<p>Broadband noise control remains challenging, especially when there is substantial low-frequency content. Most passive absorbers use acoustic mass to induce resonance at strategic frequency bands. This study begins with classic parallel and series designs using a comprehensive performance evaluation of total absorbed sound energy for a given absorber thickness. It is found that the parallel design is suitable for problems of moderate frequency bandwidth, while the series design is superior for broader bandwidth in the high-frequency region due to the suppressed acoustic mass by the inter-layer coupling. These results are used as a benchmark to assess a collection of intricate designs in literature. Analysis reveals that most such designs are comparable to but cannot surpass the performance of classic designs, and issues constraining their further optimization are discussed. The use of porous material in the cavity is found to be beneficial for all designs, especially at low frequencies due to the cavity stiffness reduction by heat transfer, contrasting with the cliche that porous material is ineffective at low frequencies. Future progress requires shifting from mass-focused design to co-designing mass and stiffness, possibly via negative stiffness, and there are new design samples that surpass the benchmark performance.</p>