This study presents an enhanced multi-chamber micro-perforated panel absorber (MC-MPPA) with varying sub-chamber depths, offering ultra-broadband low-frequency sound absorption. Traditional micro-perforated panel absorbers are constrained by a limited bandwidth, necessitating impossibly small perforations for optimal low-frequency absorption. Our innovative design addresses these constraints with a lightweight, compact panel structure that uses varied chamber depths and unique porosities. Using the two-point impedance method from graph theory, an MC-MPPA was modeled and optimized. Notably, our MC-MPPA test pieces achieved impressive sound absorption coefficients experimentally of over 0.8 in the whole frequency ranges of [397-1000] and [698-1895] Hz. The absorber's thickness is a mere 47 mm, equivalent to 1/18.2 and 1/10.5 of the sound wavelength at the minimum operational frequency, respectively. Theoretically, with a maximum sub-chamber depth of just 20 mm, average absorption coefficient values of 0.6780 and 0.6483 were observed in [200-3000] and [200-4000] Hz ranges, respectively. Our optimization algorithm permits the definition of practical geometric parameters, promising substantial industrial benefits. The results have been validated theoretically, numerically, and experimentally. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
