Constant voltage audio systems are used to distribute audio over large areas. Whether in an airport terminal PA system or fire safety notification systems, constant voltage audio systems ensure that the audio is effectively distributed to speakers around the facility. To achieve such widespread audio distribution, power amplifiers are needed within the system to drive the distributed speaker network. Each amplifier can then be controlled to send the same or different sounds, depending on the zone. An example of a sound that would be the same throughout a system is music in a shopping mall. An example of a sound that would be different, depending on the zone, is different evacuation messages for different floors in a multi-story building. Regardless of use, the power amplifier stage of the constant voltage audio system plays a crucial role. Though that has traditionally been achieved through discrete implementation, it can be done with integrated Class-D amplifiers, typically at lower cost and in a smaller area.