Another low-frequency phenomenon that occurs in most directional mics is known as proximity effect. This effect causes an increase in bass response whenever a directional mic is brought within 1′ of the sound source. This bass boost (which is often most noticeable on vocals) proportionately increases as the distance decreases. This effect can be beneficial on certain sound sources, however, if you want to compensate for this effect (which is somewhat greater for bidirectional mics than for cardioids), a low-frequency roll-off filter switch can be used. This switch is often located on the microphone body. If none exists, an external roll-off or equalizer can be used to reduce the low end.
Sound files courtesy of ArtistPro/CoursePTR, courseptr.com/artistpro (Professional Microphone Techniques, David Miles Huber & Philip Williams)