By 2050, the World Bank estimates 70 per cent of the global population will live in cities. However, to  ensure this doesn’t mean ever-expanding sprawl and further encroachment on essential agricultural and green zone areas, the compact city form is a priority. Creating this new urban ethos through infill, redevelopments and urban renewal means considering co-locating spaces in which people will work, live, shop, eat and play within the same neighbourhoods.

This is a major challenge, since, in the bustling urban landscape, transforming an existing building or a precinct to accommodate a variety of new uses often sparks a chorus of concerns from the surrounding community.

While from a planning and city-shaping perspective round-the-clock vibrant neighbourhoods are an ideal, the soundscape and interface between disparate building types needs careful consideration so that all different users can coexist harmoniously.

The usual ambient noise of city life, including traffic, sirens and the low frequency hum of plant and equipment can become normalised for residents. However, introducing new outdoor bars, restaurants or music venues can be perceived by those same persons as an assault on the senses.

Addressing noise issues arising from new uses in existing buildings or neighbourhoods that were not originally designed for this purpose can be challenging and often require costly noise control solutions. However, for new buildings or masterplans, this is much easier to achieve if an acoustician is involved in the early planning stages.  The role of an acoustic consultant is to identify all potential issues and provide practical solutions to the project team to ensure a harmonious outcome that satisfies all relevant stakeholders.

Our experience has shown it is always more effective to address the noise concerns at the beginning and designing accordingly, rather than trying to mitigate noise issues in the later stages of design or, worse, after completion, where retrofitting mitigations is not always feasible and is certainly more expensive.

All possible combinations of noise and vibration sources, as well as associated impacts from new activities and the potentially affected receivers, should be considered. For instance, when a fitness centre is introduced into an existing building, there are multiple acoustic issues to be addressed. Activities such as aerobics, high-intensity interval training, weight training and cardio classes can generate significant impact noise and vibration from equipment and footfall. Music played during gym classes or patrons leaving the premises late at night can also cause airborne noise disturbance to surrounding residences.

The acoustic design should consider all the different possibilities and provide adequate solutions for the control of noise and vibration, such as isolation of the floor, through an appropriate flooring system, walls and ceiling.

Acoustic design: Understanding the drivers

At the forefront of any acoustic design, there should be a deep understanding of the needs of all the parties involved. The client and end-user needs are as important as the neighbours’ expectations, and all should be carefully evaluated and considered.

Unlike some other disciplines such as structural engineering, where the consequences of poor design are obvious and can lead to some serious problems, the effects of ‘bad’ acoustics are not always noticed until it is too late.  

Impacts such as increased stress levels, reduced productivity, and declines in overall health and wellbeing of occupants only manifest after completion. This often leads to frequent complaints, negative feedback, litigation or can cause guests or tenants to leave a property, tarnishing the reputation of a building or development. The stakes are high, so acoustic design works to create environments that are  functional, suitable for the intended use and palatable for users and stakeholders alike.

What this looks like in practice

In the hospitality sector, for example, guest satisfaction is paramount, and one often overlooked aspect that significantly impacts the guest experience is acoustics. Whether it’s the sound of footsteps from the room above, conversations from the next room, or loud music from a nearby bar, unwanted noise can disrupt sleep and relaxation, leading to a negative guest experience.

Noise is one of the most common causes of complaint in online hotel reviews, because guests typically choose hotels for rest and relaxation; when their expectations are not met due to noise disturbances, it can result in dissatisfaction and a reluctance to return. Negative reviews may come to affect the occupancy rate and, ultimately, the business overall.

Good acoustic design is not just about reducing noise; it’s about creating an environment where people can feel comfortable and where individuals can engage in activities without disturbing or being disturbed by the surrounding areas.

Strategies for Improving acoustics and common misconceptions

A common misconception is that acoustic panels help with preventing sound transmission between spaces. This is not true, at least not directly.

Materials such as acoustic wall or ceiling panels, carpets and heavy curtains are commonly used to control reverberation – that is, the materials absorb sound that would otherwise be reflected back into the room. This can mitigate the build-up of noise within a room. However, they do not prevent sound from traveling between rooms, they can simply dial it down a notch by reducing the level in the source room.

