Imagine a concert band, sitting in a semi circle in front of a conductor. A pair of cardioid microphones in a near coincident configuration behind and above the conductor's head. There are five French horns sitting directly across from the conductor, about 10 ft / 3 m away. Drums behind the French horns.
The bell of a French horn points to the player's right rear, so away from the stereo mics pair. As a result the French horns tend to sound a bit low in the mix. The drums, being the furthest away, often sound a bit distant. Perhaps as a result of acoustics of the room, but I can't help that in the short term.
It seems to me that spot micing the French horns and drums might help. It would bring the horns up a bit, and make the drums sound a bit closer. What would be the better way to do this?
1. Two mics between the French horns and the drums, one looking down on the drums and away from the main stereo pair, the other one lower and looking into the rear of the horns, facing the main stereo pair?
2. A figure 8 in the same place to catch both at the same time? This would be pretty close to the French horns, so the players at either end might be outside the figure 8's envelope.
3. An omni in the same place to catch everything?
4. A mic behind and above the drummer looking down to catch the drums and a bit of the horns?
5. Something else?
This would be location recording, so I would rather not carry too much equipment.
One cardioid above the horn and another in front of the drum.
You want the reflected sound of french horns, so I'd point the mic to the ground instead of their bells.
Drums usually sound loud even at a distance but you need some clarity from their skins. Cardioid near the surface directed opposite to everyone else will do the job.
Horns can be tricky (I'm a horn player) because the sound is meant to be heard from in front of the player in an orchestral situation. Hence you'll want spot either over head or even with the shoulder area. Once you go behind you get direct bell sound, which is much different and sometimes even desirable. In studios, pits and smaller spaces, miking from behind and sometimes above are used. If you have to spot from behind in orchestral session, use an omni or wide cardioid back a few feet.
I have only ever used spots on the French Horns for live sound outdoors. In a situation such as yours, attempting to get something that "isn't there" for the conductor seems to me to be seeking a technical solution to a musical problem. As has been mentioned, the natural sound of the horns is less direct than the rest of the brass and that is in the nature of the sound of the instrument within the ensemble.
If the horns need to be louder or more present, that is a job for the conductor first of all, not the recordist. If he/she specifically requests some "enhancement", then go ahead. But in my book it changes the sound of the ensemble...not to mention introducing time alignment problems in re-combining the spots with the main pair...a problem which is much less if your spots are co-directional with the main pair.
When I have to spot a french horn, I'll usually go with an omni on a short stand (table top stand) some distance behind the player looking at the bell.
If you have to contend with drums, this may or may not work, but going with an omni will get the direct sound of the horn while not sounding too close at the same time.
A single overhead might help with your drum sound. Perhaps a kick mic too if needed.
Another way to consider, perhaps move the main pair back a little, making the other instruments blend better. Hard to say without hearing of course, but sometimes the answer is to get a better ensemble blend rather than just dialing in presence with spot mic's.
It's always a judgement call based on what you are hearing, so take everything here with a grain of salt.