###### Abstract
The first dimension is geometric configuration, which determines how the structure interacts with the acoustic field. SAMs are classified as either planar metasurfaces or bulk-type architectures. Metasurfaces are thin, two-dimensional systems that control wavefronts primarily at boundaries using surface-patterned features [24; 25; 26]. In contrast, bulk-type SAMs interact volumetrically with acoustic waves, enabling broadband absorption, direction-dependent propagation, and spatial sound manipulation. This integrated perspective provides a foundation for systematically explaining the inherent interactivity and multifunctional operational capabilities of soft systems, transcending conventional single-axis classifications. The second dimension of classification focuses on the dominant physical mechanism by which acoustic control is achieved [27; 28]. These mechanisms include local resonance, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Author** & **Year** & **Scope of Review** & **Classification Criteria** \\ \hline [PERSON] et al. [2] & 2018 & AMs & \begin{tabular}{c} Theories, Structures, Fabrication \\ Approaches, Applications \\ \end{tabular} \\ \hline [PERSON] et al. [3] & 2022 & Tunable AMS & \begin{tabular}{c} Tuning Mechanisms, Structural \\ Types, Applications \\ \end{tabular} \\ \hline [PERSON] et al. [7] & 2021 & AMs & Passive and Active Systems \\ \hline [PERSON] et al. [19] & 2023 & \
\begin{tabular}{c} Tunable and \\ Programmable Systems \\ \end{tabular} &
\begin{tabular}{c} Mechanical Tuning, Active Control, \\ Field-Responsive Materials \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Classification of prior reviews by scope and classification criteria. phase manipulation, amplitude attenuation, and structural reconfiguration. For example, systems based on membrane-mass units or Helmholtz resonators rely on subwavelength resonance, whereas those based on gradient index designs or delay-unit cells manipulate the phase of wave propagation [29; 30; 31; 32; 33; 34]. Other systems achieve amplitude modulation through lossy components or tunable acoustic resistors, and some utilize geometric deformation to dynamically alter acoustic pathways [35]. A summary of conventional and acoustic metamaterial mechanisms is illustrated in Figure 1.  
The third dimension addresses functional responsiveness, which refers to how systems behave in the presence of external stimuli. This classification clarifies the distinction between responsiveness and tunability--two related but distinct attributes. Responsiveness indicates how actively a system responds to external stimuli; passive systems react to environmental changes such as temperature and deformation without external power, while active systems can adjust properties in real time through electrical, magnetic, or pneumatic stimuli with feedback control. Tunability, on the other hand, refers to the ability to adjust structural or physical properties post-fabrication, encompassing both passive adjustments (e.g., rotation, compression) and active adjustments. These two attributes are interrelated but not identical. Tunability and activeness are distinct but potentially intersecting attributes; their presence within a system is governed by implementation-specific factors rather than inherent coupling. This review systematically analyzes these overlaps and differences, providing examples of practical implementation approaches and performance trade-offs. Through this analysis, we emphasize that soft metamaterial design is not merely functional insertion but represents a systemic integration of structure, material, control, and response. Importantly, these functional attributes are not determined solely by the material itself but by how it is implemented within the system. For instance, dielectric elastomer actuators and shape memory polymers may be employed in either active or tunable configurations depending on their integration and control strategy.