Experimental study for improving sound absorption of a composite helical-shaped porous structure using carbon fiber

A composite sound absorption structure constructed with fibrous layer and carbon fibers was proposed and its acoustic performance was experimentally studied. Proposed structure’s sound absorption properties depended on the gap of the air cavity between fibrous layers. To increase the absorption efficiency, carbon fiber was applied between the gaps. The normal incidence sound absorption coefficients and specific acoustic impedance were measured with the two-microphone impedance tube method to determine the effects of the carbon fibers on the acoustic properties. Random incidence absorption coefficients were determined from the measured specific acoustic impedances of the proposed structures. The measured results were compared for various fractions of carbon fibers. Modified wave propagation equations with empirical density equations were suggested to predict the acoustic behavior of the proposed absorbers. After application of the carbon fibers, the composite helical-shaped sound absorber showed better sound absorption efficiency under both normal and random incidence conditions. This suggested that the carbon fibers introduced additional sound dissipation when properly distributed along the gap of the sound absorber.