Black Box Explains... Using 24- and 70-VDC paging systems.
The size of your paging system and the distance to end devices determine whether you should use 24- or 70-volt power. In either system, speakers, horns, and other paging-related equipment tap into points along the powering wiring. You usually determine the number of taps based on a flowchart compiled at the design stage. This chart takes into account how many amplifiers (if any) you’ll be using.
In 24-VDC systems, you’re limited by how many taps you can put on a run, and the low voltage supports a much shorter distance than a 70-VDC system. For these reasons, 24-VDC systems typically suit smaller office paging systems.
In these limited-drop paging systems (with fewer than 20 speakers or horns), the devices don’t require a lot of source power because they’re self-amplified devices. Their amplifiers are either built in or are mounted near the speaker.
And because you’re using much lower power, you can run power wiring alongside telephone-type wiring and not worry about ambient noise affecting your voice communications.
In contrast, 70-volt systems depend on central amplifiers to distribute power to speakers that have their own transformers. These stepdown transformers adapt the voltages of the signal from the central amplifier to the current required by the individual speaker.
The higher-voltage, lower-current system best suits connections to speakers distributed over a greater area.
In addition, you can adapt the wattage of speakers used in a 70-VDC system to match the sound requirements of the application. You can do this through the connections on the stepdown transformer, which you adjust to determine the amount of amplified power it draws from the central amplifier, so energy isn’t wasted and speakers don’t overheat and fail. Configuring a speaker transformer for lower power consumption, for example, is suitable for areas with low ambient noise.
A 70-VDC system also often works with amplifiers that have various types of inputs, so you can connect different types of paging and audio equipment.