Omnis would be my first choice for that particular recording situation anyway, so before spending money on gear, I suggest using the microphones you already have first, especially if recording acoustic bands and chorus’ in that hall is your primary focus at this point.
Your assessment is accurate- to my thinking there is a decision matrix I sort of run through that’s developed partly by experience and partly by resources like this site, but it is multidimensional and goes different ways depending on various things: some revolve around the nature of the recording environment and the music, some have to do with microphone patterns and stereo configurations, some the attributes of your particular equipment, and then there is practicality, inclination, preference, budget, etc. It’s all interdependent and each of those things influences the decision matrix. That’s all true, but it doesn’t really point you in any immediate direction, it’s mostly just a warning against simple cut and dry answers taken at face value and a good philosophical basis to work from.
Here’s a few more-concrete things that most will agree on that to get you going:
The most important thing is good microphone location; in this situation, you already have a pretty good handle on that.
Concert recording is not like home recording or most studio recording. Most information you’ll find on the internet outside of this site deals with home or studio recording. There is some information on the old fashioned way of doing classical recording with a single pair of microphones, which is more applicable to concert recording in general. That’s even more applicable for you in this situation than it is for people around here who are recording bands in bars.
Typically with inexpensive microphones, omnis simply sound better and more natural than cardioids, ignoring all other factors which make choice of one microphone pickup pattern more appropriate than another. So if that is what you have available, and if the situation allows for them, omnis are often the better choice. I would not hesitate to use the omnis you have to record in the situation you’ve described.
Cardioids are more forgiving in getting a decent recording in any generic recording situation. ORTF is one of the best ‘all purpose’ cardioid microphone configurations and is easy to recommend as a good starting point for most situations. It might not be the best choice, but usually isn’t terrible. Most concert tapers that only own only one microphone pattern own a pair of cardioids and use them in near-spaced configurations similar to ORTF.
I’ll post later with a more fleshed out hierarchy of what’s important, but even though there are things with are more basic, check out the paper titled “The Stereo Zoom” by Michael Williams. It explains the stereo relationship between microphone pickup pattern, spacing and angle between two microphones and some (not all) of the important implications of those relationships. It describes a conceptual continuum from A-B spaced omnis to coincident X/Y figure-8 microphones. ORTF and the other common microphone configurations you’ll read about around here such as DIN and NOS fall somewhere in the middle of that continuum. The Stereo Zoom both conceptually describes the relationships and offers a direct way of choosing an angle/pattern/spacing relationship for a specific situation. It’s a useful tool for many of us, but I’m mostly recommending it for developing an understanding of the concept, more than using it to select a specific steup. Do a search here at TS for threads on it and for links to the paper which is available free on line. If you have trouble finding them, I’ll post links for you.
