Resonators in Insect Sound Production : How Insects Produce Loud Pure - Tone Songs

songs of insects may be shrill, raucous or musical, brief or sustained but, whether loud or quiet, they tend to convey information within a narrow band of sound frequencies. The narrow frequency band implies that the sound-producing system is in some way tuned. In this review, I shall address the mechanisms by which sharply tuned sounds are produced by insects and explore the acoustical and biomechanical mechanisms by which insects produce narrow-band sound signals. I shall also examine the transduction chains involved in the conversion of muscle power to sound power. What is a resonator? Resonators occur in many everyday forms such as whistles and bells, pipes and drums, the pendulum of a clock, the balance spring-and-wheel or the quartz crystal of a watch. All these resonant systems are employed for similar reasons: they vibrate at or near a single frequency, whether that is a musical note or is used as a basic timing mechanism; their vibration can be excited by an impulse, whether by a puff of air, a mechanical impact or an electrical pulse; and their vibration can be sustained by continued excitation, by supplying appropriately phased acoustic, electrical or mechanical power, as occurs in a trumpet mouthpiece or a clock escapement. Simple resonators rely on the interplay between two reactive elements. Consider the simple case of a mass swinging on a spring (Fig. 1): at the extreme of the swing of the mass, it has zero velocity and thus zero kinetic energy, but the strain energy in the spring is maximal; as the mass swings through the centre of its arc, its velocity is maximal so its kinetic energy is maximal, but the stored or strain energy in the straight spring is zero; the mass then decelerates to zero velocity as its kinetic energy is absorbed by the spring; the mass then re-accelerates in the opposite direction and so on. The frequency of the vibration or resonant frequency, F o, determined by the mass and the compliance of the spring, is given by: where m is the mass, c is the compliance and s is the stiffness (the compliance of a spring is the reciprocal of its stiffness). A similar process of transfer of energy between two components occurs in the simple electrical series resonant (1) Fo = , 1 2π 1 2π       s m Ί      …