fizyka: Infrasound

Evidence: 39 • authority: 88

The background of atmospheric infrasound in the frequency range 0.25 to 20 Hz: Statistical results. In reviewing the statistics we treat the data in two passbands. For the lower frequency passband (0.25 to 1.5 Hz) we apply beam-steering techniques to identify the azimuth, horizontal trace speed, dominant spectral peaks, and rms pressure. Magnetic tapes from October 1979 to date contained over 1000 signals. We present several detailed case studies and summary histograms of statistics showing the distributions of azimuth, horizontal trace speed, duration, time-of-arrival, and other parameters. We discuss possible sources for some of these signals. From analyses of sonograph records providing…

Evidence: 91 • authority: 72

Infrasound, sometimes referred to as low frequency sound or (sometimes ambiguously) subsonic (subsonic being a descriptor for "less than the speed of sound"), describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz, as defined by the ANSI/ASA S1.1-2013 standard). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. 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…

Evidence: 54 • authority: 92

Should limit values be set for infrasound caused by wind turbines?. The study focuses on setting outdoor exposure limits for wind turbine infrasound, as most countries currently have no specific limits for this type of noise. A review of the literature on the effects of wind turbine infrasound and the methods used worldwide to measure and assess environmental exposure to infrasound formed the basis for setting limits. According to the literature, human tolerance to infrasound is defined by the hearing threshold, which is not yet standardized. Therefore, a G96 curve (corresponding to tones with the G-weighted sound pressure level (SPL) equal to 96 dB) was used to determine the mean hearing t…

Evidence: 36 • authority: 72

A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured sound levels in an effort to account for the relative loudness perceived by the human ear, as the ear is less sensitive to low audio frequencies. It is employed by arithmetically adding a table of values, listed by octave or third-octave bands, to the measured sound pressure levels in decibel (dB). The resulting octave band measurements are usually added (logarithmic method) to provide a single A-weighted value describ…

Evidence: 35 • authority: 88

A laser pistonphone designed for absolute calibration of infrasound sensors from 10 mHz up to 20 Hz. Demand for calibration at infrasonic frequencies has emerged. It is supported by earth monitoring issues and particularly by the Comprehensive nuclear Test Ban Treaty Organization (CTBTO), which provides a global international coverage for nuclear testing ban, and requires for the IMS (International Monitoring System). In the presentation, a new laser pistonphone design is presented with the objective of establishing primary standards for sound pressure at very low frequencies down to 10 mHz. The piston is a modified accessorized loudspeaker driver whose diameter is equal to the diameter of…

Evidence: 31 • authority: 88

Influence on human body of audibility amplitude modulation low-frequency noise in residential environment. Low-frequency noise of about 100 Hz including audible frequency is positioned as one of the factors of environmental problem. First, this paper describes countermeasures of psychological complaint by low-frequency noise generated by residential environment in Japan published in the Ministry of the Environment. Next, we experimentally examined the human body influence of audibility amplitude modulation low frequency noise (AMLFN) on the psychological and physiological response measured by whole-body exposure. The AMLFN used by this research fluctuated the fluctuation cycle of the carrie…

Evidence: 31 • authority: 92

Infrasonic acoustic energy produced by offshore wind turbine energy generation may interfere with bird and cetacean navigation cues.. Offshore wind turbine farms are being planned and installed throughout the coastal areas of the global ocean. Noise concerns from these activities are typically framed within frequency bands of concern defined by governmental regulatory agencies (NMFS - OPR, 2018). A less considered noise source are the various infrasonic noises generated by large rotating blades in a pressure-dynamic medium. These noises include the infrasonic "thumps" generated by the motion of the turbine blades as they intersect the "stagnate wind area" on the windward side of the mast (C…

Evidence: 30 • authority: 72

Hearing range describes the frequency range that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal. Several animal species can hear frequencies well beyond the human hearing range. Some dolphins and bats, for example, can hear f…

Evidence: 26 • authority: 72

Acoustics is a branch of continuum mechanics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries. Hearing is one of the most crucial means of survival in the animal world and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acou…

Evidence: 26 • authority: 72

Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower-frequency electromagnetic oscillations (pulsations which occur below ~3 kHz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands. ELF radio waves are generated by lightning and by natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. Because of the…

Evidence: 25 • authority: 72

Sound is a phenomenon in which pressure disturbances propagate through an elastic material medium. In the context of physics, it is characterised as a mechanical wave of pressure or related quantities (e.g. displacement), whereas in physiological-psychological contexts it implies a hearing process. Though sensitivity to sound varies among all organisms, the human ear is sensitive to audio frequencies ranging from 20 Hz to 20 kHz. More broadly, acoustic waves encompass mechanical longitudinal waves in general. Examples of the significance and application of sound include music, medical imaging techniques, oral language and parts of science.

Evidence: 21 • authority: 72

Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light. The interval of time between events is called the period. It is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times per minute (2 hertz), its period is one half of a second. Special definitions of frequency are used in certain contexts, such as the angular frequency in rotational or cyclical properties, when the rate of angular progress is measured. Spatial frequency is def…