I am a trumpet player at a conservatory and I've been told for years that reducing the amount of air pressure through the trumpet will increase the volume of air that flows through the instrument. The people that have told me this always cite Boyle's law, but my understanding is that Boyle's law only applies to a closed system, which a trumpet is not. So my question is, will blowing harder through a trumpet actually increase or decrease the volume of air that is moved through the horn? My own very un-scientific experiment with a plastic bag over the bell of the trumpet and a stopwatch seems to show that more pressure actually increases volume, which is the opposite of what I've always been told. Are there any laws like Boyle's law that describe the volume and pressure of air moving through an open system?