OCT 2

OCT 2 - OCT meets Decca-Tree

You came here because you felt limited by the OCT setup and were looking for a system that combined the advantages of a "Decca Tree" setup with those of the OCT? Then you've come to the right place! 

The "Decca Tree" provides extraordinary, immersive reproduction of the recording environment.
OCT is well known for its meticulous and harmonious distribution of auditory elements. 
Since both systems are well understood in theory and practice, it's clear why combining them is advantageous.

Upon closer inspection, you will notice that the center cardioid microphone is placed much further forward. In OCT, the cardioid is shifted forward by 8 cm, and in OCT 2, this distance increases to 40 cm.  This increases the microphone distances, thus reducing inter-channel correlation. The results in a more spacious ”Decca Tree” type of sound.
All localization capability of the OCT system can be maintained by adding a 1 ms delay in the center channel signal.

When you can use only one system for immersive sounds and 2.0 stereo recording, OCT 2 offers some very special advantages for such demands.
OCT in general has good downmix properties already. Any sound cannot be picked up strongly by all three microphones at the same time at the same level.
Thus level differences, rather than arrival-time differences, provide the primary directional cues, and this minimizes harmful comb filter effects in the direct sound when mixing down to two channels. 

The microphones with the red and yellow ring connectors are the hypercardioid microphones and the one in the middle with the green ring connector, is the cardioid microphone.

The capsules of the hyper-cardioid microphones are 90 cm away from each other and the capsule of the cardioid is 40 cm further ahead of the virtual line between the both hyper-cardioids. This setup has a SRA of 90°, which is a good choice in many places.

Depending on your demands of the SRA, you can use the same table as with the OCT setup to adjust it to your needs.

Can OCT 2 be extended to an OCT 2-Surround setup?

Of course! - Or, to put it back to you, why not?

It may not be the best solution to all recording situations, but if spatial qualities are key, this should be considered thoroughly.
The change from a "regular" OCT-Surround setup to a "OCT 2-Surround" setup is very easy. The pipe for the front cardioid has to replaced by a pipe, that makes it possible to shift the microphone 40 cm ahead.

Wait a minute! - If you could shift it to either 8 cm or 40 cm, you might shift it to 18 or 24 cm as well!
This is why we like it. You can adjust the spaciousness by shifting the front cardioid back and forth, if you use an adapter that can be shifted easily. 

We didn't measure anything about this, so we could only say what we did above. But we welcome your data and feedback.