Acoustic Noise Level Research Articles

Assessing modelled outdoor traffic-induced noise and air pollution around urban structures using the concept of landscape metrics

Acoustic noise and particle air pollution are among the most prominent environmental stressors in cities. They often result in cardiorespiratory diseases among urban dwellers and thus counteract important urban health targets. In cities, both stressors often occur simultaneously because their main source is urban traffic. Nevertheless, little is known about the combined exposure of acoustic noise and particle air pollution and their spatial distribution in urban residential areas. Filling this gap, landscape metrics were used to explain outdoor noise and PM10 patterns. Using Leipzig in central Germany as a case study, a highly statistical relationship exists between particle air pollution concentration and acoustic noise level that differs according to the urban structure type, as determined by landscape metrics. In conclusion, landscape metrics are very useful in predicting noise and PM10 exposure, together and in combination, for people in urban structures. Conversely, landscape metrics might serve as initial indicators of potential noise and air pollution in residential areas in cases in which no measured data are available, e.g., for planning purposes.

Combined Acquisition Technique (CAT) for Neuroimaging of Multiple Sclerosis at Low Specific Absorption Rates (SAR)

PurposeTo compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety. SAR limits restrict high-field MRI applications, in particular.Material and MethodsThe study was approved by the local Medical Ethics Committee. Written informed consent was obtained from all participants. T2- and PD-weighted brain images of n = 40 Multiple Sclerosis (MS) patients were acquired by CAT and TSE at 3 Tesla. Lesions were recorded by two blinded, board-certificated neuroradiologists. Diagnostic equivalence of CAT and TSE to detect MS lesions was evaluated along with their SAR, sound pressure level (SPL) and sensations of acoustic noise, heating, vibration and peripheral nerve stimulation.ResultsEvery MS lesion revealed on TSE was detected by CAT according to both raters (Cohen’s kappa of within-rater/across-CAT/TSE lesion detection κCAT = 1.00, at an inter-rater lesion detection agreement of κLES = 0.82). CAT reduced the SAR burden significantly compared to TSE (p<0.001). Mean SAR differences between TSE and CAT were 29.0 (±5.7) % for the T2-contrast and 32.7 (±21.9) % for the PD-contrast (expressed as percentages of the effective SAR limit of 3.2 W/kg for head examinations). Average SPL of CAT was no louder than during TSE. Sensations of CAT- vs. TSE-induced heating, noise and scanning vibrations did not differ.ConclusionT2−/PD-CAT is diagnostically equivalent to TSE for MS lesion detection yet substantially reduces the RF exposure. Such SAR reduction facilitates high-field MRI applications at 3 Tesla or above and corresponding protocol standardizations but CAT can also be used to scan faster, at higher resolution or with more slices. According to our data, CAT is no more uncomfortable than TSE scanning.

Feasibility of Tracking Fish with Acoustic Transmitters in the Ice Harbor Dam Tailrace

The Juvenile Salmon Acoustic Telemetry System (JSATS) has been used at many dams but has never been deployed in the near-dam tailrace environment. The use of JSATS in the tailrace is of interest to fishery managers to evaluate downstream passage behavior of juvenile salmonids and dam approach behavior of upstream migrating adult salmon and lamprey. The acoustic noise level and detection range of JSATS were studied to determine the feasibility of deploying JSATS in the Ice Harbor Dam tailrace. The noise level measured from the powerhouse deck was less than 104 dB re 1 μPa except for the turbine outlet near the spillway, and 350 m downstream of the dam, the noise level was less than 106 dB. The measured noise levels would allow a theoretical detection range of 100 m to 350 m and 85 m to 320 m, respectively. Validation experiments showed that the detection range is 113 to 184 m using hydrophones deployed from the powerhouse deck and 148 m using hydrophones deployed 500 m downstream of the dam.

