Proximity Effect
Distance is a tone control. Bass boost from the pressure gradient; more directional patterns mean a stronger effect.
Distance as a Tone Control
The proximity effect is a bass boost that occurs when a directional microphone is placed close to a sound source. The closer you get, the more bass. Radio announcers and podcasters exploit this for warmth and intimacy. But go too close and the bass overwhelms everything.
Why It Happens
Directional mics work by sensing the pressure difference (gradient) between the front and back of the diaphragm. Close to the source, the sound field curves rapidly, and the pressure difference is exaggerated at low frequencies, causing bass boost. At a distance, the wavefronts are nearly flat and the effect disappears.
Pattern Matters
Omni mics have zero proximity effect (they sense pressure, not gradient). Cardioid mics show moderate proximity effect. Figure-8 mics show the most extreme proximity effect because they are pure pressure-gradient transducers. This is why engineers use highpass filters when close-miking with directional mics.
The HPF Solution
A high-pass filter (low-cut) is the standard tool to tame proximity effect. Most mixing consoles have an HPF on every channel. Many microphones have a built-in bass roll-off switch for exactly this purpose.
Try it: sweep the distance from 2 cm to 2 m and watch the bass shelf grow. Then compare omni (no effect) vs figure-8 (extreme).