Reducing Environmental Noise
Out of doors or in large interior spaces such as soundstages, factories, or warehouses, environmental or
general background noise tends to approach a microphone along the plane of the horizon if its source
is either reasonably distant or random in nature. Because this soundwave will, in effect, produce equal
pressure on both sides of the diaphragm of a vertically-oriented bidirectional microphone (i.e. the
diaphragm is horizontal) this noise will self-cancel and sound sources that are closer and more directly
on-axis will prevail. Jim Tannenbaum, a very active film dialog mixer in Hollywood, explained at an
AES Workshop how he uses this to good effect in recording actors in a noisy environment: By placing
a bidirectional microphone just below the camera’s view and orienting its pattern vertically, the actor’s
voice is picked-up by the front lobe while the rear lobe is aimed at his feet — which presumably are
not making any noise at all. (ref. Figure-3) The result is that the environmental noise pickup is signifi-
cantly less than the direct sound of the talent, producing clean and useable dialog.
