P11227- Active Noise Cancellationhttps://edge.rit.edu/content/P11227/public/Home

Mission Statement-Our mission is to develop and analyze the feasibility of an Active Noise Cancellation (ANC) System for automotive exhaust applications to reduce the sound level emitted while not introducing the undesirable effects of increased backpressure.

MotivationThe RIT FSAE racing team has particular requirements regarding sound level emitted from their exhaust system during competition events. While they have been able to pass these criteria in the past, there are opportunities to improve upon what currently “works” for the team. To demonstrate feasibility toward an Internal Combustion Engine (ICE) with fewer restrictions, this project aimed to reduce sound output of a single cylinder Briggs and Stratton lawn mower engine.

Lawn Mower Engine AnalysisAs P11221 did with the FSAE engine, we analyzed the lawn mower engine using spectral analysis. We see the peak frequency of the engine at ~3600RPM to be about 30Hz, and multiples of this peak frequency dominate the analysis.

Active Noise Cancellation- How It Works

Where passive designs use the sound wave and reflect it back on itself to cancel targeted frequencies, Active Noise Cancellation generates the cancelling sound wave electronically. By generating a cancelling wave identical to the original source, but perfectly out of phase 180o, the pressure waves cancel resulting in no sound.

System LayoutTo analyze the best way to direct the sound waves into each other, preliminary tests were run on a variety of setups: 4in Wye, 6in Wye, and 4in Dipole Box.

The TeamChris VanWagenen (EE)

Kyle Desrosiers (ME)- Team Lead

Brad Fiedler (EE)

Greg Wodzicki (EE)

George Slack- Faculty Guide

4in Wye: 26 dB reduction at 300Hz

6in Wye: 16.7 dB reduction at 300Hz

4in Dipole:•More Desirable Layout for ICE Application•-18dB reduction at 500 Hz•8dB reduction for lawnmower sound file

Digital Signal Processor- Selection and Function

• Sampling Rate: 48 kHz• 2-Channel Audio In, 2-Channel Audio Out• Ease of ProgrammingWhat it does:• Read input from primary and error microphones• Computes attenuation signal• Plays cancelling signal through ANC speaker

Acknowledgements:•Texas Instruments•Cenco Phyiscs (www.cencophysics.com)•VWR Education•www.sargentwelch.com

Results•Active noise cancellation effective <1000 Hz•Best results using DSP: 3dB reduction•Optimal results (ideal) suggest much greater reductions•Future groups will build on results and optimize layout, algorithm, and overall system