Airborne Noise Research Articles

Acoustic Assessment of Multiscale Porous Lime-Cement Mortars

Noise pollution is an issue of high concern in urban environments and current standards and regulations trend to increase acoustic insulation requirements concerning airborne noise control. The design and development of novel building materials with enhanced acoustic performance is an efficient solution to mitigate this problem. Their application as renders and plasters can improve the acoustic conditions of existing and brand-new buildings. This paper reports the acoustic performance of eleven multiscale porous lime-cement mortars (MP-LCM) with two types of fibers (cellulose and polypropylene), gap-graded sand, and three lightweight aggregates (expanded clay, perlite, and vermiculite). Gap-graded sand was replaced by 25 and 50% of lightweight aggregates. A volume of 1.5% and 3% of cellulose fibers were added. The experimental study involved a physical characterization of properties related to mortar porous microstructure, such as apparent density, open porosity accessible to water, capillarity absorption, and water vapor permeability. Mechanical properties, such as Young's modulus, compressibility modulus, and Poisson's ratio were evaluated with ultrasonic pulse transmission tests. Acoustic properties, such as acoustic absorption coefficient and global index of airborne noise transmission, were measured using reduced-scale laboratory tests. The influence of mortar composition and the effects of mass, homogeneity, and stiffness on acoustic properties was assessed. Mortars with lower density, lower vapor permeability, larger open porosity, and higher Young's and compressibility modulus showed an increase in sound insulation. The incorporation of lightweight aggregates increased sound insulation by up to 38% compared to the gap-graded sand reference mixture. Fibers slightly improved sound insulation, although a small fraction of cellulose fibers can quadruplicate noise absorption. The roughness of the exposed surface also affected sound transmission loss. A semi-quantitative multiscale model for acoustic performance, considering paste thickness, active void size, and connectivity of paste pores as key parameters, was proposed. It was observed that MP-LCM with enhanced sound insulation, slightly reduced sound absorption.

A Hybrid Multistep Procedure for the Vibroacoustic Simulation of Noise Emission from Wind Turbines

This paper proposes an efficient hybrid analytical-computational approach for the simulation of mechanical vibrations and sound radiation in wind turbine drive trains.The computational procedure encompasses the detailed modeling of vibrational sources and structural sound paths as well as the major panels of airborne noise radiation. The angle-varying mesh stiffness is obtained from a series of quasi-static finite element simulations. A novel procedure is proposed to obtain the time-varying mesh stiffness at fluctuating speed. The varying mesh stiffness is introduced as a parametric excitation in an analytical gear model, and the Fourier-transformed results are used as vibrational sources in a finite-element-based harmonic response analysis of the drive train. The present paper focuses on the modeling of gear contact and gearbox vibrations. The models and procedures are outlined, and computational results are compared to physical measurements on a 2.5 MW wind turbine. The results are in good qualitative agreement at tonal frequencies. This is particularly the case at fluctuating speed, where both the simulation and the measurement show the characteristic effect of frequency modulation. The computational procedure has been expanded to the whole drive train and is effectively applied in the conception and evaluation of design measures for the reduction of tonal amplitudes.

Effect of sound insulation on noise reduction in an agricultural tractor cab

Tractor cab interior noise is a risk factor that degrades operators’ work performance and threatens their health; therefore, the noise must be reduced to ensure farmworkers’ safety and efficiency. Cab interior noise can be classified as structure-borne noise and air-borne noise. Structure-borne noise has been extensively studied. However, although air-borne noise greatly contributes to cab interior noise, detailed frequency-domain analyses have not been performed. In this study, the components of cab interior noise were identified in the frequency domain through an order analysis, which helped improve the sound insulation of the cab and reduce the effects of air-borne noise. A test was performed while driving a tractor on a chassis dynamometer in a semi-anechoic chamber for reproducible measurement and evaluation. The A-weighted sound pressure was transformed by a fast Fourier transform algorithm, and its order was tracked by the engine speed signal. In addition, a direct path was identified by acoustic images using a sound camera. The contributions of major noise sources were identified through an order analysis. We proved that air-borne noise significantly contributes to the interior noise of tractor cabs and that improvement of the cab sound insulation is an effective noise-reduction technique.

