Extremely effective broadband low-frequency sound absorption with inhomogeneous micro-perforated panel (iMPP) backed with spider-web designed cavities

Low-frequency wideband noise reduction has posed a significant problem to the scientific and technical communities in recent years. A single layer of a parallel-arranged inhomogeneous micro-perforated panel (iMPP) coupled with spider-web designed cavities is offered as a composite acoustic structure in this paper. Three different spider-web shapes have been designed and studied, i.e. circular, octagonal, and square. By controlling the different inhomogeneous patterns, perforation ratio, the thickness of iMPP, and back cavity depths, a broader multipeak low-frequency sound-absorbing performance equivalent to different resonant frequencies can be achieved. To anticipate the sound absorption coefficient of the new design, both theoretical analysis and finite-element method (FEM) simulation are executed. The predicted and FEM simulation sound absorption results of the new composite structure are verified in the experimental investigation using a square-designed sound impedance tube. By a subwavelength thickness of just 100 mm, a highly effective low-frequency broadband sound-absorbing composite structure is successfully attained by integrating many inhomogeneous MPP unit cells supported with spider-web-designed cavities. The average sound absorption coefficient is over 90% (alpha = 0.94) within the bandgap of 230 Hz to 470 Hz. Compared to traditional sound-absorbing materials, the composite structure comprises inhomogeneous MPP coupled with spider-web-designed cavities, which may provide good absorption performance while maintaining a modest and robust construction for active low-frequency noise suppression.

Automated summary

Low-frequency wideband noise reduction has been a significant problem in recent years. This paper proposes a composite acoustic structure consisting of parallel-arranged inhomogeneous micro-perforated panel (iMPP) and spider-web-designed cavities. Different spider-web shapes, including circular, octagonal, and square, are studied. By controlling various design parameters, such as inhomogeneous patterns and perforation ratio, a broader multipeak low-frequency sound-absorbing performance equivalent to different resonant frequencies can be achieved. Theoretical analysis and finite-element method (FEM) simulation are used to predict the sound absorption coefficient of the new design, which is then verified experimentally. The new composite structure, composed of inhomogeneous MPP and spider-web-designed cavities, achieves a highly effective low-frequency broadband sound absorption with an average absorption coefficient of over 90% within the bandgap of 230 Hz to 470 Hz.