The Definitive Shure SM81 Review
Superb accuracy and flexibility come together in a classic mic
Reviewed by: Paul Narang
Review date: September 2024
Current price: Approximately $400
Shure SM81 Review
| Pros: | Cons: |
| Neutral and natural sound 3 High pass filters and attenuator Suitable for most instruments | Lower output than normal Highly sensitive to plosives |
Shure SM81 Review
The Shure SM81 is a small diaphragm, cardioid pattern, electret condenser microphone (SDC mic). It has been an industry standard for around 50 years, and offers versatility in the studio, with two bass roll-off options and a 10dB attenuation switch. The SM81 is a workhorse mic with a strong reputation for recording acoustic guitars, pianos and hi hats, but also excels as drum and choir overheads, and recording bowed strings, woodwinds, vocals and voiceovers.
What is it?
Shure have been leaders in the recording industry since they began operations in 1925, and are best known for their industry standard SM57, SM58 and SM7B mics. But they’ve also created other classics, cherished by established recording engineers, including the SM81 reviewed here.
The small diaphragm SM81, also known as a pencil mic, is reviewed here as a single mic, but it is often used as a pair as well. It’s known for a natural and detailed sound, and unlike some other pencil mics, has a full sound with a well-rounded bass end, and pronounced proximity effect.
Because the SM81 is so accurate, it’s best used for capturing faithful reproductions of whatever you’re recording. It won’t add unnecessary colour, but will include all the detail and nuance you’d normally hear while listening with your own ears. As a cardioid pattern mic, it’s well suited to smaller or untreated rooms, as it only picks up what’s directly in front of it.
A brief history of the Shure SM 81
The SM81 grew out of the SM82 broadcast mic, introduced by Shure in the early 1970s. The SM82 was USA made, and had a built in limiter and amplifier, so it could deliver a line level output over very long cable runs. It had the option of battery of phantom power, though the 9.8v mercury battery required are no longer made. It had superior off axis rejection, built in pop and wind filter, and is still sought after by recording enthusiasts on the secondhand market.
A few years later in 1978, the SM81 was introduced, similar to the SM82, with just the option of phantom power, but the addition of extra control features and resistant to temperature and humidity. The SM81, now assembled in Mexico, has seen continuous changes since its conception, namely lowering the noise floor, and ditching an interchangeable Shure R104A omni capsule. The omni versions are still highly regarded decades later, as you can record close up without the proximity effect, but they’re not easy to find.
In the box
As well as the microphone, the SM81 ships with:
- Storage bag
- foam windshield
- plastic microphone clamp
- 5/8 to 3/8” thread mic stand adaptor
Shure SM81 Polar pattern
The SM81 has a fixed cardioid pickup pattern, which forms a heart shaped area in front of the mic. It works as you’d expect a mic to work – picking up most of the sound from the front, but far less from the back and sides.
The cardioid pattern is a great choice for home studios where there hasn’t been much acoustic treatment. It will pick up the sound of the vocalist or instrumentalist in front of the mic, while rejecting the sound of the room.
I found the cardioid polar pattern of the SM81 to be pretty good at rejecting sound from the sides of the microphone. At the back it seemed to reject even more of the higher frequencies, leaving behind a quiet bassy sound, but that could just be the room it was in.
SM 81 pick up pattern at different frequencies
Take a look at the diagram below to see how the cardioid pattern changes on the SM81, depending on the frequency of the sound being recorded. Note that the heart shape is most heart-like at the lowest frequencies, before becoming more omni-like at 1 kHz. By 2kHz, it’s back to a heart shape, but at the highest frequencies, 5 kHz and above, it progressively picks up more from a narrow band at the back of the mic.
Phantom power for the Shure SM81?
As a condenser microphone, the SM81 will need phantom power. Phantom power is low voltage current sent to the microphone from a microphone preamp, mixing desk, or audio interface, sent through the XLR cable to the microphone.
If your audio interface or mixer doesn’t provide phantom power, there is another solution: connect your mic to an external 48 volt phantom supply. Then connect the output of the phantom supply to the mixer, or audio interface.
