Active noise control

Active noise control (ANC) shows success and potential in a growing number of commercial applications, one of which is aircraft cabin noise reduction. With the exception of utilizing ANC headsets, light aircraft, which to date offer a high noise environment, have been somewhat overlooked. The importance of weight minimization also prevents installing copious quantities of dampening and insulation materials as a passive noise control measure. While headsets are a pilot’s necessity and an obvious target for ‘‘localized’’ noise reduction, they are not conducive to either operator or passenger comfort. High noise levels not only render communication difficult but also contribute toward stress and fatigue. A more globalized region of reduced noise will be less restrictive and no doubt provide the occupants with more freedom of movement and overall comfort. Light aircraft operators boasting quieter cabins with a focus on customer comfort will no doubt have a distinct commercial advantage....

Proportionate adaptive schemes have been proposed to exploit sparsity and accelerate filter convergence in acoustic echo cancellation. Recently, combinations of adaptive filters have been extended to operate with proportionate schemes, in order to achieve more robust operation when the actual degree of sparsity of the optimal solution is unknown. Furthermore, it is possible to exploit the asymmetric distribution of adaptation energy in proportionate schemes to reduce the overall steady-state misadjustment. In this contribution, we explain how these novel adaptive filtering structures, which have been proposed and tested mainly for echo cancellation, can also be effectively extended to improve the usual performance trade-offs that appear in active noise control scenarios by introducing some minor modifications. Experimental results in realistic scenarios show that the proposed schemes provide an interesting alternative to the traditional use of a single adaptive filter.

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────────────────────────────────────────── This paper examines the technical principles and practical applications of residential soundproofing for existing wall structures. As urbanization increases and multi-family dwellings become the standard, managing acoustic transmission-specifically airborne and impact noise-is critical for resident well-being. This study synthesizes current acoustic engineering methodologies, including mass addition, decoupling, and damping, to evaluate their effectiveness in retrofitting residential spaces. By analyzing materials such as mass-loaded vinyl, resilient channels, and acoustic sealants, the research highlights how specific combinations can significantly improve Sound Transmission Class (STC) ratings. The findings suggest that while individual material application offers marginal gains, a multi-layered, integrated approach provides the most robust mitigation against diverse frequency ranges.

This paper describes a noise reduction method for capacitively coupled ECG sensors. Capacitively coupled sensors using an insulated electrode have been proposed to obtain ECG signals without pasting electrodes directly onto the skin. It can achieve better usability than conventional ECG sensors. However, it is difficult to remove noise contamination, because the high input impedance and low input capacitance are required to realize the capacitively coupled ECG sensor. Especially, base-line drift and power-line noise are more serious problem when using a single electrode structure. To address this problem, we propose a noise cancellation technique using an adaptive noise feedback approach, which can improve the availability of the capacitive ECG sensor using a single electrode. An instrumental amplifier is used in the proposed method for the first stage amplifier instead of voltage follower circuits. A microcontroller predicts the noise waveform from an ADC output. To avoid saturation caused by base-line drift and power-line noise, the predicted noise waveform is fed back to an amplifier input through a DAC. We implemented the prototype sensor system to evaluate the noise reduction performance. Measurement results show that the proposed method can suppress both of base-line drift and powerline noise simultaneously.

This paper describes a noise reduction method for capacitively coupled ECG sensors. Capacitively coupled sensors using an insulated electrode have been proposed to obtain ECG signals without pasting electrodes directly onto the skin. It can achieve better usability than conventional ECG sensors. However, it is difficult to remove noise contamination, because the high input impedance and low input capacitance are required to realize the capacitively coupled ECG sensor. Especially, base-line drift and power-line noise are more serious problem when using a single electrode structure. To address this problem, we propose a noise cancellation technique using an adaptive noise feedback approach, which can improve the availability of the capacitive ECG sensor using a single electrode. An instrumental amplifier is used in the proposed method for the first stage amplifier instead of voltage follower circuits. A microcontroller predicts the noise waveform from an ADC output. To avoid saturation caused by base-line drift and power-line noise, the predicted noise waveform is fed back to an amplifier input through a DAC. We implemented the prototype sensor system to evaluate the noise reduction performance. Measurement results show that the proposed method can suppress both of base-line drift and powerline noise simultaneously.

