The earliest devices used to achieve this were acoustic megaphones. In order to speak to larger groups of people, a need arose to increase the volume of the human voice. 5.3 Cardioid, hypercardioid, supercardioid, subcardioid.Microphones typically need to be connected to a preamplifier before the signal can be recorded or reproduced. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field the condenser microphone, which uses the vibrating diaphragm as a capacitor plate and the contact microphone, which uses a crystal of piezoelectric material. Several types of microphone are used today, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. They are also used in computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic sensors or knock sensors. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, radio and television broadcasting. A microphone, colloquially called a mic or mike ( / m aɪ k/), is a device – a transducer – that converts sound into an electrical signal.
