This kind of microphone has a circular polar pattern. Let's take a detailed look at how it is built, with reference to the following diagram:
The diaphragm is fixed to a coil inside which there is a magnet. The diaphragm is surrounded by an elastic material which hinders its lateral movements. The rear-end of the diaphragm is located in a section which is completely sealed off except for a little hole which allows for the passage of air resulting from the movements of the diaphragm. Sound can trespass obstacles [Diffraction ] , Therefore the sounds coming from behind trespass the microphone, and the compressions and dilations both contribute to moving the diaphragm. There is a slight difference between the response to sounds coming from behind and those coming from in front of the diaphragm; this is due to small losses which occurr at high frequencies which cannot overcome the obstacle of the microphone.