Noise Ingress Research Articles

Performance Evaluation of Balcony Designs for Mitigating Ground Level Noise

This study aims to tackle the challenge of high noise levels on balconies while preserving natural ventilation. Eight innovative balcony designs, incorporating elements like diffuser edges, undulating ceilings, Helmholtz resonators, grooves, or sound traps, were evaluated via finite element (FE) modeling. The insertion loss results showed that for many balcony designs, noise reduction in the balcony could deteriorate beyond an elevation of 8 m. However, the front jagged and full wavy ceiling designs were shown to be more robust in noise attenuation across balconies on different floors. The jagged ledge and grooved parapet designs yielded an overall 1.5 dBA lower SPL at the exterior regions, compared to other designs, which implies that the designs are less acoustically detrimental to nearby residential blocks as they tend to diffract and absorb incident noise. The jagged ledge design is more effective for lower floors while the jagged ceiling design is more effective for higher floors. A combination of the protruded jagged ledge for the lower floor and jagged balcony ceiling for the higher floor would result in the lowest noise ingress over three stories of residential units: this would be capable of achieving more than 3 dB noise reduction and would offer viable options for improving balcony noise mitigation, by providing valuable insights to architects and designers seeking practical solutions for outdoor noise reduction. Our study highlights that whereas the spectrum characteristics of acoustic absorption materials may be less tunable, and where reduced head space is traded for thicker material for greater ab-sorption and added affixation and maintenance cost, the jagged ledge and ceiling curvatures can actually be shape-tuned, say for every 3 to 4 floors up the high-rise to more effective reduce noise ingress and possibly improve the architecture façade outlook.

A novel method for optimizing in-car rolling noise levels within a railway tunnel environment

In-car noise levels within trains rolling on surface track are usually controlled by noise and vibration which is generated at the wheel–rail interface and then transmitted through the chassis and floor of the train cabin. In a railway tunnel environment, higher noises levels result from the build up of reverberant noise, and if left untreated this increased noise can affect passenger comfort and make it harder to listen or converse. In extreme cases, it can lead to adverse health effects: travellers may complain and avoid using the rail service as a result. Accordingly, the acoustic design of railway tunnel environments generally includes consideration of various treatments to reduce noise ingress into vehicle interiors, particularly given treatments to the vehicles themselves may not be cost effective. Modeling of in-car noise levels within tunnels has traditionally used the Sabine equation as part of the design process. Because the Sabine equation was never intended for this application given the geometry and frequencies involved, an improved method which recognized the near field effects was developed in order to provide confidence in the acoustic design. In this presentation, this novel method for modeling in-car rolling noise levels and optimizing sound absorptive treatments within a tunnel is discussed. Modeling results and measurements from a recent major rail project are used to demonstrate the effectiveness and improvements in outcomes from traditional approaches.

Assessing noise with provisions for ventilation and overheating in dwellings

In the design of residential developments, it has been common practice for façade sound insulation (to protect against outdoor noise) to be considered separately from the provisions for ventilation and for mitigating overheating. This fragmented approach has led to different designers making different, incompatible assumptions about the internal environmental quality conditions: the acoustic designer assumes that windows are closed to control external noise ingress, while the mechanical designer assumes that windows are open for ventilation or mitigating overheating. This leaves occupants with a choice between reasonable noise levels or thermal comfort, but not both. This problem is exacerbated by increased overheating risk in modern buildings and future climate scenarios. In response to this issue, the Association of Noise Consultants has produced the draft Acoustics Ventilation and Overheating Residential Design Guide – the ‘AVO Guide’. The AVO guide recommends an approach to acoustic assessment that takes regard of the interdependence of provisions for external noise ingress, ventilation and overheating. This paper describes the context, background and content of the AVO Guide. There are references to passive attenuated options for ventilative cooling to help designers avoid simply specifying mechanical cooling. Practical application: This paper is entirely focused on the practical application of the guidance in the Association of Noise Consultants’ Acoustics, Ventilation and Overheating Residential Design Guide. It describes the current practical problem that designers face, and the mistakes that are the common practice across the industry, of failing to integrate the design for noise with the ventilation strategy and provisions for overheating. It outlines how this can be achieved to enable better internal environmental quality conditions for occupants, supported by the current English Planning regime and professional good practice guidance available.

