With wireless you really need to check what channels other wireless users nearby are using. you don't want to be using a channel that has significant overlap with your neighbours else you both will get vastly reduced speeds.
To stop overlap you want to be 5 channels away from your neighbours wireless channel, so if they're on 1 you want to be on 6. In an ideal situation you can get 3 wireless networks in the same area with perfect reception using channels 1, 6 and 11.
This shows the channels and the overlap they have, so if you have multiple wireless networks in your area check their channels, and then work out which channel gives you the least (and ideally no) overlap and you'll see significant increases in speed.