La adquisicion y reproduccion en alta definicion de senales acusticas implica cumplimentar diversos requisitos en funcion de las caracteristicas de las senales y del sistema interviniente. La fidelidad del proceso de adquisicion/reproduccion de sonido, la latencia, la inmunidad al ruido y la diafonia son algunos de los factores que definen la calidad de un sistema de adquisicion/reproduccion de senales acusticas. Por lo general, en aplicaciones de metrologia acustica, estos sistemas son de elevado costo y uso privativo. En este trabajo se presenta la comparacion de la medicion de latencia de dos controladores de audio que operan un sistema para aplicaciones de metrologia acustica de bajo costo, evidenciando diferencias significativas entre ambos para dos condiciones de ensayo. Dicho sistema esta conformado por computador personal, una tarjeta de adquisicion/reproduccion de sonido estandar y programas de computo numerico. El trabajo se presenta en el marco del proyecto de diseno y de...

The distribution of the sensors and actuators in an active noise control system imposes a limit in the maximum attenuation levels to be reached. In real applications, irregular shaped cavities are often involved, whose modal characteristics are fundamental to a better understanding of the sound mechanism and any active noise reduction to be taken. The most popular alternatives are numerical methods. In this work, an approach is presented for computing acoustic properties of cavities of arbitrary shape, approximating the cavity geometry by a set of rectangular subcavities. The adjacent ones are jointed together by means of vibrating membranes. La distribución espacial de los tranductores en un sistema de control activo del ruido impone un limite a los valores de atenuación máximos que pueden obtenerse. En la mayoría de los problemas que se presentan en la práctica aparecen geometrías irregulares, cuya respuesta acústica no puede predecirse utilizando métodos clásicos de separación de variables. Las alternativas más utilizadas en estos casos son los métodos numéricos. En este trabajo se utilizan un método que consiste en la discretizacion de la cavidad por subcavidades más pequeñas cuya geometría se conoce. Las cavidades adyacentes se acoplan a través de membranas vibrantes.

Multi-channel Multi-tone Active Noise Equalizers can achieve different user-selected noise spectrum profiles even at different space positions. They can apply a different equalization factor at each noise frequency component and each control point. Theoretically, the value of the transfer function at the frequencies where the noise signal has energy is determined by the equalizer configuration. In this work, we show how to calculate these transfer functions with a double aim: to verify that at the frequencies of interest the values imposed by the equalizer settings are obtained, and to characterize the behavior of these transfer functions in the rest of the spectrum, as well as to get clues to predict the convergence behaviour of the algorithm. The information provided thanks to these transfer functions serves as a practical alternative to the cumbersome statistical analysis of convergence, whose results are often of no practical use. Keywords Active noise control • multi-tone noise • active noise equalization • user-selected noise profile • transfer function analysis.

Burgess [J. Acoust. Soc. Am. 70, 715–726 (1981)] simulated an active noise reduction system in a duct. This system utilized a version of the filtered-x LMS algorithm to obtain noise reduction over a wide bandwidth. A similar system has been implemented using the TMS-32020 signal processing chip on a PC expansion board. In the filtered-x LMS algorithm, the reference signal must be filtered by the transfer function between the transversal filter output and the error signal input in order to maintain stability of the LMS weight update. In our system, this transfer function is calculated from the measured response to a maximum length sequence generated by the noise reduction system itself. Performance results are given for this system in a test setup. Some issues regarding practical implementation of this algorithm in fixed point arithmetic will also be discussed.

