Narrow sidebranch arrays for low frequency duct noise control

Abstract

The present study investigates the sound transmission loss across a section of an infinitely long duct where one or more narrow sidebranch tubes are installed flushed with the duct wall. The finite-element method is used to compute the wave propagation characteristics, and a simplified theoretical analysis is carried out at the same time to explain the wave mechanism at frequencies of high sound reduction. Results show that the high sound transmission loss at a particular frequency is due to the concerted actions of three consecutive sidebranch tubes with the most upstream one in the resonant state. The expansion chamber effect of the setup also plays a role in enhancing sound attenuation at non-resonance frequencies. Broadband performance of the device can be greatly enhanced by appropriate arrangements of tube lengths and/or by coupling arrays on the two sides of the duct.

Optimized reactive silencers with narrow side-branch tubes

“…4). Figures 3 and 4 thus show that unlike the case of closely packed side-branch tubes, 9 the individual TL peaks are caused by resonances of individual tubes and not by concerted interplay among several tubes. Figure 5 shows the comparison of TL of the abovedescribed optimized silencer (black line) with two nonoptimized silencers with the same number of side-branch tubes.…”

“…It is also assumed that the waveguide downstream the silencer is infinite (or anechoic), so that there is no wave impinging from the right side. Within this work, as it has been adopted in the previous works, [3][4][5][6][7][8][9][10][11] the fluid is considered non-dissipative (all forms of acoustic energy dissipation are neglected), and stationary. Even if in almost all practical applications the fluid would be moving, the assumption of stationary fluid does not represent too much simplification, as Tang and Li 12 have reported that slow in-duct airflow does not affect the transmission loss of single or double sidebranch arrangements very much.…”

A Review on Natural Ventilation-enabling Façade Noise Control Devices for Congested High-Rise Cities

“…These tubes act as quarter wavelength resonators, which are able to stop the sound transmission by concerted resonance [33]. In his experiment, Field found that the weighted sound reduction index of his proposed device was around 22 dB.…”

Sub-chamber optimization for silencer design

“…For the coupling between sub-chambers, it has been shown that an array of Helmholtz resonators [20] or cavity resonators [21,22] can provide a wider TL with each resonator contributing a distinct peak. This has also been validated experimentally through the design of exhaust stack silencers [23].…”