= Loudspeaker
{wiki}
A <loudspeaker> converts an electrical <signal> into motion that drives <acoustic waves>. In a moving-coil design, <electric current> through a coil in a <magnetic field> produces a <force> on the attached diaphragm. The diaphragm displaces air, creating <sound pressure> variations.
A small coil, magnet and lightweight cup can demonstrate the conversion directly. <Loudspeakers by the University of Iowa>[University of Iowa, Loudspeakers: coil, magnet and cone demonstration]{ref} In an idealized uniform-field geometry, the driving <force> scales as $B\ell I$. The emitted <sound> also depends on diaphragm <inertia>, suspension <spring constant>, <damping> and <acoustic impedance>, so the electrical waveform alone does not specify a flat acoustic <frequency response>.
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