Mic-ing cars without capturing Dialogue

Question

I have a scene where we had to ADR the actors for their dialogue in a car. What was crucial was that the scene involved the car going faster and faster and the passenger talking louder and louder. Wish there was a way I could keep the car sounds (at least the engine or progression of the speed of the car) intact without the dialogue. So when we do ADR, I would also have a clean "car track".

If I would sit in a pre-production meeting with a similar scene in the future, what would be good advice to tell them on where to rig extra mics? (that won't capture dialogue). I'm assuming this would be taped on the exterior or something?

I'm not saying I wouldn't layer the tracks with sound fx, but it still a good track to build on even if we were to ADR.

(I am a post engineer and have basic knowledge of production audio.)

Thanks a bunch.

Answer 1

If you add a couple of microphones under the hood and in the trunk as well as have a microphone near the interior camera position as a reference for the sound, you can filter and mix the engine channels and trunk channels until it sounds similar to the near-camera mic. If needed, put a mic in the wheel well or under the car for tire noise (put it in foam and tape off the foam completely to block dirt and direct wind. How the tape incluences the sound is not relevant in this case, as you'll be filtering the highs anyway) or behind the side mirrors (tricky) for wind and mix that in at higher speeds as well.

To figure out the dampening of the sounds in the cabin, start with a gentle low pass filter.

Answer 2

A mic in the engine bay and one on the exhaust would allow you to capture two of the main elements. If you take an impulse response in side the car while it is stationary you will be able to worldise the dialogue and the dry engine and exhaust tracks to make them more believable.

Answer 3

Id look at contact mic's placed under the hood, otherwise the car's own internal will muffle the sound.