The annual Institute of Acoustics Conference was held on 5th and 6th September in Kenilworth and MACH Acoustics’ Chris Jones was honoured to be invited to speak and present his paper. Chris has been researching “STANDARDISING THE TESTING AND MODELLING METHODS OF PREDICTING THE SOUND REDUCTION THROUGH OPEN WINDOWS” and this was extremely well received.
The current approach is to simply use a 10 – 15 dB reduction across the open window. This does not account for the window type, open area or angle of incident sound. Whilst research has been conducted into these factors, the lack of a standard method of testing, modelling and quantifying the acoustic performance has prevented the uptake of an improved method by acoustic and facade engineers.
This paper builds upon the research of collaboration with MACH Acoustics and The University of Bath – Blanco, Nunes and Lo (2014) and Jones (2015) in summarising the challenges in quantifying the performance by considering existing test methodologies from British Standards and extensive laboratory testing by Napier University (2007).
The potential of using FEM and FDTD modelling as a tool of visualising and understanding sound propagation through an open window is summarised. 2D FDTD modelling by Jones (2015) has examined the effect of the window variables and the accuracy of simulations by recreating Napier University (2007) test data, before using this to propose the concept of a simple mathematical model.
The aim of this paper is not to conclusively recommend a standardised method, but to present existing information and new research in a balanced manner that will inspire a discussion within the acoustics industry as to how such a method might be agreed.
The Computational Foundry is a key building in the new Bay Campus completing the central square of the site. Working with AHR and Willmott Dixon, MACH Acoustics is delighted to be supporting on this important project.
The building is being design to create a hub for Mathematics and Computer Research and to encourage collaboration through designing spaces for interaction, meeting pods and the “research crucible”. The Bay Campus enables the University to increase its’ footprint – which pioneers the way for co working collaboration with industry and academics. They will share not only the same site, but also laboratories and facilities.
Ze Nunes has been invited to present a webinar entitled “Visualising Sound to Improve Open Window Performance”. Arpan Bakshi, Performance Evangelist for Foster and Partners spotted Ze’s posts on linked in and found some shared interests. Arpan specialises in sustainability performance and organises the Performance Network.
This online seminar on June 2nd will address energy usage within buildings from ventilation systems and how architects can design for naturally ventilated offices, classrooms and other room types. How can you treat the sound coming into a building to reduce noise levels? Which window types work better than others?
Current understanding of the performance of open windows is low, mainly because the acoustics of these buildings is difficult to get to grips with. Here, Ze answers the key questions and helps you to better understand how to treat windows at the design stage – ultimately leading to improved energy usage and more efficient buildings. The visualisation of sound; the acoustic performance of open windows; clever mathematics; incredible software; and our retro toy, the Slinky, all play a part in this forward thinking webinar.
Date & Time: Thursday June 2, 2016; 9:30 AM – 10:30 AM PDT (UK is 8 hours ahead of Pacific Time).
Learn More & Register: https://attendee.gototraining.com/r/7033392638388280578
I was captivated listening to Daniel Kish recently interviewed on Radio 6 on the Lauren Laverne show and how he uses sonar to help him navigate the world as a man without sight – but with a commanding understanding of sound.
At MACH Acoustics the Visualisation of Sound concept has proven extremely helpful in explaining how acoustics work and how sound “behaves”. Using sonar for navigation takes this concept out of the classroom and clearly demonstrates how for the majority of us sound as a sense can be developed and appreciated much further.
To listen to Daniel’s TED talk click on the link below:
Daniel explains how using this method of navigation with a form of echolocation helps him “construct and understanding of the space around him”. An interesting concept for sighted and blind alike – a powerful mix of engineering, physics and interpretation.
Weston Town Hall, Weston-Super-Mare (client North Somerset Council), a collaboration with Alec French Architects and Willmott Dixon is now a completed refurbishment project with a contract value of £9.7m.
Going over and above standard guidelines, MACH Acoustics focused on analysing the spread of sound pressure level and the speech intelligibility over distance, rather than purely focusing on reverberation time in the sense of traditional design. MACH used extensive computer modelling and produced video/audio simulations (‘auralisations’) to demonstrate the acoustic benefits in respect of the aesthetic views of the architect, the budget of the project, the low carbondesign initiative and the satisfaction of the client. This allowed us to evaluate the level of acoustic separation between desks and groups in large open plan areas, with and without noise mitigation methods including desktop screens and acoustic soft treatment.
