LAUSR

Abstract This article presents a hybrid acoustic technique applied to an acoustic shutter. It uses active noise control (ANC) at frequencies below 1000 Hz and acoustic foam, glued at the shutter walls, to attenuate frequencies above 1000 Hz. The use of the active noise control applied to acoustic shutters to increase the performance of noise attenuation in low frequencies. The control system was the Feedforward Filtered-x Least Mean Square (FxLMS) scheme and the influence of the actuator speaker position. It was implemented a low-cost active noise control using ARDUINO DUE. At low frequencies, without active noise control, the average insertion loss of the acoustic shutter is approximately 7 dB. Up to cutoff frequency (565 Hz) of the acoustic shutter, the highest attenuation due to active noise control was approximately 14 dB in 125 Hz discrete frequency and 17 dB in 400 Hz 1/3 octave band. The results between 500 and 1000 Hz were interesting since the active noise control was not expected to be efficient above the cutoff frequency of the acoustic chamber. The highest attenuation was 17.5 dB at the frequency of 710 Hz. From 100 to 8000 Hz an average attenuation of 13 dB (1/3 octave bands) was observed using the semi-active apparatus presented in this article.