Peak Sound Pressure Research Articles

Software-based noise reduction in cranial magnetic resonance imaging: Influence on image quality.

ObjectivesTo investigate acoustic noise reduction, image quality and white matter lesion detection rates of cranial magnetic resonance imaging (MRI) scans acquired with and without sequence-based acoustic noise reduction software.Material and methodsThirty-one patients, including 18 men and 13 women, with a mean age of 58.3±14.5 years underwent cranial MRI. A fluid-attenuated inversion recovery (FLAIR) sequence was acquired with and without acoustic noise reduction using the Quiet Suite (QS) software (Siemens Healthcare). During data acquisition, peak sound pressure levels were measured with a sound level meter (Testo, Typ 815). In addition, two observers assessed subjective image quality for both sequences using a five-point scale (1 very good—5 inadequate). Signal-to-noise ratio (SNR) was measured for both sequences in the following regions: white matter, gray matter, and cerebrospinal fluid. Furthermore, lesion detection rates in white matter pathologies were evaluated by two observers for both sequences. Acoustic noise, image quality including SNR and white matter lesion detection rates were compared using the Mann-Whitney-U-test.ResultsPeak sound pressure levels were slightly but significantly reduced using QS, P≤0.017. Effective sound pressure, measured in Pascal, was decreased by 19.7%. There was no significant difference in subjective image quality between FLAIR sequences acquired without/with QS: observer 1: 2.03/2.07, P = 0.730; observer 2: 1.98/2.10, P = 0.362. In addition, SNR was significantly increased in white matter, P≤0.001, and gray matter, P = 0.006, using QS. The lesion detection rates did not decline utilizing QS: observer 1: P = 0.944 observer 2: P = 0.952.ConclusionsSequence-based noise reduction software such as QS can significantly reduce peak sound pressure levels, without a loss of subjective image quality and increase SNR at constant lesion detection rates.

Making the transition from discrete shot records to continuous seismic records and source wavefields, and its potential impact on survey efficiency and environmental footprint

ABSTRACTA marine seismic method based on continuous source and receiver wavefields has been developed. The method requires continuous recording of the seismic data. The source that may consist of multiple source elements can emit signals continuously while moving. The ideal source wavefield to be used with this method should be as white as possible both in a temporal and a spatial sense to avoid deep notches in the spectrum enabling a stable multi‐dimensional deconvolution. White noise has such properties. However, equipment that can generate white noise does not exist. In order to generate a continuous source wavefield that is approaching the properties of white noise using existing equipment onboard marine seismic vessels, individual air‐guns can be triggered with short randomized time intervals in a near‐continuous fashion. The main potential benefits with the method are to reduce the environmental impact of marine seismic surveys and to improve acquisition efficiency. The peak sound pressure levels are significantly reduced by triggering one air‐gun at a time compared to conventional marine seismic sources. Sound exposure levels are also reduced in most directions. Since the method is based on continuous recording of seismic data and the air‐guns are triggered based on time and not based on position, there are less vessel speed limitations compared to conventional marine seismic data acquisition. Also, because the source wavefield is spread out in time, the wavefields emitted from source elements in different cross‐line positions can be designed such that the emitted wavefield is spatially white in this direction. This means that source elements in multiple cross‐line positions can be operated simultaneously, potentially improving the cross‐line sampling and/or the acquisition efficiency.

Acoustic characteristics of pulse detonation engine with ellipsoidal reflector**Project supported by the National Natural Science Foundation of China (Grant Nos. 11372141 and 11472138) and the National Defense Pre-Research Foundation of China (Grant No. 61426040201162604002).

