Shure SM7dB

Shure’s classic mic celebrates a milestone birthday with the addition of a built‑in preamp. We test the new SM7dB and explore its fascinating history.

The Shure SM7B has never been reviewed in Sound On Sound, because it’s older than the magazine itself. It reaches its half century this year, and thanks to its newfound popularity in podcasting and live streaming, does so as one of the few professional microphones that is instantly identifiable to everyone. To mark the occasion, Shure have introduced an active version.

Moving‑coil dynamic microphones are typically much less sensitive than capacitor mics, but at just 1.1mV/Pa, the SM7B is a gentle giant even by dynamic mic standards. This is partly because it was designed before powerful rare‑earth magnets were available, and partly because Shure’s engineers set out to maximise other aspects of its performance such as frequency response instead. This led them to omit the transformer found in other models such as the SM57, which provides ‘free’ gain but curtails the bass response, and to position the diaphragm some way behind the grille.

These decisions certainly paid off in terms of sound quality. In a studio context, the SM7B earned a place among the relatively small number of moving‑coil dynamic mics that were perceived as able to hold their own against capacitor models. Its lack of sensitivity was seldom a problem in a professional environment, and was even an advantage in roles such as close‑miking bass amps and kick drums.

For its first 35 years or so, the SM7B sold pretty much exclusively into studio and broadcast markets, earning its keep but probably not making much impact on the bottom line. Then came podcasting, live streaming, YouTubing and other neo‑verbs of the late 2000s. Suddenly, the Shure SM7B was the must‑have mic for anyone talking to other people on the Internet.

However, when people with cheap mixers and audio interfaces started trying to use their new mics to talk to other people on the Internet, they sometimes ran into a problem. Even with the input gain maxed out, they were struggling to get enough level out of their SM7B — and those cheap mixers and audio interfaces rarely sounded great with the input gain maxed out. Enter the enterprising entrepreneurs at Cloud Microphones, and the rest is history. The idea of a simple, fixed‑gain, inline preamp for moving‑coil and ribbon mics proved to be genius, to the point where it’s now almost expected that people buy a Cloudlifter along with their new SM7B.

Cloud Cover

In essence, what Shure have done with the SM7dB is to formalise that connection. The Shure SM7dB includes a custom designed built-in preamp with technology licensed from Cloud Microphones, tuned by Shure engineers specifically for the SM7dB.

The result is a mic that is outwardly pretty much identical to the SM7B, until you look at the end plate. The high‑pass and mid‑boost filters from that mic are present and correct, but they’re no longer toggled using recessed switches that need a sharp implement to move them. The new switches sit proud of the surface so that they can be moved with a thumb, and there are now four rather than two. One of the new switches engages the preamp, whilst the other toggles between two fixed gain settings: +18 and +28 dB. Given that the SM7 isn’t a mic you’d often use handheld, I don’t think there’s too much risk of accidentally nudging these switches, though the new arrangement doesn’t make the filter settings quite as visually obvious as the old one.

The end panel of the SM7dB features four switches: two to engage the built‑in filters and two relating to the new preamp circuit.

The SM7dB ships inside an outsized cardboard box. There’s no further case or bag supplied, but you do get a spare removable windshield. It attaches to the mic stand in exactly the same way as the SM7B, using an integrated yoke which also houses the XLR output connector.

Shure say that, “The integrated preamp in the SM7dB was designed ground‑up by Shure to couple directly with the SM7B cartridge and accurately/transparently amplify it — delivering consistent gain, flat frequency response and extremely low noise.” When it’s switched out of circuit, the dB should be effectively identical to the SM7B. When it’s engaged, it should provide a transparent gain boost that doesn’t otherwise change the sound. And that’s exactly what it does.

With the preamp switched out, I could detect no difference between the SM7dB and my own SM7B, either in terms of sensitivity or tone. Engaging phantom power and switching in the preamp simply made the SM7dB louder. Assuming you are using a colourless, neutral preamp such as are found in most audio interfaces, the results are indistinguishable from simply turning the preamp gain up. In effect, it’s like a pad in reverse, extending the gain range of your mic preamp by 28dB at the upper end — which, in the case of the SM7, is where it’s going to be useful. With coloured or character preamps, it also gives you the option to hit the front end of the preamp much harder than would be possible with the passive SM7B. (It should be pointed out, though, that if you have good clean preamps with plenty of gain, there’s no advantage in terms of noise to using the dB’s active circuitry or indeed any inline preamp.)

