On the theory and design of acoustic resonators,” J. A large cavity volume is often impractical and having narrow regions often results in poor attenuation of acoustic waves due to large amounts of visco-thermal losses often resulting in over-damping of the system. A limitation of these types of silencers is the requirement for large cavity volumes or narrow neck regions to achieve low frequency attenuation. 5 5.Īcoustic characteristics of perforated dissipative and hybrid silencers,” Ph.D. Dissipative materials can be introduced to achieve broadband attenuation. Different configurations of partitions can be used to alter the number of resonances. 4 4.Īnalysis of concentric-tube resonators having unpartitioned cavities,” J. As the porosity increases, the silencer behaves more like an expansion chamber. If the perforated separating panel has a low porosity, a Helmholtz resonator type of attenuation occurs. Rep.įor silencers with non-partitioned cavities and panels composed of multiple identical perforations along the length of the silencer a similar phenomenon occurs. Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems,” Sci. Quasiperfect absorption by subwavelength acoustic panels in transmission using accumulation of resonances due to slow sound,” Phys. A similar technique has been employed in the design of sound absorbing acoustic metamaterials in order to achieve perfect broadband absorption in one and two port systems much smaller than the wavelength of the sound wave. Side-loaded Helmholtz resonators can be optimised to increase their absorptive performance by changing the separation distance between subsequent resonators and by adjusting their geometry and thus visco-thermal losses to critically couple them with the pipe. Silencer design by using array resonators for low-frequency band noise reduction,” J. Multiple Helmholtz resonators can be side-loaded to the pipe, all tuned to different frequencies in order to achieve the broadband attenuation of noise.
For silencers with partitioned cavities with a single perforation, i.e., a Helmholtz resonator, excellent attenuation can be achieved at the resonant frequency of the resonator. The attenuation of acoustic waves in a pipe by silencers is typically achieved through the employment of rigidly backed cavities, connected to the pipe by a perforated panel.
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