Silencer design by using array resonators for low-frequency band noise reduction

Abstract

Helmholtz resonators are often used to reduce noise. They are particularly useful when noise has a narrow frequency band. In this study we aim to broaden its narrow band characteristics by combining many resonators. Serial and parallel arrangements of resonators have been tested to obtain broader impedance mismatch characteristics in the broader band. Theoretical and experimental results explain these characteristics in the absence of mean flow. The serial arrangement mainly increases the peak of TL at the resonance frequency. But the parallel arrangement logarithmically increases the peak of TL and expands the bandwidth. The change of acoustic characteristics is explained by introducing an "equivalent impedance analysis." This shows that the transmission loss has a maximum value when the distance between resonators is / 4 of its wavelength. In this study we propose a novel design method that optimizes the arrangement of resonators while keeping the volume minimized. Various transmission loss characteristics are possible when we select different objective functions under constraints.

Narrow sidebranch arrays for low frequency duct noise control

“…There are many derivatives proposed as well. Examples include the resonators with extended necks, 9 coupled resonators, [10][11][12] the conical tube resonator, 13 and the Herschel-Quincke tubes, 14 and this list is far from exhaustive. However, these devices can give very good sound reduction performance only at the resonance frequencies or within a relatively narrow frequency range around those frequencies.…”

Noise control zone for a periodic ducted Helmholtz resonator system

“…It provides a clear indication of the limitation of noise control. No matter what optimizing distance [8][9][10] is adopted in noise control, the values of the attenuation bandwidth and peak amplitude must be within the proposed noise control zone. The noise control zone can be used to analyze the feasibility of desired broad attenuation bandwidth and peak amplitude in noise control optimization.…”

“…Multiple-resonator arrays have been investigated to broaden the noise attenuation band in the lowfrequency range. [7][8][9][10] Some researchers have discussed the acoustic performance of periodic ducted HR systems and proposed theoretical methods of predicting the bandwidth of the noise attenuation band. However, periodic ducted HR systems struggle to obtain the necessary broad attenuation bandwidth and high-peak attenuation amplitude at the same time.…”

On sound transmission loss across a Helmholtz resonator in a low Mach number flow duct

“…6͒. The results of the recent works by Griffin et al 7 and Seo and Kim 8 show that a broader attenuation bandwidth can be obtained by coupling resonators together. However, there are research studies indicating that the Helmholtz resonator can be excited by a flow across its mouth to generate sound ͑for instance, Refs.…”