Bidirectional Microphone
The bidirectional microphone has full response at both 0 degrees (front) and at 180 degrees (back). It has its least response at the sides. The coverage or pickup angle is only about 90 degrees at the front (or the rear). It has the same amount of ambient pickup as the cardioid.
This mic could be used for picking up two sound sources such as two vocalists facing each other. It is quite useful in adding a "presence rise" to vocalists as clarity between the two can be improved. However the drawback of such a microphone in a studio environment is that if a mistake is made by one singer, they both have to do it again. Also adding effects cannot be done to individual voices.
A supercardioid has a narrower pickup pattern than cardioid, but also has some rear pickup.
A hypercardioid has a narrower pickup pattern than supercardioid, but also has more rear pickup than supercardioid. Both the Supercardioid and Hypercardioid microphones are suitable for vocalists.