[fields]

Are you sure? I don't have an iMac, but I've tested with two MBPs. They will always use the 5GHz network if it's available. This may have something to do with how good your connection to the airport is - does your signal quality say Excellent?

I can't say that this configuration change will help for everybody - I'm just reporting what I'm seeing.

[weiran]

Turns out I had to delete the old network from Network preferences and add it again, it was probably set to 2.4GHz only like it was originally.

Now I'm on the 5GHz again I seem to be getting a more consistent 450Mbps link speed although actual throughput seems the same.

I think I might just leave it on fully auto now, it seems to work pretty well.

[dade_]

I found that my aTV, MBP (Lion) and iPad 2 were always connecting to the 2.4 Ghz network with my dual band Airport extreme as well. Setting them separately, I have forced it to 5Ghz. I live in a condo building so 5Ghz has far less interference, so I don't understand the reason for the behaviour.

[agent86]

Try this on the MBP:

* Connect to the 2.4Ghz network

* Hold "Option" and click the wifi icon in the top menu

* Note the "Transmit Rate"

* Repeat this for the 5Ghz network

When I first setup my Time Capsule I noticed that my Mac often times was attaching to the 2.4Ghz network. At that point I separated the networks and did the above.

Low and behold, each time the Mac picked the 2.4Ghz network it did so because it had a higher transmit rate than the 5Ghz one in a given location.

[rm999]

My MBP and MBA fall back to 2.4GHz sometimes. This is annoying because microwave interference is common in my building.

So now I keep separately named networks and can usually connect at 450 mbps (mbp) or 150 (mba). At least I believe that is the case, I can double check at home.