A bullroarer or turndun is an early sophisticated ritual instrument of music and means of communicating over extended distances.

It consists of a longish piece of cord fixed to an oval piece of wood or other suitable material which usually is thicker in the center, and sharpish at the edges.

The cord is given a slight initial twist, and the roarer is then waved in a large circle in a vertical plane. The aerodynamics of the roarer will keep it whirling even after the initial twist has unwound.

It makes a characteristic roaring vibrato sound with notable modification from both Doppler effect and the changing speed of the roarer at different parts of its circuit.

By modifying the expansiveness of its circuit and the speed given it, the modulation of the sound can be controlled, making the coding of information possible. The low frequency component of the sound travels extremely long distances, especially on the wind.

This instrument has been used by numerous early and traditional cultures in both the northern and southern hemispheres but in the popular consciousness it is perhaps best known for its use by Australian Aborigines (it is from one of their languages that the name turndun comes).