The LG has two five watt speakers! That's definitely got to be the most sound I can recall seeing stuffed into a projector this small.
Look, the built in sound isn't going to replace a decent surround sound system, or HTIB (home theater in a box), but it does get the job done. Naturally, there's no serious bass at all, but I was impressed that I could listen to some good music while I was first setting up the LG. I fed it some Adele, Florence and the Machine, Tom Petty, and One Republic. Not bad. Not tinny, despite the lack of bass.
I found impressive that I could have respectable volume without the projector case rattling and vibrating, as often happens with small projectors, and that's something I find very annoying.
LG was very thoughtful. There's even a Digital Audio Out - the usual fibre-optic connector. With that you can take the sound coming in from, perhaps an MHL device, or, for that matter any device carrying Audio as is typical of regular HDMI as well.
From that connector you can feed the sound to a serious home audio system - a typical surround sound receiver, etc. And, of course, just because the LG has only 2 speakers, doesn't prevent you from feeding full surround sound from the source, to your external audio system.