Connecting the SM81
The SM81 uses an XLR cable to connect directly to the audio interface or mixer. XLR is the standard connector for professional studio equipment. An XLR connector is ‘balanced’, which means the cable is shielded from interference and carries a higher signal than unbalanced cables.
XLR cables are the only cables capable of carrying phantom power to the mic.
XLR connection on the Shure SM 81
The Shure SM81 Design and Build
Like you’d expect from a Shure mic, it’s well built, with a rugged metal casing, and when I pressed the grille there was no give at all. It’s clearly designed to withstand the rigours of live use as well as more gentle studio use.
The SM81 also operates under some extreme temperates: between -6.7° to 49° C (20° to 120° F), and under high humidity (up to 95%) so you could take it into some challenging environments without problems. Just remember that it’s extremely sensitive to wind noise, so outdoor use may be limited.
10dB attenuator switch
Below the capsule is a handy -10db slider pad. There’s some handling noise when your sliding this into position, so make sure to mute or turn the volume down if you need to make changes in a live situation. Although it slides smoothly from one position to another, its not incremental, just 0dB or -10dB. There is an attenuator switch lock available from Shure – a small piece of clear plastic which you can leave permanently in place by unscrewing the cartridge.
Low frequency response switches
Use the three low frequency settings to reduce the amount of bass the SM81 picks up. This can be great for offsetting the proximity effect, or rumbles from the environment.
It’s a bit fiddly to use, but that’s a plus for stopping accidental changes during live use.
The three low frequency settings:
- Flat response
This is the setting to leave on as default, as it will give you the fullest sound. It leaves you with a full bass which you can roll off in post production if you need to.
- Low fq roll off
This setting reduces the bass by 6 dB below 100 Hz. You can use this to compensate for a light proximity effect or if you’re finding your acoustic guitar is sounding too muddy. I used this setting for close miking my own (male) spoken word, and there was still a pronounced proximity effect, with a very natural sound.
- Low fq cutoff
This is a more aggressive setting, attenuating 18 dB below 80 Hz. This really thins out the bass, but does somehow still leave you with a full, natural and balanced sound – you wouldn’t know without comparison tests that it had been switched on.
The -18dB switch is handy for close miking, where the bass boosting of the proximity effect is too much. You can also use it to get a clearer sound if your instrument is sounding muddy or congested. For practical purposes, it will help eliminate knocks on the stand and low frequency rumble or hums.
SM81 Dimensions and Weight
At just under 8 and a half inches , the SM81 is a bit longer and heavier than many smaller, more modern pencil mics, such as the miniature KM 184s. The length can get in the way if you need to get into a tight corner, or close to an instrument, such as the underside of a snare drum.
- Dimensions: 212mm (8.35″) x 23.5mm (0.93″)
- Weight: 230g
Shure SM81 frequency response
From 20 Hz to 20 kHz, the SM81 has an extremely flat and wide frequency response especially above 5 kHz. This is what makes it a popular choice for recording a variety of instruments where accuracy is paramount. What you hear while you’re recording is what you’ll capture from the mic.
There’s no spike in the treble found in other small diaphragm condensers, just an unnoticeable drop of around 1 dB below 5kHz. This produces some very smooth, un-hyped upper frequencies, perfect for the zing of a cymbal or sparkle of an acoustic guitar.
The frequency response of the SM81s so consistent that Shure does not issue them in matched pairs, as they are already so closely matched.
SM81 Sensitivity and Impedance
The SM81 has a sensitivity rating of -45dBv, which is just on the lower side for a condenser mic. For reference, the less sensitive SM57 is -56dBv and the SM7B is -59dB: the lower the number, the lower the sensitivity. This means you’ll have to add a little extra gain on your pre amp or mixer when using it, compared to using some other high sensitivity small diaphragm condensers.
But the SM81’s self noise is average for a SDC at 16 dBa, so you’re unlikely to suffer from a noticeable build up of noise if you have to crank up the gain a little.
