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Microphones can be classified both according to transducer principle and by directivity or polar pattern. Transducer principle is the method of converting one form of energy to another. Since we have already covered transducer principle of an electret condenser microphone (ECM) in a previous blog article , we shall focus on types of electret condenser microphones by directivity or polar pattern. But first, a word about polar pattern. In simple terms, the polar pattern of a microphone describes how well the microphone picks up sound coming at it from different directions. In describing microphones by polar pattern we can lump them into three general classes; omnidirectional, unidirectional and bidirectional.
Omnidirectional Electret Condenser Microphones: An omnidirectional electret condenser microphone is one in which only one side of the diaphragm responds to changes in sound pressure. In this scenario such microphones pick up sound equally from all directions. The polar patternthen closely approximates a perfect circle shown below. Imagine a group of people sitting around a table and if the omnidirectional electret condenser microphone is placed in the middle of the table, the microphone will pick up the sound equally from each talker.
Unidirectional Electret Condenser Microphones: A unidirectional electret condenser microphone is one which picks up sound waves with high gain from a specific direction. There are several types of unidirectional electret condenser microphones each with a unique polar pattern, with the most common type being Cardioid shown below. Other types of unidirectional electret condenser microphones include sub-cardioid, supercardioid and hyper-cardioid, each with a unique polar pattern. An example of a possible application of a unidirectional electret condenser microphone would be where someone is giving a public lecture and the microphone needs to pick up sound waves received directly in-front of it while rejecting sound waves received from the back or sides of the microphone.
Bidirectional Electret Condenser Microphones: As the name suggests a bidirectional electret condenser microphone picks up sound waves well from either the back or the front and rejects sounds coming at it from the sides. The polar pattern mimics the figure 8 shown below. A useful application for a bidirectional electret microphone would be in situation where two talkers are on either side of the microphone and someone is recording the conversation.
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