The air gap is there because only two things can help to block sound: air spaces, and heavy mass. Air spaces work because sound travels poorly through it. I doubt a brick window would work for your purposes, so you'll have to write off heavy mass.
Solid glass or plastic would just vibrate right through.
The panes are at a slight angle to one another because if they were parallel, the air in between them would vibrate in a straight line and pass through much easier. Having them angled deflects the sound.