There is a little dial on the side of the horn that adjusts the amount of air that is allowed to pass thru it (by pinching the line, as mentioned above), thereby affecting the volume. It's almost impossible to adjust on the fly, so I just leave mine on full blast. I figure that if I need to resort to my Airzound, I want it to be as loud as possible.

Unlike xtrajack, I've had zero problems with mine (knock on wood), and so far it has worked in temps as cold as -17 degrees C (~1 degree F). Just make sure to keep the pressure topped up; it only takes a couple of strokes from my floor pump, so I make sure to do it regularly. If you need to use it a lot, there are members here who have successfully converted their Airzounds with a larger reservoir. IIRC, two of said members were AdamDZ and colleen c. Just do an "advanced search" with the keyword "airzound" and their user names.