The SM7dB is a totally logical evolution of the SM7B. The built‑in preamp will be genuinely useful in many real‑world recording, streaming and broadcast uses — and if you don’t need it, you can simply switch it off. Or, of course, you can just buy an SM7B, which remains a current product.

The SM7 Story

There’s really not much more to say when it comes to reviewing the new version, but like many people, I’m curious about some of the myths that have grown up around the SM7 and its history. Shure very kindly made their historian, Michael Pettersen, available for interview, and I began by asking him about the mic’s origins. The moving‑coil element within the SM7 is directly descended from the first ever single‑element cardioid dynamic mic. “Inside of the SM7 is a Unidyne cartridge — a Unidyne 3, the third generation — but it goes back to Ben Bauer and the introduction of the first Unidyne in 1939. You could do directional microphones before that, but it required two elements and that was expensive and hard to tune. Bauer’s breakthrough at age 23 was to figure out how to use acoustically delayed signals to create that directionality. The idea is to take the wave that’s coming from behind, acoustically delay it ever so slightly and then bring it to the back of the diaphragm. It’s still employed in virtually every directional mic today. It was kind of an axiomatic concept that people still use. Shure and everyone else!”

Michael Pettersen is Shure’s company historian.

Ben Bauer left Shure in 1957, and the next step in the evolution of the Unidyne capsule was made by another young engineering genius named Ernie Seeler. The Unidyne 1 and 2 cartridges had been suited only to side‑address mics, but in 1959, Seeler’s Unidyne 3 changed that. Introduced that year, the Shure 545 is still a current product today — and the source of lots of online misinformation. “I get so amused by reading all the experts on the Internet who say that the 545s are rejected SM57s! In today’s age, people will believe an influencer that has absolutely no knowledge whatsoever, but they won’t believe the manufacturer. If it says Unidyne 3 on it, it’s a Unidyne 3. The engine is the same. It’s got a switch on it, and the output transformer’s dual‑impedance instead of single‑impedance, but other than that — it’s funny, every now and then I’ll read something online: ‘Just bought a 545, Wow, it sounds as good as an SM57.’ Yes, it would...”

Five To Seven

Strange as it may seem now, the ubiquitous SM58 and SM57 were developed primarily for studio applications — indeed, the ’SM’ actually stands for ‘studio microphone’ — and the SM7 evolved out of another model in this range. “We were trying to get our microphones into studios in the ’60s, and one of the things we came up with was the SM5B.

“That used a Unidyne 3, and we put a really good shockmount on and we put really big windscreens on it, because we were trying to sell it as a boom mic for movies and television work. The reason we didn’t have a condenser microphone is because we didn’t have a condenser microphone! We didn’t have any condenser technology. So we took the best that we had and hoped that it would work well for booming.

“Dynamic microphones just really aren’t sensitive enough to do boom work, so the SM5 was a failure as a boom mic — but somebody in radio stations started using it as a close‑up mic for on‑air work and it had a great sound. And so we started to sell these things for radio stations and for television voiceovers as well. But the problem with radio stations and TV stations is they take care of their equipment. Once they’ve bought one or two mics, they don’t buy any more because they’ve already got them, and so it was self‑limiting. The SM5B is still really revered by many people in the broadcast area, but we never sold very many of them, because of the fact that it was too big to use on stage. It wasn’t a live mic. It didn’t really have the sound that you would use for miking the Rolling Stones in the studios. It was pretty much limited to voiceover, but there aren’t that many radio stations or TV stations.

“We wanted to come up with something that perhaps had a bigger sales potential and might be used live or in recording studios. And so we kind of took the best aspects of the SM5 and tried to shrink it down and make it smaller. The idea was to make a less expensive, smaller SM5B with some adjustable frequency response on it. And that was the SM7, which was first announced in 1972, but not sold until 1973.

“And I’m certain Ernie Seeler was part of that, because it was a Unidyne 3 element, but one of the primary persons responsible for it was a guy named Gerry Plice. Interestingly enough, he was a microphone development engineer, but he designed the way the SM7 looks. It was the only industrial design he ever did, and he got a patent on it. And it still looks modern even though it’s 2023. He just managed to kind of catch this timeless look.

“So it comes out in ’73, and it was... OK. Sales were so‑so. Some were bought for studio voiceover booths, some were bought for radio stations. In the 1980s, Michael Jackson, it was used for his Thriller album. That was a big deal as far as PR goes, but it didn’t really affect the sales. And really, for about 35 years, it just was kind of an average seller that was never a hit.”

