Reading a microphone datasheet

A microphone datasheet is full of numbers that look comparable and often are not. This is a guide to reading them.

Sensitivity

How many millivolts the microphone delivers at 1 Pa (94 dB SPL), usually at 1 kHz. Sometimes it is given in dBV re 1 V/Pa instead: 10 mV/Pa is −40 dBV, 20 mV/Pa is −34 dBV. Higher sensitivity means less preamp gain is needed. Use the microphone sensitivity tool to convert and to estimate the preamp gain.

Self-noise

The microphone's own noise, expressed as the sound pressure level that would produce the same output (equivalent noise level).

• A-weighted (dB(A)): the usual figure. 14 dB(A) is quiet, 20 dB(A) is average, 30 dB(A) or more is noisy for studio use.
• CCIR-weighted (quasi-peak, ITU-R 468): gives numbers about 10 to 12 dB higher for the same microphone. Do not compare an A-weighted figure with a CCIR figure.

The signal-to-noise ratio is 94 dB minus the A-weighted self-noise.

Maximum SPL

The sound pressure level at which the microphone reaches a specified distortion, usually 0.5 % or 1 % THD. The figure depends on that definition and on the preamp load, so two microphones with the same value can behave differently. For loud sources (drums, brass) check the figure carefully and look for a pad switch.

Dynamic range

Maximum SPL minus self-noise. A microphone with 138 dB maximum and 14 dB(A) noise has 124 dB. That is more than any recording chain can use, but it tells you how much headroom is available.

Frequency response

Look at the plot rather than the range. "20 Hz to 20 kHz" without a tolerance means little: ±3 dB or ±1 dB is a different claim. Note whether the plot was measured on axis, in a free field, and at what distance, because proximity effect and diffuse-field curves differ.

Polar diagrams

Look for the plot at several frequencies. A pattern that holds at 500 Hz but widens at 10 kHz affects both the sound of off-axis sources and the room.

Impedance

Output impedance of professional microphones is usually 50 to 200 Ω, and preamp inputs are 1 to 10 kΩ. Voltage transfer is close to complete, see Voltage bridging versus power matching.

Checklist

1. Sensitivity and gain need.
2. Self-noise (which weighting?).
3. Maximum SPL (which THD?).
4. Frequency response plot, tolerance, distance.
5. Polar diagrams across the band.
6. Phantom power and current draw, pad and filter switches.

Draft: written by an AI assistant, awaiting technical review.