Noise control challenges for auscultation on medical evacuation helicopters

A stethoscope is the standard clinical tool used for auscultation. It amplifies chest sounds and enables diagnosis of both circulatory and respiratory systems. However, in many emergency transportation environments, ambient noise levels in excess of 90dB prevent successful auscultation. In this paper, data is collected in a U.S. Army Sikorsky UH-60 helicopter to analyze the inherent noise present during routine aeromedical transport. Data is gathered with a commercially available stethoscope retrofitted with an array of accelerometers and microphones. Peak acoustic noise levels are recorded in excess of 125dB and ambient vibration levels are measured to be near 0.5g RMS. The signal-to-noise ratio is much below 1 for the entire frequency range of interest in auscultation. It is shown using a combination of simulations and experimental data that existing active noise cancellation techniques using a reference microphone would be ineffective in this scenario. However, similar adaptive noise cancellation techniques using a reference accelerometer within the device would be significantly more effective at enabling auscultation.

Acoustic Noise Levels of Dental Equipments and Its Association with Fear and Annoyance Levels among Patients Attending Different Dental Clinic Setups in Jaipur, India.

Noise is a source of pervasive occupational hazard for practicing dentists and the patients. The sources of dental sounds by various dental equipments can pose as a potential hazard to hearing system and add to the annoyance levels of the patients. The aim of the study was to analyze the noise levels from various equipments and evaluate the effect of acoustic noise stimulus on dental fear and annoyance levels among patients attending different dental clinic setups in Jaipur, India. The sampling frame comprised of 180 patients, which included 90 patients attending 10 different private clinics and 90 patients attending a Dental College in Jaipur. The levels of Acoustic Noise Stimulus originating from different equipments were determined using a precision sound level meter/decibulometer. Dental fear among patients was measured using Dental Fear Scale (DFS). Statistical analysis was performed using chi square test and unpaired t-test. The mean background noise levels were found to be maximum in the pre-clinical setup/ laboratory areas (69.23+2.20). Females and the patients attending dental college setup encountered more fear on seeing the drill as compared to the patients attending private clinics (p<0.001). The sources of dental sounds can pose as a potential hazard to hearing system. It was analyzed that the environment in the clinics can directly have an effect on the fear and annoyance levels of patients. Hence it is necessary control the noise from various dental equipments to reduce the fear of patients from visiting a dental clinic.

Acoustic Noise Characterization of Space Vector Modulated Induction Motor Drives &amp;#x2013; An Experimental Approach

This paper presents an experimental procedure to determine the acoustic and vibration behavior of an inverter-fed induction motor based on measurements of the current spectrum, acoustic noise spectrum, overall noise in dB, and overall A-weighted noise in dBA. Measurements are carried out on space-vector modulated 8-hp and 3-hp induction motor drives over a range of carrier frequencies at different modulation frequencies. The experimental data help to distinguish between regions of high and low acoustic noise levels. The measurements also bring out the impact of carrier frequency on the acoustic noise. The sensitivity of the overall noise to carrier frequency is indicative of the relative dominance of the high-frequency electromagnetic noise over mechanical and aerodynamic components of noise. Based on the measured current and acoustic noise spectra, the ratio of dynamic deflection on the stator surface to the product of fundamental and harmonic current amplitudes is obtained at each operating point. The variation of this ratio of deflection to current product with carrier frequency indicates the resonant frequency clearly and also gives a measure of the amplification of vibration at frequencies close to the resonant frequency. This ratio is useful to predict the magnitude of acoustic noise corresponding to significant time-harmonic currents flowing in the stator winding.

