Impulsive Noise Sources Research Articles

Acoustical characterization of exploding hydrogen-oxygen balloons.

Exploding balloons are popular demonstrations in introductory chemistry and physical science classes and as part of outreach programs. Anechoic measurements of various hydrogen and hydrogen-oxygen balloons were made using 3.18 and 6.35 mm microphones placed at various angles and distances from the balloon. Time waveform data from each explosion were collected at a sampling frequency of 192 kHz. Initial research, presented previously, was conducted to determine potential auditory hazard as a result of exposure to these balloons. Further analysis has been conducted on the explosions’ time waveforms and calculated spectra to characterize hydrogen-oxygen balloons as an impulsive noise source. Consideration is given to level, waveform A duration, rise time, angular variation, and repeatability. Comparisons with other impulsive noise sources are also presented.

Application of the passive control of shock wave to the reduction of high-speed impulsive noise

Strong, normal shock wave, terminating a local supersonic area on an airfoil (or helicopter blade), not only limits aerodynamic performance but also becomes a source of a high-speed impulsive (HSI) noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers details of the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes a validation against the experimental data obtained for the ONERA transonic nozzle with a flat wall. The passive control device is then applied numerically on a helicopter blade in high-speed transonic hover conditions to weaken the shock wave – the main source of HSI noise.

Measurements of exploding balloon demonstrations.

Exploding balloons are popular demonstrations in introductory chemistry and physical science classes and as part of outreach programs. However, as impulsive noise sources, these demonstrations constitute a possible hearing damage risk to both the demonstrator and the audience. Measurements of various hydrogen, hydrogen-oxygen, and acetylene-oxygen balloons were made in both a large lecture hall and an anechoic chamber. Condenser microphones (6.35 and 3.2-mm diameters) were placed at various angles, and distances from the balloon and time waveform data were collected at a sampling frequency of 192 kHz. For all balloon sizes tried, hydrogen-only balloons were found to produce peak sound pressure levels less than 140 dB at distances greater than or equal to 2 m. On the other hand, large (but reasonably sized) hydrogen-oxygen and acetylene balloons can result in peak levels exceeding 160 dB at a distance of 2 m, which constitutes a significant hearing risk for unprotected listeners at typical distances.

Measurement and characterization of army impulsive noise sources.

Peak pressure levels in army noise environments range from 140- to 195-dB near soldiers firing energetic weapons and are all dangerous to unprotected ears. Blast reverberation in confined spaces and steady noise in armored vehicles is also hazardous, so complete assessment requires the widest possible measurement range. To accurately measure pressures in the free-field or under hearing protectors, microphone considerations include type, location, orientation, mounting, shape, and shielding from flash or mechanical shock. Blast-waves rise instantaneously and return to free-field ambient within 0.3–15 ms, while in enclosures this can increase to 100 ms, requiring wide bandwidth signal processing. In addition to hazard, acoustic detection and annoyance at greater distances from weapons involve propagation effects in the atmosphere and at the ground which alter the wave-shape.

A frequency-based RF partial discharge detector for low-power wireless sensing

Partial discharge (PD) monitoring has been the subject of significant research in recent years, which has given rise to a range of well-established PD detection and measurement techniques, such as acoustic and RF, on which condition monitoring systems for highvoltage equipment have been based. This paper presents a novel approach to partial discharge monitoring by using a low-cost, low-power RF detector. The detector employs a frequency-based technique that can distinguish between multiple partial discharge events and other impulsive noise sources within a substation, tracking defect severity over time and providing information pertaining to plant health. The detector is designed to operate as part of a wireless condition monitoring network, removing the need for additional wiring to be installed into substations whilst still gaining the benefits of the RF technique. This novel approach to PD detection not only provides a low-cost solution to on-line partial discharge monitoring, but also presents a means to deploy wide-scale RF monitoring without the associated costs of wide-band monitoring systems.

