Microphone Sensitivity Calculator

Microphone sensitivity states the open-circuit voltage a capsule produces for a defined acoustic input, and that input is almost always 1 pascal of sound pressure, which equals 94 dB SPL because the reference for the decibel SPL scale is 20 micropascals. Three units express the same quantity. mV/Pa is the direct statement of output voltage. dBV refers that voltage to 1 volt, so -40 dBV is 10 mV/Pa. dBu refers it to 0.775 V, the level that dissipates 1 milliwatt in a 600-ohm load, which puts a fixed 2.21 dB offset between the two decibel scales because 20 x log10(1 / 0.775) = 2.21. Sensitivity is a voltage ratio, not a quality score. Typical figures cluster by transducer type: studio condensers run about -25 to -38 dBV (56 to 12 mV/Pa), moving-coil dynamics such as the SM58 around -54 to -56 dBV (roughly 2 to 1.6 mV/Pa), and passive ribbons lower still. Because gain and noise trade off, a microphone 20 dB less sensitive needs 20 dB more preamp gain, which is why low-output ribbons expose a preamp's equivalent input noise, typically -125 to -131 dBu on good designs. Caveats: manufacturers may quote loaded rather than open-circuit sensitivity, which reads a few dB lower; the measurement is normally taken at 1 kHz on axis, so a presence peak inflates it; and the self-noise estimate shown here is an approximation, not a substitute for a measured dB-A figure.

The measurement rests on two older conventions. The 20 micropascal reference for sound pressure was fixed in the 1930s as an approximation of the threshold of hearing near 1 kHz, and 1 pascal was later adopted as a convenient calibration point exactly 94 dB above it, which is why laboratory pistonphones and field calibrators emit 94 dB or 114 dB tones. The 0.775 V reference behind dBu descends from telephone practice, where levels were expressed in dBm as power delivered into a 600-ohm line, and 1 milliwatt across 600 ohms works out to 0.775 volts. The condenser capsule itself dates to work at Western Electric, where E. C. Wente described a practical electrostatic transmitter in 1917, giving the flat, predictable response that made quantitative microphone specification meaningful. As studio and broadcast equipment moved away from matched 600-ohm interconnection toward voltage bridging during the 1960s and 1970s, power-based units lost their physical meaning and dBV, a pure voltage reference, became the common way to state sensitivity, though dBu survived in console and interface metering. Measurement procedure was later harmonized in the IEC 60268-4 standard for microphones, which specifies the free-field conditions, test tone and loading assumptions that make published sensitivity figures comparable between manufacturers.