The SM81 sits in the lower end of sensitivity ratings when compared to similar mics. For instance it’s much lower than the more expensive KM 184s which are around -36 dBv, but just slightly lower than the AKG C451B which is around -41 dBv.
The Shure SM81 impedance level
The rated impedance level of the SM81 is 150 ohms, but you can ignore that figure – the actual impedance, when measured is 85 ohms. This is a low impedance level, typical of a condenser mic. Low impedance allows the audio signal to run through long lengths of cable, without any degradation to the signal quality. Using the SM81 with a balanced XLR cable can also help to ensure a clean signal.
Shure SM81 Sound Quality
When testing the SM81, the first and most obvious feature to me was just how accurately the mic picked up sound. Every mic has it’s main characteristics, and for the Shure SM81, it’s the ability to reproduce the sound that you’re hearing with your ears. The SM81 is not what I’d call a ‘forgiving’ mic – it doesn’t flatter the sound, or enhance it with extra colouration, it instead provides a very high quality reproduction of the sound source.
If you’re comparing similar mics, back to back, it can be a bit misleading, as other small condensers might roll of the bass or enhance the treble to provide a more polished ‘out of the box’ sound. Don’t be put off by the raw realistic sound – it can be very useful working with while mixing, because it’s easy enough to roll off the bass, scoop the mids, or whatever you need to do for your particular track.
I’d describe the sound quality of the SM81 as natural, neutral, accurate, clear and full. It has a prominent top end with no harshness whatsoever. If you’re looking for a character mic, the SM81 might sound too clean, or perhaps even sterile (the new word for accurate reproduction), but if you want real detail and clarity, it’s hard to beat. Although there’s no presence boost or high end lift on the SM81, the upper frequencies are still very detailed.
I used the SM81 in 2 rooms, one treated, and one untreated – they were both small to medium sized. I found that with acoustic guitar, placed around 9″ from the body, it sounds very clean and tight in the treated room and slightly echoey, but still very natural sounding in the untreated room. Both scenarios produced different sounds, equally as good in my opinion.
I repeated the tests with spoken word, and was quite taken aback by how good the SM81 performs as a vocal mic. You have to protect the mic against plosives by pointing it at an angle towards your mouth. I had fun seeing how close I could get to the mic with the windshield attached, with the proximity effect giving me that huge radio presenters voice, with a prominent bass, balanced with detailed highs. It definitely sounded great on my male voice which is medium deep, about 3 inches from the mic – the foam windscreen had zero affect on the sound.
The SM81 sounded just as good on voiceovers using a boom arm, placed above the head, and placed below the head. Just like with acoustic guitar, the treated and untreated rooms gave a different sound, both very usable, depending on what your using it for. I think either placement would work well for podcasts, where they’re far away from the speaker (about 12″) to not worry about plosives.
Handling the mic while using it is out of the question unfortunately, as it’s very sensitive to the slightest touch. And the provided mount doesn’t absorb any noise or low frequency rumble either. This is a mic that you’ll have to keep on a solid stand, ideally with a dedicated shock mount such as the Shure A53M, to stop accidental knocks or vibrations ruining a recording.
The SM81 proximity effect
Due to the cardioid polar pattern, the Shure SM81 has quite a pronounced proximity effect. You can use this to your advantage if you’re looking for the classic radio presenter sound – use the windshield and a pop filter about 3″ away from the mic, with it pointed to the side of your mouth for a lovely rich and balanced sound.
Taking the mic further away, the SM81 still sounded balanced and natural up to a distance of about 2-3 feet. After that there was much more sound of the room in the recording, and even further away, the sound became very thin.
If you need to mic an instrument close up, there will be a significant increase in bass – this is where the two bass roll off settings come in very handy.
The SM81 for recording guitar
The Shure SM81 is an industry standard microphone for recording acoustic guitar – in mono or as a pair for stereo recording. In my tests, I used just a single mic – a pair would have given a bigger sound, with a wider stereo image.
