Just to throw our hat in, we've just made an ambisonics microphone called the Brahma, please see the details on our kickstarter page. It's at a late development stage, we plan to ship microphones out by February 2014. We are also using electret based capsules, but larger diaphragm capsules than the Tetramic, so we should have a higher output and lower noise in comparison, also RF protection and a wind shield. Currently the capsules we are using are the TSB 140A 's. We have plans on make a large diaphragm version very soon that will be very quiet. Please keep an eye out for ambisonic developments from our company and if you can support us now, please do so. We're modifying the Zoom H2n to fit an ambisonics head inside one, as well as using a modified Zoom H2n as a 4 channel recorder. Hopefully you'll like what we're doing."
http://www.kickstarter.com/projects/1569945514/brahma-affordable-ambisonics-microphone
