Loudspeaker producing sound while connected to a circuit of an alternating current. Loudspeakers work by applying a varying electric signal to a coil of wire in the field of a permanent magnet. The varying field causes the coil to move relative to the magnet. Attached to the coil is a paper cone, whose vibrations produce sound in the air. The alternating current here produces a steady vibration. See clip K004 2699 for the loudspeaker magnet lifting metal nuts.