The adaptive algorithm satisfies the present needs on technology for diagnosis biosignals as lung sound signals (LSSs) and accurate techniques for the separation of heart sound signals (HSSs) and other background noise from LSS. /is study investigates an improved adaptive noise cancellation (ANC) based on normalized last-mean-square (NLMS) algorithm. /e parameters of ANC-NLMS algorithm are the filter length (L j) parameter, which is determined in 2 n sequence of 2, 4, 8, 16,. .. , 2048, and the step size (μ n), which is automatically randomly identified using variable μ n (VSS) optimization. Initially, the algorithm is subjected experimentally to identify the optimal μ n range that works with 11 L j values as a specific case. /is case is used to study the improved performance of the proposed method based on the signal-to-noise ratio and mean square error. Moreover, the performance is evaluated four times for four μ n values, each of which with all L j to obtain the output SNR out matrix (4 × 11). /e improvement level is estimated and compared with the SNR in prior to the application of the proposed algorithm and after SNR outs. /e proposed method achieves high-performance ANC-NLMS algorithm by optimizing VSS when it is close to zero at determining L j , at which the algorithm shows the capability to separate HSS from LSS. Furthermore, the SNR out of normal LSS starts to improve at L j of 64 and L j limit of 1024. /e SNR out of abnormal LSS starts from a L j value of 512 to more than 2048 for all determined μ n. Results revealed that the SNR out of the abnormal LSS is small (negative value), whereas that in the normal LSS is large (reaches a positive value). Finally, the designed ANC-NLMS algorithm can separate HSS from LSS. /is algorithm can also achieve a good performance by optimizing VSS at the determined 11 L j values. Additionally, the steps of the proposed method and the obtained SNR out may be used to classify LSS by using a computer.

The study of composite materials offers engineers and manufacturers essential insights into understanding failure criteria, initial failure onset, and damage propagation within laminates. This research delves into examining the growth of impact-induced damage and identifying Hertz failure thresholds and maximum force limits across three distinct composite types. Through impact testing, it is observed that the strength of composite materials significantly rises under dynamic loading conditions compared to static loading scenarios, underscoring the material's sensitivity to strain rate.Composite materials play a crucial role in providing effective ballistic protection as part of armor solutions. These materials encounter impact loads of varying energy levels depending on their specific application. Ensuring adequate protection involves a meticulous design and manufacturing process capable of withstanding low-energy impacts, such as those from dropped tools during operational and maintenance tasks, intermediate-energy impacts caused by external materials striking the surface, and high-energy impacts from weapons.Fiber-reinforced composite materials find extensive utilization across aviation, marine, and land platforms, owing to their remarkable specific strength, weight reduction benefits, and manufacturing convenience. These materials hold pivotal roles in the aerospace and defense sectors as well. Polyester resins serve as a cost-effective and user-friendly alternative to epoxy resins in many fiberglass applications. This study focuses on exploring the low-velocity impact behavior of E-Glass composites, which are more economically viable and widely produced compared to armed composites. The research examines three distinct test samples to analyze the impact characteristics of these materials.

This paper is concerned with the analysis and design of an integrated passive and active control system for reducing the haul truck noise. By using a passive enclosure with two open ends and fiberglass inner surface, a three-dimensional noise radiation problem of the engine noise is shaped to a simple problem of noise radiation from the open ends above 200 Hz. Below 200Hz where the transmission loss of the lightweight enclosure is low, a spatial global active noise control (ANC) system is constructed inside the enclosure. To improve the performance of the system, the open ends are divided into four equal diameter size ducts each followed by a louver. A single channel ANC system is set up in each duct to eliminate the noise in the frequency range from 200 Hz to 400 Hz. Experimental results demonstrate that more than 20 dB insertion loss is achieved with such a passive enclosure at frequency band above 400 Hz, and 8 dB noise reduction with global ANC systems at frequency band below 200 Hz, and 4 dB noise attenuation with single channel ANC systems between 200 Hz and 400 Hz. The results this investigation show the feasibility of hybrid noise control technique for reducing the haul truck noise.

In recent years, accompanied by economic growth, air transportation in Vietnam has rapidly risen with the introduction of many new airlines. This situation has led to an increase in aircraft movement frequency flying in and out of the airports and raised concerns about the effects of increased noise exposure levels on public health and the natural environment in the vicinity of the airports. Vietnam authority has also issued several documents to regulate the establishment of the noise contour maps to evaluate the current noise exposure levels around airports in Vietnam and recognized the noise problem in aviation as a significant issue. One of four measures to reduce the noise around airports introduced in the Balanced Approach to Noise Management of the International Civil Aviation Organization is noise abatement operational procedures. This research is one of the first attempts to provide a comprehensive study on predicting the noise levels and establishing noise contour maps arou...

