Modeling and analysis of secondary sources coupling for active sound field reduction in confined spaces

This article addresses the coupling of acoustic secondary sources in a confined space in a sound field reduction framework. By considering the coupling of sources in a rectangular enclosure, the set of coupled equations governing its acoustical behavior are solved. The model obtained in this way is used to analyze the behavior of multi-input multi-output (MIMO) active sound field control (ASC) systems, where the coupling of sources cannot be neglected. In particular, the article develops the analytical results to analyze the effect of coupling of an array of secondary sources on the sound pressure levels inside an enclosure, when an array of microphones is used to capture the acoustic characteristics of the enclosure. The results are supported by extensive numerical simulations showing how coupling of loudspeakers through acoustic modes of the enclosure will change the strength and hence the driving voltage signal applied to the secondary loudspeakers. The practical significance of this model is to provide a better insight on the performance of the sound reproduction/reduction systems in confined spaces when an array of loudspeakers and microphones are placed in a fraction of wavelength of the excitation signal to reduce/reproduce the sound field. This is of particular importance because the interaction of different sources affects their radiation impedance depending on the electromechanical properties of the loudspeakers

A Simulation Environment to Evaluate the Effect of Secondary Source Coupling for Noise Reduction in an Automotive Application

Passenger comfort has always been of pivotal importance in the interior design of an automobile. A critical aspect in reaching this goal in the automotive industry is the design and implementation of an effective active sound management system with the ability to personalize the acoustic environment inside the car. This, in turn, requires designing an active noise control (ANC) system to mitigate the unwanted noise and an active sound profiling system to implement the desired sound. Due to the complexity of the sound field inside the car cabin, having a high-fidelity model that reflects all details is a challenging task. Therefore, in this paper, we develop a simulation platform to be able to evaluate the performance of the ANC system and the distribution of the sound field as a result of this mechanism. This helps to get a better insight into the behaviours of the sound field inside the cabin before its actual implementation. One important feature of this model, which may also have a significant effect on the performance of the ANC system, is the inclusion of a full-scale numerical model of the loudspeaker. The realistic model of the loudspeaker developed in this way allows to model the effect of loudspeaker coupling in an enclosed space and investigate its effect on the ANC system. The model is compared against the simplified mathematical model of the enclosure developed in the previous work by the authors to see how the approximate geometry and simplified model of the loudspeaker would degrade the performance of the ANC system and measure the changes in the acoustic radiation impedance of the loudspeaker

Active noise control in a luxury vehicle

Structure-borne road noise is a critical sound attribute for the overall Noise Vibration& Harshness (NVH) performance of modern luxury vehicles. Currentpassive NVH solutions require structural design modifications, in order to controllow frequency sources that cause structure-borne noise. Active Road NoiseControl (ARNC) has been demonstrated to several commercial vehicles as analternative solution that does not compromise other performances of the car,especially vehicle dynamics. Automotive manufacturers of luxury vehicles, suchas Bentley Motors Limited, are expected to build cars that meet high standardsof driving performance and refinement levels. This thesis focuses on the developmentof an active sound technology for road noise with the use of NVHanalysis methods, which are a common practice in the vehicle development process.Modern NVH methods of road noise analysis reveal the locations of themost predominant structure-borne noise sources. There are significant advantagesin using NVH analysis techniques for the design of ARNC systems, sincethey o_er integrated solutions to the automotive industry in terms of time andcost reduction. A method for defining the accelerometer sensors number andtheir locations on the axles has been developed as an alternative to existingmethodologies, which are applied from the early stages of the NVH development.A physical road noise simulator was developed for replicating road noise.Four random uncorrelated forces were applied on the tyres for analysing andevaluating ARNC systems. In terms of feedforward control, a computer modelof a causal adaptive feedforward system was used to investigate the relationshipbetween the locations, DoF and the performance of the control system.An adaptive system was installed on a Bentley vehicle for conducting the ARNCmeasurements. The adaptive ARNC system was tested on the physical road noisesimulator. The vehicle's tyres were excited by broadband random forces andmaximum 10 dB(A) reduction at the centre frequency of the tyre cavity resonancewas achieved. When the control was focused on the road rumble, then overall3 dB(A) up to 500 Hz were removed from the noise levels measured at the rearheadrests. In terms of road noise testing, a portable multichannel controller wasintegrated with the vehicle electrical system for road noise data acquisition andreal-time ARNC. Finally, the performance of the portable controller is predictedbased on data acquired by the same multichannel system and therefore highlightthe potential use of this system as an ARNC controller

Tunable Electroacoustic Resonators through Active Impedance Control of Loudspeakers

