Title:

Noise Cancelling Speaker Removes 86 Percent of Noise

This project was a very ambitious idea that became more restricted over time. Originally, the idea was to create a speaker to reduce all noise in the range of human hearing (50Hz to 20kHz) in a spherical area to 20dB. While noise cancelling headphones exist, there are no speakers on the market. Knowing the task was doomed to fail, the main goal was to discover the reasons why such a device has not been produced. Creating the physicality of the speaker was not too difficult, a micro-controller was researched and chosen for speed and cost, which led to the Teensy 4.1 – a 600MHz tiny computer with a staggering 24 IO pins for the low price of 21.50 US. Then a microphone was chosen, an AT2020 with an extremely flat sound profile and cardioid pickup pattern. Speakers with a diameter of 5.25 inches were chosen to create a maximally parallel sound wave, which should have been the first clue that the original goal was unobtainable. After some research on how to initialize all the components in the Arduino sketch with the Teensy, a problem arose. To use the microphone with the Teensy, a gain circuit had to be built to bring the signal to line-level. Unfortunately, there was no safety to restrict the maximum voltage of the signal and the Teensy was killed. A week later a new Teensy and a package of 2.4V Zener diodes arrived, which allowed the input to be shunted to ground if the voltage rose close to the maximum 3.3V the Teensy’s analog pins are rated for. Then came the real problems – the code, which was originally designed to cancel noise in real time was found to have too large of a feedback issue. A rewrite was done to scan the noise and then process and cancel it. An FFT is preformed and the 16 largest signals by magnitude are reversed and played through the speakers. The problem? At best only one of these signals could line up with the source, and even then only in a specific spot. Unfortunately, this problem is with physics, not with the code. A demo code was written to play a singular frequency and its inverse to show a proof-of-concept cancellation. This demo showed a noise reduction of 17dB, but any deviation from the ideal distance breaks this effect.

Name

Comment*

Comments are viewable only by submitter

Captcha*