폭발파에 의한 음향파 생성 메커니즘의 수치적 연구

The goal of this paper is to investigate the generation characteristics of the main impulsive noise sources generated by the supersonic flow discharging from a muzzle. For this, this paper investigates two fundamental mechanisms to sound generation in shocked flows: shock motion and shock deformation. Shock motion is modeled numerically by examining the interaction of a sound wave with a shock. The numerical approach is validated by comparison with results obtained by linear theory for a small disturbance case. Shock deformations are modeled numerically by examining the interaction of a vortex ring with a blast wave. A numerical approach of a dispersion-relation-preserving(DRP) scheme is used to investigate the sound generation and propagation by their interactions in near-field.

Seismic interferometry of scattered surface waves in attenuative media

SUMMARY Seismic interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver that are emitted from a surrounding boundary of impulsive or uncorrelated noise sources. We study seismic interferometry for scattered surface waves using a stationary-phase analysis and surface wave Green's functions for isotropic point scatterers embedded in laterally homogeneous media. Our analysis reveals key differences between the interferometric construction of reflected and point-scattered body or surface waves, since point scatterers radiate energy in all directions but a reflection from a finite flat reflector is specular. In the case of surface waves, we find that additional cancelling terms are introduced in the stationary-phase analysis for scattered waves related to the constraint imposed by the optical theorem for surface waves. The additional terms are of second order even for single-scattered waves, and we show that these can be highly significant in multiple-scattering cases. In attenuative media errors are introduced due to amplitude errors in these additional terms. Further, we find that as the distribution of scatterers in a medium becomes more complex the errors in correlation-type interferometry caused by attenuation in the background medium become larger. Convolution-type interferometry has been shown to be effective when considering electromagnetic wavefields in lossy media, and we show that this is also true for scattered surface waves in attenuating elastic media. By adapting our stationary-phase approach to this case, we reveal why convolution-type interferometry performs well in such media: the second-order cancelling terms that appear in the correlation-type approach do not appear in convolution-type interferometry. Finally, we find that when using both correlation- and convolution-type interferometry with realistic source geometries (illustrative of both industrial seismics and ‘passive noise’ interferometry), we cannot necessarily expect to produce estimates with all dominant scattering events present. This is shown to be especially important if, as proposed previously for electromagnetic applications, the convolution and correlation approaches are compared to help identify errors in the interferometric estimates.

Monitoring the temporal and spatial characteristics of the noise radiated from marine piling

Noise is often an unintended by-product of offshore activities, and a significant source of impulsive underwater noise is marine piling, where a pile is driven into the sea-bed using a hydraulic hammer. This paper describes work undertaken to monitor the underwater radiated noise during offshore marine piling. The measurements made include full characterisation of the temporal variation of the resulting sound field, including frequency content of the pulses and the increasing amplitude typically observed during the soft start period. Results are also shown for the spatial variation of the field, including the effect on propagation of significant bathymetry changes (for example, due to the presence of a sand bank). The energy within each acoustic pulse is an appropriate measure of the sound field, having the advantage that it is relatively straightforward to add the contributions from each pulse in order to derive an overall sound exposure level (SEL) in a manner analogous to methods familiar from air acoustics. An example is then given of how the measured data and predictive modeling may be used to calculate an overall exposure for an animal in the vicinity, using various assumptions about the location and mobility of the animal.

Empirical evaluation using impulse noise of the level-dependency of various passive earplug designs

An objective in the development of hearing protection devices (HPDs) has been the design of a passive earplug that provides modest or no attenuation at low sound levels, with greater protection at high sound levels. This raises the issue of not only how to construct such a device, but also how to evaluate it. There is the related question of whether conventional HPDs are actually level independent. Passive level dependency is typically accomplished via an orifice that causes sound transmission to decrease as input level increases. We utilized an impulsive noise source (explosives) with peak levels from 110 to 190 dB SPL to measure the insertion loss of a variety of commercially available and developmental earplugs. The tests were conducted at frontal incidence in a reflection-free outdoor environment using the Institute of Saint-Louis acoustical test fixture specifically constructed for HPD attenuation measurements. Conventional foam and premolded earplugs exhibited attenuation that was essentially constant with level, whereas the best of the level-dependent designs provided attenuation that increased by about 25 dB over the 80-dB range of test impulse levels. This latter design has been successfully utilized since 2000 in the Combat Arms™ Plug widely fielded in the U. S. Military.