Acoustic characteristics of a pulse detonation engine (PDE) with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional (2D) non-splitting unstructured triangular mesh Euler solver based on the space-time conservation element and solution element (CE/SE) method is employed to simulate the flow field of a PDE. The numerical results clearly demonstrate the external flow field of the PDE. The effect of an ellipsoidal reflector on the flow field characteristic near the PDE exit is investigated. The formation process of reflected shock wave and reflected jet shock are reported in detail. An acoustic measurement system is established for the PDE acoustic testing. The experimental results show that the ellipsoidal reflector changes the sound waveform and directivity of PDE sound. The reflected shock wave and reflected jet shock result in two more positive pressure peaks in the sound waveform. The ellipsoidal reflector changes the directivity of PDE sound from 20° to 0°. It is found that the peak sound pressure level (PSPL) and overall sound pressure level (OASPL) each obtain an increment when the PDE is installed with a reflector. The maximum relative increase ratio of PSPL and OASPL are obtained at the focus point F2, whose values are 6.1% and 6.84% respectively. The results of the duration of the PDE sound indicate that the reflecting and focusing wave generated by the reflector result in the increment of A duration and B duration before and near focus point F2. Results show that the ellipsoidal reflector has a great influence on the acoustic characteristic of PDE sound. The research is helpful for understanding the influence of an ellipsoidal reflector on the formation and propagation process of PDE sound.

Empirical modelling for derived metrics as function of sound exposure level in marine pile driving

To protect marine life, piling activities at sea are subject to regulations on sound emission. Different regulatory authorities base different action criteria based on different statistics of the emitted sound pressure. Modelling efforts to predict these metrics have achieved mixed success. While the sound exposure level (SEL) can be predicted relatively well, it has proven harder to model the peak sound pressure level (Lpk) accurately. It would therefore be valuable to have a reliable way of estimating Lpk, based on a prediction of SEL. Correlations between SEL and Lpk and between SEL and rms sound pressure level (Lrms) are obtained from measurements during piling of the Luchterduinen wind farm off the Dutch west coast, and are used to assess the applicability of correlations found at other wind farms. A metastudy using data from Luchterduinen as well as the German Bight gives a more robust trend line for use at other North Sea sites. Lrms is computed in two different ways, involving the 90 % energy signal duration on the one hand and the effective signal time duration (Teff) on the other. The value of Lrms based on Teff is found to be more robust. [Work sponsored by BOEM.]

Parabolic equation modeling of a seismic airgun array

The numerical modelling of seismic airgun sources, with a specific emphasis on the impact of sound on the marine ecosystem, is a challenging problem. In this paper, the simplified range-independent iso-velocity problem set up as part if the International Airgun Modelling Workshop (IAMW), is solved using the Parabolic Equation (PE). The acoustic pressure and particle acceleration are computed including the arrival time series and source energy level in deci-decade bands for ranges spanning from 30m to 30 km. The particle acceleration is computed by taking the spatial gradient of the pressure on the PE computational grid. The two significant challenges this problem poses to the PE solution are the very large bandwidth (5-4500 Hz) and the computational accuracy required for time-series and particle acceleration computations. Each of the metrics outlined in the statement of the problem are computed and presented. In addition to computing the required fields, the 17-gun volumetric array is placed in a 3D ocean environment in deep water in the Gulf of Mexico, with peak pressure computed out to 30km and the band integrated Signal Energy Level (SEL) computed to 400 km.

Estimation of Cough Peak Flow Using Cough Sounds

Cough peak flow (CPF) is a measurement for evaluating the risk of cough dysfunction and can be measured using various devices, such as spirometers. However, complex device setup and the face mask required to be firmly attached to the mouth impose burdens on both patients and their caregivers. Therefore, this study develops a novel cough strength evaluation method using cough sounds. This paper presents an exponential model to estimate CPF from the cough peak sound pressure level (CPSL). We investigated the relationship between cough sounds and cough flows and the effects of a measurement condition of cough sound, microphone type and participant’s height and gender on CPF estimation accuracy. The results confirmed that the proposed model estimated CPF with a high accuracy. The absolute error between CPFs and estimated CPFs were significantly lower when the microphone distance from the participant’s mouth was within 30 cm than when the distance exceeded 30 cm. Analysis of the model parameters showed that the estimation accuracy was not affected by participant’s height or gender. These results indicate that the proposed model has the potential to improve the feasibility of measuring and assessing CPF.

