1. Noise Cancellation Device Peter Gordon, Zach Rohde, Aman Sanghera, Andrew Taylor, and Tanner Brunhoeber Critical Design Review

2. Project Objectives and Purpose The primary purpose for this project is to create a portable device that has the potential to reduce noise created by HVAC equipment. This project has the following objectives: ●The device will reduce noise by at least 10 dB between 100 Hz and 5 kHz up to 10 feet directly in front of the speakers. ●The device will be portable and easy to use. ●The device will be 120 VAC powered.

3. Functional Decomposition

4. Key Technologies ●Teensy 3.1 ●Electret Microphone Amplifier - MAX9814 with Auto Gain Control ●SparkFun Mono Audio Amp Breakout - TPA2005D1 ●6-1/2" Poly Cone Midbass Woofer 4 Ohm Speaker ●BAFX Products Decibel Meter

5. System Block Diagram

6. Noise Cancellation Algorithm 1.Input: using the Teensy Audio Library (TAL), accumulate samples from ADC. 2.Find the direction of the noise source. 3.Keep a small amount of samples (for a given time interval) for comparisons. 4.Compare the new samples with the stored samples to find any irregularities (i.e. impulses) or major differences. 5.Assuming the samples differ from the stored samples and a new HVAC noise is detected, generate an inverted signal (in antiphase) with the new samples. 6.Assuming the samples do not differ, output the existing stored samples in antiphase. 7.In order to create antiphase, apply Hilbert transform (TAL) to obtain real and imaginary parts of the samples. 8.Use the imaginary part to create the antiphase samples. 9.Output: antiphase samples via the DAC using TAL.

7. Fabrication of Frame ●Primary housing of speakers and microphones will be in a 2 foot by 2 foot wood frame. ●A 1 foot by 1 foot box will be attached to the frame and it will house the Teensy and the power supply. ●The frame will be attached to 2 feet long legs and a 2 foot by 4 foot piece of plywood. ●Caster wheels will be used to make the device mobile. ●Wiring to connect the devices to power and each other will be placed on the back of the frame.

8. Testing Initial Testing

9. Testing cont. Final Testing ●Measurement at 10’ away, exactly in the center of speakers will quantify result and be compared to client’s requirement of 10 dB noise reduction at 10’ ●Other measurements will be taken to help qualify success of device

10. Schedule

11. Current Status ●Completed the Anechoic Chamber using the sound cancelling foam previously purchased. ●Started testing on the single microphone and speaker using GNURadio. ●From the GNURadio algorithm, started determining which components of the Teensy Audio Library will be used.

12. Challenges ●Hardware o Hardware failure  Perform extensive testing and leave enough time to order replacement parts. o Teensy not powerful enough  Overclocking processor from 72 MHz to 96 MHz.  Order two Teensies and move two microphones and speakers to the new Teensy. ●Software o Teensy Audio Library not extensive enough  Find the component required via existing sources (in C language) and add to the algorithm. o Arduino library contains too much overhead  Switch from using the Arduino library to standard C microcontroller programming.

13. Challenges (continued) ●Fabrication ○Noise coming out of the back of the speaker ■Placing sound-absorbing foam on the backside of speakers ○Weight of the top frame may cause the overall frame to tip over ■Additional wood support added to bottom legs. ■Additional weight placed on bottom piece of plywood. ○Noise caused by length of wiring to reach components ■Twisted pairs. ●Management ○Ensuring we meet the client’s goals ■Stay in contact with the client.