Microphone Measurements, Standards, and Specifications

Eargle, Ch. 7

Primary Performance Specifications

Directional properties Data in polar form, or set of on- and off-axis frequency

response measurements. Frequency response measurements

Usually at 0° axis, and 90° (plus others) Output sensitivity

Often stated at 1 kHz, measured in free field Output source impedance Equivalent self-noise level Maximum operating SPL for a stated % of THD

Frequency Response

Should always state measuring distance (to access proximity effect), or assume 1 meter.

Can be shown with tolerance limits, but if so, not the measurement of a specific, actual mic

Sometimes, other distances included to show proximity effect.

Response with low-cut (high-pass) filter

Polar Response

Eargle states that due to microphone symmetry, hemispherical plots are sufficient (180°).

Most manufacturers include full sphere.

Mic Sensitivity

Pressure Sensitivity Output rms in response to 1 kHz, 94 dB SPL, in

free field.

Output Power Sensitivity Measure the output when mic is loaded with an

impedance equal to its own internal impedance

Microphone Source Impedance

Almost all professional mic’s today are low impedance.

Typically 50 to 200 ohmsTypical input load impedance in 2k to 5k

ohm range.Output impedance rating of little

consequence.

Normal Mic Design Sensitivity

Reference output sensitivity matches intended use of microphone Mic’s intended for strong sound sources will

need less output sensitivity. Distant pickups require more. Close-in (2 - 8 mV/Pa) Distant (7 - 20 mV/Pa)

Mic Equivalent Self-Noise Level RatingStated in dB(A), representing the signal

that would be picked up by an ideal mic in the rated acoustical sound field.

Capacitor mics: 7 - 15 dB(A)Tube models: 17 - 23 dB(A)Capacitor mics are 10 - 12 dB greater than

EIN of good console or preamp.Dynamic 10 - 12 dB less than capacitor.

Distortion and Dynamic Range

Studio mics: 0.5% THD at 1 kHz.Require signal levels in the 130 to 140

range.Dynamic Range is range specified in dB

between noise floor and 0.5% THD level.