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Draft for Impulsive noise (acoustics)
Existing page: https://en.wikipedia.org/wiki/Impulse_noise_(acoustics) March 30, 2020.

Keywords for Impulse noise
Keywords- select 6, Library of Congress http://id.loc.gov/authorities/subjects.html

noise (sh85092179); noise measurement (sh85092180), noise health effects (sh2010103810), industrial noise law and legislation (sh87005564), noise physiological effect (sh85092181), acoustic reflex (sh85000589); Gaussian distribution (sh85053556)

Tentative outline

 * Acoustical descriptors/bioacoustics
 * Measurement
 * Auditory risks
 * Regulation (United States, Europe, elsewhere?)

New content Impulsive noise (acoustics)
[With co-authors, Murphy, Kardous, Flamme, Suter, others?]

In acoustics, impulse noise is defined as a high-level (high amplitude) transient resulting from a sudden release of energy into air. impulse noise has been characterized for including peaks, single bursts with a duration of less than one second with peak levels 15 dB higher than background noise. Impulse noise differs from steady state noise by the properties in the time domain. The term impulsive noise can be used for both impulse noise and impact noise, which results from the collision of masses (e.g., hammer fall, punch press, etc.).

Different parameters and metrics are used in the evaluation of audible sounds

Acoustical Descriptors
[Flamme Murphy]

Firecrackers tend to have spectral peaks in the vicinity of 1000 to 4000 Hz. The spectral peaks for handguns, rifles, and shotguns usually occur between approximately 400 and 4000 Hz, depending on the type of gun and distance from the muzzle.

The magnitude of the auditory sensation created by an acoustic stimulus is called loudness. Loudness is the result of physical (e.g., intensity, frequency), peripheral (e.g., outer, middle and inner ear), and central (e.g., cognitive, emotional) factors, and loudness perceptions only occur retrospectively. Although loudness is related to stimulus amplitude, this relationship is imperfect for brief high-level sounds signal duration less than about 200 ms. rank-ordering of loudness for different gunshots in an open field is correlated to the product of peak intensity and pressure-envelope (B) duration. loudness perceptions for brief high-level sounds will underestimate the physical intensity of the signal, particularly if the A-duration (i.e., the pressure wave duration) is less than about 3 ms. This underestimation can lead a listener to incorrectly conclude that a brief sound is not hazardous because it is not perceived as very loud.

Fine Waveform Structure
in order to determine risk from exposure to impulsive noise researchers have identified several metrics that could be important factors in determining risk from exposure to impulsive noise.

Kurtosis
Waveform kurtosis is a measure of the height of the frequency-of occurrence histogram. It is a metric that can be used to quantify the departure from normality, and has been shown to be sensitive in the evaluation of temporal noise characteristics. The use of this metric has been proposed for the prediction of hazards to hearing in individuals resulting from complex occupational noise exposures.

The American National Standards Institute and Acoustical Society of America (ANSI/ASA) standard S12.42–2010 specifies data acquisition systems have a minimum sampling rate of 96 kHz (192 kHz is preferred), 16-bit digital resolution (24-bit is preferred), and the capacity to deal with impulses of 180 dB SPL. However, the 96 kHz rate might not capture the peak of many impulses. some efforts have been made recently to develop standardized systems and software optimized for brief high-level sounds. A portable, self-contained impulse noise measurement system developed by the National Institute for Occupational Safety and Health (NIOSH) in the US, can measure impulses up to 186 dB SPL (192 dB SPL using very low sensitivity polarized microphones) in real time. The system has the capability to store waveforms and provide immediate analysis and calculations of relevant impulse noise metrics (peak level, B duration, frequency spectrum as Fast Fourier Transform (FFT) and octave band, temporal spacing, number of impulses, kurtosis, and Leq).

Auditory risks from exposures to Impulsive Noises [add subsections on how to control exposures/protect hearing]
Temporal variations in the noise signal modify the risk of auditory effects. Various studies indicate that non-Gaussian noise can be more damaging than continuous noise of equivalent energy. It is necessary to understand these risks to mitigate them through exposure guidelines for occupational settings.

Multiple plausible damage pathways

•Excitotoxic / Metabolic stress

•Similar to pathways for continuous noise.

