I needed an inconspicuous way to make stereo field recordings in environments with people. An old camera bag was converted to house my basic recording kit and EM172 microphones. A stereo buffer is provided by a converted yoga block. Inconspicuous windscreens for the mics are included in the design.
Acquiring a stereo image requires the acoustic separation of two microphones. Many strategies for omni-directional mics employ a physical boundary along with some geometric and spatial separation or conditions. I’ve adapted one in particular for its simplicity and flexibility. Photos are audio samples are included in the post.
There are lots of materials and strategies for building contact microphones from piezo discs. The discs are fragile, and need some modification to work well in field recording applications (strength, shielding, durability, water resistance, etc). Audio recordings (normalized) form the basis of a qualitative comparison of different materials and their application.
A contact microphone (piezo disc) needs a special preamp to prevent the attenuation or loss of low- and mid-range frequencies in the sound signal. There are some DIY and plug/play options available. I bought a couple of modules from Stompville and installed them into plastic jars for use in field recordings of everyday objects.
There are lots of equipment options for stereo field recording. Most involve hardware that more or less serves only one function. However, its possible to create a high-quality kit from non-dedicated hardware: a mobile device; an audio interface; a usb battery pack. These three components comprise my basic recording kit for field work.
The EM172 is a small and highly cost-effective electret capsule that has high sensitivity, low self-noise, and can be built into various form factors, including those for stereo field recording. Internet references are provided for a simple circuit that allows it to run on phantom power. A Neutrik XLR connector can house the mic and related components. This configuration should adapt well to various strategies for acoustic separation in field recording.