When it comes to controlling noise transmission between spaces, solid partitions are necessary. The construction of these partitions depends on the source and receiver combination. For instance, a mechanical plantroom adjacent to living areas requires special acoustic design considerations to better control the low-frequency noise typical of certain mechanical equipment. Heavier constructions, such as concrete block walls, are generally favoured over lightweight ones.  

In the most extreme cases, such as a club located above hotel guest rooms, a solution known as a box-in-box is often necessary. This involves decoupling the building structure from the venue, effectively creating an isolated space within the building. While this is typically an expensive solution, it is also the most effective one for controlling noise transmission from very loud spaces.

In settings such as hotel rooms or office spaces, drywall partitions effectively manage sound transmission mainly because the primary source of noise will be human voices, which do not produce significant levels of the low frequencies commonly associated with mechanical equipment or music. The sound insulation provided by drywall is particularly effective at controlling the frequency range of the human voice.

In typical high-rise construction, lightweight façade materials and extensive glazing are common, and some low-rise buildings are also lightweight. Unfortunately, lightweight construction generally does not perform particularly well in controlling low frequency noise issuing from outdoors sources such as road traffic or railway noise. It is therefore important for the acoustic consultant to characterise potential external noise sources, present and future, and provide suitable acoustic design for facades and glazing. It is also important to properly design lightweight roofs – noise generated by rainfall can be a problem and solutions such as additional layers of sound insulation or dampening materials must be included in the design strategy to ensure it is controlled to acceptable levels.

Where noise is moved outdoors – for example, an open-air music venue or children’s playground – we face a different set of challenges and considerations. The materials and architectural forms in the surrounding area significantly influence noise propagation and, ultimately, the noise levels experienced by nearby residences, hotel rooms, or offices.

The primary objective is to mitigate noise at the source. This approach is typically effective for mechanical noise, where using quieter equipment or implementing engineered noise controls (e.g. noise enclosures) can be very effective. However, in certain situation, such as outdoor pub areas, restaurants, or children’s playgrounds, source control may not be feasible. In these cases, the next step is to manage the noise propagation path, often using solid noise barriers.

A prevalent misunderstanding is that urban landscaping, such as trees and vegetation, significantly blocks sound. While it’s true that a dense forest can help mitigating noise, a single row of trees in standard landscaping, although it offers some degree of sound absorption, doesn’t notably diminish sound transmission.  Studies suggest that greenery can reduce our perception of noise by creating a visual barrier between the source and the receiver, i.e. ‘if you can’t see the source you may perceive it as quieter.’

The final and least preferred method is controlling noise at the receiver. While this is feasible in certain urban renewal scenarios, it is typically more valuable when there are few existing homes in the immediate area.

In this case, project proponents can include budget for retrofits of noise mitigation measures for these homes, such as window replacement with suitable glazing systems. In situations where a double-glazing system is used, the bonus for residents is they also gain improved passive thermal comfort and lowered energy bills for heating and cooling due to the improvements.

An eye on sustainability

Acoustic consultants often use conservative factors in their designs, which can lead to over-design. This practice not only increases the project expenses but also increases the embodied carbon footprint from the extra materials and transportation involved.

To reduce the risk of over-design, acoustic design should utilise  acoustic test reports from accredited labs or qualified consultants. These reports help gauge the actual performance of a product or material, enabling accurate design without unnecessary safety factors in calculations.

Consider the existing community

Understanding the context and soundscape expectation of the community forms crucial part of a noise assessment. Community engagement is one essential step in this direction and should be done throughout the planning process. From the outset, it’s important to have open discussions with local residents and businesses about anticipated noise impacts, ensuring their concerns and needs are acknowledged and addressed.

This allows the acoustic consultant to take a holistic approach and work towards the health and wellbeing of the community as well as satisfying the client’s needs and requirements.

In conclusion, addressing acoustics in mixed-use spaces is a multifaceted challenge that requires careful planning and consideration. By involving an acoustician early in the design process, architects and designers can create environments that are both functional and comfortable for all users. Effective acoustic design not only enhances the user experience but also considers the impacts on the community and overall contributes to the success of a development.

Cundall
cundall.com

Read this other Cundall comment piece on the dangers of ‘Blade Runner’-type design