Proximity Effect

The proximity effect is a consequence of how directional microphones achieve their polar pattern. A pressure-gradient microphone responds to the difference in pressure between the front and back of the diaphragm. In the far field, sound waves are essentially planar and the pressure gradient is frequency-independent. In the near field (within about one wavelength), sound waves are spherical, and the pressure gradient increases for lower frequencies because the pressure difference between front and back becomes proportionally larger.

The effect follows an approximate 6 dB/octave boost below a frequency determined by the source-to-microphone distance. At a typical close-talking distance of 5-10 cm, the boost can exceed 10 dB at 100 Hz. This is why radio announcers and podcasters using cardioid microphones develop a characteristically warm, bass-heavy "radio voice" — the proximity effect is a feature, not a bug, in those contexts.

For measurement purposes, the proximity effect is a significant concern. A measurement microphone placed too close to a loudspeaker will show artificially elevated bass response, leading to incorrect EQ decisions. This is why measurement standards specify minimum distances (typically 1-2 meters for full-range measurements). Omnidirectional microphones, which are pure pressure transducers with no pressure-gradient component, exhibit no proximity effect — making them preferred for acoustic measurement.

SonaVyx helps manage proximity-effect-related issues through several features. The transfer function measurement reveals the frequency response including any proximity effect bias. The equipment scanner identifies microphone types and can warn about proximity effect susceptibility. The AI diagnostic considers measurement distance when evaluating low-frequency response, noting when excessive bass may be a proximity artifact rather than a system problem.