Microphone Characteristics and Specifications Audio Days 2011 Paris David Josephson Josephson Engineering, Inc. Santa Cruz, California
Jan 11, 2016
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