HVAC noise control using natural materials to improve vehicle interior sound quality

Heating, Ventilation and Air Conditioning (HVAC) unit is a major noise source in a vehicle's interior space. Reducing this noise will improve the sound quality of the vehicle's interior space and enhance passengers' experience. However, current noise control techniques are high-cost and hazardous to environment. Therefore, this paper studies the first ever usage of low-cost, biodegradable natural materials for vehicle's HVAC noise control. Jute felt and waste cotton were found to have higher sound absorption coefficients than other common sound absorbing natural materials, and were chosen as sound absorbers for noise control treatment of a prototype HVAC unit. Noise sources in the unit were identified and ranked, and the treatment was applied to these. The treatment significantly reduced the noise level (by 4 dBA) and loudness level (by 7 sones) due to the unit at the reference passenger's ear location, with negligible cost and weight. Sound quality evaluation by 24 participants showed that the treatment significantly reduced the annoyance of the vehicle interior soundscape comprising the HVAC noise. Thus, jute felt and waste cotton are low-cost, light-weight, biodegradable and recyclable natural materials with high potential for HVAC noise control.