The current trend for multipurpose rooms requires enhanced acoustic treatments capable to meet ever more demanding specifications in terms of performance, compactness and versatility. The reason is the variety of activities to be hosted and the corresponding requirements in terms of acoustic quality which may be very different and even conflicting. In any process to improve listening comfort, the treatment of low-frequency sound is a major concern. The problem stems from the proven ineffectiveness of passive soundproofing solutions of the state of the art, or from their bulkiness that may be prohibitive. This thesis focuses on the analysis, design, realization and characterization of tunable electroacoustic resonators intended to specifically address this issue. This concept deals with loudspeakers, the acoustic impedance of which can be easily adjusted in a controlled fashion. Creating an electroacoustic resonator out of a loudspeaker is the result of an interdisciplinary effort. Such a challenging task combines conceptual tools, models, and applied solutions, drawing from the fields of audio engineering, control theory, and electrical engineering, both in the analog and digital domains. A unifying theory is introduced, covering different strategies from passive electrical shunt to active control of acoustic impedance in a single formalism. This research shows that achieving a desired acoustic impedance at the transducer diaphragm is equivalent to the implementation of a specific functional relationship between the electrical current and voltage across the transducer terminals, and vice versa. From a design perspective, the specific electrical load is tailored by using an internal model of the transducer. The result is an innovative model-based synthesis methodology where the active control of acoustic impedance is reformulated as an electrical impedance synthesis, thus removing the use of sensor. This concept opens new opportunities to improve listening spaces by providing efficient acoustic absorption at low frequencies. Experiments clearly show the benefits of the proposed methodology in a field where there is currently no competitive solution. It is believed that the technological advances resulting from the coupling of a loudspeaker with a synthetic load should pave the way to innovative techniques in noise control and, hopefully, stimulate research in related areas

Active shielding base don implicit and decentralized control

Esta tesis expone un nuevo método para aplicar sistemas de control activo de ruido tradicionales para generar zonas de silencio sin colocar sensores dentro. Primero, se demuestra la factibilidad de usar controladores lineales. Posteriormente, un nuevo concepto es definido, llamado control implícito, que es el caso cuando atenuar la presión acústica en un conjunto de posiciones también implica la reducción de presión en otros lugares. Esta propiedad es usada para controlar la presión en una zona de silencio deseada usando sensores sólo en el entorno de dicha zona. Para este esquema de control el número de sensores y actuadores implican un gran costo computacional. Para reducir las limitaciones computacionales, se propone el control descentralizado y una analogía desde la teoría de juegos, analizando el equilibrio de Nash como el valor de las señales de control después de convergencia.This thesis shows a new method to apply traditional active noise control systems to generate silent zones without locate sensors inside. First, it is demonstrated the feasibility of using linear controllers. Then, it defined a new concept called implicit control, which is the case when attenuating acoustic pressure at a set of locations and it also implies attenuation at other locations. This property is used to control the pressure inside a desired silent zone using sensors only at its boundaries. For this control scheme, the number of sensors and actuators implies high computational cost. In order to reduce hardware limitations, decentralized control and a game theoretical approach are proposed, analyzing the Nash equilibrium as the value of control signals after convergence.Doctor en IngenieríaDoctorad

Theory and Design of Spatial Active Noise Control Systems

The concept of spatial active noise control is to use a number of loudspeakers to generate anti-noise sound waves, which would cancel the undesired acoustic noise over a spatial region. The acoustic noise hazards that exist in a variety of situations provide many potential applications for spatial ANC. However, using existing ANC techniques, it is difficult to achieve satisfying noise reduction for a spatial area, especially using a practical hardware setup. Therefore, this thesis explores various aspects of spatial ANC, and seeks to develop algorithms and techniques to promote the performance and feasibility of spatial ANC in real-life applications. We use the spherical harmonic analysis technique as the basis for our research in this work. This technique provides an accurate representation of the spatial noise field, and enables in-depth analysis of the characteristics of the noise field. Incorporating this technique into the design of spatial ANC systems, we developed a series of algorithms and methods that optimizes the spatial ANC systems, towards both improving noise reduction performance and reducing system complexity. Several contributions of this work are: (i) design of compact planar microphone array structures capable of recording 3D spatial sound fields, so that the noise field can be monitored with minimum physical intrusion to the quiet zone, (ii) derivation of a Direct-to-Reverberant Energy Ratio (DRR) estimation algorithm which can be used for evaluating reverberant characteristics of a noisy environment, (iii) propose a few methods to estimate and optimize spatial noise reduction of an ANC system, including a new metric for measuring spatial noise energy level, and (iv) design of an adaptive spatial ANC algorithm incorporating the spherical harmonic analysis technique. The combination of these contributions enables the design of compact, high performing spatial ANC systems for various applications