Ubiquiti AirMAX AC

In contrast to airMAX M series devices (built on 802.11n protocol), airMAX AC devices benefit greatly from physical-layer & MAC-layer efficiencies associated with 802.11ac protocol. The image below outlines the maximum throughput related to each network type at various modulation rates, where greenfield AC networks (i.e. exclusively AC devices) enjoy the greatest benefit:

When retrofitting legacy networks, it is therefore always recommended that you upgrade the AP device first to experience the most initial benefits. Note too that M series devices cannot reach the 8x MCS rates enjoyed by AC series devices.