As a very flat, neutral mic, the sound of the guitar was reproduced in a natural and honest manner. It was full, from the lowest to the highest frequencies. It reflected what I was hearing in the room, rather than what I’d generally hear on a finished track.
Using a typical guitar miking technique, with the SM81 positioned around a foot away, pointing towards the 12th fret, I found the sound overly bassy, due to the proximity effect, and engaged the first -6dB bass roll off switch to get a good sound.
But moving the mic around the guitar had a huge impact on the sound and bass response. the higher up the fretboard, the less bass, and the closer to the sound hole, the more bass. You can also position the SM81 to the left of the sound hole, above the bridge, for a medium bass, almost nasally sound which I quite liked.
Its crucial to experiment with mic placement to see what suits your taste, using the bass roll off switches when you need to get a denser sound nearer the sound hole. There’s probably more sonic options than you imagine, and they all sound valid and natural in their on way with the SM81, with fantastically tight definition, and a natural well rounded low end.
Although the SM81 is a pro engineer’s standard choice for any acoustic guitar, I’d particularly recommend it for a very bright or thin sounding model, or a small parlour guitar, as the fullness will naturally compliment the sound. The same goes for recording a classical guitar with nylon strings – the SM81 will make sure you’re capturing a full sound.
You can start by acquiring a single SM81 and then add another at a later date to experiment with lush stereo recordings. Or you can pair it up with a large diaphragm condenser over the sound hole, and the SM81 higher up along the fretboard.
I also tried recording electric guitar – with the SM81 placed in front of a cab. I can only describe the sound as very clean and contained sounding. Not the most exciting sound, but good to know its available should you be looking for something less aggressive than the norm.
The Shure SM81 as a studio and live mic
The SM81 is equally at home in the studio or on stage, and suits and incredible array of acoustic instruments. As well as the guitar, it also suits similar, but smaller plucked instruments, such as the mandolin, banjo and ukellele.
Something that surprised me was how good it sounded on vocals. I wouldn’t recommend this for live stage use, as as there’s too much rick of plosives. But in the studio or in a podcast setting, on a boom arm, the SM81 is more than capable of delivering a highly detailed and rich sound.
You can make use of the proximity effect when you need to – it suited my male voice very well, or you can use the built in filters, or post processing EQ to roll off the lows if that’s what’s required.
The SM81 is a wise choice for drum overheads, or as spots on individual drums. Many engineers will only use a Shure SM81 for cymbals and hi hat, as it captures all of the detailed high end without introducing a harsh or brittle sound. But with it’s high SPL, it also sounds great as a snare mic, both above and underneath, with one of the low cut filters engaged.
Any other percussion with high end detail – tambourines, shakers and triangles will also benefit from the smooth upper frequencies of the SM81. If you’re recording other instruments at the same time, use the -18dB attenuator to minimise bleed – you’ll only need the mid and high frequencies.
I didn’t get to test this scenario for the review, but I have used an old stereo pair of SM81s to record a grand piano in the past with very favourable results. In fact, the Shure SM81 suits classical recordings, folk, jazz, or anything where you’re looking for a natural and faithful reproduction of the sound. This goes for whole sections of the orchestra, such as woodwinds or stringed instruments, as well as solo instruments such as violins, violas, cellos, and flutes. Alison Krauss is known for using the SM81 onstage for her live fiddle performances – see her in action here.
Of course I had to try it with Herbert my sax, and I was actually pleasantly surprised. Of course I still love the silky sound of my Royer R-121 ribbon, but the SM81 gave me a very usable alternative, which I’ll be putting to use in the near future.
Condenser vs dynamic microphone
The two most common types of microphones are dynamic microphones (like the Shure SM58) and condenser microphones like the SM81. These two types of mics each have pros and cons and both are useful in different ways.
Dynamic microphones
The mechanism inside a dynamic microphone is more durable and sturdy than a condenser, making them ideal for live gigs. They’re also less likely to be damaged during the rough and tumble of touring life. Dynamic mics are generally less sensitive than condenser microphones, and better at rejecting background noise and feedback. But the lack of sensitivity means they aren’t capable of reproducing as much nuance or dynamic detail, especially in the higher frequencies.
