Noise Transmission Research Articles

Loudspeaker-based sound reproduction for evaluating noise transmission into the car cabin

Virtual and laboratory-based design techniques can accelerate the development process over conventional prototype-and-field-test procedures. In car acoustics, the transmission of outside airborne noise into the cabin needs to be understood and managed. Here, we evaluate the accuracy of sound field recording and reproduction techniques for investigating the transmission of airborne noise into the driver's cabin of a car. Reference measurements of a real sound field, generated by a truck with idling engine to create a realistic scenario, were carried out in a semi-anechoic chamber. The reference sound field was recorded inside and around a test car. Additionally, a spatial recording of the reference sound field was carried out and used to reproduce the reference sound field over a loudspeaker array in a different, fully anechoic chamber, where the sound field was again measured inside and around the same test car. A comparison of the measured loudness inside the test car shows that this key parameter for sound quality could be reproduced rather faithfully over a loudspeaker array in a controlled testing facility.

Acoustical performance of horizontal-sliding-panel operable partition walls

Field measurements of airborne sound transmission loss were made on several operable partitions of the horizontal-sliding-panel type between conference rooms. Apparent Sound Transmission Class (ASTC) and Noise Isolation Class (NIC) ratings were computed. Very significant deviation of field-measured sound transmission ratings and manufacturers' Sound Transmission Class (STC) ratings were found. Clients were not satisfied by actual sound isolating performance. Transmission of voice was clearly audible. Some deficiencies of field conditions were found. Some deficiencies of partition installation were found. Modifications were made; acoustical performance did not change significantly.

Development of a Unique Experimental System Investigating Vibroacoustic Characteristic of Geared Transmission Systems

Gearboxes are widely using in industry, especially in automotive transmission systems. In actual technology level, different component-based quality control methods are applied for the quality control of powertrains but test systems, designed for assembled products, are based on subjective evaluations and scalar measurement of total sound pressure. These systems, especially operating in industrial conditions where background noise is effective, cannot meet the technical requirements. In this paper, the development of a unique experimental platform, capable of testing the powertrain under real operating conditions (torque, rotational speeds), and the experimental results are explained. In the system where transmission error, noise and vibration measurements are carried out, defective samples were determined according to statistical evaluations and errors were classified. In future studies, using the ability to calculate mechanical efficiency based on measurements, the correlation between deviations in mechanical efficiency and transmission error will be examined.

Overview of Robotic Reducer Testing Technology

As a high-performance precision reduction transmission equipment with large transmission ratio, high transmission efficiency, high transmission accuracy, stable transmission and low noise, reducer has been widely used in many fields such as industrial robots. The definition of the reducer is studied, the development history of the reducer is briefly introduced, and the classification and characteristics of the reducer are summarized, including traditional reducer, RV reducer, harmonic planetary reducer and cycloid reducer, A new generation of reducer and influencing factors such as transmission accuracy, transmission efficiency, backlash, torsional stiffness, noise, and assembly. The problem of precision reducer is analyzed, and finally the application and development trend of reducer are studied.

Impact of a tunnel on the TL of a vehicle floor in bare and trimmed conditions and investigation on the most suitable simplified geometry able to better represent such impact

