The four types of omnidirectional capsules provided by SCHOEPS – MK 2, 2H, 2S and 2XS – differ in their degree of upper-frequency accentuation, designed to compensate the damping of high frequencies in diffuse sound fields. Because of this effect, a distinction is often made between free-field equalized vs diffuse-field equalized omnis. A choice between these types of omnidirectional capsules is made mostly for aesthetic and stylistic reasons. In Europe, the MK 2S and 2H capsules are more popular, whereas engineers in the US tend to gravitate toward the free-field equalized MK 2 instead.
Small-membrane omnis tend to exhibit directional characteristics at higher frequencies due to a buildup of pressure, causing a constant roll-off of highs in the diffuse sound field (i.e. off-axis). This phenomenon gives this type of microphone its typical warm room tone. All SCHOEPS omnis have the same polar pattern; the difference lies only in their degree of diffuse-field equalization, i.e. the uniform accentuation of higher frequencies in all directions.