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13.03 Ventilation-Enabling Sound Insulation Devices, Part 2

Noise reduction of plenum window with add-in dual staggered sound scatterer arrays
Time: 3:20 pm

Author: Xiaolong LI

Abstract ID: 1866

In present study, a 1:4 scaled down model was used to explore the noise reduction across the plenum window with add-in dual staggered scatterer arrays (sonic-crystal). Reverberation time inside the model space was measured firstly to eliminate the effect of the possible reverberation variation on the sound transmission loss of the plenum window. Two sonic-crystal arrays, the two-by-two and two-by-three scatterer arrangements, were adopted for measurement. A total of four arrays was thus tested after the staggering. Computational simulation was conducted for the sound field inside the plenum chamber to study the noise reduction mechanism of the present window system. Results show that the noise reduction of the plenum window was improved by varying degrees due to the placement of the dual staggered sonic-crystal. The Installation of the dual staggered sonic-crystal increased the sound energy reflections out of the plenum window inlet and decreased the sound energy that passed through the plenum window cavity. At the same time, the resonances inside the window cavity also contributed to the sound transmission loss of the plenum window. The noise reduction across the plenum window was enhanced.  The improvement was between ~2 to ~2.7 dBA.

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Numerical simulation of air inlets sound insulation
Time: 8:00 am

Author: Julien Puig

Abstract ID: 1976

Breathing healthy air at home requires efficient ventilation which is generally achieved by mechanically controlled ventilation systems. However, the installation of air inlets, at the top of windows, reduces sound insulation. Actually, laboratory tests must be processed by manufacturers to measure the SRI (sound reduction index), which is calculated from the difference between the source and receiving sound power levels in the one-third octave band. The addition of melamine, a widely used porous material with interesting acoustic properties, slightly decreases the transmitted noise through air inlets, but the sound reduction remains far from that of a window without any inlet at all. Moreover, experimental settings induce uncertainties, particularly when low frequencies are involved. Numerical simulation is thus an interesting alternative for studying air inlets’ vibro-acoustic behaviour. Many parameters can be considered without the need to carry out new experiments, thus greatly reducing financial costs. Calculations must be computationally efficient to enable an optimization approach. To this end, the proposed numerical model is based on the patch transfer function method which is a substructuring approach. Here, each subsystem of complex geometries is discretized by finite elements while porous materials are modelled using an equivalent fluid or localized impedance.

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Assessing a parallel baffle splitter, an experimental and numerical study on insertion loss and pressure drop
Time: 2:40 pm

Author: Juan Escudero

Abstract ID: 2176

HVAC systems are composed of different noise sources and paths. The non-attenuated propagation of noise through the system has detrimental effects on acoustic comfort of people inside the premises. To mitigate the propagated noise, parallel baffle splitters are used which reduce the transmitted noise through acoustic coatings. Different methods have been developed to predict the insertion loss of those elements, however, if the input data is not well known these models can lead to deviated results. On the other hand, the use of splitter in HVAC systems produces pressure drop which can damage the equipment used if that is not well predicted. Different models are available in the literature, which relates dimensional features and design velocity to estimate the pressure drop coefficient. However, models can give overestimated results. In this work an experimental rig was implemented to assess a splitter installed inside of a test duct. Measurements were performed to estimate insertion loss and pressure drop coefficient, following the guidelines exposed on the ISO 7235 standard. The results were compared with analytic methods. Finally, a numerical method analysis of the test rig was performed, showing the correlation between these results and the experimental data.

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Soundproof Window – Natural Ventilation
Time: 3:00 pm

Author: Vinícius Ávila Ferreira

Abstract ID: 2361

Expansion of brasilians cities worsen noise pollution in these places, forcing people to maintain their doors and windows closed. Domestic environment enclosing lead to necessity of air conditioning system, however the frequent use of the equipment may cause many health problems, such as respiratory difficulties and spread of diseases , not to mention high costs with energy. Considering these facts, there is the need of soundproofing windows with air supply , that allows passage of air without noise passage, guarantee a well-ventilated environment, with thermic and acoustic comfort without the use of acclimatisation systems . we have developed two prototypes with significant opening that allows air supply (passage) (0,35m2) and noise reduction (Rw+Ctr) reaching 8 to 10 dB. In the first study, we considered people inhabiting really noisy surrounding areas, who has already installed a regular window. In this particular case, we developed a soundproofing window air supply that can be installed over the existing one. A second study considered new constructions to focus the environment where the person sleeps and then elaborate a soundproofing window air supply for bedrooms. Keywors: soundproofing windows, air supply, sound insulation. noise pollution

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The effect of aspect ratio on the inerstion loss of lined ducts
Time: 3:40 pm

Author: Caoyang Li

Abstract ID: 2871

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Handbook provides tabulated information that can be used to determine the insertion loss of a variety of lined and unlined ducts.  However, the tabulated cross-sections are primarily for square ducts.  Not surprisingly, there is a need for information on the insertion loss of ducts having different aspect ratio cross-sections.  Hence, the insertion loss for large aspect ratio cross-sections are investigated using a previously validated finite element simulation approach.  A coupled structural-acoustic finite element analysis is performed, and data is compared to measurement results from the literature for a few configurations.  An analysis campaign is then performed which better explains the effect of aspect ratio on duct insertion loss.

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Noise reduction of enhanced acoustic balconies on a high-rise building block
Time: 8:20 am

Author: SK Tang

Abstract ID: 3050

A new device called ‘enhanced acoustic balcony’ is installed in a new housing estate in Hong Kong. It is intended to help reduce the impact of traffic noise on the residents. This balcony is basically an enlarged form of a plenum window and with three openings. Apart from the outdoor air inlet, there is the balcony door and a side-hung window on the interior balcony wall for natural ventilation of the indoor space. Sound absorption of NRC 0.7 is installed on the balcony ceiling and its sidewall facing the incoming traffic noise and an inclined panel is installed outside the balcony to provide noise screening. A site measurement of its noise reduction is carried out in the present study in a newly completed housing block.   A 28 m long loudspeaker array is used as the sound source. The indoor noise levels are measured according to ISO standard. The results show that the difference between indoor and outdoor noise levels in the presence of this balcony form varies over a relatively narrow range between 10 to 13 dBA for an elevation angle from 25 to 60 deg. There is a weak increase of the noise level difference with elevation angle.

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Aerodynamic and acoustical effects caused by placing two prefabricated duct silencers in series
Time: 8:40 am

Author: Karl Peterman

Abstract ID: 3208

It once was not uncommon to find ductborne noise control designs and recommendations that would attempt to provide high sound attenuation values, especially for problematic lower frequencies, by using a pair of prefabricated duct silencers in series with one another, sometimes immediately adjacent but typically separated by some distance. Similarly, heating, ventilating, and air-conditioning (HVAC) duct silencers are occasionally required to accommodate fire dampers or access sections that effectively break up the silencer along its length, creating an empty gap between the noise-attenuating internal elements. Typical published performance characteristics of prefabricated duct silencers do not include effects from the use of additional silencers nearby and little information is available in common duct design and application literature. This paper will present information from a series of tests of various silencers in different configurations and spacings in an aero-acoustic test facility that will help describe the effects on insertion loss, generated noise, and pressure drop.

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