A Powerful High Frequency Siren

This paper describes the design, construction and performance of a high intensity, high frequency (3–34 kc) siren and some rather striking phenomena which occur in the intense sound field produced by it. The siren is of the usual type consisting of a rotor which interrupts the flow of air through orifices in a stator. The rotor consists of a disk, approximately 6 in. in diameter, with 100 equally spaced slots and is driven by a small 23s hp high speed motor whose speed is varied by changing the applied voltage. The 100 corresponding holes in the stator are circular in section. For better radiation at the lower frequencies a plywood horn is mounted on the siren. The siren itself is small, and may be operated in any orientation. In its initial form, operating with chamber pressures in the neighborhood of 0.2 atmosphere, its measured efficiency was between 17 percent and 34 percent in the frequency range 3 to 19 kc with an acoustic output between 84 and 176 watts. There is a fair amount of parasitic noise, b...