Refraction of Sound Waves
The pulse period showed great variability among and within individuals .. The lack of such a relationship in AD-stridulation sounds is probably. In the above animation a spherical wave pulse propagates in a medium where The speed of a sound wave in air depends on the temperature (c= + T). The velocity of sound in air depends on the temperature of the air. recorded signal so you can see a close pair of pulses (the first pulse represents relationship is A = k/R, where k is a constant determined by the amplifier gain, speaker type.
Fish have evolved the largest diversity of sound-producing mechanisms among vertebrates, and sounds are emitted in numerous contexts: Representatives of some catfish families possess two different sound-producing mechanisms .
High-frequency stridulation sounds are emitted when pressing ridges of the dorsal process of the pectoral spine against the groove of the pectoral girdle while abducting or adducting pectoral spines . In contrast, vibrations of the swimbladder by sonic muscles result in the emission of low-frequency drumming sounds .
The Nature of Sound – The Physics Hypertextbook
The elastic spring is rapidly pulled forward during contractions of sonic muscles which originate at the occipital bone and insert at the elastic spring . Effects of temperature have not been studied in broadband stridulation sounds so far, but have been studied in low-frequency sounds such as drumming sounds. In general, the sound duration and the fundamental frequency increased with rising ambient temperature, whereas the pulse period decreased due to the higher muscle contraction rate Gobiidae: Brawn  observed a temperature-dependent increase in the number of sounds produced in the cod Gadus callarias.
Fish depend on hearing for analyzing the acoustic scene, for orientation, prey and predator detection and for intraspecific communication .
Ambient temperature affects hearing in invertebrates and ectothermic vertebrates. Such effects have been examined in insects amphibians  and reptiles .
In general, raising the temperature increased both the most sensitive best frequency and the absolute sensitivity . The number of action potentials increased and the temporal tuning of auditory neurons shifted to higher rates of amplitude modulation . Similar results have been found in the tuning of the auditory system in cicadas and locusts . In fish, only a few studies investigated the effects of temperature changes. Dudok van Heel  found that the European minnow, Phoxinus phoxinus, can discriminate between higher frequencies at higher ambient temperature.
In goldfish, Carassius auratus, warming increased the spontaneous activity and sensivity of auditory neurons, the best frequency at a given signal level and the responsiveness to an acoustic stimulus . The walleye pollock, Theragra chalcogramma, showed a reduced auditory sensitivity at lower ambient temperature within hours . Differences between temperatures were more pronounced in the eurythermic catfish species.
Sound characteristics are important for coding information in agonistic and reproductive contexts conflict resolution, distress situations, courtship, establishment of territories. Fish often produce series of short broad-band pulses, for example in the stridulation sounds of catfishes and gouramis with distinct temporal patterns and variable interpulse intervals . Severals studies suggest that temporal patterns are important carriers of information in fish .
Wysocki and Ladich  showed that the auditory system of the catfish Platydoras armatulus formerly P. The present study was designed to investigate the effects of temperature on 1 sound production and sound characteristics, 2 the absolute auditory sensitivity and 3 the ability of the auditory system to resolve temporal patterns of sounds in the Striped Raphael catfish. The neotropical catfish P.
Groups with accessory hearing structures that couple air-filled cavities acoustically to the inner ear are most likely affected by temperature changes as shown previously .
A Mirror-Image Relationship Between Temperature and Pulse
Platydoras armatulus inhabits the Amazonian river system and is known to emit both types of sounds in distress situations . This is the first study in which the effects of temperature on both vocalization and hearing have been examined in the same fish species. In acoustics, however, sound waves usually don't encounter an abrupt change in medium properties. Instead the wave speed changes gradually over a given distance. Often the change in the wave speed, and the resulting refraction, is due to a change in the local temperature of the air.
For example, during the day the air is warmest right next to the ground and grows cooler above the ground. This is called a temperature lapse. Since the temperature decreases with height, the speed of sound also decreases with height.
This means that for a sound wave traveling close to the ground, the part of the wave closest to the ground is traveling the fastest, and the part of the wave farthest above the ground is traveling the slowest. As a result, the wave changes direction and bends upwards. This can create a "shadow zone" region into which the sound wave cannot penetrate.
The sound waves are being refracted upwards and will never reach the observer. A temperature inversion is when the temperature is coolest right next to the ground and warmer as you increase in height above the ground.
- Refraction of Sound Waves
- The Nature of Sound
Since the temperature increases with height, the speed of sound also increases with height. This means that for a sound wave traveling close to the ground, the part of the wave closest to the ground is traveling the slowest, and the part of the wave farthest above the ground is traveling the fastest.
As a result, the wave changes direction and bends downwards. Temperature inversions most often happen at night after the sun goes down when the ground or water in a lake cools off quickly, while the air above the ground remains warm.