Sony 154283011 Mikrofon - ecm-AC2 kalibratie-microfoon (mono) – FixPart
Core Sound - The Importance of Individual Calibration for Ambisonic Microphones Fedele De Marco asked about the importance of calibration for ambisonic microphones. He also asked which of the manufacturers do calibration.
McIntosh Labs Calibration Mic Microphone with Cable Part No. 036188 | Reverb
Replacement APM7008 Calibration Microphone For Pioneer MCACC AV Home Receiver | eBay