NVH engineers are faced with the challenge of designing trim parts for vehicle interior and exterior, like inner dash insulators, carpets, underbody shields or engine encapsulations, which can be made with very different Bills of Materials (BOMs) including among others foams, felts or heavier layers. The measurables commonly used to rank various solutions are Transmission Loss (TL) and absorption. Depending on the numerical analysis method, different approaches may be considered for the evaluation of the TL of an automotive component. In particular, in Statistical Energy Analysis (SEA), automotive components are modeled as an assembly of panels having a simple shape, e.g. flat panels and/or panels with single or double curvature. Furthermore, in SEA the trim is normally modeled by means of the Transfer Matrix Method (TMM), which is essentially a 2-dimensional methodology. This paper intends to analyze in some depth the level of approximation that these practices bring with themselves, specifically in relation to the modelling of an automotive floor. More in detail, the aim of the paper is first to investigate what impact has the presence of the tunnel on the TL of a vehicle floor in bare and trimmed conditions and then to evaluate if the presence of the tunnel can be better modeled by using a semi-cylinder or three flat plates welded together in a trapezoidal shape, both shapes considered as a reasonable simplification of the actual geometry of a typical tunnel. The analysis is carried out at simulation level using FE. To investigate both air bone noise and structure borne noise transmission, two types of excitations are used: a diffuse acoustic pressure field applied to the entire floor surface and an imposed displacement applied to the edge of the floor surface. Furthermore, 3 different kind of trims are taken into consideration in order to analyze if and how the tunnel modeling strategy may influence the evaluation of the trim effectiveness.

Efficient prediction of construction equipment exterior and cabin interior noise over broad frequency range using novel SEA method

Statistical Energy Analysis (SEA) is commonly used for the prediction of interior cabin noise from construction equipment such as excavators, dump trucks, or graders. While traditional SEA method is computationally efficient and effective for the prediction of total radiated noise, it isn't suitable for prediction of sound diffraction around machinery and evaluation of spatial variations in sound field. As a result, prediction of cabin airborne interior noise transmission using SEA method typically requires experimental measurements in order to estimate incident sound field over the exterior boundary of the cab which makes it unsuitable for use in early stage design where test data isn't available. A novel SEA method that accounts for spatial gradients in the reverberant field has been developed and is introduced in this paper. It's usage for prediction of both exterior and cab interior noise over broad frequency range is demonstrated along with experimental validation for construction equipment under operating conditions.

Design of a metamaterial-based muffler for a target frequency range

This work proposes an acoustic metamaterial-based muffler that effectively blocks a transmission noise for a target frequency range. Since the acoustic metamaterial-based muffler consists of arrayed unit cells, its noise attenuation performance is strongly affected by the internal layout of the unit cell. The wave transmission characteristics of an acoustic metamaterial is explained by the effective bulk modulus and dispersion curve of an unit cell. Therefore, the internal layout of the unit cell should be optimally designed so that its band gap should include the target frequency range of a muffler. To the end, an acoustical size optimization problem is formulated to design a unit cell of the muffler and is solved for a given design requirement. The noise blocking frequency range of the unit cell is characterized by the bandgap in its dispersion curve during the optimization process. The wave transmission characteristics of the metamaterial muffler is validated experimentally.

Optimization of gear macro-geometry for reducing gear whine noise in agricultural tractor transmission

Agricultural tractors generate various noise sources, such as the engine, transmission, and hydraulic systems. In particular, tractors generate considerable transmission gear whine noises during operation, and such noises need to be reduced for the driver’s comfort. The gear whine noise level is related to peak-to-peak static transmission errors (PPSTEs), and the PPSTE can be minimized through the gear macro-geometry optimization method. Here, we optimized the gear macro-geometry of a 75-kW agricultural tractor transmission through a genetic algorithm (non-dominated sorting genetic algorithm III; NSGA-III) to minimize PPSTEs. The two gear pairs were optimized to maintain the gear mesh efficiency at similar levels and to minimize the PPSTE to less than 25 % of the existing gear specifications. To determine the improvement in noise, the noise levels were evaluated and compared using a 3-axis dynamometer tester. The overall noise level in the transmission operating range was found to reduce by 3.1 dBA, and all the noise levels of the gear harmonic components were reduced effectively.