Design of a hydro sound intensity probe for quantification and localization of acoustic sources — Applied to a hubless marine rim drive

The reduction of hydro noise emission by ship propulsion systems is of importance since background noise levels in the oceans have increased by 21 dB in the past decades. Thus, the acoustical improvement of ship propulsion systems is a necessary and challenging task. It involves not only the ship propeller but also the components of the entire drive train like diesel or electrical engines, electrical inverters as well as gearboxes. Acoustical measurement systems for the quantification and localization of noise sources are essential for any kind of optimization and are state of the art in the airborne noise field. This is not the case in the hydro acoustic field and measurements are mostly limited to the recording of the hydro sound pressure using single hydrophones. The objective of this paper is the presentation of a new three dimensional hydro sound intensity probe capable of acoustical sound power quantification and noise source localization. The probe can be used for the determination of the hydro sound pressure, the 3D sound intensity vector and the sound power. Furthermore, the probe can be utilized for hydro sound source localization purposes using beamforming methods based on virtual acoustical arrays. The developed probe was used for hydro acoustic investigations of a full scale marine rim drive during a measurement campaign in the river Warnow in Rostock, Germany. The results indicate the different hydro sound generating mechanism of the rim drive.

Experimental Study of an Engineering Prediction Approach for Shipboard Cabin Noise

At present, the prediction of shipboard cabin noise is mainly obtained by simulation calculation using FEM, BEM or SEA. These methods are not convenient for rapid engineering prediction. By making a test platform of shipboard cabin noise prediction, we make an experimental study of a simplified engineering prediction approach for shipboard cabin noise based on Source-Path-Receiver system approach. The experimental study shows that this approach is feasible and valid when applied to predict air borne noise level in a sound source shipboard cabin.

Comparative studies on air borne noise and flow induced noise of a double suction centrifugal pump

The Flow Induced Noise (FIN) of a centrifugal pump directly affects the Air Borne Noise (ABN) of the same. But, the information regarding focus on ABN of a pump in relation to its FIN is very scarce. This paper presents the comparative study performed on the ABN and FIN of a double suction centrifugal pump. Experiments were conducted on a double suction pump of specific speed (ns) 19 to measure ABN. Free field noise measurements for ABN, aligning with the industrial standards were conducted using FFT analyzer for 3 speeds such as 990 rpm, 1200 rpm, and 1450 rpm. For each speed, the normalized flow ratio (QQn) covered were 0.4, 0.6, 0.8, 1 and 1.2 for measurements. For FIN prediction, transient numerical simulations were conducted for the same pump at 990 & 1450 rpm. Detached Eddy Simulation (DES) and Fast Fourier Transform (FFT) were used to understand the noise generation at the blade passing frequency (BPF) and the variation of discharge flow recirculation in impeller outlet at different speeds. Moreover, for FIN, a generalized quadratic equation with parabolic form is derived for a speed of 1450 rpm. Also, the derived equation at 1450 rpm has been used to develop a relation to predict the FIN at other speeds. Further, the derived FIN relations are used to predict the ABN at different speeds by expressing ABN in terms of FIN for particular speed. Overall, the developed FIN function is useful in predicting the FIN in dB at BPF of a double suction pump for impeller Reynolds number and specific speeds in ranges 2.7∗106≤Re≤8.2∗106 and 19≤ns≤52 respectively with error ranging from +7.5 % to −7.5 %. Empirical correlation is also developed to predict the FIN with error ranging from +6 % to −6%, where FIN was the function of structural (geometrical) parameters and hydraulic (fluid and flow) parameters of the pump. Also, the methodology is used to predict ABN at BPF from the calculated FIN for that particular speed with error ranging from −2.5 % to +2.5 %.

