Improvement in Noise Transmission Across Firewall of a Passenger Car

Firewall of a car separates the engine compartment from the cabin and acts as a barrier for engine noise entering the passenger compartment. Hence noise transmission through the firewall plays an important role in determining the interior noise of a car. Noise Reduction measurement technique is useful to evaluate existing and potential acoustic treatments of the firewall of a car. This paper presents two systematic measurement approaches for quantifying the acoustic performance of firewall insulation materials across the firewall of a car. First a Volume Velocity Source was placed in the passenger compartment and noise reduction was measured across the firewall with different configurations of firewall acoustic treatments. Similar exercise was repeated by installing an actual vehicle firewall in a sound transmission loss suite and measuring the noise reduction across the firewall. Measurement techniques such as leakage detection and sound intensity mapping were used to enhance the understanding of the noise transmission paths through the firewall and to rank the dominant leakage areas.

Based on the above, appropriate modifications to the car have been carried out and evaluated for reducing the noise transmitted through the firewall of the car. To assess the influence of improvement in noise reduction across the firewall on the interior noise of the car, in cab noise measurements were carried out with the engine running on the test track.