1 EQUALIZED ALGORITHM FOR A TRUCK CABIN ACTIVE NOISE CONTROL SYSTEM Guangrong Zou, Marko Antila, Antti Lankila and Jari Kataja Smart Machines, VTT Technical Research Centre of Finland P.O. Box 1300, FI-33101 Tampere, Finland guangrong.zou@vtt.fi, marko.antila@vtt.fi 1 INTRODUCTION The noise inside a truck cabin is caused by various sources such as the engine, transmission, wheel vibrations, wind, and some other external sources. In general, the interior noise of vehicles is composed of two components: one is synchronized with the engine rotation or other periodic noise, while the other is caused by stochastic sources [1]. For most midsized trucks with an in-line four-cylinder engine, periodic noise is the dominant part of the internal noise. Such periodic noise is a combination of the harmonic noise components, also known as noise orders. Furthermore, the order frequency range is relatively low, typically below 500 Hz. That makes Active Noise Control (ANC) effective in attenuating the order-related noise. The most commonly used strategy is narrowband feedforward ANC with a Filtered-x Least Mean Squares (FXLMS) algorithm [1]. The FXLMS algorithm, first derived by Widrow in 1981, has been used successfully for many applications, such as broadband noise in an enclosure [2], single frequency noise in a duct [3], multiple frequency noise in a helicopter [4], and time- varying noise in a tractor [5]. As the speed of truck engine changes, the order frequencies change continuously during operation. That compromises the overall performance of the ANC system because the FXLMS approach exhibits the frequency-dependent convergence behavior. Although several variations to the FXLMS algorithm have been developed in an effort to overcome the performance degradation, their drawback is that they either increase the computational burden of the algorithm or add the algorithm’s complexity. Recently, a new approach known as the Eigenvalue Equalization Filtered-x Least Mean Squares (EE-FXLMS) algorithm has been developed by Thomas et al. [6], and already been proven effective to overcome the frequency dependent performance, and to improve the overall performance in the desired frequency range [6], [7], [8]. More importantly, the implementation of the equalized algorithm is straightforward and only minor modifications are needed to the existing FXLMS algorithms. In this paper, a narrowband feedforward ANC system for a truck cabin is presented. A normal FXLMS algorithm and an equalized FXLMS algorithm based on the former case are implemented, and the performance of the approaches is compared experimentally. 2 THE ACTIVE NOISE CONTROL SYSTEM Based on a real truck cabin provided by Dongfeng Motor Company (DFL) from China, the recordings of the noise data at all relevant driving speeds are measured and analyzed [9]. According to the results, at each gear, the most dominant periodic component throughout the range is the 2nd order, the firing frequency of the engine. There are also other two orders which are clearly detectable orders in the spectra, the 4th and the 6th orders. As suggested [8], the orders 2, 4 and 6 are attenuated consequently as much as possible in the practical ANC