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Title: An investigation into the possibility of noise cancellation with a blower in the automotive industry
Author: Ostad Hassan Panjehali, M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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The aim of this project is to design and develop hardware and software of a low cost and reliable acoustic noise cancellation device for the automotive industry. Actives noise control is a real time application of adaptive digital filtering which requires digital signal processing. Much effort has been focused on broadband feedfoward active control and the use of sensing microphone to provide the time function of the noise signal which in practice adds undesirable additional acoustic feedback and the multiple channel system, while existing work continues to concentrate on adaptive digital filtering. In this project however, the feasibility of narrowband feedfoward active control to cancel acoustic noise in a blower duct has been demonstrated. A reflective sensor is mounted close to the blower fan to detect the frequency which is directly related to the shaft revolution frequency which provides synchronisation and timing function in place of the sensing microphone to eliminate acoustic feedback. The attenuation of sound in ducts is related to wavelength, an auxiliary sound source placed in the duct wall provides the solution to the problem, and for high attenuation adaptive electronic control is applied. For this application the system was implemented using TMS320C10 digital signal processor. Two experimental set-ups were demonstrated, firstly, using two loudspeakers, one microphone and a function generator, the microphone was placed between the loudspeakers. One loudspeaker produced constant noise source by function generator and the second generated antinoise signal. This experiment was merely used to prove the software and the functionality of the system. Secondly, using one loudspeaker, one microphone, a reflective sensor to provide synchronisation and timing function and a blower. A Jaguar blower was used to provide source of the noise with loudspeaker placed at the outlet of the duct and microphone being placed between the blower and the antinoise loudspeaker. From experimental results it was found that the stability performance of the system not only dependent upon the volume of the feedback loop, which is an inherent problem in the operation of a closed loop system with acoustic feedback, but also on the distance of the microphone and the antinoise loudspeaker as well as synchronisation signals. Noise reduction of 30dB was achieved between 30HZ to 250HZ with cancellation time of 1sec to 20sec at coefficients of 0.1 to 0.05 in time domain analysis. Above and below the aforementioned frequencies the system became unstable. In comparison the frequency domain cancellation time was reduced by half the amount.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available