Slow Internet Question

Question

I'll try to be brief but complete.
A few days ago I posted about slow internet and in response it was suggested I go to OpenDNS, which I did, and everything sped up considerably.
I applied OpenDNS via System Prefs>Network>Advanced>DNS.
Now, I'm back to a crawl (almost like the old dial up days).
Here's my set up:4 Mac network via Airport Extreme with an Express to boost range in the house. Both are set to Chanel 3. I have Cox cable high speed.
I did not do anything with OpenDNS to the Airport(s) - out of fear I might mess something up.
All bars on the Airport; interference robustness enabled.
Airport Utility is showing a signal of -80 and noise of -92 on the main Base Station, and a signal of -48 and noise of -94 on the Express extension.
I checked OpenDNS (via their website) and am seeing an IP address in the upper right hand corner of the web page that does not match anything I can find. Don't know if that means anything.
AP Grapher is showing several neighborhood networks but nothing unusual. Under the Airport status in the menu bar, I'm only showing 2 of my neighbors' locked networks. So I don't think I have an interference issue.
Speed is slow in Firefox and Safari. I tried clearing caches, and that did nothing.
With this background, any step by step ideas on how to get my internet speed back, and to keep it? Like I said, for a few days after going to OpenDNS I was like a rocket, and now it's gone back to a medium crawl.
Most Appreciated & Thanks!

Answer 1

Realize also that cordless phones and microwave ovens interfere with them all.
And don't forget "Baby Monitors". They can be really bad, as some of them use spread spectrium tricks and do not just camp on a single channel. So got any new parents nearby?
1, 6, and 11 do not use frequencies that overlap. I'm not sure if they all follow a sequential pattern in that 2 is clear of 7, 3 is clear of 8, etc.
Each channels uses 5 channels worth of bandwidth. So picking on channel 6 as an example, its signal strength is strongest on Channel 6. It overlaps and is relatively strong on channels 5 and 7. It continues to overlap but will be weaker on channels 4 and 8. Think of the signal as a bell curve with the strongest portion of the curve being centered on channel 6.
Now apply that 5 channel bell curve to any channel you choose, and that channel will be overlapping the adjacent 2 higher and 2 lower channels.
Channel 1 uses frequences below channel 1, plus 2 and 3. Channel 6 uses 4,5,6,7,8 and Channel 11 uses 9,10,11,12,13 (I only mention 12 and 13 because some countries, but not the US, actually allow these 2 channels).
So you can pick channel 2, but if someone is using channel 1, your 5 channel bell curve and channel 1's 5 channel bell curve will overlap a good deal, and unless the neighbor using channel 1 is a good distance away, you will interfere a great deal with each other.
I only recomend usng channels other than 1, 6, and 11 if there are totally saturated, and then it is a game of trying to find the place where a 5 channel bell curve will overlap with the weakest neighboring signals.
Message was edited by: BobHarris