Reference mics are vital tools for audio work. They’re awarded for their flat frequency response, and are often used for characterizing the audio response of a room or space. OpenRefMic aims to be an open source design for producing reference mics without paying exorbitant retail prices.
The heart of the build is a preamplifier that runs off standard 48 V phantom power, and is responsible for both biasing the electret microphone element and acting as a buffer for the mic signal. It’s designed specifically to work with the PUI AOM-5024L-HD-FR mic capsule, chosen for its good performance and low noise characteristics. However, other electric mics should work, too. The hardware is wrapped up in a 3D printed case which can readily be made on most basic printers. It’s complete with a press-fit grille that holds the mic capsule in place.
The prime goal of the project is low noise; the project creator, [loudifier], notes that most commercial reference mics focus first on flat frequency response and then reducing noise. OpenRefMic performs well in this area, and its lack of a perfectly flat frequency response is countered with calibrated equalization. It also works with regular pro-grade XLR cables and phantom power, rather than needing fancy laboratory-spec cables and interfaces.
The final result is a credit to [loudifier], who demonstrates a strong understanding of the principles of reference mic design. We’ve seen some other great low-cost reference mics recently, too!