The Hear Back PRO system consists of two main components: the Hub and the Mixer. The modular Hub consists of four card slots, which can be populated with any configuration of input and/or output cards to fit your exact needs. Each Hub has the ability to supply signal and power to as many as 32 Mixers (8 per Network Card), each over a single standard Cat5E/6 cable. And with the built-in HBus In/Out ports, multiple Hubs can be daisy-chained together, allowing for truly unlimited system expansion.