1. Senior Project – Computer Engineering Active Noise Cancellation For the Attenuation of Sound Stephen E. Lee Advisor – Prof. Catravas
Results
One Dimensional Wave Equation:
N108 Acoustics:
Ambient Noise: ~55 dB
N108 Resonances (Hz): 237, 273, 303 with SPL of 79.5 dB, 76.0 dB and 75.8 dB respectively
Sound attenuations of 10 – 30 dB are possible with proper speaker placement.
Sound pressure level acts opposite to what is expected for small speaker separation distances.
Design Goals
Design a system to attenuate a simple acoustic signal
Refine the system to allow for sound attenuation of an arbitrary signal
Background The basis for noise cancellation is that a signal can be manipulated in a such a way that it will destructively interfere with itself. Active noise cancellation works by employing an adaptive filter that uses a cost function to decide how to adjust the filter coefficients.
Room Acoustics Terms
Reverberation – All of the reflected sound in an enclosed area
Resonances – Frequencies of sound that are amplified due to the environment
Absorption – The material in the room affects how sound is reflected and dampens certain frequencies
Experimental Setup
Preliminary: A set of speakers were driven by a function generator. They were oriented to be facing the same direction with a distance d of separation. Measurements of the sound pressure level were taken at a distance of x = 0.5 – 1.0 m.
Future Work
Implement an adaptive filter in software
Compare the performance of a Kalman filter to the performance of a LMS filter.
Automate measurements of the sound field.