly right across the top of the mic and it still sounds good some way down the side of the grille before dropping off sharply with excellent rejection at the rear.
Shure won the handling noise battle ages ago with its proprietary pneumatic shockmount system. It’s been tweaked for the KSM8 and joined by the new Diaphragm Stabilization System [patent-pending acronym alert – Ed] that gives extra protection from plosives and knocks. If you take the top off the KSM8 and tap the diaphragm assembly directly, then tap on the body of the mic, the difference in output levels is around 30dB and quite astounding when you hear the difference as an A/B comparison.
NEED TO KNOW
Shure KSM8
Dualdyne Handheld Dynamic Microphone
DUAL DIAPHRAGM TECH
Shure Product Manager, John Born, was one of the small development team that worked on the KSM8 project. He said the idea for the KSM8 came out of what Shure had learnt while building the KSM9 handheld condenser: “We knew from the KSM9 that if we could get a second diaphragm into the cartridge, we could use it as part of the acoustic network to control proximity effect. It had never been done on a dynamic due to the physicality of trying to make it fit. There’s all these parts in the way — coil, air cavity, pole piece — to put a second diaphragm in the spot, you have to break everything in the process.”
Such a design would also allow Shure to get rid of the presence peak that’s a byproduct of making a single diaphragm mic directional. Born cites two reasons for its existence. “One, you need the peak to offset the proximity effect when you get right up on the microphone, so it’s not muddy. Secondly, physics make it hard to get rid of it even if you wanted to.”
When confronted with the task of developing a dual diaphragm dynamic, Shure’s engineering team stipulated they couldn’t be beholden to any existing parts or processes — they literally started out with nothing. What they ended up with was a unique design.
Born: “When you make a microphone directional, you allow sound to strike the front and back of the diaphragm. You delay the sound that goes through the back of the cartridge and time align it to achieve rejection. With the KSM8, in addition to the resistance delay we also have a diaphragm which delivers proximity effect control. As the source gets closer to the microphone, the second diaphragm starts seeing that low frequency energy more, and starts blocking that energy from building up as the source gets closer and lower. At 0Hz, it basically tricks the front diaphragm into thinking the capsule is sealed and the mic is omnidirectional.
“Omni-directional microphones don’t have proximity effect, so we reap the benefits of that. But we do it in a way where we don’t actually sacrifice polar pattern. As you creep up into the audio band at 20Hz, it starts becoming more cardioid to a point where the second diaphragm is transparent to high frequencies. The KSM8 is pure cardioid right down to 100Hz without any electronics or a crossover band-pass network.”
There’s no fixed crossover frequency point where the diaphragm becomes invisible, it’s conditional on the distance between the source and the microphone. “It’s based on both the Inverse Square Law — whereas a source gets closer, it gets louder — and on frequency” explained Born. “A single diaphragm microphone goes almost bi-directional in its low end response as you get close to the source; that’s what causes the proximity effect. At further distances, a single-diaphragm microphone exhibits its purest pattern.
“The second diaphragm breaks that, rendering a more stable pattern at varying distances. In the acoustic chamber, you can run tests at different distances and see the pattern control and frequency response maintain its consistency. We play a balancing act between maintaining good pattern control and subjectively realising the proximity effect benefits of omni-directional patterns.”
The KSM8 was seven years in the making, but Born says six years of that was spent fixing everything they broke in the process of trying to fit a second diaphragm into a dynamic mic. Born: “That’s where the reverse air flow comes into play. We had to connect everything — the resistance network, the pneumatic shockmount, the specifically-sized air cavity to get the correct tune up — back together using four tubes which wrap around the cartridge.
“During alpha testing I had 20 units comprising sawn-off SM58 handles connected to a 3D printed part that we’d glued a 3D printed cartridge into. We put some foam around it and glued on some machined grilles. It wasn’t shockmounted, but acoustically it was there. We literally had a piece of cardboard on it for a frequency tune up issue — if you dropped it, it would have exploded.
“I took the 20 samples out to users — James Taylor, a couple of festival gigs, some broadcasters, a couple of local guys and some small venues — and asked them to put it on a background vocal, not touch it or take it out of the stand and tell me if it sounded good. It’s not like anything else on the market, it’s super flat and doesn’t trigger compression and EQ in the way other dynamics do. I also wanted to make sure gain before feedback was going to be okay, because the KSM8 is a really textbook cardioid, whereas an SM58 is kind of super cardioid. 19 out of 20 people said it was like nothing else they’ve ever heard.
“We’re relishing this one for now. We definitely don’t have anything else in the works yet. We learnt a ton about dynamic mics in the process — the leverage we have, what makes dynamic microphones tick, how we can tweak, modify, change and replace parts. We had to go back through the lab note books and re-learn how the Unidyne III worked, strip it down to its core and build it back up. I think it’s the beginning of some really cool dynamic microphones.”
PROXIMITY OF DESIGN
Reducing proximity effect in dynamic microphones isn’t a new pursuit. Credit must be given to Electro-Voice’s Variable-D design — found on mics like the RE20 — for providing the first solution in 1954 to the ‘problem’. Rather than a second diaphragm, it spaces separate ports for high and low frequencies down the body of the microphone to control the time at which each frequency range hits the rear of the diaphragm. By manipulating the delay of different frequencies, EV’s Variable-D mics net similar effects to Shure’s Dualdyne, namely that proximity effect is reduced, better control over polar pattern, and the source is tonally consistent over different distances. Shure even tried a similar approach with the SM53 and SM54 handheld dynamics with rear entry ports halfway down the microphone handle. You only needed one port to be unobstructed for the microphone to work properly, but Shure never produced a similar mic after they went out of production. Likewise, Electro-Voice has mostly limited the Variable-D design to its larger, broadcast microphones, with the bobble-headed RE16 handheld dynamic holding on as the lone exception. None of its newer line of handheld dynamic mics carry the feature.
RESPONSES