'X' consists of a weighted aerofoil, a rectangular slat of wood about 15 cm (6 in) to 60 cm (24 in) long and about 1.25 cm (0.5 in) to 5 cm (2 in) wide, attached to a long cord. The cord is given a slight initial twist, and the ____ is then swung in a large circle in a horizontal plane. The aerodynamics of the ____ will keep it spinning about its axis even after the initial twist has unwound. The cord winds fully first in one direction and then the other. It makes a characteristic vibrato sound with notable modification from both Doppler effect and the changing speed of the ____ 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.
'X'?
'X'-Bullroarer
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