As I mentioned in another thread, be very wary of trying to actually to get them to work once you've got hold of them.I would suggest you try working up from a very low pressure - say 1 bar - preferably well away from anybody. (And wearing ear defenders!) St Albans South was given a pair of horns off a Eurostar. When we tried them out at the box at the nominal working pressure we rapidly got complaints from our neighbours. We are currently awaiting delivery of a variable pressure regulator to enable us to run them at a lower pressure and hence volume.