In the very well-written article found at http://www.build.com.au/window-acoustics-and-noise-control and related articles, double-glazing is mentioned, offering up to 57% noise reductions using the configuration given. What configuration or process do airports use to control (and eliminate) airplane noise? What desiccant can be used for a DIY project for a gap of 100 mm)? Silica gel packs? How much per ft2? Will they need to be replaced? What type of caulk or sealant should be used? Is there a way to reduce the noise vibrations by placing the panes on some rubbery or foam-like frame? Is there some information on the type of material that should be used to block certain specific frequencies (such as bus accelerating noise that vary considerably based on year, maintenance, type of motor or muffler used,...)? Has any experiment been done on the effectiveness of using films that can be applied on windows, such as ones that can be applied with a heat gun, or those films that are placed with water? Sorry for the number of questions.
We've discussed your questions with some window experts, and the simple answer to these questions is that producing 'good' double glazing is a fairly exact and careful process. With DIY, there are just too many different things that can go wrong.
Some window films do offer some acoustic dampening, but obviously it's worth paying attention to the frequencies and amounts of noise they're designed to deal with. We don't have any specific studies to point to, but our understanding is that for most practical purposes double glazing will easily outperform pretty much all retrofit window film for acoustic control.
Our advice would be to have a chat with some soundproofing or acoustics specialists and see what kind of solutions they're able to recommend for your particular situation.
Hope this helps,
The BUILD team.