Design of an Active Noise Reduction System for a Cogeneration Plant

Active noise control (ANC) aims at reducing the amplitude of a primary sound source by emitting a controlling sound wave through one or more devices, so that the two waves sum out of phase at the listening point. To generate such out-of-phase signal, the ANC system requires a specific algorithm, usually run on a Digital Signal Processing (DSP) unit. Applications of ANC systems cover a wide range of markets, from industry or vehicle interiors to consumer products, such as headphones. In this paper, a structural ANC system applied to a cogeneration plant is investigated, making use of electrodynamic shakers, accelerometers, and a microphone. The algorithm employed for generating the cancelling signal is a filtered-X Normalized Least Mean Square (FxNLMS). First, measurements of primary and secondary paths performed on the cogeneration plant are presented. Then, the off-line theoretical cancellation performance is evaluated, based on the signals’ coherence. An off-line implementation of the FxNLMS algorithm was developed and processed in several configurations, from single reference, single-input, single-output (SISO) to multiple reference, single-input, multiple-output (SIMO). Eventually, a real-time laboratory test was performed with the hardware-in-the-loop technique. The designed architecture demonstrated remarkable performance, with a noise reduction up to 4 dB(A) in the frequency range 50 Hz – 250 Hz.

I. Introduction

The problem of environmental noise is becoming increasingly serious with the capillary diffusion of industrial plants, transportation, and infrastructures. In solving acoustic noise related problems, traditional passive techniques [1], [2] such as enclosures, barriers, and silencers, are relatively large, costly, and ineffective at low frequencies. For this reason, the use of Active Noise Control (ANC) techniques is more and more common, providing better results at low frequencies with potential benefits in size, weight, volume, and cost. The areas of application for ANC systems are multiple and include automotive [3], appliances, industry, and transportation.