Multi-Faceted Analysis of Airborne Noise Impact in the Port of Split (I)

This multi-faceted study deals with the analysis of the impact of noise emissions from the cargo terminals in the port of Split, especially in view of the proximity to inhabited areas and the growing number of registered issues and concerns due to its particular location. Three objectives are pursued: the identification of noise sources in the port area, an overview of strategic noise maps and simulations of noise propagation from ships at berth, and the calculation of external costs of noise pollution. In the first, preliminary part of the research project, by conducting a monitoring campaign and analyzing the data on strategic noise maps of the studied area, road and rail traffic were estimated as the main noise sources causing excessive noise emissions for all assessment periods: day (Lday), evening (Levening), night (Lnight), and day-evening-night (Lden) period. Industrial resources, including ports, were identified as having marginal noise emission levels. The calculation of the total external noise costs results in a damage value of €190,166/year, considering the number of affected inhabitants and the assumed noise levels. As an added value of the study, the simulation results of two scenarios have determined the noise propagation of a ship at berth and highlighted the zone of excessive noise under certain conditions. The results of this study should encourage the relevant institutions to strengthen noise management plans and introduce effective and continuous monitoring of noise emissions in critical areas.

Overview of technical certificate program from the Institute of Noise Control Engineering

Standards are often misunderstood by even the most seasoned of acoustic professionals, let alone new technicians and engineers in the field, as they are often very complicated, written in piecemeal fashion by committees and are updated often. Some of the standards even conflict with one another. To help alleviate this problem, the Institute of Noise Control Engineering (INCE) is developing two technical certificate programs designed to educate and evaluate participants on the details of common standards used in the noise control industry. Each program will contain education, testing, and continuing education on ASTM International and Acoustics Society of America (ASA) standards. The first program will cover general acoustical measurements and environmental noise measurements. The second program will cover field testing of building acoustics, including airborne and impact noise insulation as described in ASTM E336, ASTM E1007, and associated standards. The courses are currently being developed with a target launch date of early 2023. Comparisons to similar programs that have been developed in other countries will be included. A business case will be made on how these programs will save noise control engineering firms time and money in training new staff.

The use and application of pressure-based acoustical metrics adopted within the International Building Code

The 2021 International Building Code (IBC) includes pressure-based metrics as the field acoustical standards for conformance. These include normalized noise isolation class (NNIC) and normalized impact sound rating (NISR) (ASTM E336-20 and ASTM E1007-21, ASTM International; 2021 International Building Code, Section 1206, International Code Council). Pressure-based metrics were intentionally used in lieu of power based metrics. The authors here address why pressure-based metrics are more appropriate than power-based metrics for field verification, following from previous work [LoVerde and Dong, “Field impact insulation testing: Inadequacy of existing normalization methods and proposal for new ratings analogous to those for airborne noise reduction,” JASA 118, 638 (2005); LoVerde, Dong, and Rawlings, “Sound pressure-based ratings for evaluation of in situ sound isolation,” Denver (2022)]. Furthermore, the authors shall present the application of these metrics as they pertain to Building Code requirements. This paper will include and present code interpretation as it relates to sample size and evaluation for compliance as it relates to Building Code and sampling of systems for acceptance.

Airborne Sound Power Levels and Spectra of Noise Sources in Port Areas.

Airborne port noise has historically suffered from a lack of regulatory assessment compared to other transport infrastructures. This has led to several complaints from citizens living in the urban areas surrounding ports, which is a very common situation, especially in countries facing the Mediterranean sea. Only in relatively recent years has an effort been made to improve this situation, which has resulted in a call for and financing of numerous international cooperation research projects, within the framework of programs such as EU FP7, H2020, ENPI-CBC MED, LIFE, and INTERREG. These projects dealt with issues and aspects of port noise, which is an intrinsically tangled problem, since several authorities and companies operate within the borders of ports, and several different noise sources are present at the same time. In addition, ship classification societies have recently recognized the problem and nowadays are developing procedures and voluntary notations to assess the airborne noise emission from marine vessels. The present work summarizes the recent results of research regarding port noise sources in order to provide a comprehensive database of sources that can be easily used, for example, as an input to the noise mapping phase, and can subsequently prevent citizens’ exposure to noise.

