A Novel Approach to Active Noise Control using Normalized Clipped Adaptive Algorithm

Hybrid noise control is the combination of both active noise and passive noise control. For high-frequency noise, we generally use passive noise control technique, and for low-frequency noise of less than 200 Hz, we use active noise control technique. Passive noise control is achieved by introducing passive techniques such as enclosures, physical barriers, and silencers to attenuate the undesired noise, whereas active noise control (ANC) is achieved by introducing a cancelling “anti-noise” signal generated by a processor or electronics circuit. Digital filters can be used for this purpose with an appropriate adaptive algorithms such as FXLMS, FXNLMS, FBLMS, SE-FXLMS, and FULMS. The development of an ANC simulation model can be divided into two parts: the modelling of primary noise and the modelling of secondary or counter noise. The anti-noise generated by the ANC system can be modelled only if we have the information of primary noise. For successful simulation of secondary noise, we have to model the control system and its interaction with the surrounding acoustical space. This article describes the practical application of active noise control as well as passive noise control to a server room, greatly reducing the level of noise in the whole area through appropriate adaptive algorithms. The results obtained using different algorithms are compared and analyzed.

Commercial active noise and vibration control systems for vehicles are gradually developing, mainly in Japan, for both active noise control of interior sound and active control engine mounts [1]. There have been four Japanese commercial applications: • Active control for booming noise by Nissan in 1991, • Active vibration mount for idle noise and vibration by Toyota in 1997, • Active vibration mount for diesel engines by Nissan in 1998, • Active control for low-frequency road noise by Honda in 2000. Other manufacturers have, of course, developed similar systems, but these have not progressed to production applications. Additionally, active control engine mufflers using cancelling loudspeakers have been successfully demonstrated. A new type of active muffler, using a controlled oscillating butterfly valve in the exhaust line has been developed recently. The future of active control in vehicles is dependent on customers who are willing to pay the higher price for additional noise and vibration control, so that cost reductions are the essential factor in further commercial products. Trends towards fuel efficiency and lighter vehicles run counter to reducing noise and vibration. This has given new interest in active noise control and active control engine mounts as a solution to these conflicting issues.

Experimental study of active noise control for a full-scale plenum window in a domestic apartment

The authors present a delayed least mean square (LMS) algorithm which introduces delay in the reference input for active periodic noise control applications. Results show a reduction in out-of-band overshoot and coefficient quantization noise for fixed-point implementation. Computer simulations show an average of 5 dB overshoot constraint and 10 dB quantization noise reduction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetorheological (MR) dampers have received remarkable attention due to being a potential technology to conduct semi-active control in mechanical systems in order to effectively suppress vibration. It is therefore important to understand the dynamic behaviour of such devices whose non-linear hysteresis is a complicated phenomenon. In the study, an MR damper has been designed, fabricated, tested and then its dynamic behaviour has been modelled with the classical Bouc-Wen hysteretic model. After that, the seven parameters of this model have been expressed in terms of only current excitation. By this, the total damping force has been given by a compact form in which the only independent variable is the current excitation. Finally, the model has been verified with experimental data and a good agreement has been observed.

Application of active noise control for engine related cabin noise

In most practical applications of active noise control, acoustic feedback is a major problem that often interferes with the operation of the control system and even renders it unstable. The optimal collocated positions of secondary source and two microphones are studied and the theoretical equations that reduce the influence of acoustic feedback are developed based on plane-wave transmission theory of sound in a duct. The original signal of primary noise is obtained from the measured signals of reference microphone and error microphone, which are transformed to frequency domain by FFT and operated. In this study, the performance of the proposed method is compared with other traditional time-domain methods by means of simulation and analysis using LabVIEW programming language. The results showed that the proposed method can effectively reduce the influence of acoustic feedback. In practical application of active noise control in a duct, the adaptive control or other control method incorporating the proposed method in this paper will improve the stability and performance effectively.

This paper focuses on acoustic modeling for active noise control applications. The desired model must be finite dimensional and efficient numerically to meet implementation requirements. It must also be parameterized by the position considered inside the cavity. This additional characteristic is desirable for addressing specific active noise control applications such as optimizing microphone placement, estimating acoustic pressure at different positions of the considered cavity, and finally attenuating noise level in a subarea of the cavity. The main contribution of this paper is to propose a finite-dimensional, low-order, and parameterized acoustic model of a cavity, suitable for active noise control applications. The resulting model is defined as a gray box that combines a one-dimensional analytical model of acoustic propagation, which handles the physical parameterization, and a black-box model that copes with actuator and sensor dynamics as well as modeling errors. The parameters of the proposed model are optimized in order to reproduce the frequency behavior of the real system (LS2N active noise control platform) in a frequency range. This model allows one to accurately reproduce the dynamics at any position in the considered cavity. The prediction performance of the proposed model was compared to a classical black-box model (usually used for active noise control applications) and validated experimentally using the LS2N active noise control platform. The analysis highlighted that the proposed gray-box model can predict the acoustic behavior in a great range of positions.

