I've got a programme coming up in a couple of weeks, where the characters spend most of the episode crawling around inside a big air conditioning shaft. I'm taking charge of foley, and obviously want to shoot the sound as authentic as I can. I want to get some material together ready for the session, so the question is, how would you guys approach this - in terms of metal props, mic placement etc? Any reference material you might recommend as well? Thanks in advance!
Unless you have access to a big piece of duct to bring to the foley stage, I suggest finding a real shaft and recording your foley on location. It'll sound much more natural. A big part of that sound is the long metal decay. Bring different shoes etc. and perform a wide variety of feet on the outside of the shaft (walking, runs, scuffs etc) and cut the foley later.
Contact mics work great on big pieces of metal, so I'd place one (in addition to a shotgun closer to the action) further down the duct; away from where you're performing your foley to allow the impacts to resonate.
There's some great foley in an air conditioner shaft in Toy Story 2.
+1 on Justin's suggestions: simple, direct, effective!
Depending on the scale of actions in the ducting, and the delicate-vs-aggressive range, maybe having a length of articulated metal clothes-dryer ducting could help with the smaller bits, or as a sweetener. It's very flexible, being almost like very thick aluminum foil, and might offer some mid-high frequency content for your mix.
If this is for a scene with people who crawl through a metallic shaft, go get a large flexible metal serving tray/platter and bend it around for all of the knee-steps and crawling noises - I think that would sound great.
Get a Schoeps MK capsule or possibly even an SM57.
Just to add to the belated replies, in this kind of situation it may be worth looking into software such as Logic's impulse response utility to create a reverb that is true to the film location. This would help in matching post production audio to dialogue and wild track recording.
This was asked back in July so I'm sure it's all history now. However ..... Here's my take. (my 1st)
Being in an a big air conditioning shaft sounds like an tense situation. I'm hearing more actor's dialogue with reverb over whatever background music will be used to help set the mood. Adding in all the metallic shuffling about might be overkill.
Bottom line: ask your director. It's their call.
Also, listen to the "shaft" scene in Aliens.
creaks, rats, a ratchet, moans