Shure SM57 and SM58

by Andrew Thompson

History

The Shure SM57 and SM58 are by some distance the best-selling and most used microphones in the world. There might be microphones whose names are as widely known to the general public or whose silhouettes are as widely recognised, but no microphone has expressed the industry standard like these two models. Though initially rejected by the market, their introduction to the professional audio and broadcast community in Las Vegas in the late 1960s and 1970s eventually led to their complete proliferation throughout the music and broadcast industries and their remarkable ubiquity in live amplification settings.

The SM57 – the older and slightly more widely used of the two – was introduced in 1965 as an evolution of Shure’s model 545, using the same Unidyne III capsule employed in its predecessor. The 545 had itself marked something of a step-change in studio microphone design, repackaging Shure’s by-then famous Unidyne cardioid capsule in a compact, top-addressed package that enabled it to be positioned extremely close to sources, thereby maximising the potential of the cardioid pattern’s off-axis rejection when the source was obliged to compete with other sounds. Another innovation was an internal pneumatic shock mount employed around the capsule which significantly reduced handling and mechanical noise.

Introduced in 1966, the SM58 retained the basic design and Unidyne-III capsule of the SM57 while adding features tailored to the amplification of live vocal performances. A slightly steeper low-frequency cut contributed further to the minimisation of handling noise, while a ball grille containing an integrated pop filter helped reduce troublesome plosive sounds while enabling the performer to move freely about the stage.

The SM58 and SM57 are both top-addressed pencil-type moving-coil dynamic microphones. The microphones are transformer-balanced and possessed of similar electronics. Sensitivity is rated at -56.0 dBV/Pa, and Shure claim a maximum SPL before distortion of around 150dB at 100Hz. Construction is extremely, and famously, rugged in both microphones – the SM58, in particular, is to all intents and purposes functionally indestructible, as numerous formal and informal studies will attest. Physically both microphones are very similar excepting the SM58’s ball grille, which adds about 10mm to its total length.

Responses

On-axis frequency response describes a similar theme in both microphones, though a number of small differences may be of interest when assessing their relative suitability for a given application. First, the SM58 claims a nominal response range of 50 to 15kHz, and the SM57 a slightly wider range of 40Hz to 15kHz.

In the bass and lower midrange frequencies, response stays fairly close to zero between around 110Hz and 1.5kHz on-axis. However, the SM58 starts and ends this range slightly above 0dB, describing a smooth and very shallow “smile” which dips just below zero at around 650Hz. By contrast, the SM57’s lower mids show a narrower and more pronounced dip to about -3dB at 400Hz, deviating from zero at 275 and 600Hz.

In the SM58, lower presence frequencies are generally emphasised with a steady ramp up to a +5db plateau between 4 and 7 kHz. Response dips back to +1db at 7.5kHz, and a separate, more acute brilliance peak exists at 10kHz, with sensitivity dropping off sharply above this point. The SM57’s response also curves up through the upper mids but reaches a more pronounced peak of +6dB at 6kHz. The brilliance peak is present at 10kHz, but the “notch” separating it from the presence lift is less dramatic – the overall effect is that sensitivity is generally considerably positive of zero between 2kHz and 15kHz. This is a crucial frequency range and should provide a basis for initial comparison – at first glance, on a vocal source, the SM58 could be expected to sound more “honky” or “nasal”, whereas the SM57 might be more susceptible to excessive sibilance, but this will, of course, depend on the individual use case.

Bass frequencies in the SM58 roll off at a rate of about 7dB/octave below 100Hz, while the SM57 shows a longer but deeper roll-off in the lower bass: from -10dB at 50Hz, only reaching 0dB at 200Hz. Users may wish to bear this in mind when recording baritone-voiced acoustic instruments such as violas, saxophones, trombones and guitars, as 200Hz can fall well within the fundamental range of these instruments.

The dome-shaped grille of the SM58 was developed to incorporate an integrated plosive filter, but it also had the effect of limiting the microphone’s susceptibility to proximity effect, as it necessarily distances the source from the capsule. The SM57’s grille is much flatter, and its outer surface is much closer to that of the cardioid capsule, allowing for the creative use of proximity effect when desired. Taken together, these two factors often provide a criterion by which to choose one microphone over the other for a given application.

Rear rejection for both microphones is greatest at 500Hz, where the cardioid pattern is most pronounced. The pattern begins to lose integrity below this point and above 1kHz, tending toward omnidirectional at 125Hz while developing a modest hypercardioid rear lobe beyond 1kHz. According to Shure’s published graphs, the SM57 becomes most hypercardioid at 4kHz before its nascent null points flatten out at 8kHz, but in the SM58, this process is reversed – it is most hypercardioid in the high frequencies, the cardioid pattern somewhat less distorted at 4kHz. Depending on the acoustics of the recording environment and the sonic characteristics of any nearby sound sources, an engineer might choose one microphone over the other for this reason, the better to take advantage of off-axis rejection.

Uses

The no-nonsense devotion of the two microphones to the most significant midrange frequencies has helped to fuel their popularity, especially but not exclusively in live music – either microphone can be found on vocalists, guitar amplifiers, acoustic instruments of all kinds, or in sound reinforcement applications. There may be an element of the self-fulfilling prophecy about their ubiquity – how could one ever be considered to go wrong when choosing to use a microphone whose voicing is so familiar? It must surely be admitted, however, that both microphones, at the very least, constitute a marvel of mid-20^th-century engineering. Their physical resilience and consistency of manufacture lend them a degree of reliability that would make them difficult to overlook when engineering live sound with amplified sound sources, while their effective limiting of mechanical noise will ensure both microphones remain popular choices for performing vocalists. In the studio, their unfussy handling of high sound pressure levels ensures the SM57 especially will always find applications on loud sources, while the SM58 will continue to have a loyal following of recording vocalists (especially louder singers) who enjoy the microphone’s slight presence enhancement.

Andrew Thompson

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