The phrase "ac router" is correct and usable in written English.
It is typically used to refer to a type of wireless router that supports the 802.11ac Wi-Fi standard, which provides faster wireless speeds and improved performance.
Example: "I just bought a new ac router to improve my home network's speed and reliability."
Alternatives: "802.11ac router" or "wireless ac router".
And an AC router can only deliver peak performance to gear capable of receiving AC signals, regardless of what speeds are touted on the box or the sales copy.
So why aren't I or anyone else getting 1.3 Gbps wireless connectivity from their AC router?
If centrally located, an AC router should be able to douse a 3,500 square foot house with Wi-Fi.
In the real world, walls and ceilings can limit Wi-Fi reception to a few yards, which is where an AC router comes in handy.
There are ways of getting faster and wider connections either via setting up a 5 GHz network on your current N or AC router, buying a new AC router, extending your Wi-Fi's reach via an extender/repeater, or hooking up with a new ISP and getting more megabit bang for your buck.
If you live in a multi-level dwelling, or you want coverage on your patio or out by the pool, and your AC router is located anywhere other than the center of the house, you'll need a Wi-Fi extender or repeater.
Other AC routers similarly brand themselves to reflect their top theoretical speeds -- the Asus RT-AC3200, the Belkin AC 1750, the Buffalo AirStation Extreme AC 1900, the D-Link AC3200, the Linksys EA9200 AC3200, the TP-LINK Archer CP AC1900, the TRENDnet TEW-828DRU AC3200, to name a few.
All AC routers are marketed to reflect their theoretical top speeds.
Instead of just transmitting indiscriminately in all directions, AC routers use "beamforming" -- transmissions are concentrated to where the router senses AC devices are located.
Both 802.11n and 802.11ac (or just N and AC) Wi-Fi are delivered over both 2.4 GHz and new-ish 5 GHz frequency bands that deliver higher performance at greater range; so-called "tri-band" AC routers broadcast Wi-Fi over 2.4 GHz and separate high and low 5 GHz bands.
We also have three items from Linksys, including the AC1200 SMART Wi-Fi Wireless Router ($169.99), the Wireless AC Wi-Fi 5 GHz Universal Connector Bridge ($149) and the Mini Wi-Fi Wireless Dual-Band USB Adapter ($59.99).