•Mechanical / Tissue strain

•Eardrum rupture

•Basilar membrane rupture

•Synaptopathy

•Lost connection to auditory nerve dendrites

•Difficult to measure

Conditions leading to damage in humans is unknown

SOURCE: The impulse noise of firearms and their effects on the cochlea are well documented in animal models (Dancer & Franke, 1975; Liberman, 1984; Liberman & Dodds, 1984; Liberman & Kiang, 1984; Price et al, 1989; Kaltenbach et al, 2000; Yang & Tan, 2007) and in humans (Melinek et al, 1976; Ylikoski, 1994; Konopka et al, 2000; Pawlaczyk-Luszczynska et al, 2004; Nottet et al, 2006).

SOURCE: From Suter and other, several paragraphs till standards to be adapted: In one of these early investigations Luz and Hodge57 developed a model to explain delayed recovery from TTS in terms of mechanical and metabolic damage to the cochlea from impulse noise. Henderson et al58 and Hamernik et al82 have found this multi-phase recovery in chinchillas exposed to high levels of impulse noise at 155-160 dB, and concluded that mechanical damage occurred at these levels. Spoendlin83 observed the effects of direct mechanical destruction in cats for a 200-millisecond stimulus at 120 dB.

From Suter and other, several paragraphs till standards to be adapted: Roberto et al84 used a 200-millisecond B-duration impulse with 4 impacts/second.Henderson et al59 estimated the critical level in chinchillas to be between 119-125 dB. Further investigations by members of the same team confirmed that range for the critical level. The authors concluded that the critical level varies not only with peak level, but with waveform, spectrum, duration, and repetition rate.59-60, 85-86 Using the guinea pig model, Lataye and Campo47 estimate a critical level of 111 dB.

SOURCE: From Suter and other, several paragraphs till standards to be adapted: Rather than producing some kind of savings from intermittency, the conditions in the above experiments involving impulse/impact noise seem to follow an equal energy pattern at lower levels until they reach a critical exposure, at which point the damage to hearing is greater than would be predicted. The concept of the critical level is important to the discussion of the ER in that any adjustments to an ER that best fit hearing loss predictions need to take into account the effects of impulses and impacts, and in this case, the critical levels or exposures. Although the specific parameters may not be completely spelled out at this time, these adjustments could eventually be accomplished through the development of appropriate measurement methods and instrumentation.

SOURCE: From Suter and other, several paragraphs till standards to be adapted: The C-weighted minus A-weighted values of most occupational exposures are only 2 to 3 dB,87-88 indicating a lack of significant low-frequency dominance in most cases.

From Suter and other, several paragraphs till standards to be adapted: Impulse noise may occur at levels from about 100 to >185 dB89 and typical levels of impacts could be about 95-135 dBA.60

Standards and legislation for impulse or impact noise [separate into subsections, standards vs legislation, standards for measurements vs standards & legislation for exposures]
Much of the research on this topic involving human subjects were obtained prior to 1980 and led to a recommended damage risk criterion based upon peak exposure level and the duration of the impulse. Noise exposures that are predominantly impulsive are mainly found in the military, but in some civilian occupations as well, especially among police officers, other public safety personnel, and in certain occupations in the construction industry. They may be differentiated from impact noise, which occurs primarily in manufacturing occupations and construction, although there is necessarily some overlap.

SOURCE: From Suter: "The U.S. Department of Labor has defined impulse noise by default. Section (b)(2) of the noise regulation states that if variations in noise level involve maxima at intervals of one second or less it is considered continuous noise. "

Integrated levels for brief high-level sounds can be assessed for an equivalent 8-hour exposure, adjusted for duration and the number of impulses. A modification of this metric, named SELA (A-weighted Sound Exposure Level), replaced the 8-hour term with a 1-second term in the calculation of equivalent energy. The Department of Defense Design Criteria Standard for Noise Limits, MIL-STD-1474E gives users a choice between the Auditory Risk Unit (ARU), which is calculated using the AHAAH model, or the LIAeq100ms model to predict auditory hazard. The American Institute of Biological Sciences recommended further research and validation of certain of its critical assumptions, especially with regard to the influence of the middle ear reflex. (citation?). MIL-STD-1474E also offers user thwe alternative of using the LIAeq100ms, a variation of the Leq8 metric tailored for impulse noise, which represents the equal energy equivalent of the sound exposures averaged over 100-ms intervals.The standard states that the Leq8 has an empirical foundation based on human response to impulsive noise but that it can overestimate the hearing damage risk for long duration impulses. Therefore, the LIAeq100ms method includes a correction for long A-duration impulses, i.e. A-durations more than 0.2 ms.70 Simplicity as well as its relevance to complex noise environments would argue for the method based on Leq8.