Optimal design of noise reduction and shape modification for traction gears of EMU based on improved BP neural network

Under high-speed operating conditions, the noise caused by the vibration of the traction gear transmission system of the Electric Multiple Units (EMU) will distinctly reduce the comfort of passengers. Therefore, analyzing the dynamic characteristics of traction gears and reducing noise from the root cause through comprehensive modification of gear pairs have become a hot research topic. Taking the G301 traction gear transmission system of the CRH380A high-speed EMU as the research object and then using Romax software to establish a parametric modification model of the gear transmission system, through dynamics, modal and Noise Vibration Harshness (NVH) simulation analysis, the law of howling noise of gear pair changes with modification parameters is studied. In the small sample training environment, the noise prediction model is constructed based on the priority weighted Back Propagation (BP) neural network of small noise samples. Taking the minimum noise of high-speed EMU traction gear transmission as the optimization goal, the simulated annealing (SA) algorithm is introduced to solve the model, and the optimal combination of modification parameters and noise data is obtained. The results show that the prediction accuracy of the prediction model is as high as 98.9%, and it can realize noise prediction under any combination of modification parameters. The optimal modification parameter combination obtained by solving the model through the SA algorithm is imported into the traction gear transmission system model. The vibration acceleration level obtained by the simulation is 89.647 dB, and the amplitude of the vibration acceleration level is reduced by 25%. It is verified that this modification optimization design can effectively reduce the gear transmission.

Hierarchical Federated Learning for Hybrid Data Partitioning Across Multitype Sensors

Emerging hardware technology enables the utilization of a large number of multitype sensors with diverse sensing capabilities for data collection and the training of AI models. Each sensor collects partial data samples on a type-specific feature space, which results in hybrid data partitioning across the local datasets and brings challenges to developing a novel communication-efficient and scalable training algorithm. We propose a hierarchical federated learning framework for such hybrid data partitioning with a multitier-partitioned neural network architecture. Specifically, we adopt a primal-dual transform to decompose the training problem on both the sample and feature space. Then, a stochastic coordinate gradient descent ascent algorithm is implemented with intratype and intertype over-the-air aggregation for the update of the primal variables and dual variables, respectively. The incorporation of over-the-air aggregation for signal transmission naturally harnesses the channel perturbations and interference for lower communication complexity and preserved privacy. Despite the influence of transmission noise and channel distortion, convergence analysis is provided for general objective functions, which illustrates the robust training performance of the proposed algorithm with a theoretical guarantee.

Blind Recognition of Forward Error Correction Codes Based on a Depth Distribution Algorithm

Forward error correction codes (FEC) are one of the vital sections of modern communication systems; therefore, recognition of the coding type is an important issue in non-cooperative communication. At present, the recognition of FEC codes is mainly concentrated in the field of semi-blind identification with known types of codes. However, based on information asymmetry, the receiver cannot know the types of channel coding previously used in non-cooperative systems such as cognitive radio and remote sensing of communication. Therefore, it is important to recognize the error-correcting encoding type with no prior information. Although the traditional algorithm can also recognize the type of codes, it is only applicable to the case without errors, and its practicability is poor. In the paper, we propose a new method to identify the types of FEC codes based on depth distribution in non-cooperative communication. The proposed algorithm can effectively recognize linear block codes, convolutional codes, and Turbo codes under a low error probability level, and has a higher robustness to noise transmission environment. In addition, an improved matrix estimation algorithm based on Gaussian elimination was adopted in this paper, which effectively improves the parameter identification in a noisy environment. Finally, we used a general framework to unify all the reconstruction algorithms to simplify the complexity of the algorithm. The simulation results show that, compared with the traditional algorithm based on matrix rank, the proposed algorithm has a better anti-interference performance. The method proposed is simple and convenient for engineering and practical applications.