Prototype development of underwater noise impact alert region prediction system

Offshore wind farms are the main project in western Taiwan. Since the underwater noise generated by piling poses a threat to the marine mammals, the issue of detrimental impact of noise on Sousa Chinensis is proposed. To avoid causing behavioral disturbance and injury from pile driving noise, Underwater Noise Impact Alert Region Prediction System (UNIARPS) was established to estimate the acoustic field at any depth and distance from piling source. The system can be illustrated as four components, environment databases, acoustic propagation model, source modeling, and noise level prediction. The ocean numerical model (TCONFS) generates time spatial dependent temperature profiles for water column variability, and geo-acoustic and bathymetry databases are imported as environmental inputs. Adiabatic mode theory is used to simulate the piling noise propagating in shallow water and the impulsive noise emanating from source is evaluated via finite element method. While the auditory threshold of cetacean set as criterion level, the system can demonstrate the modeling outputs and predict noise impact region, and these results are useful to prior planning on how to station the guarding boats in preventing dolphins entering the noise impact region. [The financial support provided by Bureau of Energy (Grant No.102-D0105) is gratefully acknowledged.]

A Simplified Modulation Strategy for Three-leg Voltage Source Inverter Fed Unsymmetrical Two-winding Induction Motor

This paper presents a simplified modulation strategy for the three-leg VSI fed twowinding induction motor. The strategy provides independent unbalanced voltage control for the main and auxiliary windings. This make the motor can be reversed rotation through the range of motor speed operation without limitation of voltage boost of the auxiliary winding. To study the advantages of the proposed drive, the experimental results such as voltage stresses, hysteresis band of the currents in locus, and also acoustic noise levels of the three-leg VSI are compared with those of the conventional two-leg topology. The results obviously show that the proposed technique achieves superior performance compared with the traditional scheme in case of dramatic increase of DC bus utilization, effective reduction of harmonic voltages content, and also significant enhancement of motor efficiency.

Examining Passive Flow Control using High Speed Shadowgraph Images in a Mach 1.5 Cavity Flow Field

A rectangular cavity with an L/D of 5.67 was tested at Mach 1.5 with a corresponding Reynolds number of 7.35 × 106/m. High speed shadowgraph movies were simultaneously sampled with dynamic pressure sensors at 75 kHz. Fourier analysis was performed on the high speed movies as well as the dynamic pressure data, which resulted in the determination of spatial and temporal characteristics of the dominant cavity frequencies in the flow field. Four passive flow control devices were tested, two of which have historically performed well at reducing the acoustic tones and broadband noise levels. The other two devices were less effective. Flow physics based on the detailed analysis of the high speed shadowgraphs and dynamic pressures sensors is presented.

Development and Evaluation of a Frequency Related Source Intensity Prediction Model of the Traffic Acoustic Noise

Two expressway sections including the south section of the beltway in Xian and the start section of the Xi'an-Lantian expressway were selected in this study. By monitoring the acoustic noise level at different frequencies and vehicle speeds, a frequency related source intensity prediction model of the traffic acoustic noise was developed. Experimental results show that the spectrum distribution varies greatly among different kind of vehicles. The noise source intensity produced by large vehicles mainly distribute in low-frequency area. Different from large vehicles, medium vehicles mainly produce medium or high frequency noise, especially when the vehicle's speed is above 60 km/h. When the vehicle's speed is below 60 km/h, the acoustic noise intensity produced by the medium vehicles is relatively weak. The accuracy of the source intensity prediction model is further proved by comparing the predicted data, determined data, and the data obtained in the literature under similar experimental conditions.

Two-parametric model of the spectrum of traffic noise in Tomsk

The technique of mapping urban noise is proposed on the basis of a two-parameter model of the acoustic noise spectrum. The acoustic noise and spatial distribution of the decay rate in Tomsk are mapped. The factors influencing the formation of the acoustic noise of traffic flow are described. Analysis is performed on how different operating modes of a vehicle’s internal combustion engine affect the background level of acoustic noise.

Research of the wind energy resource distribution in the Baltic region

Governmental support and the availability of large unpopulated areas on the coasts of the Baltic countries make attractive the use of these lands for siting large wind power plants (WPP). Studies in the area of wind energy resource distribution are carried out by the IPE with collaboration with the VeU. The observations of wind speed were made using the measuring complex NRG LOGGER 9200 Symphonie. The results of long-term observations on the wind energy density fluctuations at heights of 10–60 m in the area on the Baltic Sea coast of Latvia are presented in the form of tables, bar charts and graphs. The wind speed distribution is analysed. The coefficients of approximating functions for two areas of different terrain types have been calculated, and extrapolation results for the distribution curves of wind speed and energy density obtained. The acoustic noise level distribution around a planned WPP has been modelled.

