Active Rocket-firing Noise Cancellation with Variable Step-Size Algorithms

• Main Authors: Ji-Yao Liu, 劉繼堯
• Other Authors: Min-Chun PAN
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/01722812461730671836

碩士 === 國立中央大學 === 機械工程研究所 === 92 === Abstract The main purpose of the study is to suppress the transient and nonstationary high sound-pressure-level (SPL) noise perceived by drivers inside the control chamber during rocket launching. A full-size acrylic model is built up for mimicking the sound field of the control room of a rocket-launching vehicle. For achieving the noise reduction, the adaptive algorithm called as FXLMS is applied to implement the active noise control (ANC) system. The convergence speed and stability of the FXLMS-type systems depend on the step-size values mainly. They are usually difficult to be decided for fast converging, and keeping the system stable. In the study, the variable step-size algorithms are applied to automatically select an appropriate step size varying with system status for the desired performance. In addition, a commercial electrical headset is modified for noise-cancellation purpose to obtain best noise reduction and convenience. The performance of the modified active headset is compared with the multi-channel ANC system, which employs 8-inch loudspeakers to generate anti-phase sound waveforms. Considering precisely modeling the secondary path for practical applications, an on-line modeling technique is combined with the ANC headset, and validated using both the complex harmonic noise and rocket-firing noise. Besides, the needed order of the secondary path for different distances and estimated frequencies is also described in detail. Experimental results show that the ANC system with the variable step-size algorithm performs well both in complex harmonic and transient high-SPL shock noise environments. Additionally, the on-line modeling method provides more noise attenuation for complex-harmonic noise.