Life

Noise control

Provided by Jian Kang, Professor of Acoustics: School of Architecture, University of Sheffield

 

What, Why, When, How, Extras

 

What is it?

While noise control covers a wide range, from producing quiet machines to the use of earplugs, noise control in the built environment generally includes: strategic plan of building locations and orientations so that the impact of various urban/rural noise sources is minimised; design of building shape and envelope so that noise transmission paths between internal and external spaces are well controlled; and design of internal spaces, boundaries and materials so that the disturbance from internal noise sources is controlled and the reverberation in each space is appropriate.

Why use it?

Potential effects of noise include hearing impairment, startle and defence reactions, aural pain, ear discomfort, speech interference, sleep disturbance, cardiovascular effects, performance reduction and annoyance responses. These health effects, in turn, can lead to social handicap, reduced productivity, decreased performance in learning, absenteeism in the workplace and school, increased drug use, and accidents. Noise could also have economic impacts such as loss of property value. Overall, an indoor or outdoor space is more sustainable with a good sound quality.

When to use it?

Noise control is strictly required by a range of regulations and standards, including environmental noise limits for different categories of urban/rural areas; internal noise limits for different building and space types; sound insulation requirements for various building elements; sound absorption requirements for various interior surfaces in order to control reverberation sound; and noise limits for various building service products.

While it is essential to achieve the requirements in various regulations and standards, noise control and acoustic design should also be regarded as a source of creativity, for creating comfortable and interesting sonic environment, as an integrated part of architectural space creation. Not only controlling unwanted noise, but also encouraging and using pleasant sounds as a part of soundscape creation, is important.

How to use it?

Key points:

  • Sound level of external noise sources, at 1m from the façades in a standard way
  • Sound insulation of building envelope, including walls, windows, ventilators and roof
  • Noise disturbance between different spaces in a building, considering the sound insulation of internal building elements such as walls and doors
  • Reverberation of various internal spaces

Design procedure:

  • Step 1: Identify the environmental noise limit for the building to be designed, according to relevant regulations. This depends on the type of area where the building is located, and the type of building. Environmental noise is unwanted or harmful sound, usually generated by human activities, including road traffic, railways, air transport, industry, recreation and construction.
  • Step 2: If required, control environmental noise in terms of sound path, considering various possibilities including distance attention based on inverse square law, ground profile, noise barriers, vegetation, ground absorption, wind direction, and strategic plan of a group of buildings so that some could shield noise for others. Sound reflections from various urban elements such as façades of other buildings should also be paid attention.
  • Step 3: Building forms can be designed self-protective from external noise to a certain extent. For examples, in Figure 1a the podium, usually for commercial use, acts as a noise barrier for the main building which is typically residential. In Figure 1b the higher floors, typically bedrooms, are farther from the noise source and also, they are protected by the lower building blocks due to the screening effect. In Figure 1c the balconies can effectively stop direct sound from source to windows/doors. In Figure 1d the wall of the courtyard acts as a noise barrier.
Self-protected buildings

Figure 1. Principles and examples of self-protection buildings, cross-section view.
Jian Kang

  • Step 4: Design building envelope to satisfy required noise limit according to relevant standards. For a homogeneous impervious panel such as brick wall mass-law holds – the sound transmission loss increases at a rate of about 6dB for each doubling of frequency and by about 6dB for each doubling of surface density. Consequently green walls and green roofs would be helpful for improving sound insulation due to the added mass.
  • Step 5: While a building envelope normally contains several elements, it is noted that even a small opening on a solid wall can noticeably increase the transmitted sound. Silencers for ventilation openings and acoustic windows can be used to improve the overall sound insulation performance. The principle of ‘acoustic lock’ can also be considered, as shown in Figure 2, if a free flow of people is needed.
Acoustic lock

Figure 2. Schematics of an 'acoustic lock', for reducing transmitted noise from inside to outside or from outside to inside the building, plan view.
Jian Kang, University of Sheffield

  • Step 6: Inside a building, various noise sources should be identified, as well as the noise limit for each room (e.g. classroom, theatre, meeting room) according to relevant standards. Correspondingly, the room locations can be well planned acoustically. For example, some rooms may generate noise but they also require a low background noise level. If a free flow of people is required but this could cause noise disturbance, the acoustic lock principle (see Figure 2) could be used, both on plan and in cross-section.
  • Step 7: For each room, in addition to choosing appropriate envelope elements such as doors and partition walls based on measured acoustic data and requirements from standards, sound leaks between rooms through holes and gaps should be paid particular attention, even they are airtight. Flanking noise transmission must be considered too, for example, through the ceiling space or the floor joist space, around the end of the partition through the adjacent wall, or through light switches, telephone outlets and recessed lighting fixtures. 
  • Step 8: In addition to airborne sound, impact sound through floors must be considered. As well as choosing appropriate floors and designing appropriate details to reduce impact sounds, floating floor and suspended ceiling could be considered to improve the noise control performance, where particular attention must be paid to detailed designs, such as the hangers for suspended ceilings. 
  • Step 9: When a vibrating machine is rigidly mounted to a floor (or wall), structure-borne sound will be transmitted with little attenuation, and a resilient element between the machine and the support can be effective for increasing the attenuation. Some acoustically sensitive rooms could be put on spring, especially when the vibration source in outside the designer’s control (i.e. underground trains). 
  • Step 10: Appropriate reverberation time, as well as a series of other room acoustics indices, is an essential requirement for many types of architectural space. From the viewpoint of noise control, reducing reverberation will minimise the effects of sound reflections, and this in turn, will bring reduction in noise level. Generally speaking, up to 10dB noise reduction can be achieved by reducing reverberation through adding absorption.

 

Related strategies

Materials Site planning Site planting

Conflicting strategies

Stack ventilation Cross ventilation

Take this further

  • Egan, M D, 1988, Architectural Acoustics, McGraw-Hill.
  • Kang, J, 2007, Urban Sound Environment, Taylor & Francis
  • Lord, P and Templeton, D, 1996, Detailing for Acoustics, E&FN Spon

 

Case studies

The Sheaf Square outside the Sheffield Railway Station is a good example of soundscape design. The large steel sculpture acts as a noise barrier from traffic noise and also, generate pleasant water sounds.