An improved air horn is provided which includes a housing having an inlet for receiving a pressure medium to operate the horn and an outlet for the pressure medium. A first chamber is disposed between the inlet and outlet and receives the pressure medium from the inlet. A conventional sound-emitting horn is connected to the housing for receiving the pressure medium from the outlet, with the horn having a predetermined frequency. A closed resonating tube is connected to the other side of the housing, and a diaphragm is disposed between the first chamber and the resonating tube for oscillating movement in response to pressure changes in the first chamber and the resonating tube. A relatively small diaphragm having a natural frequency higher than the horn frequency is selected, as it is more economical and requires less energy to vibrate it. The resonating tube is selected to have a frequency which acts as a dampening effect on the diaphragm to prevent the diaphragm from vibrating at its natural frequency so that it is forced to vibrate at the desired horn frequency.