Abstract: The invention provides a silencer and silencing method which ensures adequate silencing with no deleterious increase in back pressure (which creates a lift-off force) or decrease in device performance. Pressurised gas is supplied to a driver chamber by a bleed-hole having an effective bleed-hole area and, during use of the device for particle delivery, gas is vented to the atmosphere via a silencer having an effective venting area. The bleed-hole area and venting area are chosen to ensure that the mass flow rate of gas through the effective venting are is substantially equal to or greater than the mass flow rate of gas through the effective bleed-hole area. This ensures that there is no build up of gas in the silencer device which tends to increase back pressure and hence lift-off force. Preferred embodiments of the device comprise a silencer having a large volume and a small particle exit opening. Further, there is disclosed an embodiment using one or more transfer ducts to assist particle mixing.