Condenser microphones
By contrast, condenser microphones have quite a delicate mechanism, so you’ll need to take good care of them. They’re able to record with greater detail and clarity than dynamic mics, often with a bright and sparkly top end. This is often just what you need for studio recordings, which is where you’ll find the majority of condenser mics.
As the Shure SM81 is a small diaphragm condenser microphone, its better suited to producing clear and detailed recordings in the studio than a similarly priced dynamic microphone. Within condenser microphones, you have two types, small diaphragms (generally 1/2″ or less) like the SM81 and large diaphragms (like an AKG C414)
Small diaphragm vs large diaphragm condensers
Small diaphragm condensers
Small diaphragm condensers, or SDCs, have a lighter and smaller membrane than the large diaphragm condensers (LDCs). This makes them good for picking up the transients (the beginning portion of the sound), of guitars, drums and percussion.
Compared to LDCs, they’re not as sensitive, so you have to watch out for self-generated noise. But in a quality mic such as the SM81, this won’t pose a problem for music production. They make up for this by capturing incredible detail and nuance across the frequency spectrum, capturing the lowest to the highest frequencies.
They tend to have a flat and accurate response, described as neutral, natural or uncoloured, and are often used for acoustic instruments, such as violins or flutes, where you need a direct representation of the actual sound you can hear.
The other main difference between a SDC and a LDC is the shape and function of the mic. Large diaphragm mics are often housed in large casings, and suspended in a cradle to stop vibrations. They’re normally ‘side address’, picking up sound from one of the sides.
The smaller diaphragm mics fit into slimmer cases, and are normally ‘end address’ – you point the mic towards the sound source. Being smaller, they’re also easier to position on a stage or in the studio.
Large diaphragm condensers
LDCs are known for their warm, larger than life character, and they’re generally more flattering, though less precise than an SDC. They often add their own character, which will come at the expense of accuracy.
With less self noise than an SDC, the large diaphragm mics often incorporate a presence peak, making them great for lifting vocals, and sometimes come with a range of selectable polar patterns.
Shure SM81 vs Neumann KM 184
The Shure SM81 and Neumann KM 184 are both industry standard small diaphragm condenser mics and are often used for the same recording purposes. You’ll find both SM81s and KM 184s in professional studios around the world, because they each offer different qualities.
While the SM81 is assembled in it’s Mexico plant in Juarez, the KM 184 is entirely handmade in Germany. This is reflected in the cost, with the Neumann KM 184 nearly double the price of the SM81. They’re also so much shorter (at 4″ length) and lighter (at 80g) than the SM81s that they could be considered miniature microphones.
Despite the price difference, both mics have a very similar sound, both capable of capturing the finest nuances in any recording, across the entire width of the frequency spectrum. The main difference in comparison, can be seen in the frequency chart. The KM 184 has a bass roll off, and a boost in the treble. This gives it a refined, balanced sound, perhaps just a touch warmer sounding.
On most instruments, it can be difficult to tell which of he two mics was responsible for the recording, especially after EQ, where you can remove all the bass you need to from an SM81. One exception I’ve noticed is in recording the acoustic bass, where the KM 184 is just more dynamic sounding, more alive, making the SM81 sound dull in comparison.
For recording guitar, the EQ curve of the Neumann KM184 results in a more polished sound, and in A/B comparisons, can make the Shure SM81 sound muddy or overly bassy. But this is an area where the SM81 has some extra features – the ability to roll of the bass at either -6dB or -18dB under 100 Hz. The KM 184 has no such options, or the option of -10dB attenuation.
Although the Neumann badge looks impressive in any studio, I would be more inclined to use the SM81s, simply because they deliver the full sound. And it’s easy to roll of the bass in post production with EQ, as and where you need to within the context of the mix. If there’s no bass recorded to start with, there’s no real way of adding it later.
