Well the official standard ORTF is a couple of cardio 110°@17cm appart
I use ORTF as "grab bag" for many similar arrangements.
In that case the setup is much different since B&O are ribbon so fig.8
Yes and no.
All these "minimal array" options, including Blumlein crossed 8 (which this ribbon is) and M/S, use intensity stereo.
That is there is no appreciable time difference between L/R for these microphone arrangements, only level difference between L/R.
This does two things, first, there is much less comb filtering if mixed down to mono and the angle of incidence covered is very wide.
https://sengpielaudio.com/Aufnahmebereich01.pdf
The problem is, below ~700Hz the stereo placement and effect is less determined by level intensity and more by time delay difference.
Decca tree used Neumann M50 if I'm right, so omni pattern... Neumann created this ref. for that special config. at a time.
Yes.
The Decca Tree is an attempt to get "laufzeit stereo" with a clear center image, where there would normally be a "hole in the middle" as the placement of the L/R microphones is too wide.
The result is a great room impression and a clear centre, but overall instrument placement in the phantom soundstage is poor. Minmal "point" arrays are pretty much the opposite.
Experiments in the 80's led me to a system that is "2-Way" and radically different.
But I only did it for coursework as I normally did Rock'n'roll, so I never did much with it.
So you propose to replace the center mic by an ORTF couple... and add another omni pair (with EQ as you said) farer behind the front ones, let's say 4-5 meters away ?
No.
I propose a classic Decca tree equivalent with a "small" directional array up front (ORTF & Blumlein are the posterchildren for that) instead of a mono microphone and suitable microphones at the rear. No need to obsess about "M50".
I propose to create a means for a time delay correction for all microphones used, to allow seamless mixing.
And I propose to use microphones with excellent low frequency characteristics (anything but omnis sounds weedy in the bass and EQ don't quite fixes it) for low frequencies with an arrangement that gives the best stereo localisation for low frequencies and microphones with excellent high frequency characteristics (e.g. 1/4" Cardioid Condensor or ribbons) with an arrangement that gives the best stereo localisation for medium and high frequencies.
I then propose to create a crossover between the two sets of microphones at around 700Hz. In the "old days" I did that with RL circuits and used allpass circuits (front array delayed with RL ladder) to compensate the 1.5m distance between front array and rear microphones.
My "Box" contained standard east German Microphone transformers and simple discrete 2-Transistor microphone pre X 4, neccesary buffers and four stereo faders to set the mixdown levels for these signals:
Front highpassed,
Front full range,
Rear lowpassed (lowpass adjustable 100....1000Hz)
Rear full range
This allowed the the then common (in commie east germany) recording directly to 2 track tape, with gain riding "live" to compress dynamics manually (yes, at one time my job was "compressor").
Thor