Investigation of Acoustic Emission Caused by Filtration of an Air Flow through a Porous Medium

We study characteristics of acoustic emission caused by an air flow filtered through samples of solid porous pumice either partially filled with glycerin or dry. Some peculiarities of the laboratory setup and the performed experiments are described. Samples of different porosity and several values of the air pressure drop are tested. Physical reasons for the difference in acoustical emission spectra of samples of different porosity and in the relaxation times of the acoustic emission level caused by different porosity and fluid saturation are discussed. It is proposed to use the phenomenon of acoustic emission for detecting the fluid trapped in the pores of cores. The existing results based on the borehole field experiments are rough. The frequency range of signals recorded in these experiments is less than 5 kHz (up to 10 kHz). It is shown by our laboratory measurements that the required frequency band should be up to 50 - 60 kHz to reflect the features of the spectral composition of the acoustic emission in predicting the fluid content. The level of acoustic noise under field conditions is much higher, i.e., by 10 - 15 dB, than the noise achieved under laboratory conditions. Since the sensitivity of the recorders and the frequency range are considerably higher in our experiments, they are unique when applied to the solved problem.

Comparasion of prediction and measurement methods for sound insulation of lightweight partitions

It is important to know the sound insulation of partitions in order to be able to compare different constructions, calculate acoustic comfort in apartments or noise levels from outdoor sources such as road traffic, and find engineer optimum solutions to noise problems. The use of lightweight partitions as party walls between dwellings has become common because sound insulation requirements can be achieved with low overall surface weights. However, they need greater skill to design and construct, because the overall design is much more complex. It is also more difficult to predict and measure of sound transmission loss of lightweight partitions. There are various methods for predicting and measuring sound insulation of partitions and some of them will be described in this paper. Also, this paper presents a comparison of experimental results of the sound insulation of lightweight partitions with results obtained using different theoretical models for single homogenous panels and double panels with and without acoustic absorption in the cavity between the panels.

A Survey Analysis of Acoustic Trauma Related to MR Scans

The maximum limit of MR scanner noise and necessity of ear protection is defined in the IEC standard (IEC60601-2-33) of MR safety. With improvements in MR scanner performance, pulse sequences generating higher scanning noise have been used clinically. In this study, we investigated the factors significantly related to potential acoustic trauma cases (PATC) after MR examinations. To consider the future direction for MR safety and prevention of acoustic trauma, issues related to noise generation by MR scanners and acoustic trauma were systematically reviewed. A statistical analysis was performed using the data set from a survey (n=974) conducted in 2010 by the JSMRM safety committee. Hierarchical clustering analysis was used to extract the characteristics of the responders. With this classification as a reference, tests of independence and a residual analysis were employed to evaluate the factors related to PATC. No significant relationship was observed between the ear protection policy and the incidence or the reported outcome of PATC. While the two main clusters out of the six clusters extracted were associated with who reported the PATC and the confirmation process of the acoustic noise level of MR scanners, no cluster was associated with the frequency of PATC. An absence of PATC was significantly less reported (p=0.03) and more PATC was reported (p=0.04) by facilities with 3T MR systems. Although the total frequency was 4 cases, it should be noted that persistent hearing disturbances are a possible consequence of MR examinations. Neither the condition of the subjects nor the ear protection method was significantly related to the probability of PATC, suggesting the difficulty of predicting the potential risk of acoustic trauma. It is recommended to more systematically follow up PATC cases and clarify the risk factors.

Could image processing enable reduced acoustic noise during MRI scans?