Investigation on flow oscillation modes and aero-acoustics generation mechanism in cavity

Unsteady flow and multi-scale vortex transformation inside a cavity of L/D = 6 (ratio of length to depth) at Ma = 0.9 and 1.5 were studied using the numerical simulation method of modified delayed detached eddy simulation (DDES) in this paper. Aero-acoustic characteristics for the cavity at same flow conditions were obtained by the numerical method and 0.6 m by 0.6 m transonic and supersonic wind-tunnel experiments. The analysis on the computational and experimental results indicates that some vortex generates from flow separation in shear-layer over the cavity, and the vortex moves from forward to downward of the cavity at some velocity, and impingement of the vortex and the rear-wall of the cavity occurs. Some sound waves spread abroad to the cavity fore-wall, which induces some new vortex generation, and the vortex sheds, moves and impinges on the cavity rear-wall. New sound waves occur. The research results indicate that sound wave feedback created by the impingement of the shedding-vortices and rear cavity face leads to flow oscillations and noise generation inside the cavity. Analysis on aero-acoustic characteristics inside the cavity is feasible. The simulated self-sustained flow-oscillation modes and peak sound pressure on typical frequencies inside the cavity agree well with Rossiter’s and Heller’s predicated results. Moreover, the peak sound pressure occurs in the first and second flow-oscillation modes and most of sound energy focuses on the low-frequency region. Compared with subsonic speed (Ma = 0.9), aerodynamic noise is more intense at Ma = 1.5, which is induced by compression wave or shock wave in near region of fore and rear cavity face.

Attenuation of earmuffs used simultaneously with safety spectacles in exposure to impulse noise

Impulse noise is particularly hazardous to the hearing of exposed individuals. In many real-life scenarios, the only protective measure used to reduce the level of impulse noise is hearing protectors. These scenarios include firing ranges. Aside from hearing protectors, shooters use personal safety spectacles. The purpose of this paper was to determine the effect of the simultaneous use of earmuffs and safety spectacles on the sound attenuation of earmuffs during exposure to impact noise. The research was completed with the MIRE method and included the determination of sound attenuation changes in five different models of earmuffs, used simultaneously with three different models of safety spectacles and prescription glasses. The impulse noise source used was a starting pistol, which generated C-weighted peak sound pressure level at a mean of 136.7 dB. The tests demonstrated that the simultaneous use of safety spectacles and earmuffs reduces the impulse noise attenuation of the earmuffs by up to 9 dB. Such sound attenuation changes occurred during simultaneous use of earmuffs with safety spectacles, which feature temples with a rectangular cross-section. The tests also demonstrated that the effect of prescription glasses on sound attenuation was unusually high; prescription glasses reduced the impulse sound attenuation of earmuffs by as much as 18 dB. Keywords: acoustics, noise protection, impulse noise, hearing protectors, earmuffs, noise attenuation

MRI Noise and Hearing Loss

MRI Noise and Hearing Loss

Developing a method to assess noise reduction of firearm suppressors for small-caliber weapons

Firearm suppressors have the potential to reduce the muzzle blast by diffusing the initial shock wave of a gunshot. Currently, the American National Standards Institute does not have any standards that specifically address suppressor measurements. A recent NATO standard, AEP 4875 has been proposed to characterize suppressor performance, but the scope of this standard does not include suppressor effects at the shooter’s ear. Additionally, the standard requires firing the weapon from an elevated platform 4 meters above the ground with microphones positioned with regular spacing of about 18 degrees at 5 meters from the muzzle. This study evaluated fourteen different firearms with and without a suppressor. Different loads of ammunition were used to vary the speed of the projectile. For ten of the guns, both supersonic and subsonic conditions were measured. Twelve microphones were positioned at 30-degree spacing in 3-meter ring at 1.5 meters above the ground. One microphone was positioned at 1 meter to the left of the muzzle and two microphones were positioned at 15 centimeters from the right and left ears. The suppressors were effective in reducing the peak sound pressure levels between 3 and 28 dB and 8-hour equivalent energy (LAeq8) between 2 and 24 dB.

Exposure to impulse noise at an explosives company: a case study

Impulse noise encountered in workplaces is a threat to hearing. The aim of this study was to assess the occupational exposure to impulse noise produced by detonation of dynamite on the premises of an explosives company. Test points were located on the blast test area (inside and outside the bunker) and in work buildings across the site. Noise propagation measurement was performed during 130 blast tests at nine measurement points. At every point, at least 10 separate measurements of A-weighted equivalent sound pressure level (LAeq), maximum A-weighted sound pressure level (LAmax) and C-weighted peak sound pressure level (LCpeak) were made. Noise recorded in the blast test area exceeded occupational exposure limits (OELs). Noise levels measured in buildings did not exceed OELs. Results of the survey showed that for 62% of respondents, impulse noise causes difficulties in performing work. The most commonly reported symptoms include headaches, nervousness and irritability.

