El-Bardisi M.

The present works deal with active noise attenuation as a method for noise reduction of low frequency periodic noise source . The low frequency noise is considered one of the most annoying problems facing noise reduction experts as it deals with a long wave length which can not be reduced by the normal passive noise reduction methods. The system described in this work used to check and to confirm the active noise attenuation phenomena, methods used to attenuate a single frequency source (feedback, feed forward systems) and the variables affecting the active noise control system. The wave equation was analyzed and investigated as a prerequisite for the experimental work. The experiments began with a single source and attack periodic noise source (speakers) inside a duct to study the destructive interference phenomena between the two waves, the test was repeated for several low and high frequencies, several approaches was made to attenuate the sound source, the results was used to attenuate the sound of a electric hover machine inside the duct. Using a simple feed back control system with a phase shifter to control the sound of the hover machine a noise reduction of about 6-21 dB was achieved at various frequencies.