AbstractMagnetic resonance imaging (MRI) coils are typically associated with high acoustic noise levels, which can pose problems for the patient and attending medical staff. Lorentz forces are generated by gradient coils, which are switched rapidly. The Lorentz forces displace the coil former and promote a pressure wave that is responsible for acoustic noise up to 130 dB. The high noise levels are an unavoidable consequence of requiring the gradient coils to generate highly homogeneous linear magnetic fields. However, in this article, we present a mathematical method for designing coils that achieve a drastic reduction in noise level by deliberately sacrificing field linearity. We show that useful images can nevertheless be obtained from the nonlinear fields associated with these quiet coils. Examples are given that demonstrate the robustness of the method. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 39B: 191–205, 2011

Acoustic resonant sensor for ultra high energy neutrino detection

The characterization of the cosmogenic neutrino flux would give insights into cosmological source evolution, source spectra and composition at injection, through the partial recovery of the degraded information carried by the ultra high energy cosmic rays. A suitable technique for the detection of these ultra high energy neutrinos relies on the observation of the coherent radio Cherenkov signature emitted by the interaction vertex shower. The detection of the concomitant acoustic pulse is further desirable in order to unambiguously demonstrate the origin of the radiation. Therefore, R&D activities around the design and construction of an acoustic sensor adequate for the detection of neutrino-induced acoustic pulses in ice, coincident with radio Cherenkov signals, down to an energy threshold of about E ν ≈ 10 18 eV, were undertaken. The description of this new digital multi-channel sensor and its performance are presented in this paper. Moreover, the utilization of this sensor as a tool of choice for determining very low environmental acoustic noise levels is discussed.

Effect of load-generated transformer noise in a substation

The objective of the project was to assess the severity of load-generated transformer noise in neighborhoods of the substation by performing the acoustic noise level dBA measurements around power transformer at different loads and distances. The results showed that 125 Hz frequency noise becomes dominant at ≈80% of the full-load with fans out of operation and varies linearly with the load. The regression equations between MVA loading and the average sound pressure level at 2 and 70 m away from the transformer were established. The increase in the average sound pressure level from no-load to full-load was found to be ≈3.60 dBA. When the fans were on, the increase in the average sound pressure level due to the load was negligible, as the fans' noise was the dominant noise source. It was determined if the fans operate in night, it may cause some complaints from people living near the substation. Copyright © 2010 John Wiley & Sons, Ltd.

Tikhonov regularization approach for acoustic noise reduction in an asymmetric, self‐shielded MRI gradient coil

AbstractWe consider a mathematical method for minimizing the acoustic noise of self‐shielded magnetic resonance imaging gradient coils designed to produce an asymmetrically located target field within a cylindrical chamber. During imaging, the gradient coils are being constantly switched on and off, subjecting the coil to large Lorentz forces. These forces cause the chamber to buckle, creating a pressure wave in the bore which manifests as acoustic noise at sound pressure levels up to about 130 dB. In this model, the linearized coil deflection, the pressure wave, and the acoustic noise level inside the chamber are all solved for in closed form. The closed‐form nature of the solutions permits simple insights into the behavior of the system. Although reductions of only 0.6 dB were achieved, the method allows some flexibility if other design sacrifices are made. The gradient coil switching frequency plays a major role in the magnitude of the acoustic noise and is studied here. Results are presented for two basic switching functions for shielded gradient coils. Unshielded gradient coils, other switching functions, and other penalty functions can be easily accommodated using the method presented. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 167–179, 2010

The Strategy of Designing Seek Current Profile to Reduce Acoustic Noise and Residual Vibrations

The acoustic noise level of hard disk drive (HDD) is becoming more important for HDD in home entertainment applications. The residual vibration is a significant factor not only to the acoustic problem but also to the performance of HDD. In this work, a pseudo sinusoidal wave is used to design a smooth current profile to reduce acoustic noise. With consideration of current saturation limit and the maximum seeking velocity limit, a systematic method is proposed to design parameters such as the period of sinusoidal wave, the saturation time and the coasting time such that the residual vibrations are significantly reduced.