It worked normal one day, but then I turned the computer on, and suddenly only one the left speaker works. Headphones work normally.
UBUNTU 14.04 LTS
I faced the same problem, only one speaker was working. I tried everything I could get my hands on. But the solution was rather simple
I used the following command in the terminal
Then In the mixers I noticed that on everything except the master volume the green-white bars were half I increased them to full and then the bars became full and my problem was solved. It seems that only one channel is open by default.
VERY WEIRD, WHY WOULD YOU DO THAT,
Maybe your speaker is not balanced properly.