An apparatus for generating air pressure and air pressure pulses in a cavity comprising: a housing (81) having a pulsating pneumatic chamber (87) and a first opening, a first diaphragm (89) mounted on the housing (81 ) closing the first opening, a drive means (116, 119) connected to the first diaphragm (89) operable to oscillatingly move the first diaphragm (89) with respect to the pumping chamber (94), a means (61 ) which has a passage adapted to connect the pulsating pneumatic chamber (87) of the housing (81) to the cavity to bring air and air pressure impulses to the cavity, a first cover (92) located on the first diaphragm (89 ) and separated from it having a first pumping chamber (94), first means (93) fixing the first cover (92) and the first diaphragm (89) to the housing (81), characterized in that it comprises a collecting chamber ( 88) separated from the pulsating chamber (87) by an internal wall (86) of the housing sa (81), said collecting chamber (88) being in air communication with said first pumping chamber (94), at least one valve (99) mounted on the inner wall (86) being operable to allow air flow from the collecting chamber (88) to the pulsating chamber (87) and preventing air from flowing back from the pulsating chamber (87) to the collecting chamber (88), a means (167, 181) for regulating the air flow to restrict the flow of air into and out of the collecting chamber (88) to control the air pressure in the collecting chamber (88), a variable speed motor (118) connected to the actuating means (119), so that, by operating the motor (118), the drive means (119) oscillatingly moves the first diaphragm (89) to propel air into the pulsating chamber (87) and cause air to flow from the collecting chamber ( 88) towards the first pumping chamber (94) and out of it and increase the air pressure in the chamber Mara manifold (88), said valve (99) allowing air to flow from the collecting chamber (88) into the pulsating chamber (87) when the air pressure in the c