Shock wave strength reduction by passive control using perforated plates

Strong, normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a source of a high-speed impulsive helicopter noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes an extended validation against the experimental data for relatively simple geometries of transonic nozzles. It is a first step towards a full simulation of a helicopter rotor equipped with a noise reducing passive control device in hover and in forward flight conditions.

Shock wave smearing by passive control

Normal shock wave, terminating a local supersonic area on an airfoil, limits its performance and becomes a source of high speed impulsive noise. It is proposed to use passive control to disintegrate the shock wave. Details of the flow structure obtained by this method are studied numerically. A new boundary condition has been developed and the results of its application are verified against experiments in a nozzle flow. The method of shock wave disintegration has been confirmed and detailed analysis of the flow details is presented. The substitution of a shock wave by a gradual compression changes completely the source of the high speed impulsive noise and bears potential of its reduction.

Shock wave smearing by wall perforation

Normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a significant source of a high-speed impulsive noise on the rotor blade of a helicopter. It is proposed to apply passive control to disintegrate the shock wave by smearing pressure gradients created by the shock. Details of the flow structure obtained by this method are studied numerically. A new boundary condition of a perforated wall is verified against experimental data for a passive control of the shock wave in a channel flow and on an airfoil. This method of shock wave disintegration is proven to work for internal flows in transonic nozzles and appears to be effective for transonic airfoils as well. The substitution of a shock wave by a gradual compression changes completely the source of the high-speed impulsive noise and bears potential of its reduction.

A means to see noise sources

There are many candidates to visualize noise/sound sources. For example, acoustic holography is one of them. However, to get acoustic holography, we need many microphones and associated data acquisition and processing unit. Especially, when noise is impulsive, the holography system requires two-dimensional microphone array. Depending on the type of noise sources, we have to select the best means that can provide us what we want to have, which can be noise sources’ locations or entire sound distribution in space. This paper addresses various methods that can predict where noise sources are, or how noise is distributed in space. This includes beam forming methods to determine steady or impulsive noise sources, conventional acoustic holography, time domain acoustic holography and moving frame method that can show moving noise sources. We compare these methods and show a guideline that can lead us to select the best means to see noise sources. Various industrial examples are introduced. Time domain acoustic holography of plasma display panel that shows very interesting vibration pattern, beam forming method that depicts short and small noise generated by thermal expansion of a TV set, and moving frame method that shows tire noise are some of the examples.

Impulsive noise of printers: measurement metrics and their subjective correlation

In the office and home computing environments, printer impulsive noise has become a significant contributor to user perceived quality or lack thereof, and can affect the user’s comfort level and ability to concentrate. Understanding and quantifying meaningful metrics for printer impulsivity is becoming an increasingly important goal for printer manufacturers. Several methods exist in international standards for measuring the impulsivity of noise. For information technology equipment (ITE), the method for detection of impulsive noise is provided in ECMA‐74 and ISO 7779. However, there is a general acknowledgement that the current standard method of determining impulsivity by simply measuring A‐weighted sound pressure level (SPL) with the impulsive time weighting, I, applied is inadequate to characterize impulsive noise and ultimately to predict user satisfaction and acceptance. In recent years, there has been a variety of new measurement methods evaluated for impulsive noise for both environmental and machinery noise. This paper reviews several of the available metrics, applies the metrics to several printer impulsive noise sources, and makes an initial assessment of their correlation to the subjective impressions of users. It is a review and continuation of the work presented at InterNoise 2005 (Baird, Bray, and Otto).

Determination of noise descriptors and criteria for pyrotechnic noise sources

A noise study was conducted to determine appropriate noise descriptors and criteria for assessing pyrotechnic noise sources. The study was carried out to support an environmental impact statement (EIS) that defined sensitive land uses adjacent to reservoirs in New York City area, where potential noise impacts from avian dispersion measures would occur. The pyrotechnic techniques defined as impulsive noise sources are among the avian dispersion measures that would be used at the reservoirs. Determining appropriate noise descriptors and criteria was critical to the EIS because of the distinctive sound characteristics of pyrotechnic impulse noise sources, the lack of published literature on assessing them, and the absence of corresponding noise regulations. Noise descriptors and criteria used for EIS in the United States were investigated, and noise measurements for pyrotechnic noise sources and some impulsive noise sources were also performed. The study results demonstrate that C-weighted DNL is an appropriate descriptor for assessing noise impacts from the pyrotechnics based on the U.S. Army Environmental Noise Management Program criteria, and peak hour A-weighted Leq(1) is a suitable noise descriptor for determining noise impacts for avian dispersion measures, including the pyrotechnics, based on the New York City Environmental Quality Review criteria.

