Schoeps KFM 360 - Try of a rebuild

Schoeps KFM 360

This system was published, produced, and sold over two decades ago. However, it is very interesting and fascinating if you take a closer look.
To use it, you will need an artificial head like the one shown here and two additional figure-of-eight microphones. Yes! They are hard to find unless you want to spend half of  a fortune on them.

First, let's have a look on what we are talking about.
This is the original version of Schoeps, designed by Jerry Bruck.

Here we see the Schoeps KFM 6 (the grey sphere) with two omnis on each side. The additional, external micropühones are "figure-of-eight" microphones, also from Schoeps.

As these things are neither no longer produced, nor easy to get, nor in any way in our budget, we developed a prototype as shown here.

This is our artificial head equipped with two AKG SE 300 Bs, each with a CK 94 figure-of-eight capsule. Please bear with us as the mechanical design is an early prototype in urgent need of an update; however, it worked anyway.

The magic lies in its "post-production" capabilities.
As you know, you can alter a microphone's pattern, by adding (or substracting) some signal from an other microphone. 

The schematic above illustrates the approach designed by Jerry Bruck. The magic is in the way the signal for the channels are build.
For the "Center" channel the sum of both omnis (left and right) is provided, with a reduction of about 6 dB, to meet the other gains.
The "Left" and "Right" (front) will be provided as a regular channel of the left and right omni. 
The LFE will be also another mono-sum of the omnis, routed through a HPF with a frequency of abot 80-120 Hz. Depending on your setup and personal taste.
For the LS and RS the omni and the figure-of-eight on each side will be mixed into a mono channel and routed to the corresponding channels of your 5.1 setup.
When you add a little delay to these channels, you may "resize" the room; within certain limits.

We believe this system is an excellent choice if you need a versatile and flexible native 5.1 surround recording system. The cool thing is, you can record it with your four-channel handheld recorder, like a Zoom H6 or a Tascam Portacapture X8 or any other handheld recorder with at least four microphone inputs.

The big challenge will be to get SDC figure-of-eight microphones for a "budget-price". Of course it works great with Schoeps microphones—who would ever doubt that?
However, four such high-quality microphones will cost you about $6,000 USD. (Plus taxes, transportation and customs fees.)
Our solution is less than one-eighth of it! - Your choice!
Well ... just when you can find any figure-of-eight SDCs somewhere.

We will provide a tutorial once it is finished. Please check back later. It will take some time. 

For those who want to know all technical details HERE is the original manual of the KFM 360, unfortunately only available in German.