Boost Quicktime Volume
However, with some files, you might find that the audio is too quiet to hear. If you have turned up the volume to full and your Mac's speakers still aren't playing it loud enough, there is a simple way to get an extra volume boost.
If you hold the Shift key before clicking one the Quicktime volume control the slider has more range than normal. This also works when viewing Quicktime movies embedded in a web page.
If you have opened up the file in Quicktime, you can get the same results by choosing "Show A/V Controls" from the Window menu (Command-K). In the A/V controls there is a slider that goes higher than the maximum volume on the slider in the Quicktime window.