Measurements and modelling of dynamic stiffness of a railway vehicle primary suspension element and its use in a structure-borne noise transmission model

The noise inside railway vehicles is transmitted by both structure-borne and airborne paths and, although there are many sources, the rolling noise is often the most important. This paper focuses on the structure-borne transmission of rolling noise in a metro vehicle. Measurements are presented first of the vertical and lateral dynamic stiffness of a primary suspension element consisting of conical rubber/metal elements. Results are presented for various constant preloads over the frequency range 60–600 Hz. An analytical model of the suspension element is also developed, based on a mass-spring system and including wave motion within the rubber elements. The dynamic stiffness results are used in a finite element model of the running gear, consisting of the bogie frame, wheelsets and suspension elements. The excitation is provided by the combined wheel/rail roughness at the contact point. This model is used to calculate the blocked forces at the connection points between the secondary suspension elements and the car body. The blocked forces are combined with measured vibro-acoustic transfer functions from these mounting points to the vehicle interior to determine the structure-borne noise inside the vehicle. The proposed methodology is validated against measurements during operation in terms of acceleration levels, blocked forces and structure-borne noise levels inside the vehicle, showing reasonably good agreement. Including the dynamic stiffness for the primary suspension leads to improved agreement between 100 and 500 Hz compared with using a constant stiffness.

Achievable secrecy rate analysis in mmWave ad hoc networks with multi‐array antenna transmission and artificial noise

Achievable secrecy rate analysis in mmWave ad hoc networks with multi‐array antenna transmission and artificial noise

Floquet scattering of quadratic band-touching semimetals through a time-periodic potential well

We consider tunneling of quasiparticles through a rectangular quantum well, subject to periodic driving. The quasiparticles are the itinerant charges in two-dimensional and three-dimensional semimetals having a quadratic bandtouching (QBT) point in the Brillouin zone. To analyze the time-periodic Hamiltonian, we assume a non-adiabatic limit where the Floquet theorem is applicable. By deriving the Floquet scattering matrices, we chalk out the transmission and shot noise spectra of the QBT semimetals. The spectra show Fano resonances, which we identify with the (quasi)bound states of the systems.

A Dynamic Data Driven and Data Segregation Approach Image Restoration Using Neural Networks

Image restoration is the method of restoring an image to its original state by removing noise and blur. Image disclarity is crucial to maintain in a variety of cases, including photography, where motion blur is caused by camera shake when taking images, radar imaging, where the impact of image system reaction is removed, and so on. Image noise is an unwanted signal that appears in an image from a sensor, such as a power / energy signal, or from the atmosphere, such as rain or snow. Coding artefacts, resolution limitations, transmission noise, object motion, camera shake, or a confluence of events could cause image degradation. With the intention of separating HF and LF objects, image decomposition is used to decompose the distorted image into a pattern layer (High Frequency Component) and a framework layer (Low Frequency Component).

Stochastic optimal control analysis for the hepatitis B epidemic model

Mathematical formulation of a stochastic hepatitis B virus (HBV) model with the application of optimal control and randomly noise transmission has been focused in this paper. For the ease of understanding, the model is divided into four different classes of healthy or susceptible, acute infected, chronically infected and the class of the recovered population. All four cases have been perturbed by the white noise. By applying optimal control techniques, we investigated both deterministic and stochastic model for control. The approximate solution method of the deterministic model has been used in the numerical solution of the required stochastic model. The simulation of both models has been drawn against the given data and compared with each other.

A time-domain simulation method to predict insertion loss of a dissipative muffler with exhaust flow

Insertion loss (IL) is a more useful acoustic index than noise reduction and transmission loss for muffler design, but it is harder to predict because the prediction of IL requires knowing the characteristics of the muffler itself and the acoustic source. A muffler with porous material and complex meanflow makes the prediction even more challenging. Although calculation of noise reduction and transmission loss with the transient computational fluid dynamics (CFD) can naturally solve the flow–acoustic interaction problem, the published CFD methods have not been adopted to evaluate the IL of the dissipative muffler with exhaust flow. In this paper, a time-domain simulation method is developed to predict the IL of a complex engine muffler with porous material. The noise reduction and load impedance of the muffler were first calculated using a three-dimensional CFD model, in which the porous material was simulated by the governing equations modified with the material porosity and flow resistivity. The IL was then predicted from the noise reduction, the load impedance, and the engine source extracted from the measured exhaust noise. This developed method explores the application of the three-dimensional CFD method in calculating noise reduction, load impedance, and insertion loss of complex dissipative mufflers with exhaust flow.