The method of least mean square (LMS) is the commonly used algorithm in Adaptive filter due to its simplicity and robustness in implementation. In Active Noise Control application, a filtered reference signal is used prior to LMS algorithm to overcome the constraint on stability and convergence performance of the system due to the existence of the auxiliary path. This is known as Filtered-X LMS algorithm. In conventional Filtered-X LMS algorithm, each filter weight is updated once on every audio sample. This paper proposes the improved version of Filtered-X LMS algorithm with the use of multiple iteration of filter weight on every sample of audio signal. The proposed work uses field programmable gate arrays to realize real-time simulation on hardware for the noise signal of 500 Hz. Results from the real-time hardware simulations have shown much faster error convergence and better adaptation performance for different selections of learning constant μ, as compared with the conventional method.

Objectives: In case of medical emergency, an ambulance uses siren (which produces noise up to 120 dB) to alert the traffic on the road to give way. However, siren noise is troublesome to the patient lying inside. This calls for noise control inside the ambulance. Methods/Statistical Analysis: The passive noise control methods are not feasible and economically inviable so active noise control (ANC) method is applied. The ANC is electro-acoustic technique in which the noise signal is acquired and noise with opposite phase is produced and overlapped on input noise to suppress the same. The weights are updated using adaptive algorithms so as to reduce the error in ANC system. In present work, least mean square (LMS) and filtered- reference least mean square (FxLMS) algorithm based ANC systems are applied and compared for ambulance siren noise reduction. MATLAB is used for simulating the ANC systems. Findings: Both the algorithms are compared on the basis of residual noise and smoothened ensemble average square error (SEASE). From the results, it is found that both algorithms LMS and FxLMS are good in noise reduction. The noise reduction for FxLMS based ANC system is 28 dB whereas it is 25 dB for LMS based ANC system, which indicates the superiority of FxLMS algorithm over LMS algorithm. The results are obtained analytically as well as indicated by power spectral density (PSD) plots of the residual noise. The comparison of SEASE for both algorithms also indicates better performance for FxLMS algorithm. The ANC system based on FxLMS algorithm is more stable as it considers the secondary path which includes practical components such as ADC, DAC, etc. Applications/Improvements: The results indicate that FxLMS algorithm based on ANC system can be implemented on the hardware using DSP processor. It can be further used for the other applications of noise reduction such as server noise, vacuum cleaner, etc. Keywords: Active Noise Control, Ambulance Siren Noise, FxLMS Algorithm, LMS

Affine projection (AP) algorithms have demonstrated faster convergence speed than conventional least mean square (LMS) algorithms, thus providing an attractive solution in the active noise control (ANC) field. However, the AP algorithms demand high computational cost, restricting their practical use in real-time ANC applications. Recently, a multichannel filtered-x error-coded affine projection-like (FXECAP-L) algorithm with evolving order has been proposed to reduce the computational burden by maintaining the convergence speed of AP algorithms. In order to obtain an efficient and robust FXECAP-L algorithm with evolving order, the scaling factor and encoder resolution need to be adjusted manually, which is a time-consuming and costly effort that must be carried out by expert designers. To reduce these costs and efforts, we introduce, for the first time, a strategy for automatic adjustment of the scaling factor and encoder resolution that benefits the rapid development of practical ANC applications. To demonstrate its practical use, we applied the proposed strategy for controlling the noise in an acoustic duct. The practical results demonstrate the automatic adjustment of the FXECAP-L algorithm which maintains high convergence speed at the expense of a small compromise in terms of processing time.

Actuator performance is a critical part of active noise and acoustic control. The loudspeakers that are normally used as actuators in many active noise and acoustic control applications add significantly to the dynamics of the control loop and are detrimental to the controller’s performance. By compensating a loudspeaker with a technique similar to motional feedback, the loudspeaker performance is enhanced in applications such as control of acoustic enclosures. In this work, a method to easily and reliably compensate a loudspeaker in order to approximate constant volume velocity behavior over the piston-mode frequency range is presented and demonstrated. This reduces the influence of the environment upon the actuator, reduces low-frequency distortion of the speaker, and minimizes magnitude and phase shifts of the intended control signal. Numerical simulations and experimental results of the proposed methods are included. [Work supported in part by the Lord Corporation and the National Science Foundation under Grant No. CMS 95-01470.]

Active control for vehicle interior noise based on DWT-FxLMS algorithm using a piezoelectric feedback system

Application of active noise control (ANC) was discussed as method to prevent the occurrence of an inner acoustic mode inside the semi-closed cover placed in the diffuse acoustic field. The effect was validated by the experimental measurement using a reverberant room. The results show that the acoustic mode formed by semi-closed cavity has locally-coherency at its occurrence frequency and the inside cover acoustic mode can be controlled by applying ANC. It has been confirmed that noise reduction of ANC for the peak level caused by the acoustic mode is approximately 5dB.

Optimization of noisiness of mechanical system by using a pneumatic tuner during a failure of piston machine