EE331L Analog Electronics Laboratory 2

An Active Noise Cancellation System

Introduction: 

Most of you have or are currently taking “Feedback Control Systems”.  In this lab you will build an ANC System that cancels a low frequency noise that is sourced by a speaker and cancelled by “Anti-Noise” from a second speaker facing the first one.  A microphone centrally located between the two speakers will be the sensor used to provide the feedback so that your system can converge to a reduced noise level.

Procedures:

  1. Measure the physical “plant” transfer function

§   Set up the two speakers, microphone and stereo amplifier in the configuration that you will use in the demonstration.

§  Replace the microphone signal with a test signal from a function generator and measure the transfer function to the microphone output at a set of frequencies that span the range of interest (100-300 Hz).

§  Record the magnitude and phase at each frequency as this is the “open-Loop Transfer Function” of your “Plant”.
Note:  DSP-based ANC systems normally do this measurement and automatically develop the corresponding adaptive equalizer as part of the system design.

  1. Design your feedback equalizer

·         Design a filter (AKA loop equalizer) to guaranty loop stability while allowing good noise reduction (>10dB at the microphone) and reasonable speed of convergence (< 1 second) of your noise cancellation system over the designated range of noise frequencies (100-300 Hz).

  1. Simulate your system in MatLab and using Multisim to show performance

·         Determine the Gain and Phase margin of your feedback system.

·         Capture the dynamic performance at representative noise frequencies for your report.

·         Test your system to determine performance achieved and present your results to the class.

 

Analysis and Report:

Please complete a brief lab report (2-3 pages).  Focus on explaining your design process.  Explain how you chose the overall circuit design and the key components.  Explain the important parameters and effects of your circuit, as well as how it could be improved in the future, or with more resources.  Your report should address the following:

§  Circuit/System Diagrams

§  Waveforms, both from simulation and physical tests.

§  Sensitivities to component precision.

§  General considerations

 

Your lab report will be due in one week.