Development of metrics to identify military impulse noise

Urban encroachment of military bases continues to be a serious problem, affecting training exercises and overall military readiness. The military currently performs noise monitoring around bases to ensure that environmental conditions are favorable for tests or exercises. Despite refinements, current monitoring systems still suffer from occasional false positives and rely heavily on human interpretation. The long range goal of this work is to create a more accurate and autonomous noise classifier. The specific aims of the work are to create a library of recorded military impulse noise sources and to develop, test, and refine the noise classifier algorithms. Representative, high quality field measurements of various noise sources (25 mm and larger) will be conducted at a few military bases under varying environmental conditions. Measurements of wind noise and thunder will also be recorded. The software will be developed in MATLAB and will employ several common impulse noise metrics used for hearing conservation, including rise, peak, and fall times, crest factor, A- and B-durations, Lpk and kurtosis, among others. A neural network will be trained to discern between the recorded military noise sources and naturally occuring noise based on these metrics. Preliminary results from the measurements and analysis will be presented. [Work supported by SERDP.]

Numerical and Experimental Study on Three-Dimensional Localization For Ultra-Wideband Impulsive Noise Sources

This paper presents a three-dimensional (3-D) localization system for ultra-wideband (UWB) impulsive noise sources. The localization algorithm is in terms of time difference of arrival (TDOA). Firstly, a feasibility study of the 3-D localization scheme is carried out numerically. Then, the effectiveness and limitation of the scheme are revealed. Our proposal is validated by measurement in an open site.

잡음 속에 묻힌 임펄스 소음원 위치 추정

This paper addresses the way in which we can find where impulsive noise sources are. Specifically, we have an interest in the case that the signal is embedded in noise. We propose a signal processing method that can identify impulsive sources` location. The method is robust with respect to spatially distributed noise. This has been achieved by the modified beamforming method with regard to cepstrum domain is used. It is noteworthy that the cepstrum has the ability to detect periodic pulse signal in noise. Numerical simulation and experiments are performed to verify the method. Results show that the proposed technique is quite powerful for localizing the faults in noisy environments. The method also required less microphones than conventional beamforming method.

Robust decorrelating decision-feedback multiuser detection in non-Gaussian channels

Multiuser detection research has been pursued under the Gaussian noise hypothesis. However, in many realistic channels where impulsive noise sources are ubiquitous, the Gaussian statistical model is hardly justifiable. There is, therefore, a strong motivation for the development of robust non-Gaussian signal processing techniques to safeguard against the influence of outliers from degrading detector performance in impulsive channels. This paper investigates a simple approach to robustify the decorrelating decision-feedback (DDF) multiuser detector. The proposed detector involves a chip-based nonlinear front-end for impulsive noise filtering followed by the classical DDF detection. The nonlinear front-end exploits knowledge of the users’ signal amplitudes to constrain the useful signals to fall within the linear region of the nonlinear clipping function. The performance of the proposed robust DDF detector is investigated through extensive computer simulations, and it is shown that substantial improvement in performance can be achieved by incorporating the nonlinear front-end when the channel noise follows heavy-tailed non-Gaussian distributions.

A direction-finding technique for wide-band impulsive noise source

A direction-finding technique for wide-band impulsive electromagnetic interference is presented. An experimental investigation was performed using a spark generator as the impulsive noise source. The signals were captured using a two-antenna array directly sampled at 1 Gs/s. A digital signal processing based correlation technique allowed assessment of the time delay between the antennas. The results in a nonideal radio propagation environment show the bearing can be estimated to an accuracy of 20.