Impulsive Sound Signals Research Articles

Use of artificial neural networks to assess train horn noise at a railway level crossing in India

Urban environment noise is a complex mixture of transportation, industrial, household, and recreational noise, which is identified as an emerging environmental threat. Present study monitors and evaluates a noise pollution hotspot: a railway level crossing, where several activities related to transportation noise were involved. Train honking, train movement, road vehicles, and pedestrians contribute to the noise level at a railway level crossing. Train horns are generally performed as train approach railway level crossings and they are mandatorily used to alert road users. However, the train horns are regarded as nuisance to the nearby residents. A detailed evaluation of train horn effectiveness is very much essential in the current contemporary environment. Thus, the main objective of this study is to measure noise levels emanating from train horns at a level crossing with due consideration to train types and climatic conditions. A comprehensive noise monitoring survey was conducted at an access-controlled level crossing. Furthermore, an artificial neural network (ANN)-based railway noise prediction model was developed to forecast maximum ([Formula: see text]) and equivalent (Leq) noise levels. Results revealed that train horn produced impulsive sound signals which fall under high frequency one-third octave bands causing severe irritation to trackside inhabitants. The proposed ANN models produced accurate results for [Formula: see text] and Leq noise levels and this model is identified as a vital tool for railway noise abatement. The results from this study are helpful to the urban planning and development authorities to implement strategic laws and policies to eradicate the urban environment noise.

Experimental realization of enhancing low-frequency sound emission by metamaterial enclosure

A solution to the low radiation rate of a sound source has been proposed by using metamaterial enclosures of degenerated Mie resonances [J. Zhao, L. Zhao, and Y. Wu, J. Acoust. Soc. Am. 142(1), EL24–29, July 2017]. This talk presents our experimental realization of this enhancement for a monopole source. The enclosure with a low sound speed is created by a coiling-space structure fabricated by 3D printing. A small balanced-armature speaker with a 1 mm speaker mouth is placed at the enclosure center to radiate impulsive sound signals. The diameter of the structure is only one seventh of the wavelength of the sound at the maximum enhancement, corresponding to the lowest resonance. The enhanced sound pressure is more than two orders of magnitude larger than the sound pressure without the enclosure. The measurements of sound pressure at different angles in the space show the omnidirectionality of the enhancement. This enhancement is demonstrated as a result of enhanced density of states, i.e., the increased number of modes per unit frequency range and per unit volume, which we relate to Fermi's Golden rule and Purcell effect in quantum systems and find the analog in acoustics.

Comprehensive summary of the impulsive pile driving sound exposure study series

The high intensity controlled impedance fluid filled wave tube (HICI-FT) was used to expose fishes, in the laboratory, to impulsive sound signals under controlled conditions. Fish species were exposed to pile driving signals under different experimental paradigms, followed by detailed investigations of their physiological tissue response (aka, barotrauma injuries). Most often the cumulative sound exposure level (SELcum) was held constant while varying the number of pile strikes and the single strike sound exposure level (SELss). Altering these three variables proved the equal energy hypothesis irrelevant; the higher SELss values with fewer number of strikes caused a highest injury levels. The first dose-response curve was generated for fish responses. Comparisons between different species showed fish with no swim bladder at low injury risk, fish with a closed swim bladder (physoclists) at a high injury risk, and fish with an open swim bladder (physostomes) at a moderate injury risk. If fish find safe haven in the wild, they have potential to heal within 10 days of receiving moderate injuries. Tissue injury appears to occur before damage to hair cells occurs. And most recently, fish show injury after exposure to as few as 8-impulsive signals that have a high SELss value.

Fluctuations of the peak pressure level of man-made impulsive sound signals propagating in the ocean

The theory of wave propagation and fluctuations in random media has been broadly studied; however the works studying the influence of a changing underwater acoustic environment on the spatial decay and fluctuations of the peak pressure in broadband and impulsive signals are limited. Using a method based on the formulation developed by Dyer and Makris to estimate intensity fluctuations of sound signals in the ocean in conditions of saturated multipath propagation, this paper presents an approach to model peak pressure fluctuations of transient signals propagating underwater. In contrast to the formulation of Dyer and Makris, the approach presented in this work applies extreme value theory using the properties of the peak pressure as a maximum value taken from a Rayleigh distributed amplitude. The location and scale parameters obtained from the best fit to a Gumbel distribution are used to estimate the probability of the peak pressure level staying below a certain threshold. The theory was applied to measurements of signals from an airgun array and offshore impact pile driving, resulting in good agreement in both cases.

