Very slow download speed over wifi?

[#1]

Recently switched from talktalk who promised me what plusnet now provide (70+meg) nearly double what I was getting. Receiving between 70-72 wired on the desktop but very happy with that although download speeds on the laptop on wifi seem very poor and to max at 1.9meg per sec was getting nearly 4 per sec on just 40meg  on talktalk. Speed tests on the wireless come in at around 40meg and dowbload speed of 1.9 max where I was getting around 4 on the similar speed before.. Is the router just not capable of carrying fast download speed on wireless? When I stick an Ethernet in to the modem get around 8meg which is more what I was expecting any help be great?

[#2]

Have you tried changing your wireless channel?
http://www.plus.net/support/broadband/wireless_broadband/wireless_signal.shtml#channel

[#3]

Is this a likely solution never heard of having to do this, is this because the supplied router is only single band?

[#4]

To add I don't think it's an issue of poor signal strength everything loads fine all over house and outside the house just the download speed seems poor