"Sound" - what is it, definition of the term
An acoustic phenomenon consists of longitudinal pressure disturbances that travel through gases, liquids, or solids as alternating compressions and rarefactions; the propagation speed depends on the medium’s elasticity and density, and when these vibrations reach a biological receptor they are interpreted as audible sensations.
Detailed information
Acoustic phenomena arise when objects cause pressure variations in a medium, typically air, that travel as longitudinal waves. These waves are characterized by frequency, amplitude, wavelength and speed, all measurable with calibrated microphones or laser vibrometers. Frequency determines pitch, while amplitude governs intensity, expressed in decibels relative to a reference pressure. Propagation follows the equation v = f λ, where v is the speed of the wave, f its frequency and λ its wavelength. In gases, speed depends on temperature and molecular composition; at 20 °C in dry air, it approximates 343 m s⁻¹.
In arthropods, acoustic emissions serve communication, predator avoidance and mating. Certain hemipterans generate substrate‑borne vibrations by abdominal tremulation; these vibrations travel through plant tissue and are detected by conspecifics using mechanoreceptive organs. The resulting signals often occupy low‑frequency bands (20–200 Hz) and can be recorded with contact piezoelectric sensors.
Ticks produce faint clicks during locomotion, generated by the rapid flexion of their legs against the substrate. The clicks fall within the ultrasonic range (above 20 kHz), rendering them inaudible to most vertebrates but detectable by specialized recording equipment. Such emissions may function as incidental cues for host detection.
Bugs, including true bugs (order Hemiptera), emit characteristic stridulatory sounds by rubbing specialized body parts. The frequency spectrum typically spans 2–8 kHz, with pulse patterns that encode species identity. Recordings reveal a harmonic structure where the fundamental frequency is reinforced by integer multiples, creating a distinctive timbre.
Lice, being obligate ectoparasites, lack dedicated sound‑producing apparatus. However, the movement of their mandibles against host skin generates minute acoustic signatures detectable only with high‑sensitivity accelerometers. These signatures are broadband, lacking clear tonal components, and reflect the mechanical interaction between parasite and host.
Fleas produce a rapid series of taps when jumping, caused by the sudden release of stored elastic energy in their resilin pads. The taps generate broadband acoustic bursts centered around 10–15 kHz. High‑speed audio recordings capture these bursts as short, high‑amplitude spikes, useful for behavioral studies.
Key measurement practices for these insect‑related acoustic events include:
- Calibration of recording devices against known pressure standards.
- Use of anechoic chambers to minimize reflections and external noise.
- Application of Fourier analysis to extract frequency components and temporal patterns.
- Correlation of acoustic data with video recordings to link sound events to specific behaviors.
Understanding these acoustic signatures enhances taxonomic identification, pest monitoring and the development of bio‑inspired sensors.