Table 2 Comparison and characteristics of passive and active acoustic treatments in a nutshell
Characteristics | Porous materials | Static passive metamaterials | Mechanically tunable metamaterials | Activelly controlled transducers |
|---|---|---|---|---|
Principle | Interconnected dissipative pores | Resonant based | Tunable resonance-based | Actively tunable resonators |
Frequency range | - Broadband, - Medium/high frequency | - Narrow band, - Increased bandwidth with collective resonances | - Narrow band, - Increased bandwidth with collective resonances | - Narrow-band for resonant transducers - Broadband for plasma transducers, - Broadband impedances can be artificially synthesized |
Reconfigurability | - Static, - Not reconfigurable, - One application per design | - Static, - Not reconfigurable, - One application per design | - Mechanically reconfigurable (limited by design), - Several applications possible | - Electronically reconfigurable at will |
Dimension | - Quarter wavelength, - Frequency dependent | Subwavelength | Subwavelength | - Intrinsically subwavelength for the transducers themselves - But requires additional electronics and power suppliers |
Weight | - Lightweight (foams, wool,..), - Size and frequency dependent, - e.g. ρ ≈ 1.6 g.cm−3 (melamine). | - Light/medium weight: mainly air-filled 3D printed cavities/resonators or thin membranes, - e.g. ρ ≈ 1 g.cm−3 (filament) | - Light/medium weight: mainly air-filled 3D printed cavities/resonators or thin membranes + weight added mechanism | - Lightweight for piezo diaphragms, - Lightweight, nonresonant & transparent for plasma transducers - Medium weight for loudspeakers, + Medium/high for the required external electronics. |
Real world integration | - Easy, - Widely implemented for room acoustics and sound absorption, - Limited cost - Durability | - Still in development and industrialization phase (mostly for noise mitigation) - Limited cost thank to 3D printing | - Still at the research and development phase - Medium cost and integrability due to the added mechanics | - Still at the research and development phase for sound absorption and active metamaterial purposes (possible application for sensing, routing, communication,…) - Widely implemented and commercialized for ANC (headsets, …) and room acoustics enhancing systems - Medium cost and integrability due to the added electronics - Transducer dependent durability |