Overall, when you consider the price, the sound quality and the extra features of the SM81, I think they make more sense, especially if you’re considering buying a pair. Having said that, if you know that you won’t be messing with the refined sound of the KM 184 in post production or you need a lower self noise rating, the Neumann KM 184s are also a very worthy consideration if you have the budget.
Shure SM81 vs AKG C451
The AKG C451 is another classic small diaphragm condenser mic, with many similarities to the Shure SM81. On first glance they look quite similar, with slim and rugged metal bodies, but the C451 is 2 inches shorter and nearly half the weight of the SM81 at 125g.
The AKG C451 is a brighter microphone, with a pronounced boost from 6 kHz, and a gentle bass roll off from 200 Hz. But it pulls this brightness off with sonic style – not a hint of harshness at all, but instead, what can only be described as a smooth silkiness.
The bass roll off helps to compensate for the strong proximity effect of the SM81, achieving a remarkably balanced sound. The C451 is also far more sensitive than the SM81, so you won’t have to boost the signal as much to get the same volume.
Both the Shure SM81 and the AKG C451B have plenty of sound enhancing features – two bass roll off settings, and two attenuation pads on C451 compared to just one on the SM81. They also both sound great on vocals, with the distinct advantage of being able to hold the AKG C451 B in your hand without creating any noise.
Both instruments excel at recording a large range of acoustic instruments in fine detail, including drums, percussion, piano and orchestral instruments. Although both the Shure SM81 and the AKG C451B are solid choices for recording guitar, to my ears the C451B has the edge in its ability to bring out a larger than life, sparkling recording, with just one mic.
What else do you need?
The Shure SM81 only comes with a windshield and stand-mount, so you might have to spend a bit more money later on if you want some accessories.
Extra parts to consider:
- Shock mount
I would advise in investing in an external shock-mount – it’s not imperative if you’re on a budget, but will help eliminate any stand noise or vibrations getting into your recordings. Shure do their own
Shock Stopper Isolation Mount (A55HM) for any mic with a diameter of 25 to 30 mm. I haven’t tried it myself but have heard good things about it. If you need something cheaper there’s a reasonably priced one here.
- Pop filter
As well as the included windshield, a pop filter is a ‘must have’ if you’re recording vocals, to avoid plosives – those short bursts of air which can ruin a recording. I’d even consider using two pop shields considering how sensitive the SM81 is to air noise. You can make one yourself out of an old pair of tights, or easily pick up an inexpensive one.
- Microphone stand
High quality condenser mics like the SM81 have to be mounted on a stand, to reduce any handling noise. Try a good quality boom stand, with a tripod base like the K&M 210/2
- XLR cable
If you’re investing in condenser microphones for your studio, start getting into the habit of using good quality cables. That way, when you add more high quality mics, you can use the same cables. If you want the best quality XLR cables, try these. Go for the shorter lengths where possible.
Conclusion
An industry standard small diaphragm condenser mic, capable of capturing every detail and nuance you place in front of it. Known for it’s accuracy, the Shure SM81 has full and neutral sound, capable of recording a huge variety of instruments, from acoustic guitar, to hi hats, to vocals to pipe organs. The SM81 is a reasonably priced classic workhorse mic with an honest flat response, suitable for the majority of tasks in a recording studio.
Shure SM81 Frequently Asked Questions
Does the SM81 need phantom power?
The Shure SM81 is a condenser microphone, so it does require phantom power. You can receive power from the mixing desk, audio interface or a stand-alone unit
Can you use the SM81 on stage?
Although you would normally try to stay clear of expensive condenser mics on stage, the SM81 is small and rugged, and can often be seen on stage recording everything from orchestras, choirs to drum kits and acoustic guitars.
Which instruments is the Shure SM81 suited to?
The SM81 is an extremely versatile mic, known especially for recording acoustic guitar, piano and hi hats, but also regularly used for pipe organs, choirs, orchestras, mandolins, banjos (Alan Munde) violins (Alison Krauss), strings and woodwinds.
Read about our pick of the best mics for recording vocals