This paper describes the concept of adaptive noise cancelling (ADC), in alternative scheme of estimating signals corrupted by additive noise or interference. The main objective of the noise cancellation is to estimate the noise signal and to subtract from original input signal plus noise signal and to obtain the noise free signal. An alternative scheme called adaptive noise cancellation for estimating a speech signal corrupted by an additive noise or interference. This technique uses a primary input signal that contains the speech signal and a reference input containing noise. Its reference input is adaptively filtered and subtracted from the primary input signal to obtain the estimated signal. In this technique the desired signal corrupted by an additive noise can be recovered by an adaptive noise canceller using least mean square(LMS) algorithm and recursive least square(RLS) algorithm. This adaptive noise canceller is useful to improve the signal to noise ratio.

This paper describes the concept of adaptive noise cancelling (ADC), in alternative scheme of estimating signals corrupted by additive noise or interference. The main objective of the noise cancellation is to estimate the noise signal and to subtract from original input signal plus noise signal and to obtain the noise free signal. An alternative scheme called adaptive noise cancellation for estimating a speech signal corrupted by an additive noise or interference. This technique uses a primary input signal that contains the speech signal and a reference input containing noise. Its reference input is adaptively filtered and subtracted from the primary input signal to obtain the estimated signal. In this technique the desired signal corrupted by an additive noise can be recovered by an adaptive noise canceller using least mean square(LMS) algorithm and recursive least square(RLS) algorithm. This adaptive noise canceller is useful to improve the signal to noise ratio.

The van under study presents a problem of booming when the engine periodic noise excites some low-frequency modes of the cabin. The aim of this work is the design and implementation of a multichannel active system to alleviate this problem. First, a reference signal is searched correlated with the noise measured by a microphone in the driver head position. The best reference signal is the longitudinal vibration picked up by an accelerometer under the differential group. Then, the acoustic field inside the van is modeled by the normal modes theory. Optimization by simulated annealing allows one to find the best locations for six loudspeakers and six microphones. Finally, the multichannel active noise control is implemented by using a commercial system. Measurements of noise reduction have been carried out in the semianechoic room at NECT-E under usual driving conditions (third gear, slow acceleration). [Work supported by CICYT, Project AMB97-1175-C03-01.]

This article provides a broad overview of the recent advances in the field of active noise control techniques to reduce unwanted noise over a certain spatial region of interest. By both commercial and technological advances in local active noise control systems extending the size of the quiet zone seems to be a crucial step to develop the next generation of active control systems for a more personalized and quieter audio products. In this review article, the advances over the past decade in design and development of spatial active noise control techniques to enlarge the controlled sound zone is reviewed. The focus is specifically on the adaptive control techniques and the methods proposed in the frequency domain to control the sound field. The study has paid a specific attention into the most important performance measures in designing a spatial active noise control system such as convergence rate, stability and robustness of the algorithm, and the size of quite zone and how it can ...

This paper presents the design and implementation of adaptive feedback active noise control system (ANC) for head phone applications. Active Noise Control is a technique of acoustic noise reduction using a secondary source of sound which produces “antinoise” to cancel the primary noise. In this paper, narrow band single channel feedback ANC for headsets application is focused upon. The filter weights are updated by using the feedback form of Filtered-X LMS (FXLMS) algorithm. Performances for the IIR-based filter, FIR-based filter are compared with those of the algorithm by using ADALINE. The real time implementation of the system is performed using TMS320C6713 DSP Starter Kit (DSK) and the performance is analyzed for two tone sinusoidal noise.

Accurate and secure localization is a critical requirement for autonomous navigation systems. While Global Positioning System (GPS) technology has traditionally served as the primary positioning mechanism, its reliability is significantly compromised in environments characterized by signal blockage, interference, and intentional disruption. This article presents a conceptual discussion of a noise-resilient and secure localization framework designed for autonomous navigation without reliance on GPS. Emphasizing robustness, resilience to environmental noise, and security awareness, the framework supports reliable navigation under uncertain and hostile conditions. The discussion avoids technical exposition and instead highlights system-level design principles, safety implications, and relevance for future intelligent transportation systems.

