In the progression to incorporate hands free microphone technology into automobile rear view mirrors, the problem of buffeting, a velocity driven wind noise, arises.  This project’s short term concern was to examine the external factors affecting buffeting at a microphone placed in the rear view mirror.  The design problem then is to eliminate buffeting caused by the automobile’s HVAC (heating, ventilating, air conditioning) system.

Principle requirements include zero buffeting at all HVAC conditions, usable in mirrors currently offering mirror technology, clear sound at all audible frequencies, and a complete testing of variables affecting buffeting.  The revised problem was to find what velocity causes buffeting, how the angle of a vehicle’s windshield, defrost blower, and angle of wind incidence on the microphone affects this velocity.

While concepts for microphone placement and mountings were created, hypotheses about airflow behavior dominated the project.  It was hypothesized that the closer the microphone is to the windshield, the lower the buffeting threshold will be due to higher airflow velocity near the windshield.  Also, buffeting threshold will be higher for steep windshields such as trucks than for less steep windshield such as sports cars due to a greater distance from the glass.  In addition, airflow at the top of the microphone will be faster than the bottom because of its proximity to the windshield and thus have a lower buffeting threshold.  Through tests performed to obtain wind velocities and sound files of buffeting, these hypotheses were narrowed and either confirmed or proven false.

By no means has enough data been gathered to make a final conclusion, but through tests performed, general trends begin to emerge.  Buffeting occurs at lower velocity on the bottom of the microphone than the top, making the top a better position for placement, at least preliminarily.  Also, the steeper the windshield is, the lower the buffeting threshold, possibly because the angle of incident air has some effect on buffeting.

These trends provide a platform for further study and recommendations for variables still to be tested.  The nature of this project is ongoing, so the conclusions drawn are preliminary and need further data for support.  However, this research is vital to the completion of the design problem.