Active Noise-Canceling of Vehicle Exhaust Noise

and cancel out that signal. Lower amplitudes, or ideally a complete canceling, will occur and little or no
sound will be heard from the exhaust pipe by those around.
The project can be separated into three distinct parts- measuring the sound frequency and
amplitude, using a computer program to create an inverse wave based off of the measurements, and
broadcasting that new sound wave through a speaker to create destructive interference and cancel out
the sound waves.
The sound will be measured with a microphone placed just outside of the exhaust pipe of an
Infiniti G35 sedan. The best type of microphone to use to gather data will be determined between a
condenser, dynamic, and piezoelectric styles. Once the most effective type of microphone to use is
determined and an accurate precise measurement is accomplished, the microphone will be moved farther
into the exhaust pipe. This will simulate where the microphone would be in a working noise-canceling
system.
LabVIEW will be used to gather the data from the microphone onto a laptop computer. Tests will
be performed with the car in a stationary position at various RPM levels to measure the sound
frequencies and amplitudes at each respective level. The signal will be inverted and the new signal will be
sent to an amplifier and a speaker. The term “active” in active noise-canceling comes from this process of
the computer continuously sampling the frequency and amplitude of the exhaust tone and reprocessing
the inverted signal.
The speaker will be placed just in front of the microphone and will broadcast the new signal. The
placement will be such that the new signal is not measured by the microphone. Adjustments will be made
in speaker position to allow for optimum noise-cancellation. The speaker will also be moved farther back
with the microphone, but will be located in a separate pipe next to the exhaust instead of in the actual
exhaust pipe.
To measure the affect of the speaker on the exhaust tone, a second microphone will be placed a
short distance from the exhaust pipe to measure the amplitude of the sound waves now exiting the pipe.
A comparison will be made between the amplitudes of the samples taken with the speaker and without
the speaker to determine the difference.
Outcomes
Once the project has been completed, a detailed research paper will be printed up to describe the
results of the project. It is expected that a simple system will be completed to measure and cancel out the
exhaust tones that will also be presented in this paper. It may even be possible to create some sort of
prototype device once the research paper is complete that could lead to further research and
development of the idea. The main goal, however, is to develop a method of accurately measuring and
recording the frequency and amplitude of the exhaust tones and be able to reproduce an inverse signal.
Project Timetable
By February 1 st , the type of microphones needed for sampling will be determined. By March 1 st , the
method of acquiring and analyzing the samples taken by the microphone will be determined. By March
15 th , the experiments will be completed. By March 20 th , the first draft of the research paper will be
completed. By March 25 th , the second draft will be completed. On April 4 th , the final draft will be
finished and turned in.
i
http://www.euro.who.int/en/what-we-do/health-topics/environmental-health/noise
ii
http://www.bose.com/controller?url=/shop_online/headphones/noise_cancelling_headphones/index.jsp
Other sources:
http://www.who.int/occupational_health/publications/noise6.pdf
http://www.chrisruckman.com/ancfaq.htm