The omnidirectional microphone has a polar pattern that picks up sound from every direction. This polar pattern requires a quiet room with little noise. The omnidirectional is used for orchestra, theatre, and choir performances. The microphones would be hung from the rafters of the performance hall, in strategic locations, in order to capture the range of all the instruments and/or voices. The audience members are generally quiet during the performance, although if an audience member coughs or sneezes during a quiet passage, that will be picked up as well.
The bidirectional microphone has a polar pattern that picks up sound from two directions, the front and the back of the microphone element. This pattern blocks sound waves entering from the sides of the microphone. The bidirectional microphone would be used for interviews so any extraneous noise from the audience is blocked and the microphone can be shared. The interviewer and interviewee would be able to hold their discussion without an additional set up.
The cardioid microphone has a “heart-shaped” polar pattern, in which only the sound waves coming from one direction is picked up by the microphone element. This type of microphone is used by speakers during a presentation and vocalists needing to isolate the sound of their voices.