The design and operation of a vehicle’s heating, ventilation, and air conditioning (HVAC) system has great impact on the performance of the vehicle’s Automatic Speech Recognition (ASR) and Hands-Free Communication (HFC) system. HVAC noise provides high amplitudes of broadband frequency content that affects the signal to noise ratio (SNR) within the vehicle cabin, and works to mask the user’s speech. But what’s less obvious is that when the airflow from the panel vents or defroster openings can be directed toward the vehicle microphone, a mechanical “buffeting” phenomenon occurs on the microphone’s diaphragm that distresses the ASR system beyond its ability to interpret the user’s voice. The airflow velocity can be strong enough that a simple windscreen on the microphone is not enough to eliminate the problem. Minimizing this buffeting effect is a vital key to building a vehicle that meets the customer’s expectations for ASR and HFC performance. Systems design principles must be applied to ensure that the placement of the microphone and vents, HVAC airflow management, and active noise reduction solutions are all designed in concert to reduce exposure to the problem.
In this paper, we examine the objective effect that HVAC buffeting has on the ASR system, above and beyond the masking noise provided when the airflow is directed away from the microphone. We discuss vent and microphone placement that can contribute to the error state, and propose design guidelines or active solutions that can help reduce the occurrence and impact of HVAC buffeting.