A directional microphone is one that picks up sound from a certain direction, or a number of directions, depending on the model involved. In truth, all microphones could be considered directional to a certain degree. However, a directional microphone is often broken down into one of two major types, an omnidirectional microphone or a more limited version.
The omnidirectional microphone is a type that picks up sound from every direction. This is a very good all-purpose microphone used when there is no need to discriminate where the sound is coming from. This type of microphone is very common in recording studios and even on stages where all sound is trying to be captured. Such a microphone can also pick up ambient sounds, which may also be desired, depending on the type of recording or broadcast being done.
Cardioid microphones are a little more selective in the sounds they pick up and turn into electrical signals. This type of directional microphone will pick up some sounds from the sides, but its best use is when the user is directly in front of the microphone. Sounds off the sides, while they may be picked up, will often come in very low and may not be able to to heard clearly by other users. Therefore, this type of microphone may be good to use in situations where noises from other directions are not desired. This includes in applications such as telephone headsets. This is one of the most popular types of microphones, quite possibly making up the majority of handheld microphones on the market.
There is another type of directional microphone called the hypercardioid directional microphone. Like the cardioid, the purpose of this microphone is to mainly pick up sounds from the front. While it will pick up some sounds from the side as well, this microphone is even more selective than the cardioid. Therefore, it makes it an even better choice when outside sound is not truly desired.
The other type of microphone is the bidirectional microphone. This type of directional microphone works by picking up sounds directly in front of it and directly behind it. In fact, it may be impossible to identify, on such microphones, which is the front and which is the back. This type of microphone has some benefit especially for those who are doing interviews or perhaps doing a duet in a recording studio. However, this microphone may not have very many cases where its use is practical.