Development of a Novel Cavitation Monitoring System for Hydro Turbines Based on Machine Learning Algorithms

Operating hydro turbines in off-design conditions increases the risk of cavitation occurrence, which in turn, leads to numerous problems such as performance degradations, structural vibrations, and most importantly, mechanical damage due to erosion. It is therefore crucial to develop a monitoring system that detects the occurrence and severity of cavitation in real time. For this purpose, a cavitation detection methodology has been developed that is based on the analysis of acoustic emissions of a turbine with machine learning algorithms. In this method, a conventional microphone is used to record the airborne noise emitted from a turbine under different working conditions, and then, a supervised learning algorithm is trained to classify the recorded noise signals into cavitating and non-cavitating categories. The detection system was developed based on laboratory tests and was validated in Ernen hydropower plant located in Canton of Wallis in southeast of Switzerland. This power plant consists of two identical double-flux Francis turbines each having a maximum power of 16 MW and a net head of 270 mWC. The preliminary results obtained from a two-day experimental campaign in the Ernen powerplant are very promising in terms of cavitation detection with a classification accuracy of more than 90 %. The system could be implemented either for real-time monitoring of cavitation occurrence allowing the operators to avoid such a condition or as a post processing tool to evaluate the number of hours a turbine has worked under severe conditions. Work is still ongoing to deploy more complex learning algorithms for this task to minimize expert intervention and/or interpretation during the setup process.

Active Air-borne noise suppression for pipe break early warning in smart water networks

Acoustic alarm systems using IoT (internet of things) smart sensors (e.g. accelerometers) for leak detection in water networks are rapidly gaining popularity. One of the issues for such systems is the false alarms which often occur as a result of signal contamination by environmental noise, especially by air-borne noise resulting in additional vibration. This research proposes a dual-sensor concept for active air-borne noise suppression in accelerometer signals that are excited by both fluid-borne noise (including the leak signal) and air-borne environmental noise. In the proposed arrangement, a microphone adjacent to the measurement station is used to measure the air-borne noise simultaneously to the accelerometer mounted to the pipe. Three methods have been applied in this paper: 1) using the non-coherent output power (NCOP) between the accelerometer and microphone signals; 2) using a Wiener filter; and 3) using adaptive least mean square (LMS) filters together with adaptive infinite impulse response (IIR) filters. Field tests have been carried out on a cast iron water main embedded in a water distribution system. A speaker was used to generate air-borne noise around the measurement station and to excite unwanted vibrations in the pipe. The results show that all three methods can effectively suppress air-borne noise from the accelerometer signals mounted to the pipe. A noise reduction of 30 dB can be achieved using the NCOP in the frequency domain or using the Wiener filter in the time domain. The adaptive filters are relatively less effective and the effectiveness reduces with the increase in bandwidth of the air-borne noise. However, the adaptive filters have the potential to be applied online for real-time processing.

Experimental study on airborne sound insulation performance of lightweight double leaf panels

To create a healthy and comfortable indoor environment, higher requirements are put forward for the airborne sound insulation performance of buildings. The control of airborne noise transmission is a key measure to improve the airborne sound insulation performance of buildings. In this study, the airborne sound insulation performance of the lightweight double leaf wall was studied, and the influence of stud type, stud spacing, cavity filling (type and thickness of filling materials), panel layers (type, layer number, thickness and mass) on the airborne sound insulation performance of the lightweight wall was emphatically analyzed. The test results show that the airborne sound insulation performance of the lightweight double leaf wall can be improved by the following five measures: (1) increasing the stud spacing; (2) expanding the size of the independent panel; (3) using stone wool or glass wool as the filling materials; (4) increasing the number of panel layers or panel mass; and (5) reducing the structural connection.

