Papers by Keyword: Noise Control

Abstract: This study investigates the micro-drilling parameters to minimize perforation error in biodegradable and composite materials: Oil Palm Fiberboard (OPF), Polylactic Acid (PLA), and Printed Circuit Board (PCB). Two biodegradable materials (OPF and PLA) were compared to a standard industrial PCB for benchmarking. Micro perforated hole is important in sound absorber to provide better absorption performance. A Taguchi L27 design of experiments was used to assess the effects of support presence, post-penetration spin time, and spindle speed on dimensional accuracy. For OPF, the lowest average error (0.031 mm) was achieved using no support, a 1 second spin time, and a spindle speed of 6,000 RPM, minimizing tool deflection in the fibrous structure. PLA showed the best result (0.344 mm error) with no support, no spin time, and a moderate spindle speed of 8000 RPM, reducing thermal distortion. For PCB, a layered and brittle material, a sandwiched support setup, no spin time, and a high spindle speed of 10,000 RPM achieved the lowest error (0.040 mm), reducing delamination and chipping. Although the exact optimal settings were not found in the experimental runs, very similar combinations yielded the best accuracy in each material. These findings validate the inferred trends and emphasize the importance of spin time and spindle speed over support. The results provide actionable guidelines for high-precision fabrication of eco-friendly acoustic absorbers, contributing to environmentally sustainable material processing and enhanced indoor acoustic control.

Abstract: During the last few decades many researchers have been interested in acoustic wave propagation in artificial periodic composites known as sonic crystals. Sonic crystals have received renewed attention because they exhibit acoustic band gaps where there are only evanescent waves. Sonic crystals consist of a periodic array of scatterers embedded in a host medium. The host medium and/or scatterers are fluids. We investigate the band structure of acoustic waves propagating in a sustainable sonic crystal composed by miriti fibers and air, regarding square and triangular lattices. Miriti fibers are extracted from buriti palm petiole (Mauritia flexuosa Mart.), which is a typical specie that grows in Amazonian region. We also study the influence of miriti fiber cross section, i.e. circular, hollow circular, square and rotated square with a 45° angle of rotation with respect to x, y axes. Plane wave expansion method is used to solve the wave equation. Acoustic band gaps are observed for all miriti fiber cross sections and lattices. The best performances of the sustainable sonic crystal are for triangular lattice, regarding circular and rotated square miriti fiber cross sections, and for square lattice with circular miriti fiber cross section. We suggest that the sustainable sonic crystal should be feasible for noise management.

Abstract: This research focuses on the sound absorption coefficient of three different natural fibers reinforced epoxy composites. The natural fibers used are coconut coir, kenaf, and sugarcane bagasse. All of these fibers were mixed with epoxy resin and hardener with a ratio of 4:1. The mixtures were then poured into a circular mold and compressed by using compression molding technique. It was left for curing for 24 hours at standard room temperature. The results were obtained using the two-microphone transfer functions impedance tube method according to ASTM E1050-12. It is found that as the fiber loading increased, the sound absorption coefficient of the composites increased. 20wt% Coconut coir epoxy composites and 20wt% kenaf fiber epoxy composites have the highest sound absorption coefficient with almost similar sound absorption of 0.078 at 5000Hz. While, 20wt% sugarcane bagasse epoxy composites have sound absorption of 0.075 at 5000Hz.

Abstract: Within an ongoing project, we explore the potential of double skin facades to provide both noise control and natural ventilation capability. Three strategies are investigated: i) Manipulation of sound paths via offset of the openings in the two shells of the façade; ii) Application of absorbing materials in the interstitial space of the façade; iii) Active noise cancelling methods utilizing wave-destructive interference. This contribution describes the overall project but focuses primarily on the active noise cancellation approach. Aside from a comprehensive background research on existing technology, we undertook the design of an actual setting for noise cancellation testing with suitable low-cost components as a proof-of-concept. Results of the experiments are expected to inform subsequent efforts to include noise-cancelling technology in double skin facades.

Abstract: Commonly, millions of employees are exposed to occupational health issues, including noise exposure during working hours. Noise is most encountered in industry sector but can also be found in a wide range of other workplaces (airports, concert halls, offices, etc). In this article, we review the noise levels inside a machine shop, for a single working place, with the scope to assess the occupational safety, discuss research approach in identifying the noise issues, control and reduce it. Generally, noise exposure is an expensive issue, with many particularities to be solved and the exact cost is difficult to calculate. This study offers the perspective of what can be done for similar working places and how to perform this in order to protect the employees to be noise exposed above the legal noise limits and relevant conclusions are offered in this direction.

Abstract: Recent approaches to preventive maintenance have shifted from periodic maintenance based on static parameters to a continuous and a periodic maintenance that deploys high-tech tools to track remotely the “health” of equipments. In this paper, we propose an approach to maintain a high level of reliability and to achieve the maximum efficient use of the working parts within vehicles and machines. This paper marks the use of various techniques in the remote maintenance and diagnostics by means of classical and new methods for monitoring equipments remotely. And hence identifying their failure at earlier stages and preventing their breakdown. The technique relies on an onboard device that monitors and analyses the vibrations of the targeted parts using local knowledge stored within the middleware data base and global knowledge obtained remotely from the server.

Abstract: From physiology perspective, always disturb people to rest, the sound that learn and works, namely do not need to voice, all are considered noise. When noise to the people and the surrounding environment adverse effects, the formation of the noise pollution. This paper analyzes the harms and the effects on people, and puts forward prevention and control measures.

Abstract: The rules of the China vehicle noise control are summarized. By analyzing the sources of vehicle noise, the important parts of vehicle noise are introduced. The main control technology and measures of reducing the noise of vehicles are presented. Because of the complexity of the vehicle noise control, at present there are a lot of technology and applications are blank in the research area.Reduce vehicle noise is an important subject of future automotive technology.

Abstract: — The performance of an ANC system depends on the convergence factor. A suitable value of convergence coefficient is extremely important as it impacts both the speed of convergence and the stability of the adaptive algorithm. Traditionally, in active noise control systems fixed convergence factor is used. In this paper, a novel approach of time-varying convergence factor μ is used and the results are compared with traditional feedforward and feedback noise control systems. This algorithm leads to faster convergence and provides reduced mean-squared error compared to the conventional fixed parameter algorithm.

Abstract: — Active noise control is used to reduce low frequency noises. A hybrid ANC structure combines feedforward and feedback structure to generate an anti-noise wave, which results in high performance in control of unwanted noise. In this paper, a hybrid structure for active noise control (ANC) is developed. The hybrid structure utilises a variable step size LMS algorithm for faster convergence. This structure also incorporates variable step size (VSS) online secondary path modelling, the white noise injection is stopped at the optimum point when the modelling accuracy is sufficient. Comparative simulation results shown in this paper indicate the effectiveness of the proposed approach in reducing acoustic noises.