This technical guide expands the experimental proposal of Part 34 into a step-by-step laboratory procedure suitable for a newcomer to optical interferometry and frequency metrology. The experiment generates two coherent optical fields from a common laser, imposes a commanded frequency difference ∆f using an AOM/EOM driven by a DDS referenced to a stable clock, and measures the accumulated relative phase Φ(t) of the heterodyne beat. If photon energy differences are fundamentally quantized in steps ε, the experiment searches for non-reachability of offsets below ∆f_min = ε/h, manifesting as snapping, hysteresis, or loss of linear phase accumulation when ∆f is scanned through zero. I. What is being tested and what is measured Hypothesis under test. There exists a fundamental energy quantum ε ("joulino") such that distinct photon energies must differ by at least ε. Equivalently, frequency differences satisfy ∆f = m ε/h, so that offsets below ∆f_min = ε/h are forbidden or unstable. Primary measured quantity. The experiment does not attempt to directly resolve tiny frequencies on a counter. Instead it measures the unwrapped phase Φ(t) of the heterodyne beat and checks whether it accumulates linearly: Φ(t) ≈ 2π∆f t + Φ0. Derived quantity. The realized frequency difference is obtained from the fitted slope: ∆f_meas = (1/2π) dΦ/dt.

The transmitted noise reduction (NR) of passive and active hybrid panels is experimentally studied. The concept of hybrid panels is based on a combined approach for noise controls: a passive approach for mid and high frequencies and an active approach for low frequencies. Active and passive hybrid panels are demonstrated. An active-hybrid single panel is made with a plate structure on which piezoelectric sensor/actuators are bonded in conjunction with a simple controller. Sound absorbing material is bonded on the structure to effectively reduce the transmitted noise in mid frequencies. An active-hybrid double panel is also made by using another single plate to maintain an air gap. To prove the concept of hybrid panels, an acoustic measurement experiment is performed. Instead of using the active control system, a passive shunt damping is used for the NR in low frequencies. This is called a passive-hybrid panel. The use of sound absorbing material and an air gap is effective for noise control in mid and high frequencies. Meanwhile, the active approach and the passive shunt approach are useful for noise control at lower resonance modes. These hybrid panels demonstrate the potential for NR at broadband frequencies.

Adaptive filtering techniques are used in a wide range of applications. Adaptive noise canceller is one of the most interesting applications for adaptive filters, especially for the Least Mean Square (LMS) algorithm, due to its strength and calculus simplicity. Noise problems in signals have gained huge attention due to the need of noise-free output signal in numerous communication systems. The adaptive noise cancellation principle is used to remove an unwanted noise from corrupted signal by subtracting it from the corrupted signal. This paper presents an idea behind the hardware designing of ADC and simulation of ADC controller code used for FPGA Implementation of LMS Algorithm for Audio Applications. Since Xilinx Spartan3 FPGA doesn't have a facility of providing audio input directly designing of ADC is very important.

This thesis presents boundary element formulations for three-dimensional acoustic problems of active (ANC) and passive (PNC) noise control. A new boundary element strategy, referred to as RABEM (Rapid Acoustic Boundary Element Method), has been formulated and implemented for acoustic problems. The assembly time for both the system matrix and the right hand side vector is accelerated using a Hierarchical-matrix approach based on the Adaptive Cross Approximation (ACA). Two different H-matrix-GMRES solvers (one without preconditioners and one with a block diagonal preconditioner) are developed and tested for low and high frequency problems including noise emanated by aircraft approaching an airport. A new formulation for solving the ANC based on attenuating the unwanted sound in a control volume (CV) rather than cancelling it at a single point is presented. The noise attenuation is obtained by minimising the square modules of two acoustic quantities - the potential and one component of...

Aircraft cabin noise control in the past has relief heavily on improving sidewall attenuation by passive ‘‘add-on’’ treatments. The conventional passive methods, such as adding mass, damping, or acoustic absorption, etc., not only impose a stiff weight penalty, they are also ineffective in improving the low-frequency sound transmission loss of an aircraft fuselage sidewall. Active control of sound inside aircraft cabins has been the focus of research in recent years and has shown considerable promise. Laboratory and in-flight tests of prototype active control systems for tonal noise reduction using secondary speakers have demonstrated the feasibility of active noise control (ANC) in aircraft cabins. In recent years active structural acoustic control (ASAC) has also been applied to aircraft fuselage structures in controlling low- to mid-frequency structural sound radiation. In the ASAC technique, control forces are applied directly to the vibrating structure by actuators (such as pie...