Development and validation of a hybrid method for predicting helicopter rotor impulsive noise

Prediction of helicopter rotor impulsive noise is practically a very challenging task. This paper describes a hybrid method to predict rotor impulsive noise for both high-speed impulsive noise and blade–vortex interaction noise. The hybrid solver has been developed by combining the advantages of three different methods: (1) a computational fluid dynamics method based on Reynolds-averaged Navier–Stokes equations to account for the viscous and compressible effects near the blade; (2) a vorticity transport model to predict rotor wake system without artificial dissipation; and (3) an acoustic calculation method, based on Ffowcs-Williams Hawkings equation implemented to a permeable data surface. The developed hybrid solver is validated through available test data, for the cases of UH-1H model rotor, AH-1 Operational Loads Survey rotor, and Helishape 7A rotor. Peak sound pressure level of high-speed impulsive noise is accurately predicted with relative errors less than 7%. Additionally, acoustic waveform of blade–vortex interaction noise is well captured though it is sensitive to small changes in aerodynamic load. It is suggested that present hybrid method is versatile for the prediction of rotor impulsive noise with moderate computational cost.

The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

Objective: This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. Design: The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. Results: The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB LAeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. Conclusions: Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.

Parametric Prediction Model of Micro-Pressure Wave Outside the Tunnel

Based on the existing micro-pressure wave calculation model, the micro-pressure wave parametric prediction model is put forward. The micro-pressure wave is obtained by using the high order spectrum difference and perfectly matched layer boundary condition technologies. Then the function relationship between micro-pressure wave and spatial distance is discussed. The relevant parameters of the model are got at last .The results are compared with the experimental results. Conclusions are drawn as follows: The peak sound pressure of the micro-pressure wave is proportional to the tunnel axial distance r-0.87, r-0.86, r-0.85, r-0.83 at 200km/h, 250km/h, 300km/h and 350km/h speed, respectively. Comparing the computing results with the experimental results shows the model is of high precision.

Prevention of Noise-Induced Hearing Loss from Recreational Firearms.

In the United States and other parts of the world, recreational firearm shooting is a popular sport that puts the hearing of the shooter at risk. Peak sound pressure levels (SPLs) from firearms range from ∼140 to 175 dB. The majority of recreational firearms (excluding small-caliber 0.17 and 0.22 rifles and air rifles) generate between 150 and 165 dB peak SPLs. High-intensity impulse sounds will permanently damage delicate cochlear structures, and thus individuals who shoot firearms are at a higher risk of bilateral, high-frequency, noise-induced hearing loss (NIHL) than peer groups who do not shoot. In this article, we describe several factors that influence the risk of NIHL including the use of a muzzle brake, the number of shots fired, the distance between shooters, the shooting environment, the choice of ammunition, the use of a suppressor, and hearing protection fit and use. Prevention strategies that address these factors and recommendations for specialized hearing protectors designed for shooting sports are offered. Partnerships are needed between the hearing health community, shooting sport groups, and wildlife conservation organizations to develop and disseminate accurate information and promote organizational resources that support hearing loss prevention efforts.

Sound pressures generated by exploding eggs

Manufacturers of microwave ovens caution people to avoid re-heating certain food products because the rapid heating process can pose a danger to the user. Examples of such products are potatoes and eggs. Heating a potato in a microwave can generate steam under pressure. The internal steam pressure induces high tensile stresses in the potato skin, sometimes leading to its sudden (and unpredictable) bursting. A re-heated hard-boiled egg can also explode unpredictably but its bursting mechanism works differently than the potato. It is now believed that the egg yolk develops many small pockets of superheated water, leading to an increasingly unstable condition. When the egg yolk is disturbed by an internal or external stimulus, the pockets spontaneously boil, thereby releasing considerable energy (i.e., an explosion). An acoustical investigation was conducted using nearly 100 eggs that were re-heated under controlled conditions in a calibrated microwave oven. About a third of the re-heated, boiled eggs exploded outside the oven. For those eggs that did explode, their peak sound pressure levels ranged from 86 up to 133 decibels at a distance of 300 mm. The paper will describe the test protocols and discuss the results.

