Microphone Characteristics and Specifications

Audio Days 2011

Paris

David Josephson

Josephson Engineering, Inc.

Santa Cruz, California

A bit about standards

• in the beginning ... US ANSI, DIN, European and UK national broadcasters

• how standards work today

• measurement standards

• legalisms

Basic electrical specifications

• sensitivity – determines preamp requirements• noise level – quieter than recording ambient level?• impedance – does the cable and preamp affect signal?• power requirements – can the preamp supply?

Sensitivity

• millivolts per pascal (mV/Pa)

Microphone Type Sensitivity

Preamp Gain Needed for +4 dBu

Modern dynamic and ribbon, some condenser mics with transformer out

1 – 3 mV/Pa

54-64 dB (more for quiet sources)

Modern condenser mics

10-20 mV/Pa

38-44 dB

High output condenser mics

50-60 mV/Pa

28-30 dB

Impedance

• actual source impedance

• minimum load impedance

• balance

Noise level

• “A”-weighted vs ITU-R BS.468• rms average vs quasi-peak• why the number isn’t enough

Power Requirements

• IEC 61938 phantom power

• “the feeble phantom”

Frequency Response

• under what conditions?– direction– distance– sound source geometry

• tolerance?

• smoothing?

Proximity effect

• not only bass boost up close, but bass rolloff at a distance

• disappears when there is no gradient (at 90º)

Midrange and HF characteristics

• midrange often associated with pressure gradient venting or diaphragm resonance

• high frequency variations often due to scattering

• ...and we’re still only talking about on-axis, anechoic response

Time-domain characteristics

• mostly affect high frequencies

• reflections from grille

• resonators to boost HF response

References

www.josephson.com/refs