I recently went to vendor training on wifi deployment and learned something I never knew before and figured I'd share it with you.
I'd like to begin by describing the wifi RF (radio frequency) spectrum as a road. 2.4Ghz is like an old rural highway. Not many lanes (3 channels) and you've got to keep your eyes peeled for things that might slow you down (RF interference from microwaves or pretty much any other kind of electrical machinery... your old plasma globe from the 80's for example). 5Ghz is like your new more modern super interstate highway. Lots of lanes and not a lot to slow you down.
Got that example in your mind? Good, now we can proceed forward.
So... what can slow you down on either kind of highway? That's right, slow drivers. Each lane in the road is a channel in the spectrum. Most home networks use 2.4Ghz by default from your ISP. At any given time your home network is using one of those channels (I'll talk about 40Mhz or "Wide Load" channels later). Now, imagine that each iteration of the 802.11 standard is an evolution of the automobile. 802.11 started as a Model T and at most can transmit 1 or 2 Mbit/second. 802.11ad has a top speed of 6.7Gbit/second so we'll call that the Red Bull Formula One car. Now... take out of the equation the possibility that the F1 car would be in front... how fast would both cars go? You probably guessed... you can only go as fast as the slowest car. Just drive southbound on I-95 at rush hour and you'll see first hand proof of that.
So armed with this new revelation I realized that I had been sabotaging my own home wifi network. My trusty old Playstation 3 only has 802.11bg which has a theoretical maximum speed of 54 Mbits/sec but my home router uses 802.11n which can get up to 150 Mbits/sec if I were to enable 40Mhz channels. The router is your traffic cop. As long as all of the devices on your network are 802.11n you can cruise along at top speed but the instant that a slower/older standard is detected the radio drops the speed down to ensure that it can communicate with the slower device. You can only use the one radio with that one channel... having two radios on the same channel would create an insane amount of interference if they were on the same router. So that one radio transmitter has to talk to all of the devices on that same channel so this is the cause for the "fast as the slowest device" phenomenon.
Q: So what do you do if you have slow devices?
A: In my case I turned the wifi off of the PS3 and used powerline ethernet for it. Another option would be to get another router and set up a separate wifi network solely for your slower devices. They will be on another channel and so won't interfere with your other network. Whatever it takes to get your slower devices off of your main network.
Q: Didn't you mention something about 40Mhz channels?
A: Think of a 40Mhz channel as one of those BIG semis hauling a house with the "Wide Load" sign on them. A 40Mhz channel basically means you are using the main channel and then one adjacent to it. On the 2.4Ghz spectrum there are only 3 channels so this isn't a good idea. You are using either channel 1 and 6 or channel 6 and 11. Being such a wide swath of the spectrum means that you are going to be more suseptible to interference but theoretically if you are in a low interference area you can get away with it and increase you speed significantly. Only 802.11n or better will allow 40Mhz channels. Now 5Ghz is a whole other ballgame. There are 23 channels we can use in the USA so it is far easier to find an adjacent pair where nothing is going on. By all means, if you have 802.11n devices and your router will support it go ahead and configure it for 40Mhz.
I hope this will help each of you get the most from your wifi environment. :)