Omnidirectional microphones (also called pressure transducers), which have no directivity in the low frequency range, become increasingly directive towards high frequencies (from approx. 4 kHz) due to the pressure buildup effect and rear-shading of the sound. As a result, the diffuse field frequency response above 4 kHz increasingly differs from the free-field curve.
A diffuse-field-equalized pressure transducer shows a linear diffuse field frequency response. The SCHOEPS MK 2XS is such a microphone capsule. At the same time, the free-field frequency response of the MK 2XS is overemphasized in the highs.
For example, a diffuse-field-equalized microphone capsule can be used to pick up distant room sound outside the reverberation radius.