Title says it all. I had a setup/soundcheck session today for a recording of cello duet and am not happy with the sound. Figured I'd come on here to ask if anyone can help me out with any ideas, from the audio samples, of how to improve it? (My first time attaching audio samples so I hoped this worked.)

I had the 2 cellists spaced 1m apart (measured from mid-point of the bridge), angled only very slightly inwards - how they'd normally play in concert. I used only my Line Audio mics. (I'd hoped to get some others before the session but it wasn't possible to arrange a trial in time due to dearth of useful gear shops in my area.) 2 CM4s and 2 OM1s, into my Mix Pre 6.

I tried 2 cardioid spots and an omni pair as someone suggested on here, but I didn't like the spot sound. Then I tried to modify suggestions from Decca book for solo cello/string quartet. I tried:

Modification of 'solo cello' setup: omni pair nearer the cellos (c.2m up, 25-30cm apart, 2m back) with cardioid pair in ORTF 2.5-3m back. Didn't like the cardioids here or think they added anything and the combination of the pairs was unconvincing.

I then moved the cardioids to be c. 1m behind the performers, c. 2.5m up, in XY with rear pointing to performers - aiming for an upward facing ambient pair. I thought they sounded ok by themselves but again didn't blend well with the other pair. Maybe the room just doesn't have a sufficiently resonant acoustic to be worth capturing?

Focussing on the omnis as the main pair, I tried many different placings to get an optimal sound. I ended up with them c. 2m high, 27cm apart, 1.9m away from the performers, pointing one mic so far as possible at each bridge (roughly at the perpendicular). I tried different spacings, distances and heights and ended up with this but I'm still not happy. To me, the sound is simultaneously somewhat muffled/unfocussed and also a bit thin. But when I was recording a single cello in a similar position, I was much more convinced by the results.

Are there any quick fixes or other ideas I can try before starting the recording proper in about 9 hours time?

First sample (37) is just the omnis, second is both pairs together.

In particular: is there anything I can do in spacing, direction etc to improve the sound of the omni pair? Or is it just a combination of the mics themselves, that room etc?
(The room is 5 by 7.5m, used as a studio for other engineers and is full of gear and furniture etc, not sound-treated, has 1 bare stone wall several metres behind the performers, the long walls are somewhat covered with furnishings, the other short wall facing the performers at the far end has a large central window, the roof is quite sharply angled with wooden beams, the floor is wooden with carpets in some areas but not directly under the performers.)

And how can I better blend the other pair? Is there a modification of the string quartet setup I should try? (The one I read of has ORTF-type pair with 80-90* angle, 60cm behind an omni pair.) I didn't like the cardioids in ORTF at all but maybe I had them too far back and with too wide an angle.

Is the (in my opinion) bad matching of the pairs due to something like source angles not matching? I was aiming to get an image angle of something like 30* on the omni pair, to make 50% of the full image width. Is what I'm doing with the cardioids giving a different image width? How can I calculate this?

If anyone has suggestions in the very short time remaining of anything I can do with the kit at my disposal, I'd be extremely grateful. The musicians have spent a lot of time preparing and I'd really like to get a better result for them... Also tips for the future are of course also gratefully received. I realise I'm very much a beginner in this field and am probably making many errors.

Replying to add audio samples.

You don’t need spots for this. A single main pair is appropriate. Since I don’t know the space where you are recording, I will suggest that you use a boojum/jnorman array (lots of threads about that and other similar OCCO arrays). The array is 4 mics on a single stand and stereo bar - two cardioids in either ORTF or NOS, flanked by a pair of omnis. Keep a relatively close distance to the performers, maybe 6-8 feet out. In post, you can choose either the cardioid pair (which may need a bit of good digital reverb), or the omni pair, depending on how good the room sounds, or you can blend the two pairs, starting with the cards as mains, and adding just enough omnis to give you some room sound, or starting with the omnis and adding just enough of the cardioids to give some definition to the stereo image. Your line audio mics are quite capable of stellar results when used properly. Good luck and have fun.

Clearly, the room is way too small and dead for a typical classical acoustic sound, which is what you would want with celli and the type of material. Record close to keep out as much as possible of the room and add good quality of artificial reverb is what I would recommend if you have to use this room.

Both Jim and Earcatcher's advice is solid...it's too small and damped a room for effective bloom of the instrument sound...so I recommend simply walking the room and singing, clapping your hands until you get something coming back from the walls that sounds a little pleasing, and put the players there. Keep away from the damped and carpeted areas, try maybe somewhere central in the room, or start with bare walls behind the players.

The 4 mic array gives you mix options later, with CM4's try 47cms spacing between the 2 mics and 45 degrees angled out (90* total) from the middle of the bar. Put the OM-1's either side of the CM4 pair, to make another outer pair on the same bar with 67cms spacing. Probably don't angle these omnis out. Aim all mics down towards the bridge of the cellos

Go back around 2 metres (from the centre line between the players), go up about 2.0-2.5 metres high and listen to how that sounds on headphones...adjust height and distance for sufficient detail and ambience (if any)

If the players are amenable, an alternative is to have them face each other, with 1-2 metres space between them, and put the mic stand in the centre between them, with the all mics facing down at the floor (keep the 45* outwards splay on the CM4's)

If the mic bar is at 90* to the players you'll get the cello's largely overlaid on each other (ie little stereo spread between them) If that's not liked, turn the bar 90* so each bar-end faces a player, and you'll get a stronger stereo separation, if that's what is wanted ?

Expect to add reverb to one or both pairs to overcome the dry room, you can adjust the mix blend between the 2 mic pairs after the session at home. What's mostly wrong with the setup is the too small/damped room...look for a nice old church or meeting hall next time !

Best of luck !

i'd use a single directional spot on each instrument plus a spaced omni 'main' pair - or just a single main pair in ortf - and i'd definitely add efx!

Many, many thanks for these helpful suggestions. I will try these out (as many as I can in the time or until something sounds good) and report back. Feeling somewhat more hopeful...