Influence of windscreen on impulsive noise measurement

The nearfield noise from jet engines may contain impulsive sound signals with high crest factors. Most jet engine noise measurements are performed outside in potentially windy conditions, and it may, therefore, be necessary to use windscreens on microphones to reduce the influence of wind induced noise on the microphone. The windscreen will, however, influence the frequency response of the microphone especially at high frequencies. This will change both the magnitude and the phase response and, therefore, change the measured impulse. The effect of different sizes of windscreen is investigated and the effect on impulsive type signals is evaluated both in the time domain and the frequency domain.

An acoustic valve within the nose of sperm whalesPhyseter macrocephalus

Sperm whales Physeter macrocephalus emit impulsive sound signals in short series of rhythmic clicks (codas) for communication, and in long series of single acoustic events (usual clicks) for echolocation. Both click types are generated pneumatically within the hypertrophied nasal complex, at the ‘monkey lips’ at the rostral end of the right nasal passage. Each individual click comprises repetitive pulses decaying in intensity. However, the decay rate is distinctly higher in usual clicks than in coda clicks. The mechanism of decay rate control in the clicks is still unclear, and it is unclear why the right nasal passage crosses the nasal acoustic pathway between two hypertrophied acoustic fat bodies (spermaceti organ, junk), so that it resembles a ‘bent acoustic horn’. We present a new concept to explain how the flat right nasal passage can serve as a variable acoustic valve, and how the amount and distribution of its air filling can be controlled by muscle action. This mechanism allows the whale to determine the pulse decay rate and thus switch between the two modes of click production. Coda clicks are generated by reverberations within the spermaceti organ (partial trapping of sound) and by the release of sound energy in fractions through the air-filled right nasal passage. In contrast, echolocation clicks as single events are released during the partial collapse of the right nasal passage between the spermaceti organ and the junk. This interpretation of the right nasal passage as an adaptive acoustic valve elucidates why the spermaceti organ and the junk are separated from each other by an air-filled space of variable volume crossing the sound path of the ‘bent acoustic horn’ in the posterior part of the nasal complex.

Low-frequency attenuation and sound-speed measurements in marine sediments using an impulsive source.

Low-frequency (200–1000-Hz) sediment attenuation and sound-speed measurements were conducted at a site on the New Jersey Shelf where additional data sets from a chirp-sonar bottom profiler (2–12 kHz) and an acoustic-probe system (10–80 kHz) are available. Impulsive sound signals, generated by automated light-bulb implosions, are received by a 16-element vertical line array at short ranges (<500 m). Precursor arrivals and signals reflected from the R-reflector are used to estimate sediment sound-speed and attenuation. Attenuation in dB/m/kHz is estimated using the spectral-ratio technique and sound-speed is estimated from the travel-time analysis. Frequency dependency of sound-speed and attenuation is also investigated within a wide frequency band (200 Hz–80 kHz) using the results from impulsive source, chirp-sonar, and acoustic-probe measurements. Measured attenuation and sound-speed values seem to be well predicted by an extended Biot theory for sediments with distributed pore sizes. [Work supported by ONR.]

Internal combustion engine sound-based fault detection and diagnosis using adaptive line enhancers

In an internal combustion engine, the impulsive sounds are very often radiated owing to the faults of the engine. Thus it is important for a noise, vibration, and harshness engineer to detect and analyse impulsive sound signals for both fault diagnoses. However, it is often difficult to detect and identify impulsive signals because of interfering signals such as those due to engine firing, harmonics of crankshaft speed, and broadband noise components. These interferences hinder the early detection of faults and improvement of sound quality. In order to overcome this difficulty, a two-stage adaptive line enhancer which is capable of enhancing impulsive signals embedded in background noise is developed. This method is used to pre-process signals prior to time—frequency analysis via a bilinear methods such as the Wigner—Ville distribution and the Choi—Williams distribution.

Application of analytic wavelet transform to analysis of highly impulsive noises

Time–frequency ( T– F) domain analysis is necessary to characterize highly transient signals. The analytic wavelet transform (AWT), which has features of both the Fourier transform and the wavelet transform, is advocated as an ideal T– F signal analysis tool in this paper. Underlying theories and basic properties of the AWT are discussed in comparison with a commonly used short-time Fourier transform (STFT) method. The AWT is set up specifically for acoustics applications to describe T– F changes of the signal in sound pressure level, and applied to characterize two highly impulsive sound signals. Comparing the results from the AWT and the STFT clearly demonstrates the advantage of the AWT, which captures temporal and spectral characteristics of the signal in much more detail. A potential application of the AWT to risk assessment of impulsive noise-induced hearing loss is discussed.