I wasn't referring to steam locomotives blowing their whistles on air - most collectors do not have a steam supply but can get to air and will try to blow them.

Their are some technical books of the late steam era that did promote the use of air horns instead of steam whistles. Using an air compressor and air horn uses less steam than opening a hole in the boiler to blow the whistle.

Hancock made a fairly decent sounding air whistle for diesel use that was adopted by a few lines. New Haven, Santa Maria Valley and M&ET used them at one time or another for a few examples. Metrolink tried Ohio Brass air whistles for a while before going to the horrible Nathan Ps behind the pilot trying to make blowing for crossings more politically acceptable.