Simulating the effect of acoustic treatment types for residential balconies with road traffic noise

Development of design guides to estimate the difference in speech interference level due to road traffic noise between a reference position and balcony position or façade position is explored. A previously established and validated theoretical model incorporating direct, specular and diffuse reflection paths is used to create a database of results across a large number of scenarios. Nine balcony types with variable acoustic treatments are assessed to provide acoustic design guidance on optimised selection of balcony acoustic treatments based on location and street type. In total, the results database contains 9720 scenarios on which multivariate linear regression is conducted in order to derive an appropriate design guide equation. The best fit regression derived is a multivariable linear equation including modified exponential equations on each of nine deciding variables, (1) diffraction path difference, (2) ratio of total specular energy to direct energy, (3) distance loss between reference position and receiver position, (4) distance from source to balcony façade, (5) height of balcony floor above street, (6) balcony depth, (7) height of opposite buildings, (8) diffusion coefficient of buildings and (9) balcony average absorption. Overall, the regression correlation coefficient, R², is 0.89 with 95% confidence standard error of ±3.4 dB.     

Scale model study of balcony insertion losses on a building façade with non-parallel line sources

The screening effect of balconies on a building façade in the case where the noise source is not parallel to the façade is studied using scale model experiment in the present study. Results show that the angle of source inclination to the façade has substantial effects on the balcony insertion loss in the presence of a traffic noise spectrum. Less amount of noise amplification is observed when the source is inclined compared to the case of parallel source in the presence of balcony ceiling reflections. Regression formulae in terms of three independent angles which determine the positions of the balcony and its ceiling relative to the noise source are developed for the prediction of balcony insertion loss. The discrepancy between measurements and predictions is within engineering tolerance.     

Prediction of the sound field into high-rise building facades due to its balcony ceiling form

This study presents the acoustic performance off tall building facades closed to roadway due to one of balcony configurations, namely ceiling, with an inclined form in terms of traffic noise reduction. Three inclined angles are tested (5,10, and 15°) with different balcony depths by using a Pyramid Tracing model developed by A. Farina. The results in terms of A-weighted sound pressure level reduction are expressed in free field into the balcony back wall. The protection level, defined as the difference in noise levels before and after inserting the proposed balcony form, has been used to assess the reduction offered by that configuration. A maximum reduction due to using these forms is obtained at higher floors and at balcony of 2 m depths and more. As a consequence of simulation results, it is found that the prediction of protection levels from 10th to 15th floor can be calculated from an empirical equation.     

A simple formula for evaluating the acoustic effect of balconies in protecting dwellings against road traffic noise

This study explores the noise reducing effect of a balcony and describes the development of a simple theory pertaining to the propagation of traffic noise from a road into a balcony. A new methodology is proposed that is based on the well-known prediction scheme—“Calculation of Road Traffic Noise” (CRTN)—developed in the UK. A geometrical ray theory is developed for the prediction of noise levels inside a balcony due to road traffic. The source level of road traffic noise is obtained as per the standard CRTN methodology. However, road sub-segmentations and new approaches for the prediction of noise levels at illuminated and shadow zones inside a balcony are proposed. Field measurements have been conducted on four different types of balcony to validate the proposed methodology. The insertion loss, defined as the difference in the noise levels with and without the presence of a balcony, has been used to assess the shielding effectiveness of a balcony against road traffic noise. The simple theory is validated by outdoor field measurements. It is also found that a properly designed balcony can provide considerable screening effects in protecting dwellings against road traffic noise.     

The acoustical influence of balcony depth and parapet form: experiments and simulations

The influence of balcony depth and parapet form on the acoustical performance of building facades close to roadways have been investigated. Various depths and two inclinations of parapet have been modeled on an eight floor building. Pyramid ray-tracing simulations and scale model measurements have been carried out. The predicted and measured A-weighted sound pressure level reductions over the balcony back wall and in free field conditions have been compared. The results have been used to derive empirical equations for predicting protection as a function of geometrical parameters. The protection obtained by various parapet depths ranges between 4 and 8 dB(A), while an additional protection of between 0.5 and 4 dB(A) can be obtained by inclining the parapets.