Identification of Noise Sources of an Automotive HVAC by Acoustical Duct Method

As the current market trend is emerging towards the compactness, better comfort and less emission, it is quite important that factors contributing to these aspects should be kept under control and maintained within the desired range. Heating ventilation and air conditioning (HVAC) noise is one such factor which significantly contributes in occupants’ acoustic comfort. It creates discomfort to the occupants while HVAC is in operation and eventually lead to fatigue. In a HVAC, there are several different types and sources of noise which cumulatively impacts the overall noise level. However, few of them are quite prominent and has maximum impacts on overall noise. It is very important to identify and measure these sources in order to take appropriate countermeasure to mask or eliminate them. In order to identify and measure the noise sources, various methods are used. One such method is acoustical duct method in which an acoustic duct is used to isolate the source for measuring the noise level and identifying the intensity of source. The present paper describes the source identification and measurement of various noise sources by acoustical duct method. An automotive HVAC, designed for passenger car was considered for the investigation of noise sources. The HVAC was kept in a semi-anechoic test chamber and desired DC supply was provided to the HVAC. An acoustic insulated duct was prepared as per standard and used to measure the noise level. Noise sources from blower motor and fan, recirculation air entry, fresh air entry, face discharge, defrost discharge and foot discharge were marked and measurement was done for those areas. Comparative matrix was prepared out of all the sources and evaluation was done to assess the noise level. The study showed a distinguished difference between the sources and thus the most prominent source was identified. The method is quite helpful in order to prioritize the noise sources and take appropriate countermeasure to reduce the noise.