For over a decade, spongy and fibrillar materials have dominated the sound absorption market. These materials, however, fail to tackle noise below 500Hz, and low frequency sound absorption remains one of the most challenging topics in the field of acoustics. This thesis discusses the use of decorated membrane resonators (DMRs) in shielding and absorbing low frequency noise below 1000Hz. DMRs possess unique acoustic characteristics in both its resonance and anti-resonance modes. In its resonance mode, both transmission and absorption of sound reaches a local maximum, and the absorption coefficient of a single layer of DMR is theoretically bounded by 0.5. In its anti-resonance mode, contrarily, the DMR membrane has an average displacement of almost zero, and transmission of sound...[ Read more ]

For over a decade, spongy and fibrillar materials have dominated the sound absorption market. These materials, however, fail to tackle noise below 500Hz, and low frequency sound absorption remains one of the most challenging topics in the field of acoustics. This thesis discusses the use of decorated membrane resonators (DMRs) in shielding and absorbing low frequency noise below 1000Hz. DMRs possess unique acoustic characteristics in both its resonance and anti-resonance modes. In its resonance mode, both transmission and absorption of sound reaches a local maximum, and the absorption coefficient of a single layer of DMR is theoretically bounded by 0.5. In its anti-resonance mode, contrarily, the DMR membrane has an average displacement of almost zero, and transmission of sound drops to a local minimum. These acoustic characteristics of DMRs can be altered by adding a sealed layer of gas and a hard plate behind the membrane layer. This composition is a hybrid membrane resonator (HMR). By changing the thickness of the sealed gas layer, the HMR’s surface impedance can be tuned to match the impedance of air to achieve total sound absorption in its anti-resonance mode.