Search results
Results from the WOW.Com Content Network
Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body. The study of such sound waves is sometimes referred to as infrasonics , covering sounds beneath 20 Hz down to 0.1 Hz (and rarely to 0.001 Hz).
Infrasound is sound at frequencies lower than the low frequency end of human hearing threshold at 20 Hz. It is known, however, that humans can perceive sounds below this frequency at very high pressure levels. [1]
The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating. [5] This phenomenon is an important factor in submarine warfare. The deep sound channel was discovered and described independently by Dr. Maurice Ewing, and Leonid Brekhovskikh in the 1940s. [6]
The examples include ground vibrations produced by elephants whose principal frequency component is around 15 Hz, and low- to medium-frequency substrate-borne vibrations used by most insect orders. [15] Many animal sounds, however, do fall within the frequency range detectable by a human ear, between 20 and 20,000 Hz. [16]
Although sounds of such low frequency are too low for humans to hear as a pitch, these sound are heard as discrete pulses (like the 'popping' sound of an idling motorcycle). Whales, elephants and other animals can detect infrasound and use it to communicate. It can be used to detect volcanic eruptions and is used in some types of music. [35]
Bat call frequencies range from as low as 11 kHz to as high as 212 kHz. [20] Insectivorous aerial-hawking bats, those that chase prey in the open air, have a call frequency between 20 kHz and 60 kHz, because it is the frequency that gives the best range and image acuity and makes them less conspicuous to insects. [21]
Sound spectrum: High frequencies are more quickly damped by the air than low frequencies. Therefore, a distant sound source sounds more muffled than a close one, because the high frequencies are attenuated. For sound with a known spectrum (e.g. speech) the distance can be estimated roughly with the help of the perceived sound.
A spectrogram of the soundscape of Mount Rainier National Park in the United States. Highlighted areas show marmot, bird, insect and aircraft noises. Soundscape ecology is the study of the acoustic relationships between living organisms, human and other, and their environment, whether the organisms are marine or terrestrial.