Presuming your volume is set to something above "2", you shouldn't have any problems hearing a standard level mp3 track. I can fill a small room with quiet music with the volume set to 10/30 on my Ativ S. If you're barely able to hear things, I'd wonder if you have a defective unit.
I've had the same thing happen on mine twice. You play music through the speaker and it plays so quietly you have to hold it right up to your ear, regardless of what the volume is set to. I have to experiment but I was thinking if I say played a game and turned the volume down in game, and it was still running in the background, would that app lock the volume to whatever the in game volume was? I restarted my phone both times to fix it.