Microphones
From Ambisonia
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[edit] Tetrahedral Microphones
The most satisfactory way of making a first-order Ambisonic B-format recording of a soundfield is to use a "soundfield" microphone, which consists of four tightly-packed capsules and associated electronics or software to convert their signals into B-format. (For higher than first-order, more capsules are required). Microphones of this type are available commercially, or can be made DIY as a number of enterprising individuals have shown. See the lists below:
[edit] Commercial tetrahedron microphones
- A range of microphones are available from SoundField Ltd. A well known industry standard for soundfield microphones.
- The TetraMic from Core Sound. Less expensive and calibrated using software.
- AGM Digital are working on a successor to their DPA-based MR1.
- The E32 Eigenmike® microphone array from mh acoustics has 32 high-quality pressure microphones embedded in a 8.4 cm rigid spherical baffle. The array can decompose the sound-field for up to fourth-order spherical harmonics.
- The Oktavausa MK-012AM Ambient Microphone is a 4-D preamp which could be used as part of a tetrahedron mic.
[edit] Home made tetrahedrons
- Henry's Tetrahedron
- Nick Mariette's portable
- Etienne Deleflie's SoundThief
- Rafael Kassier's mic built from Oktava capsules
- Paul Doornbusch's DIY mic
[edit] Native B-format Microphones
An alternative approach, which is limited to horizontal only, is to use three microphones to capture the omni and two figure-of-eight signals directly. This approach has long been used commercially by the Nimbus record company, and is also a practical method for amateur use. The requirement is for small microphones that can be placed close together in vertical alignment; the only widely available microphone ranges that are suitable and have the necessary figure-of-eight capsules are AKG's Blue Line, Sennheiser MKH, the Schoeps range, and Neumann's modular ranges. Photographs and descriptions of the Nimbus arrangement (using a B&K omni and two Schoeps figure-of-8s) and similar ones using AKG Blue Line microphones can be seen here and here.
[edit] Commercial native B-format microphones
- The Josephson C700S microphone is a commercial microphone with B-format output (though they don't talk about it that way). The version with only one fig8 capsule is shown here.
- Schoeps make a mount that can be used to hold their capsules in a native B-format arrangement, although they prefer to suggest their "dual-MS" arrangement using two side-address cardioids and one fig8, from which the B-format signals can easily be derived. This is understood to be because of the improved matching between the capsules without further equalisation.