A full-textile triboelectric nanogenerator with multisource energy harvesting capability

This study develops a full-textile triboelectric nanogenerator to harvest energy from multiple sources, such as sound, human motion, and wind, individually. The textile device consists of three layers, an elastic electrically conductive fabric knitted by silicone-coated yarn as the negative component and electrode, a commercial silk fabric as the positive component, and a conductive fabric as the second electrode. Under the mechanical impact (force ∼50 N, frequency 3 Hz), the device can generate 888.08 ± 4.75 V peak-to-valley voltage, 2.01 ± 0.50 μA short-circuit current, and 138.55 mW/m2 maximum instantaneous power density. It can also convert low-frequency sound (e.g., 75 Hz) into 174.66 ± 2.59 V peak-to-valley voltage (short-circuit current 6.62 ± 0.13 μA, maximum instantaneous power density 19.4 mW/m2). We also used the forced vibration analysis and the intrinsic output characteristics to model the acoustoelectric conversion. The modeling showed good agreement with the experiment results. We further demonstrated the ability to harvest energy from multisource individually, such as airborne noise generated by a working machine, human motion, and wind. The electrical power generated can run commercial electronic devices (e.g., 37 LEDs) or accumulate in a capacitor. In addition, the device has high air permeability and good softness. It may be useful for developing wearable energy generators for various high-tech applications.

Quantitative comparisons of resilient channel designs in walls and ceilings

Resilient channel is common within lightweight construction to improve the airborne and impact noise isolation of wall and floor-ceiling assemblies. The authors have previously presented results from systematic studies of resilient channels in wood stud wall assemblies (Internoise 2009; International Congress on Acoustics 2010) and wood-joist floor assemblies (International Congress on Sound and Vibration 2015) in which the effect of brand and model of resilient channel was compared in various assemblies. These studies documented the clear and significant acoustical performance differences between makes and models of channel that would have been considered equivalent before the release of this work. Additional comparative studies have been performed adding to the data previously presented. Acoustical performance is compared and conclusions about products are presented.

The application of tuned mass dampers to the Tire Pavement Test Apparatus to minimize the impact of rig resonance

The 'Tire Pavement Test Apparatus (TPTA)' at Purdue University is a device that was originally developed to study a tire's air-borne noise radiation in the frequency range 300 Hz to 2 kHz. However, in recent years, the device has mainly been used to quantify a tire's contribution to structure-borne noise by measuring the force and acceleration at the hub. Hence, the frequency range of interest has shifted to frequencies below 300 Hz. By comparing measurements and FE simulations, undesired vibration was observed around 160 Hz in the measurement data. It was speculated that the rig supporting the tire exhibits resonant vibration in a frequency range that hinders the measurement of tire force in that range. To identify the cause and mechanism of the rig resonance, Experimental Modal Analysis (EMA) was performed. In addition, to mitigate the influence of rig resonance, tuned mass dampers commonly used in vehicle suspension systems were applied to the connecting arms of the TPTA. Careful adjustments of their mass and stiffness were performed to maximize vibration suppression performance by matching the major natural frequency of the TPTA support arms. As a result, significant vibration attenuation could be achieved, which has made it possible to highlight the pure tire effects in the measurement data.

Effects of anthropogenic noise on anuran amphibians

ABSTRACT Anthropogenic noise is widespread in nature and has been shown to produce a plethora of impacts on wildlife. Sounds play a fundamental role in the lives of amphibians, with species relying on acoustic communication for social and reproductive behaviour, and thus noise can potentially interfere with these activities. Here, we provide a literature review on the effects of anthropogenic noise on anuran amphibians, based on 32 studies (63 species from 14 families) that document noise-driven changes in species behaviour, physiology and ecology caused by urbanisation, transportation and energy production. Experimental and observational studies found evidence that both airborne and seismic anthropogenic noise influence anuran calling activity, with consequences in mate selection, and induce physiological changes including increased stress, suppressed immune function and colouration changes. Negative noise effects in species abundance and attendance over the reproductive season were reported. Even though adaptations and behavioural adjustments enable species to respond to these noises, it is yet to be understood whether these changes alleviate the negative impacts. Furthermore, collaborative efforts between scientists, stakeholders and private/public institutions are imperative to create conservation guidelines and legal instruments to be implemented during urban expansion projects and mitigate the effects of noise pollution on amphibian anurans.

