Abstract
The potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date acoustic metamaterials have not been experimentally tested in an automotive silencer for performance enhancement. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. These results are then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of the acoustic labyrinthine DENORMS cylinder proved to be the most significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. It was also found that the traditional hard wall internal baffle silencer performance can be improved by replacing it with a DENORMS internal baffle. Acoustic metamaterials have potential as a novel method for automotive companies to attenuate sound of specific frequencies.
Highlights
In an automotive exhaust system, the silencer is used to reduce the noise output to the surrounding environment created by the engine
Internal cylinders are a common method of increasing transmission loss in an automotive silencer, this test was conducted to establish if a metamaterial cylinder could be used to improve the silencer performance
This paper investigates the effects acoustic metamaterials have when applied to an automotive silencer
Summary
In an automotive exhaust system, the silencer is used to reduce the noise output to the surrounding environment created by the engine. A petrol engine with no silencer radiates exhaust noise between 90 and 100 dB(A), while a diesel engine with no silencer, under identical conditions, radiates exhaust noise in the range from 100 to 125 dB(A) [1]. Without a silencer, these noise levels would cause health issues in both humans and wildlife. The transmission loss is the difference in the sound power level between the incident wave entering and the transmitted wave exiting the silencer when the silencer termination is anechoic [3]
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