built into the loudspeaker enclosure. This design is common in compact personal speakers such as those used to amplify portable digital music devices. In a fully active loudspeaker system each driver has its own dedicated power amplifier. The low-level audio signal is first sent through an active crossover to split the audio signal into the appropriate frequency ranges before being sent to the power amplifiers and then on to the drivers. This design is commonly seen in studio monitors and professional concert audio. Hybrid active designs exist such as having three drivers powered by two internal amplifiers. In this case, an active two-way crossover splits the audio signal, usually into low frequencies and mid-high frequencies. The low-frequency driver is driven by its own amplifier channel while the mid- and high-frequency drivers share an amplifier channel, the output of which is split by a passive two-way crossover. Integrated active systems The term "active speakers" can also refer to an integrated "active system" in which passive loudspeakers are mated to an external system of multiple amplifiers fed by an active crossover. These active loudspeaker systems may be built for professional concert touring such as the pioneering JM-3 system designed in 1971 by Harry McCune Sound Service, or they may be built for high-end home use such as various systems from Naim Audio and Linn Products. History Some of the first powered loudspeakers were JBL monitor speakers. With the addition of the SE401 Stereo Energizer, introduced in 1964, any pair of monitor speakers could be converted to self-powered operation with the second speaker powered by the first. The first studio monitor with an active crossover was the OY invented 1967 by Klein-Hummel. It was a hybrid three-way design with two internal amplifier channels. An early example of a bi-amplified powered studio monitor is the Altec 9846B, introduced in 1971, which combined the passive 9846-8A speaker with the new 771B Bi-amplifier with 60 watts for the woofer and 30 watts for the high frequency compression driver. In the late 1970s, Paramount Pictures contracted with AB Systems to design a powered speaker system. In 1980, Meyer Sound Laboratories produced an integrated active 2-way system, the passive UPA-1, which incorporated lessons John Meyer learned on the McCune JM-3. It used active electronics mounted outside of the loudspeaker enclosure, including Meyer's integrated active crossover with feedback comparator circuits determining the level of limiting, often connected to third-party