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VOICE CANCELLATION

Roman Stemprok, Pin-Hui Tan University of North Texas

Abstract

Developed societies experience an increased level of noise pollution which can be associated with industrial activities or higher human concentration. There are several noise categories, such as transport noise or social noise. A transportation system is a necessity and few places in urban development exist where transport noise cannot be heard. Social noise, however, is the greatest source of nuisance noise and complaints. Surveys from various geographical areas of the US estimate the adult population is/was bothered by neighborhood noise, more so than road traffic noise or aircraft noise. Engineers strive to improve the situation; however, people are people and they will make noise.

Solutions include the active control of sound. Making an anti-noise for every known noise volume, will cancel the two out. This is an old concept. "Fight noise with noise," was researched to solve noise pollution problems. Active Noise Control (ANC) is the reduction of unwanted system noise by introducing noise that is the inverse of (180° out of phase with) the unwanted noise. Active control systems are best suited for predictable, low frequency noise. Frequencies below 500 Hz have wavelengths longer than one meter and can be effectively canceled over large areas. Higher frequencies have shorter wavelengths so the noise may be either canceled or doubled. This university research project investigated this phenomena and optimized the system to work effectively to explore the noise cancellation effect.

This student noise cancellation project was a success. The equipment managed to mask the unwanted noise in an experimental box. Atmospheric silence is 57.5dB and the lowest noise cancellation level was 64.1dB during the experiment. The result can eliminate noise created by traffic, but requires improvement to mask human conversation (60dB).

Introduction

Noise control adopted passive systems, where the sound was reduced by insulation, padding, and over weighting of physical noise barriers. Sometimes these passive methods were obviously not effective and could not be applied to smaller systems such as single rooms, working cubicles, cars or a table in a restaurant and spectral shaping methods are necessary1. An active noise cancellation technology is presented in this research. The idea of "fight noise with noise“ can be adopted to solve problems of noise pollution. Active Noise Control (ANC) is the practice of reducing unwanted sound in a system by introducing additional sound that is the inverse of (180° out of phase with) the unwanted noise, Figure 1. Active control systems are best suited for predictable, low frequency noise. Frequencies below 500 Hz have wavelengths long enough

Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright © 2002, American Society for Engineering Education

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Tan, P., & Stemprok, R. (2002, June), Voice Cancellation Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--11028