I was looking at a wikipedia page about the sound barrier, and thought a question that there was no answer to in the page. If you had a liquid that was about to be a solid if you put a little more presure. then you set an explosion would the resulting wave be able to go faster than the sound barrier? The equations don't account for phase changes. Something really interesting to try is to see if you can have a liquid close to being a solid with a little more pressure, and set it up to take the pressure away afterward. Could you do this with air?