DIY Ambisonic microphone
A home built Ambisonic microphone using Panasonic WM-56A103 electret microphone capsules and a phantom power microphone preamplifier design from Elliot Sound Products. Total cost was around $250 (Australian), and it took about 5 days to build.
Many other ambisonic microphones are being built as DIY and commercial projects, and I mention a few of them on my blog under proliferating ambisonic microphones.