Effect of boundary layer trip on reduction of jet noise in over-expanded nozzle flow

A flow resonance accompanied by the emission of acoustic tones occurs in an over-expanded convergent-divergent (C-D) nozzle when operated at comparatively low pressure ratios. This phenomenon is distinguished from conventional screech tones and is referred to as “transonic tones”. In contrast to screech tones, the peak resonant frequency for transonic tones increases with pressure ratio; the peak sound pressure level exceeds 110 dB. In this study, we investigated the basic characteristics of transonic resonance and tones using a circular C-D nozzle in an anechoic room. The effects of the boundary layer trip were also evaluated using a tripping wire for the suppressing transonic resonance and tones. The results of acoustic measurements show that several predominant peaks correspond to transonic tones. However, the boundary layer trip inside the nozzle effectively eliminated these tones and suppressed the unsteadiness of the flow inside the nozzle.

Space vector based random pwm algorithms for acoustic noise and harmonics reduction for voltage source inverter fed ac drive

Conventional Space vector based Pulse Width Modulation (PWM) method is superior to Sinusoidal PWM technique in terms of its better DC bus utilization as well as harmonic reduction. But it doesn’t give solution to reduce acoustic noise which is more annoyance to the driver and the passenger or the human beings in certain applications such as electric propulsion or accessory drives. This paper presents space vector based random PWM techniques - a solution to reduce the acoustic noise as well spread spectrum resulting in low harmonic distortion as suppression of peak sound pressure levels. The techniques employed for a VSI fed Induction motor drive are 1) Random Zero vector PWM 2) Dual Zero Random PWM and 3) Variable Delay Random PWM. The spectrum plots of stator current demonstrate the effectiveness of the proposed PWM techniques. The feasibility of the proposed PWM techniques has been confirmed in terms of acoustical noise and harmonic distortion is presented in this paper.

Noise impact assessment on Indo-Pacific Humpback Dolphin in the habitat of the East Taiwan Strait during the first two pile driving activities of demonstration offshore wind farm

Foundation piles of the first two wind turbines were driven off the coast of Miaoli, Taiwan in 2016. However, that area is also the habitat of the critically endangered Eastern Taiwan Strait (ETS) population of Indo-Pacific humpback dolphin (Sousa chinensis). To assess potential noise effects from pile driving on the humpback dolphins, we collected underwater noise data during the construction and found that the sound pressure level (Lrms) at 750m was less than 180dB re 1μPa and the peak sound pressure (Lpk, flat) was less than 190 dB re 1μPa. We also presented recommendations of noise and marine mammal monitoring for future pile driving activities. It includes an exclusion zone of radius 750m from the piling location and the peak sound pressure (Lpk, flat) not to exceed 190~220 dB re 1μPa at 750 m distance, and an observation zone extends to 1500m radius where both marine mammal observers and passive acoustic monitoring are posted. [This work was sponsored by Ministry of Science and Technology of Taiwan (105-3113-E-002 -002 -CC2), Taiwan Bureau of Energy and Industrial technology Research Institution (05HZT56002), and U.S. Marine Mammal Commission’s Research and Conservation Grant.]

Noise reduction of pile driving and unexploded ordinance detonations at offshore wind farm installation sites

Pile driving noise during the installation of monopile foundations for offshore wind farms can produce very high noise levels, and strict regulations on this underwater noise exist around the world. In addition, the controlled detonation of unexploded ordinance (UXO) at offshore wind farm installation sites in European waters is an additional challenge and reduction of this noise is a major challenge. This paper discusses a tunable acoustic resonance-based underwater noise abatement system for use on marine pile driving, controlled UXO detonations, and other applications. The system consists of arrays of underwater air-filled resonators, which surround the noise source and are tuned to optimally attenuate noise in a frequency band of interest. System demonstrations that were conducted at two offshore wind farm sites in the North Sea will be discussed, in which peak sound pressure level reduction of nearly 40 dB was measured, and almost 20 dB sound exposure level reduction was measured. Laboratory testing on noise generated by a combustive sound source, used to simulate UXO noise, will also be discussed. The method of deploying these resonator arrays in a simple collapsible framework, operational advantages of this approach, and future projects using this technology will be shared.