Microphones
Rafael's
Ambisonic
Microphone (RAM)
This
page details a side-project of mine to create an ambisonic microphone.
Genesis of the RAM (Rafael's Ambisonic Microphone):
After toying with using my two Rode NT5 microphones as half of the microphone (like Etienne Deleflie's "Soundthief"), I decided on using four Oktava MK-219 capsules as the heart of the microphone. These microphones have a large condenser diaphragm, but are let down by the case (the improved Oktava MK-319 features almost identical capsules and electronics in a revamped case). As the MK-219 cases will not be used in the RAM, they seemed to be ideal candidates for the job. Because the capsules need to be exposed to soundfield on both sides, the capsules will need to be mounted in a tetrahedral array similar to the Soundfield ST-250.RAM Construction:
Click a picture to see a larger view:| 4 Original Oktava MK-219 Microphones |
Disassembled |
Outer Cage |
Outer and Inner Cages |
Suspended
Tetrahedral Capsule Array |
 |
 |
 |
 |
 |
| Circuit Boards and Capsules Installed |
Felt-Wrapped |
Finished RAM |
With Multicore Cable |
With Break-Out Box |
 |
 |
 |
 |
 |
The use of 1" cardioid capsules, whilst increasing potential sensitivity, created a number of design challenges, least of which is the design of a suitable housing that was neither overwhelmingly large nor unmanageably heavy.
The design challenges facing the construction of the RAM were as follows:
- Mount the four capsules as if they were individually at the
centre of the four faces of a regular tetrahedron
- Allow open access to the soundfield for the capsules
- As lightweight as possible
- Allow easy access to the electronics in case of maintenance issues
- Allow for suspension of the capsules to reduce shock transmission
- Allow ease of connection between the RAM and my digital
audio interface.
Most of the design concerns were addressed with the use of an internal four-pillared cage which allows for the suspension of the tetrahedral capsule array and the mounting of the four circuit boards onto bracing struts that are able to rotate outwards to give full access to the circuit boards. A mesh outer cage screens the capsules and electronics and provides impact protection. The use of a mesh screen significantly decreases the potential weight of the microphone body whilst allowing open access to the soundfield for the capsules and effectively screening the capsules and other electronics from interference.
The final design consideration was met by using a four-pair multicore cable that uses 10-pin connectors (4 pairs of signals and two ground connections) to connect the microphone body to an aluminium break-out-box that houses four XLR sockets. The multicore cable is a total of 15m long, with further extention possible with the use of long XLR cables. This multicore cable will allow unobtrusive rigging of the RAM at recording venues.
Upgraded Electronics:
Most of the on-board electronics were upgraded using information from an article in Recording Magazine by Scott Dorsey and advice from Michael Joly of www.oktavamod.com. Upgraded and "stock" electronics boards were informally compared and the upgraded electronics were found to be sonically superior, prior to the upgrade of all boards.
Acoustical Test Results and Recordings:
To follow!
Hosting by: 4UHosting.co.uk