The PhD who investigated this acoustic data gave a very comprehensive interview on radio 18 hours ago. He is almost certain (90% confidence) the noise was NOT MH370.
He feels more likely it represented a small earthquake or ice breaking off Antarctic shelf.
He did say low frequency sounds (at or below lower limit of human hearing) can be detected many thousands of km away. Main variables are:
1. topography of the bottom (helpful if the ocean bottom at the source sound was sloped towards the listener, as this will "lens" (reflect) noise towards the listener.
2. temperature layers (deep water channel)
He also confirmed frequencies in range of pingers would be limited to just a couple of km regardless of conditions.
Worth a listen if you are interested. Maybe available online (2gb.com). But he didn't leave much room for doubt.