Application of acoustical control through building codes and regulatory requirements

The International Building Code (IBC) establishes minimum acoustical performance requirements for permanent and transient housing facilities. The lab parameters for acoustical performance within the IBC are useful during the design and permitting process but fail to provide code officials, builders, designers, and residents a method for evaluating the success of a completed building. The latest update to the IBC in 2021 establishes standards and metrics for use in evaluating post-construction code compliance to mutually protect all stakeholders (builders, code officials, occupants, municipalities, etc.) in housing facilities and reduces historic ambiguity in the code. Historically, the nature of the metrics and their ability to evaluate success has been limited (“Field impact insulation testing: Inadequacy of existing normalization methods and proposal for new ratings analogous to those for airborne noise reduction,” LoVerde/Dong, JASA, 2005). There is some historic precedent regarding the application and measurement requirement for field metrics (“Coping with uncertainties in the design and evaluation ofacoustical assemblies,” LoVerde/Dong, ASA Hong Kong, 2012). This presentation expands this conversation to examine regulatory requirements and discusses application of field verification of acoustical performance metrics.

Noise and vibration characteristics of sub-fractional horsepower single-phase BLDC drives

Single-phase brushless DC (BLDC) drives are a cost-effective alternative for three-phase sub-fractional horsepower drives in automotive auxiliary applications. Inherent features of single-phase permanent magnet machines, such as high cogging torque and torque ripple, can, however, make them more audible than their three-phase counterparts. As some of these auxiliary drives are close to the passengers, where even a small amount of noise can be disturbing, the investigation into noise sources is essential to further address this challenge. In this paper, the dominant noise and vibration characteristics of single-phase BLDC machines are investigated for two different stator structures, i.e., salient-pole and claw-pole, and compared. Magnetic force density waves and finite element (FE) analyses are performed to analyze the electromagnetic forces resulting from the open-circuit condition as well as different switching strategies in the load condition. Structural analyses show that due to the mechanical structure’s lower stiffness and natural frequencies in the audible range, the example case machine with the claw-pole stator develops higher structure- and air-borne noise than the machine with the salient-pole stator.

Assessment of the impact of anthropogenic airborne noise on the behaviour of Cape fur seals during the breeding season in Namibia

The increase of anthropogenic noise in the environment is a global phenomenon occurring in various types of habitats. Its impact on wildlife is therefore a growing research concern for many taxa. Due to their amphibious lifestyle, pinnipeds are exposed to anthropogenic noise in both aquatic and terrestrial environments. Using playback experiments, the present study assessed the impact of engine noise (car and boat) on the behaviour of Cape fur seals at the Pelican Point breeding colony, Namibia. Groups of individuals (35 groups, 369 individuals) were exposed either to low, medium or high amplitude levels of in-air noise, broadcast from the land or sea side. During the noise exposure, we found a significant increase in energetically costly behaviours: time spent awake, vigilance and locomotion for both females and pups. This was to the detriment of vital activities such as resting and nursing that decreased considerably (from 5.9 to 45% decrease) compared to the pre-playback phase without noise exposure. Animals' behavioural disturbance was limited to the 2-min period of noise exposure and we observed a rapid recovery when the noise ceased. We found stronger responses to boat motor noise broadcast from the sea side compared to car motor noise from land. Noise pollution from vehicles and boats in the vicinity of seal breeding colonies may threaten their health and the survival of their young by modifying their natural behaviour. It is therefore important to develop regulations for vehicles (speed, distance) in these areas with increasing tourist and recreational activities to limit disturbance.