Double MS
A time coincident, compact and adjustable surround configuration
The principle of the double MS technique is using a front- and a backwards pointing MS set, sharing the same Side microphone. Therefore, just three microphones are needed, but quite a processing/mixing task is necessary. As always with MS set-ups, two different transducer technologies are used for the cardioid Mid mic and the bi-directional Side mic resulting in risk of different frequency and phase responses of sound reproduction from the sides or the front.
Therefore, this double MS technique can be attained by using four identical - even matched - DPA 4021 cardioid microphones angled 90° to each other.