Sengpielaudio.com: a great resource for all sorts of technical information, including comparing old and new mic sensitivity figures!
I’m assuming that a Beta 87A is hotter than an SM58. I know there’s a difference in response curve, but for a typical voice application, how many dB hotter is it?
SOS Forum post
SOS Technical Editor Hugh Robjohns replies: Both the Beta 87A and SM58 are designed as stage vocal mics, but the former uses an electret (capacitor) capsule while the latter has a moving‑coil capsule. Given these different technologies it’s reasonable to expect the Beta 87A to be the more sensitive (ie. to have a ‘hotter’ output), but calculating a definitive number of decibels for the sensitivity difference is frustratingly difficult as Shure’s published specs are surprisingly inconsistent!
In principle, the data needed to answer this question comes from the Sensitivity or Output Level specification, and this can be presented in a couple of different ways. It is normally measured as the output signal voltage at 1kHz for a sound pressure of 1 Pascal at the diaphragm. 1 Pascal (1Pa) of sound pressure equates to 94dB SPL and that is fairly typical of a modest singing voice close to the mic. The resulting output signal is typically expressed either as a voltage in mV/Pa, or in decibels relative to a voltage, as dB re 1V/Pa (often abbreviated to dBV/Pa).
Vintage microphone spec sheets often use different ‘imperial’ references of 1µbar of pressure (1µbar = 0.1Pa), or dBV/dyne/cm² (1dyne/cm² = 0.1Pa). A handy converter for these antiquated specs to their modern equivalents can be found at www.sengpielaudio.com/calculator-transferfactor.htm
While this small difference in sensitivity is unlikely to make a great deal of difference to the audience, it will certainly affect the gain structure optimisation through the console and PA system.
The relevant sensitivity figures for the Shure Beta 87A and SM58 vary over about a 3dB range depending on where you look. Moreover, I’ve found inconsistencies between the mV/Pa and dBV/Pa equivalents in Shure’s own Tech Portal data... However, I think reasonably representative figures for the SM58 and Beta 87A are 1.6 and 2.37 mV/Pa (or ‑55.9 and ‑52.5 dBV/Pa) respectively. If you accept those figures, the calculations report the Beta 87A to be around 3.4dB ‘hotter’ (ie. louder) than the SM58, which seems a believable outcome.
In practice, while this small difference in sensitivity is unlikely to make a great deal of difference to the audience, it will certainly affect the gain structure optimisation through the console and PA system.