Through past projects it has been often found tricky to determine how much acoustic treatment is needed in a space. MACH have experienced complaints from open plan offices with high quantities of treatment, to very little complaints from occupants in an effective concrete frame with no acoustic treatment.In addition BCO guidance recommends a highly acoustically absorbent soffit, which poses problems with low carbon exposed thermal masses, aesthetics and additional cost. Hence this traditional reverberation time based approach is seen to be limited in open plan developments
Our approach focused on the reduction of sound pressure level (SPL) over distance, and the level of speech intelligibility (STI) between individual and grouped desk areas, presenting results through auralisations and videos to provide a cost effective sustainable solution.
A multitude of CATT Acoustics models were created to assess several factors. Firstly effective was the addition of acoustic treatment in the form of suspended rafts above the walkway between desks and later above desks, Whilst the absorption coefficient of these are similar to BCO traditional guidance, the quantities of panels are vastly reduced by specifically placing them in the most effective areas over desks and cabinets/shelves to reduce noise transfer (Figure 1).
Figure 1: Increasing acoustic separation by placing suspended acoustic rafts over desks
The next step was to introduce screens to enhance the acoustic separation between desks (Figure 2). The most effect. Whilst combining the full extent of suspended rafts and screens provide the best option acoustically, it was considered by the design team that a combination of the screens and the initially proposed amount of suspended treatment was the most cost effective solution. Still, this achieved a reduced transmission of sound in line with what traditional BCO guidance would have provided, with the benefit of reduced costs and a lower carbon footprint.
Figure 2: Increasing acoustic separation by placing screens between desks
Presentation of Results
As an acoustic consultancy we understand that it is our client and end users that benefit or suffer from the result of our work. We therefore prioritize the importance of good communication. The illustrations within this document have been taken straight from our acoustic report and were complimented by a set of auralisation videos that were distributed to the design team and client. Links to these three videos are provided below.
A new build range of large residential projects within an Asian capital city (confidential) for the public sector fitted well with our commercial research and development. MACH’s uniqueness in this field facilitated the creation of a new in house software package, implementing Finite-Difference Time Domain (FDTD) mathematics. This software package allows us to model bespoke constructions on a project by project basis, such that solutions are new and innovative.
Sound Insulation of Open Windows and Balconies
The use of purge ventilation to naturally ventilate a building, can provide a significant challenge in regards to external noise ingress through the façade and open windows. Typifying the burgeoning requirement for affordable and luxury city centre accommodation, our client wanted bespoke options for a number of confidential, high-rise residential,overseasprojects.
The challenge is providing noise control measures without the use of bulky attenuators, thermal dampers and ugly weather louvers. We pooled our experience in building acousticswith Dr Steve Lo, Senior Lecturer in Sustainable Environmental Engineering at the University of Bath, to investigate the potential of noise mitigation by balcony shaping and other façade design options, in order to screen open windows from external noise sources such as road traffic.
Acoustic Modelling of Noise Ingress and Mitigation
The FDTD software was mainly developed in-house, but also through two MSc projects being supervised by Dr GwenaelGabard and Dr FillipoFazi at the ISVR, funded by MACH Acoustics.
FDTD is similar to commercial Finite Element (FE) modelling but has the advantage that the sound pressure field can be animated over time, allowing the wave propagation to be visualized, measured and assessed. A visual representation is a strong advantage in understanding the reflection and diffraction around walls, windows, balconies and screens.
Balconies exhibit interesting differences in sound propagation depending on the height and distance from the road.The linked model video belowshows the nature of sound reflections off the balcony façade and soffits, used to assess one of the towers within this development. Adjusting the shape and finishes of these surfaces has shown value in reducing noise ingress into the proposed residential accommodation.
Figure 1: FDTD video of road traffic noise propagating into balconies of a high rise residential building
From the above model, a more detailed view can be presented to show just a single flat/balcony. The images below show a standard single balcony, with a reflector then built from the soffit in the direction of the source (road traffic) to direct sound back away from the balcony.
Figure 2: FDTD model of a single balcony with (bottom) and without (top) a noise mitigating reflective panel