Due to the weird construction of the room I have to run longer speaker cables for my rear speakers. Is 12 gauge sufficient for 40 feet long runs? I need 40 feet for one speaker and 30 feet for the other rear speaker. Are there others that have runs longer than 40 feet? Also should I make the other one 40 feet also to have them equal length if I have any left over (I bought 100 feet spool)?
12 gauge is more than enough (see the chart on
this often linked page). There is absolutely no need to cut the wires to the same length. Since electricity travels at nearly the speed of light (186,282 miles per second) along wires, the difference in lengths between two wires would have to be many miles before you could hear any delay. Use only what you need to go between the speaker and the amp.
Peter is correct, you should have no problems. I have one run that is over 50 feet and it works great.
What Peter said.
It won't hurt to leave a little slack at each end just to be safe...
Awesome response! I'm gonna run the wires this weekend and I'll take some pics of how I ran the wires. By the way I bought Axiom bulk 12 gauge and its so flexible which is perfect for how I'm gonna run the cables in tight places. Pics coming soon!
Just remember to try and keep it away from your AC electrical if possible.
Somebody, with just a little electronic knowledge, has probably talked to him and confused group delays, at much higer transmission frequencies than at audio.
You're right, a few 10s of feet is nothing to worry about with audio transmission!!
Even with a couple ground loop filters, I've got horizontal bars on some weaker channels, but no 60Hz hum 
My mains and center run on Axiom 12 ga cables that are 14' each.