so the speaker requires only an AC power cable. Weight A powered speaker usually weighs more than an equivalent passive speaker because the internal amplifier circuitry usually outweighs a speaker-level passive crossover. A loudspeaker associated with an integrated active system is even lighter because it has no internal crossover. A lightweight loudspeaker can be more easily carried and it is less of a load in rigging (flying). However, active speakers using lightweight Class-D amplifiers have narrowed the difference. Trucking for a sound system involves transporting all of the various components including amplifier racks, speaker cabling and loudspeaker enclosures. Overall shipping weight for an active loudspeaker system may be less than for a passive system because heavy passive speaker cable bundles are replaced by lighter AC cables and small diameter signal cables. Truck space and weight is reduced by eliminating amplifier racks. Cost The expense of a large concert active speaker system is less than the expense of an equivalent passive system. The passive system, or integrated active system with external electronics, requires separate components such as crossovers, equalizers, limiters and amplifiers, all mounted in rolling racks. Cabling for passive concert systems is heavy, large-diameter speaker cable, more expensive than smaller diameter AC power cables and much smaller audio signal cables. For high-end home use, active speakers usually cost more than passive speakers because of the additional amplifier channels required. Ease of use In professional audio and some home cinema and hi-fi applications, the active speaker may be easier to use because it eliminates the complexity of properly setting crossover frequencies, equalizer curves and limiter thresholds. Cabling is not as simple, however, because active speakers require two cables instead of one (an AC power cable and a cable with the signal, typically an XLR cable). In home audio, some audio engineers argue that a passive speaker, in which an unpowered speaker is connected to an amplifier, is the easiest to install and operate. Servo-driven speakers By including a negative feedback loop in the amplifier-speaker system, distortion can be substantially reduced. If mounted at the speaker cone, the sensor is usually an accelerometer. It is possible to monitor the back emf generated by the driver voice coil as it moves within the magnetic gap. In either case, specialist amplifier designs are needed and so servo speakers are inherently powered speakers. Bass amplifiers Some bass amplifier manufacturers sell powered speakers designed for adding