For most purposes, there are two different styles of microphones - unidirectional and omnidirectional. Both receive vibrations from outside sources and convert them to electronic impulses, but unidirectional microphones only pick up sounds aimed directly into their centers. This is ideal for one speaker or solo instrument, but not as useful when sounds arrive from all directions. Omnidirectional microphones can pick up sounds from virtually any direction, because the electronic pick-up is placed in the center of a mesh-covered dome.

Omnidirectional microphones can be easily identified by their distinctive rounded ends. Unidirectional microphones usually end in a flat mesh. The sensitive electronics of an omnidirectional microphone are usually protected by a heavy mesh bulb. This mesh keeps foreign materials from entering the inner chamber and potentially contaminating the filament. Some omnidirectional microphones take this protective shell one step further. A cover made from foam rubber is often used as a protective sleeve. The foam does not prevent sound from entering the microphone and also acts as a shield against wind and explosive breath sounds. Ambient noise is a common concern with omnidirectional microphones. A unidirectional microphone is usually protected with a thick wire mesh, but no foam rubber sleeve.

The most common uses of an omnidirectional microphone involve groups of singers or instrumentalists. It can be suspended from the ceiling into a choral group or positioned between a vocalist and an accompanying piano or guitar. Solo vocalists can hold an omnidirectional microphone in various positions and still be amplified. Unidirectional microphones, on the other hand, are usually held in one position and the vocalist or speaker must adjust accordingly. Small wireless microphones called lavaliers may be omnidirectional or unidirectional. These mikes are generally clipped to the speaker's lapel or blouse and fed to either a concealed wireless transmitter or a channel on an audio mixing board. Omnidirectional lavalier microphones also have the distinctive round shape of their larger counterparts.

Omnidirectional microphones do have some drawbacks, however. Because the microphone cannot discriminate between wanted and unwanted sounds, ambient noise from the environment can be picked up and amplified. Some performers may want the sounds of an enthusiastic audience to be included in the session, but others may want these extraneous noises blocked out. Only a unidirectional microphone can keep background noise completely out of the recording equation.

Another risk with omnidirectional microphones involves the triangle between microphone, performer and speakers. If an omnidirectional microphone is placed too close to the speakers, it will pick up extraneous noise. This noise is then fed back into the system through the microphone and amplified again. The result is a very unpleasant phenomenon called a feedback loop. Great care must be taken to avoid putting an omnidirectional microphone directly in front of the speakers.

Omnidirectional microphones in general solve more audio problems than they create, so it pays to invest in a few for most public speaking functions and band performances.