Fine Margins

Much Internet mythology has grown up around the design of the SM7, and especially the differences between that mic and the more humble SM57. “We get people asking how to turn an SM57 into an SM7,” laughs Michael. “And this guy says ‘You take out the transformer in the back of the SM57 and remove all the potting material, and all of a sudden your SM57 is an SM7!’ No. You ruined your SM57, but it’s not an SM7 now.”

Although the cartridge in both mics is designated Unidyne 3, that doesn’t mean it’s exactly the same. Subtle changes needed to be made to adapt the capsule to work without the SM57’s transformer. “The transformer not only changes the impedance but also kicks up the level. So, the SM7 coil has more windings on it. This makes it a little bit harder to move, if you will, because it is heavier. But it’s also the reason that you’ve got to kind of be on top of the microphone, and sounds from farther away don’t really pick up that well, because it’s just harder to get that diaphragm and voice coil to start moving because of the extra mass.”

Does that not also change the high‑frequency response? “A little bit,” agrees Pettersen, “but we can offset that with resonators and so forth. Also, the flexibility of the diaphragm is a little bit different. It’s not the same Mylar. It has a different flexibility, which affects the low end, and of course, you’ve got the bigger acoustical space behind it. So you combine all those things and it affects the low‑frequency response. You know, microphones move millionths of an inch, so it doesn’t take much of a tweak anywhere to really change how it sounds.

“When you get down to what the differences are, it’s just miniscule stuff. And people say ‘The SM7 doesn’t have enough output!’ the reason is the diaphragm is set back from the edge of the microphone. Primarily we did that to control proximity effect and to control ‘p’ popping. If it was forward, right up the edge, where the grille is, I don’t think people would like it as much — but because of that, you gotta have a little more gain than folks are used to.”

From A To B

Another topic that has provoked online discussion is the differences between SM7 variants. As Michael explains, these reflect functional development that made little discernible change to the sound of the mic.

“The SM7 came out for sale in 1973, then the SM7A came out in 1999. And the only difference was we added a much more effective humbucking coil, because radio stations were replacing paper copy with computer monitors and they were placing them very close to the microphones. And certain computer monitors did not have very good shielding and the SM7 would pick up hum. So we had to come up with a better anti‑hum mechanism, to put in the SM7. So that was the A.

“The B came about only three years later, and we did that primarily for two reasons. They were being used now by people who didn’t really know mic technique that well, and so better pop protection would help, but the other reason was to make it look like the SM5B, because there were radio stations and particularly older engineers that just said, ‘You guys are so stupid. That was the best microphone we ever had. Why did you discontinue it? And one of us said, ‘Maybe if we make it look more like the SM5B, It would sell better,’ and sure enough, it did. So we put the fat windscreen on there, and it helped you work closer, but also made it look more like an SM5B.”

Michael Pettersen: In 2007‑2008, all of a sudden, SM7 sales started to climb. We do a little research and we find out, this thing called podcasting is taking off. We were not advertising it for podcasting. I doubt we probably knew what podcasting was!

Lucky Seven

The SM7 found a home in many recording and broadcast studios, and remained a solid but unspectacular seller for 35 years or so. And then... “In 2007‑2008, all of a sudden, SM7 sales started to climb. We do a little research and we find out, this thing called podcasting is taking off. We were not advertising it for podcasting. I doubt we probably knew what podcasting was! And then, of course, because podcasts are done at home studios, there’s far more of those than there are radio studios — and there’s also a lot of podcaster see, podcastser do.”

Perhaps the oddest thing about this whole episode is that it’s not the first time something like this has happened. “The SM58 was not a success for about 10 years. We were trying to push this as a radio and TV interview mic, and all of a sudden in the mid‑’70s, it starts to take off and we said ‘Man, people are using this for live sound. What’s going on?’ Many times, our history is that we’re in the right place at the right time with the wrong tool, or we’re talking to the wrong people. And the market comes around, says ‘Hey! This is really what you want it for!’ And that’s what happened with podcasting.

“So, you know, the podcasting did not surprise us. We were really shocked when gamers started using it, though. Gamers are gonna pay that much money for a mic? Still, you can’t deny it sounds great, and certainly when you’re in a room that’s less than perfect, it does tend to pick up less background noise than a condenser microphone does. And so you combine all those things, and it’s just been great. I mean, we just opened up another manufacturing facility, and a lot of it is dedicated to making SM7s. In 2023, compared to 20 years ago, we sell probably about a hundred times more than we used to!”

Though its makers were unaware, the SM7B was clearly the right mic in the right place at the right time. It’s not hard to imagine that it could still be available another 50 years from now — and who knows what unexpected uses people will find for the new active variant?