What is the best way to use two different mics?
 

I will be shooting a bedroom scene. I have access to an AT4033 for a day in addition to the AT4073a that I used through the rest of the movie. What use should I put the former to? How should I position it? It is a cardiod.

The 4033 is a large diaphram, side-address, studio microphone. It's the sort of thing I'd think of to use in studio for recording vocals and close miking acoustic instruments or for voice-over and ADR work. Unless one of your characters bursts into song at the glories of his or her lover in this bedroom scene, I'm not quite sure what your best use of it might be in that setting <grin>.

I agree with Steve. Unless the bedroom is chock full of curtains, carpet and pillows, which is certainly possible, then I don't think you'd be able to get the 4033 close enough to be truly effective and keep it out of the shots.
On the other hand if this environment is acoustically very soft and the characters aren't yelling at each other, then your 4073 will be great.
If the bedroom is harder, especially if the characters are using louder voices, then neither mic is going to be that pleasing or easy to use.
Do you have any other alternatives to use if this room is full of hard surfaces? And tell us more about the bedroom and the specifics of the scene and how it will be acted and shot.

Thanks for the input, team. I actually shot the scene last night (it went well). I converted the dining room, which has a hardwood floor, into a bedroom. I put the studio mic on its stand (it was actually an AT4040) and used it for "back-up". Monitoring the audio levels, I noticed that the AT4040 picked up much less noise. In other words, when the actors were not talking, the AT4073a recording something, but the AT4040 went quiet. I should note that the dining room is situated next to a busy street. Isn't the conclusion that the AT4040 a more appropriate mic to use under these circumstances? (I don't doubt that there may be other mics more suited to this environment that both of these.)

Well, that mic has a cardioid pickup and if it was facing away from the street noise that could account for it. The problem I see is one of distance - those mics are designed to be used close up, like with a foot or so of the performer's mouth. Whille they'll certainly pick up sound at much greater distances, their performance at the distance they need to be to be out of frame in most circumstances isn't going to be optimal.

Thanks, Steve. Which one do you think would be more susceptible to off-axis coloration (due to reflections, of course)?

Because of the physics of the interference tube that shotgun mics use to achieve their high directivity, the shotgun will show more off-axis colouration of the tonal balance of the sound than will a regular cardioid. Shotguns are highly directive in the mid-range and more like a cardioid or in some cases even omnidirectional in the low end. As a result, the lower frequencies of reflections arriving from off-axis are hardly attentuated at all while the mid-range components of those sounds are strongly affected, hence the hollow boomy quality of reflected and other off-axis sounds with a shotgun. Couple that with the comb filtering effect caused by the arrival time differences of direct versus reflected sounds and you can get some strongly coloured results. Cardioids and hypercardioids don't have the same extreme frequency-dependent directivity characteristics because they use different physical principles from shotguns to obtain their directional properties.

The best way to avoid the interfering noise from the street is to cover the windows, etc, with sound absorbing blankets and then get the mics close enough to the talent that you don't need to run up the gain to hear them clearly. There is nothing that will substititute for getting the mics close-in and nothing that will do as good a job at getting high-quality sound.