First I researched audio noise canceling theory. Then I designed, prototyped and tested a noise canceling circuit that had only a 180 degree phase adjust. Later I researched variable phase adjustment methods and output delays. I built additional circuits that allowed a notch phase adjustment and finally a uniform phase adjust across the frequency range from 20Hz-10kHz. My most complex design worked over the full 20-20kHz range. For each design, I tested the efficiency of the circuit with test instruments and my ears. :: Circuit Boards, Bread Boards, Multi Meter, Function Generator, Headphones, Microphones, Computer, Solder, Soldering Iron, misc. electronic components, Computer Software, Display board, Spray Glue, Photos taken with my Mom's digital camera.
All of my noise canceling devices worked very well at suppressing all kinds of repetitive noises (like a motor), but the circuits with phase adjustments worked much better than those without. Being able to adjust the phase made a big difference and gave my circuits the ability to better suppress noise by lining up the canceling and source waves.
In this project I learned how audio noise canceling devices work and I built many complex circuits. Even the noise canceling circuit that didn't have a phase adjust did surprisingly well and canceled many common machine noises. I can think of many applications for this powerful technology.
This project was to understand how electronic noise canceling devices work and to design and build my own operating circuits with various features.
Science Fair Project done By Frederick J. Meyer