Microphone Proximity Calculator — Signal Level, Proximity Effect & Gain

Proximity effect is a low-frequency (bass) boost that occurs when a pressure-gradient microphone (cardioid, supercardioid, hypercardioid or figure-8) is placed very close to a sound source — typically within 30cm. It is a near-field effect: the low-frequency output rises by roughly 6dB per halving of distance, and a figure-8 mic at 5cm can gain more than 20dB at 100Hz. The slope is the same for every directional pattern; only the magnitude differs, scaling with how much the mic relies on pressure-gradient sensing — a cardioid shows about half the boost of a figure-8. The boost only affects low frequencies (it is roughly zero above 500Hz–1kHz) and is used intentionally for a warm, full vocal sound, but can cause muddiness if excessive. Omnidirectional mics do not exhibit proximity effect.

Microphone sensitivity (dBV/Pa) tells you how much output voltage the mic produces at a reference SPL of 94dB. A higher (less negative) sensitivity value means a stronger output signal, requiring less preamp gain. A large-diaphragm condenser at -32dBV is much more sensitive than a ribbon mic at -55dBV. This calculator uses that relationship to estimate actual output voltage at any SPL.

Sound follows the inverse square law: doubling the distance from a point source reduces the SPL by approximately 6dB. Halving the distance increases it by 6dB. So a source at 90dB SPL at 1 metre will produce about 96dB at 50cm and 102dB at 25cm. This makes close-miking very effective for capturing loud, quiet or detailed sources.

The required preamp gain depends on the mic output level and your target recording level (typically -18 dBFS). Dynamic and ribbon microphones often need 50-65dB of gain, while condensers typically need 30-45dB. If your preamp's noise is a concern at high gain settings, use an inline booster or a preamp with a very low equivalent input noise (EIN) rating.

Noise floor margin is the difference between your microphone's output signal and the inherent noise of the mic and preamp system. A margin of 40dB or more is desirable for clean recordings. If the margin is below 20dB, the noise floor will be audible, especially during quiet passages. Choose a quieter mic or a lower-noise preamp to improve the margin.