Horn loudspeakers are the oldest form of loudspeaker system. Horn-loaded subwoofers have a subwoofer speaker that has a pathway following the loudspeaker. This signal current is carried to a guitar amplifier that drives a loudspeaker. The exponential horn was replaced by an amplifier and a loudspeaker. When connected to an electronic amplifier and loudspeaker, it worked. This integration of amplifier and loudspeaker is known as an active loudspeaker. Dynamic microphones use the same dynamic principle as in a loudspeaker, only reversed. The impedance of a loudspeaker is partly resistive. Only the resistive part of the loudspeaker impedance is used. Consider sound reproduced by a loudspeaker into a room. Western Electric designed a wide-audio-range horn loudspeaker for cinemas. The enclosure plays a major role in the sound of the loudspeaker. The cabinet of the loudspeaker is known as the enclosure. The audio escapes through a simple low-pass filter into the loudspeaker.