A: Choosing an air compressor is less about the air horn and more about how and how often the air is going to be used. Lower pressure systems (110-130 PSI work well with our compact horns. However, the larger horns sound best when used with a 150 PSI system. Our 230, 630 & 730 train horns all sound best with 150 PSI and at least 3 gallons of stored air. If you are looking for more capacity and/or would like to use the air for tire inflation, air tools etc, the 6350 & 6450 Air Systems will perform great with any air horn. For air tool use, an inline pressure regulator is recommended.