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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