interesting read:
http://www.schoenharting.de/3.html

A good space to record is the biggest consideration. A space that will let the instrument expand to its full potential. You CANNOT record a bass in a small room and expect it to sound like anything. A good microphone like a AT4050 or a BK4006 would be my choices for a microphone that will record the bass well yet not sound tubby.

I have had success with a QTC50 on the F hole about 8 Inchs away. I have also tried mixing that with a mic stuff in the bridge. I used foam to keep it there. That way the artist can move about and the mic bridge mic will stay in the right spot. The bridge mic I mainly used to bring out the body not the strings. The QTC50 I used for that.

For classical, do NOT ever put a mic on the instrument... Just isn't going to sound good. Rather, a mic pair with a good low-end that isn't tuby is the way to go.

My successful solo bass recordings have been using Schoeps CMC5MK21, Sennheiser MKH800, and DPA 4011. On a couple of the recordings, because the hall was boomy, I placed a pair of coles on a short stand at the edge of the stage.

Omnis are great for capturing the low end, but be aware that they can sometimes capture too much low end resulting in a lack of clarity. For recording bass, I will only use omnis to open up/extend the sound of a recording where I have an ORTF or similar pair.

As a spot in ensemble settings, I've also had great luck with the SE 3300 A (which is huge and not great for many concerts) and the Sanken CU 31. I would imagine that the CU 31 in an ORTF pair would also sound quite nice.

--Ben

Not to get too far off the original question, but Ben brings up a good point; spotting it in an ensemble is a little different than solo recital work. And if you're talking several basses in a larger orchestra, you've got to make a choice on which one(s) to go after - usually the firsts. They fly all the mics in Verizon Hall for the Phila. Orchestra, and each section, including the basses, is mic'd from overhead. Not sure what's on the bases; but it's an SD mic like all the rest.

For my purposes, I prefer a short stand with an LD mic on it, putting the mic about bridge-height. Depending on what's handy with what I have in my kit, sometimes it's an AT4033, other times it's a couple of other things, but almost always LD mics. I feel like I get more of the overall sound of the instrument that way, and with a cardioid pattern I can get in tighter into the space of the instrument and lose some bleed from other surrounding instruments.

Of course you've gotta watch out for those big bows. I always ask them before I sign off on the placement if it's OK with their personal space and bowing action. It's just something you do NOT want to have happen to mic OR the bow.

For jazzers in quartets and such, they almost always have a pickup and/or mic on the bridge, and we usually mic it as well. When Mixing back in the studio, it's nice to have both options.