When dealing with microphones, proximity effect actually has two meanings. The first meaning deals with an increase in low frequency response when a microphone is very close to the sound source. It is an inherent characteristic of direct tonal microphones, or those with a directional pickup pattern such as cardioid or super-cardioid. Omnidirectional microphones do not exhibit this type of proximity effect. They maintain a more even sounding tone no matter if the sound source is close to the mic element or a little further away from it. That is why a lot of lapel or lavalier microphones are omnidirectional patterned mics. Also, the very popular earset type microphones are mostly omnidirectional too.
Earset mics eliminate the second type of proximity effect that occurs when using a lapel clip-on mic. Usually the lapel mic is clipped onto one side of a blazer or blouse and when the speaker turns their head away from the mic they sound very distant. Also, when the mic is placed on a tie and the speaker looks down to read, the sound becomes very loud and harsh. This can be very unpleasant for the audience. Earset mics eliminate this second type of proximity effect by placing the mic element just to the side of the mouth and no matter what direction the speaker's head moves, the sound coming from the speaker stays the same in terms of volume and tone.