Loudspeaker Or speaker, device used to convert electrical Energy into Sound. It consists essentially of a thin flexible sheet called a diaphragm that is made to vibrate by an electric signal from an Amplifier. The vibrations create sound Waves in the Air around the speaker. In the common dynamic speaker, the diaphragm has a cone shape and is attached to a wire (see Conductor) coil suspended in a Magnetic Field. A signal Current in the suspended coil creates another magnetic field that interacts with the already existing field, causing the coil and the diaphragm attached to it to vibrate. Quality sound systems employ three different sized speakers. The largest one, the woofer, reproduces low Frequencys; the medium-sized one, called a mid-range speaker, reproduces middle frequencies; the smallest one, called a tweeter, reproduces high frequencies. They are typically contained in a single cabinet (used in pairs for Stereophonic Sound), but a pair of small cabinets with a mid-range speaker and tweeter and a third cabinet with a single woofer is also now common, and some home entertainment systems use five such small cabinets for more realistic sound reproduction.