Not sure about the 2013 model, but this is a well-documented issue for many (including me) for the 2012 model.
Plenty of work-arounds and apps out there that profess to improve the volume, but I've yet to read / find a definitive solution, while its seems this is an ongoing issue for Google / Asus with the Nexus 7 and they indifferent to resolving it. Everyone hoped that the last OS upgrade would resolve it, but...nothing. I suspect the same is hoped for with Kit-Kat. Not sure what the problem is (certainly the bizarre placement of the speakers doesn't help) as one suspects the speakers can't possibly be any smaller/worse than those found on, say, your Lumia. And I get, in comparison, practically room-filling sound with the one speaker on my old iPhone 4.
And oddly, I have found some items have better volume than other - for example, the NBC Nightly News, streamed via Sparse RSS and played via MX Player Pro seems to be louder than just about anything other I playback, including stored video also played on the same app. No idea.