Abstract: A single-tone inverted toroidal whistle for producing a uni-directional output of about 135 decibels at 100 feet on axis at a frequency of about 420 hertz. A hollow cylinder having a closed base end is combined with a toroidal body to provide an annular sound chamber the working length of which determines the wavelength of sound generated by passage of air or steam under pressure through an annular slit formed in the interior of the cylinder and impinging against a spaced tapered lip on the inner cylindrical wall of the toroidal body.

Abstract: A toroidal shaped closed chamber whistle produces a warning signal capable of being easily heard at relatively great distances from the whistle. The toroidal whistle emits a bidirectional sound which is phase-locked to a particular pitch. The toroidal whistle has a circular plate positioned within a hollow cylinder to form an air passage leading to an annular air slit. Incoming air under pressure flows through the air passage and out of the annular air slit into a toroidal chamber. Within the toroidal chamber, a sound wave is formed which passes out of the toroidal chamber through a chamber mouth. Optionally, two toroidal chambers can be used in combination to produce a dual-tone sound. Additionally, a tremulant device can be used to produce a warbling effect in the emitted sound.