Wireless Slow On All Computers

There are several wireless devices connected to my home network, but for simplicity, let's keep it limited to 3, and call them A, B, and C. They are different manufacturers, but what I'm seeing isn't specific to a computer. When they are wired in, they all have expected levels of performance, but when then are wireless, there is a strange pattern.[code] Provider is Comcast on a Cisco wireless router. Looked at isolating devices, limiting traffic, changing locations, etc and nothing usage-wise has affected the at-home numbers. So I know I am most likely looking at a router setting, but I can't seem to narrow in on why only one device works as expected and everything else is painfully slow.