Most likely either the range & signal strength or other WiFi systems & 2.4GHz devices in the area. (Including non WiFi such as wireless cameras and many other gadgets). The speed rapidly drops off as the signal strength decreases.
There are only three usable channels on 2.4GHz for 11g (54Mb) systems. 11n systems typically use 2/3 of the entire band - any other 11n or overlapping 11g system within range is guaranteed to cause interference and slowdown, as in effect each hogs the whole band and prevents any other device transmitting. As you have a dual band router, you would be better off using 5GHz channel - there are a lot more available and a lot less interference for other systems and devices.
Obviously, the ultimate solution is just to run ethernet cables... WiFi was never intended for streaming-type used and it is not a technically good system for that type of service. It's waaay overloaded and it's capabilities are massively overstated by most equipment makers.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.