How do you mount two microphones for stereo 'coincident/crossed-pair' recording?
It's tempting to fix a spacer bar to a vertical mic stand to mimic the 'crossed-pair' pictures you see with the mics pointing inwards at 90 degrees to each other:-
But... if you look inside the grills, the actual capsules are still a
long way apart, and the mics also get in each other's way by casting an
audio 'shadow' in the horizontal plane.
Overlapping the mics one above the other would solve both problems, but
to keep them horizontal requires an extender to raise one mic higher...
and how do you do this with large diaphragm mics?
After a lot of head-scratching, I realised that mounting the spacer bar to a horizontal fixture would allow both types of microphone to be horizontally 'coincident' with no shadows. The boom section would seem the obvious choice but this creates further problems: a hefty counterweight is reqd. especially for large diaphragm mics; it can also be cumbersome & accident-prone in confined areas. With this in mind, I came up with these arrangements:-
My mic stand has a boom arm which is the same diameter as the upper telescopic tube; you may have to adapt the following if your mic stand is different.
Remove the boom arm (not reqd.) and unscrew the boom mounting adapter from the vertical tube. Slide the adapter over the upper vertical tube and lock it in place with the small boom-locking screw. You now have a miniature boom stub (right-hand photo), i.e. a threaded socket which can be locked in the horizontal position with the large locking screw:-
To attach the spacer bar to this, you'll need a suitable bolt. The central hole on my spacer bar was already tapped, which prevents a bolt from tightening properly, so you can either enlarge the hole or drill a separate one. I drilled a new hole (to the left of centre in photo)... but don't be too hasty yet; I ended up drilling more, so read on before turning it into Swiss cheese!
The mics, cradles & cables are quite a weight, so use a serrated washer between the bar and the adapter to stop it coming loose.
This is where it stopped being a 5-minute job! The two mics need to be
as close as possible without touching, so another hole was drilled. The
distance between the holes depends on the lengths of your particular
mics; you also need to allow for the mics sagging in their elastic
cradles, so 'measure twice, cut once'...
...however, still not home and dry as some cradles won't fit flush to the bar unless they are at the ends:-
So you can either butcher the bar even further and cut it to the correct length, or make a new bar. If your cradles don't have this problem, you could make or buy a generic bar with slotted holes to allow different sized mics to be used.
Large diaphragm mics using the home-made spacer bar:-
Small diaphragm mics using a standard spacer bar; you didn't cut it, did you?! Rotate the bar and mic mounts at a slight angle so the mics overlap and remain horizontal:-
These are quite sturdy arrangements as they are directly fastened to the vertical section of the mic stand; the whole mounting can still be tilted if necessary and raised/lowered if the section is telescopic. You can still attach this spacer bar to the boom arm for more versatility (vs. stability), in which case you'll need to fasten it with a nut if it doesn't have a threaded central hole.