Performance analysis of differential quadrature phase shift keying modulation schemes for a radio over fiber system

Radio over fiber systems have become one of the best options for backhaul due to their larger bandwidth, low propagation loss, and competitive cost. Advanced modulation formats play a key role in enhancing the performance of fiber optic communication systems by providing higher bit rates and less susceptibility to noise in long distance transmission. This paper presents a detailed analysis of differential quadrature phase shift keying modulation in a radio over fiber system at 60 GHz for 5G applications. The differential quadrature phase shift keying modulation is combined with two different advanced phase modulation formats, i.e., return-to-zero and carrier suppressed return-to-zero to provide higher spectral efficiency. The performance of the system has been investigated at 10 and 20 Gbps data rates for 10 to 50 km transmission lengths of different types of fiber. Overall, it has been observed that carrier suppressed return-to-zero differential quadrature phase shift keying is better as compared with return-to-zero differential quadrature phase shift keying at both 10 and 20 Gbps data rates up to a transmission length of 50 km.

Evaluating annoyance mitigation in the screening of train-induced noise and ground vibrations using a single-leaf traffic barrier

External sources such as traffic and construction work cause noise and vibration in nearby buildings, potentially annoying human residents. Today, almost every fifth European is harmfully affected by traffic noise and vibration. Wave barriers placed on or embedded within the soil between the source and the receiver can mitigate the transmission of ground vibration, and the airborne noise transmission can be reduced in a similar manner with a screen acting as a noise barrier. As a novel approach, the present work explores the efficiency of combining ground vibration and noise barriers into one. To this end, numerical experiments were performed by a semi–analytic finite-element method for ground vibration and the boundary-element method for sound propagation. This involved time-harmonic analyses carried out in order to study the performance of various configurations of barriers focusing on vertical barriers rigidly attached to the ground surface or embedded into the soil. Parametric analyses were conducted on the achieved vibration and noise mitigation with different types of ground-vibration barriers and noise barriers, respectively. The combined effect of the noise and ground vibration barriers were then assessed to investigate their potential for possibly reducing the negative impact on lineside residents. The aim of this work, though, is to highlight a metric, recently developed, which reports the probability on the number of residents who could be annoyed by intrusive railway noise and vibration. It is shown that a single structural-element can target a combined reduction of around 15% probability in annoyance to vibration levels combined with a 12 dB insertion loss which amounts to a 30% reduction in probability of annoyance due to railway traffic intrusive noise.

Passive noise control in buildings: An engineering case study of ducted systems

The most common noise sources in buildings are related to Heating, Ventilating and Air Conditioning (HVAC) systems, plumbing systems, electrical systems and exterior sources. Passive Noise Control (PNC) techniques in buildings have been implemented in several ways. The aim of this work is to analyses the use of silencer to attenuate the noise in the ducts that are part of the ventilation systems in buildings, internal combustion systems, fans, gas conduction systems, boilers, etc. The main objective of a silencer is to reduce the transmission of noise, disturbing as little as possible the circulation of gas or liquid. In the first instance, the silencers are classified as reactive and dissipative, depending on whether the attenuation of the noise is produced by reflective or dissipative mechanisms, respectively. In a reactive silencer, the losses occur essentially due to the reflections of the sound waves in impedance discontinuities, such as widening or narrowing of the tube. In dissipative silencers, the flow is in contact with a large surface of absorbent material. The attenuation of the noise is then produced by visco-thermal losses in the porous material. In this work, a practical issue will be addressed with a noise reduction of 19 dBA in 60 Hz. Practical application Noise is a current issue in residential areas that could lead to health problems for people. The origin of these noises within buildings is very diverse, one of them is produced by ducts. Appling the PNC technique in modern building construction would be a good prevention practice. For this reason, in this project a PNC system was carried out in the ducts of a residential building, which could be used as a praiseworthy solution, avoiding problems for the inhabitants of these spaces.