Silent Room: A (non)sensory interactive art installation

Simon Heijdens, a London-based Dutch artist, was commissioned by South by Southwest (SXSW), an annual film, media, and music festival in Austin, TX, to create an installation artwork to premiere at SXSW in March 2016. In reaction to the sensory overload of the festival, he created Silent Room. Students and professors from the University of Texas at Austin worked alongside Mr. Heijdens to design a portable, self-sufficient, reusable space providing sound isolation and absorption from outside and inside the chamber, respectively. Housing the space in a shipping container, Silent Room was successfully built and showcased at SXSW in downtown Austin to hundreds of visitors, achieving a minimum sound reduction of 27 dBA at 40 Hz and a maximum reduction of 55 dBA at 1.45 kHz. These results were achieved using a suspended floor and decoupled wall/ceiling construction of Auralex rubber U-Boats, 2” x 4” wood studs, mineral fiber insulation, plywood, Auralex SheetBlok vinyl, and acoustically treated gypsum board. After initial acoustical measurements, more U-Boats were added, decoupling the container underside from the street and isolating it from ground-borne vibration. However, the room performance worsened after this change, possibly due to exposure to a new air-borne path for noise ingress.

Combining noise mapping and ventilation performance for non-domestic buildings in an urban area

Maximising the natural ventilation of a building can be beneficial in terms of comfort and reduced reliance on air-conditioning. However, in urban areas this can conflict with the need to reduce the ingress of external noise. In this paper a method is presented to quantify the interaction of building noise exposure with natural ventilation potential. Finite element models of ventilation aperture sound reduction index were used to determine façade sound insulation values for naturally ventilated buildings in two locations. Road traffic noise levels at the building façade were obtained from a calculated noise map of Manchester (UK). Window openings were adjusted in the thermal simulation package and modelled with mixed mode cooling ventilation strategies (both natural and mechanical). This enabled noise considerations to be quantified in terms of building ventilation and energy use for cooling at the whole building level. For a tolerated internal road noise ingress of 34 dB(A) cooling energy consumption for the example buildings in the quieter noise locations was found to decrease by 22%–45% compared to the noisier locations. Most importantly, the introduction of noise reduction measures equal to 10 dB(A) resulted in reductions in cooling energy consumption that varied from 28% to 45% of the original cooling energy consumption. This study illustrates the importance of an integrated approach to both noise exposure and ventilation performance in urban buildings.

Innovative green acoustic techniques to control noise ingress and sound propagation and to reduce energy consumption.

The current LEED rating system currently does not give credit for any elements of acoustic design within the point system. Too often, projects can become too focused on obtaining the points within the defined categories while sacrificing the basic elements of acoustic design (i.e., noise ingress from natural ventilation). The acoustic consultant must often find innovative ways to incorporate acoustic design into the building that will support the sustainability goals of the building and can be used to support and/or obtain a LEED point. Three innovative methods of green acoustic design in project case studies will be presented: natural ventilation techniques to maintain privacy, acoustic comfort in indoor working environments, and energy saving techniques for performing arts facilities. If applied to a project in an innovative method, the acoustics of a project need not be compromised and could be used as a LEED credit for innovation in design.

Modeling the acoustical and airflow performance of natural ventilation inlet and outlet units

One aspect of the trend towards designing green buildings has been the increasing use of natural ventilation for buildings which otherwise might have required mechanical ventilation or even full air conditioning. However, the pressure differentials available to drive the natural ventilation process are small and hence relatively large inlets and outlets with low resistance to flow are required. These apertures constitute significant acoustic weak points on building facades and hence need to be treated to reduce noise ingress. Although there are a number of natural ventilation units available they have frequently been designed from the application of simple principles without any attempt to optimise both their airflow and acoustical performance. In this paper the results of a series of computer modeling exercises are described using acoustic FEM and BEM plus Computational Fluid Dynamics (CFD) which seeks to establish recommendations for the optimum design of natural ventilation inlet and outlet devices for both acoustical and airflow performance.

Reducing the ingress of urban noise through natural ventilation openings

For buildings in busy urban areas affected by high levels of road traffic noise the potential to use natural ventilation can be limited by excessive noise entering through ventilation openings. This paper is concerned with techniques to reduce noise ingress into naturally ventilated buildings while minimizing airflow path resistance. A combined experimental and theoretical approach to the interaction of airflow and sound transmission through ventilators for natural ventilation applications is described. A key element of the investigation has been the development of testing facilities capable of measuring the airflow and sound transmission losses for a range of ventilation noise control strategies. It is demonstrated that a combination of sound reduction mechanisms -- one covering low frequency sound and another covering high frequency sound -- is required to attenuate effectively noise from typical urban sources. A method is proposed for quantifying the acoustic performance of different strategies to enable comparisons and informed decisions to be made leading to the possibility of a design methodology for optimizing the ventilation and acoustic performance of different strategies. The need for employing techniques for combating low frequency sound in tandem with techniques for reducing high frequency sound in reducing the ingress of noise from urban sources such as road traffic to acceptable levels is demonstrated. A technique is proposed for enabling the acoustic and airflow performance of apertures for natural ventilation systems to be designed simultaneously.