Commercial audio installations often require large numbers of speakers to be powered from a single amplifier. These systems often called “100V line” or less common in Australia “70V line” are found in most large buildings including shopping centres, schools, offices etc. These audio systems are typically used for general announcing, public address, background music and vitally important fire/evacuation messaging.
We find there is a lot of confusion amongst installers and trades about how these systems are wired up. Largely this is caused by the fact that these speakers are not wired in the traditional way low impedance or home hi-fi speakers are. In fact, it may seem completely counter intuitive!