The only problem with my computer speakers occures when I restart the PC from Windows into EOS. If I shut down the computer - when it starts again into eOS everything works well, but if I keep restarting - there is no sound into the speakers.
Try to shut it down, if you didn't already and check if it is ok when you start it again.
I have the same problem when I restart the computer from Windows into Elementary OS. No matter what I do the speakers would not work until I shut down the computer and start it again - reinstalling drivers, tuning settings - no change. Try to shut down and then check if speakers work again.
I've had this happen on my Dell, though it's not a chromebook, but maybe a similar issue. Speakers work, but not the headphones, I was able to fix it by plugging in the headphones and executing alsactl restore