ABSTRACT

A microphone is a transducer that converts acoustical sound energy into electrical energy, based on the principle described in Fact File 3.1 . It performs the opposite function to a loudspeaker, which converts electrical energy into acoustical energy. The three most common principles of operation are the moving coil or ‘dynamic’, the ribbon, and the capacitor or condenser. The principles of these are described in Fact Files 3.2-3.4

The moving-coil microphone is widely used in the sound reinforcement industry, its robustness making it particularly suitable for hand-held vocal use. Wire-mesh bulbous wind shields are usually fi tted to such models,

and contain foam material which attenuates wind noise and ‘p-blasting’ from the vocalist’s mouth. Built-in bass attenuation is also often provided to compensate for the effect known as bass tip-up or proximity effect, a phenomenon whereby sound sources at a distance of less than 50 cm or so are reproduced with accentuated bass if the microphone has a directional response (see Fact File 3.5 ). The frequency response of the moving-coil mic tends to show a resonant peak of several decibels in the upper-mid frequency or ‘presence’ range, at around 5 kHz or so, accompanied by a fairly rapid fall-off in response above 8 or 10 kHz. This is due to the fact that the moving mass of the coil-diaphragm structure is suffi cient to impede the diaphragm’s rapid movement necessary at high frequencies. The shortcomings have actually made the moving coil a good choice for vocalists since the presence peak helps to lift the voice and improve intelligibility. Its robustness has also meant that it is almost exclusively used as a bass drum mic in the rock industry. Its sound quality is restricted by its slightly uneven and limited frequency response, but it is extremely useful in applications such as vocals, drums and the micing-up of guitar amplifi ers.