dBx Jargon Buster
Welcome to the dBx Acoustics jargon buster! In this section, we list some common acoustic terms as well as standards and guidance you may be asked to comply with. If there’s something you need to know which we haven’t covered here, please let us know.
An A-weighting is a correction applied to the individual frequency bands measured, to provide a single figure which represents the relative loudness of sound perceived by the human ear. A noise level presented in terms of dBA has been A-weighted.
Approved Document E (ADE)
Approved Document E (ADE) sets out the required airborne and impact sound insulation standards for new and converted residential dwellings. The document contains useful information on the design of separating walls and floors and detailing.
Before a residential development is signed off by Building Control, it is a requirement that pre-completion acoustic testing should be carried out. The testing must be carried out by an organisation which is either UKAS accredited for this specific testing, or registered with the Association of Noise Consultants for sound insulation testing. dBx Acoustics is UKAS accredited for pre-completion sound insulation testing (laboratory number 9473).
The Acoustics Ventilation and Overheating Residential Design Guide recommends an approach to acoustic assessments for new residential developments which considers the interdependence of acoustics, ventilation and overheating. Use of AVO is intended to demonstrate good acoustic design as described in ProPG Planning and Noise.
Building Bulletin 93 (BB93) is a comprehensive document setting out the acoustic requirements for the design of schools. BB93 forms part of the Building Regulations applying to school buildings, and applies to new builds, refurbishment and extensions.
BB93 sets performance standards for noise levelsand reverberation times within rooms, and acoustic separation between rooms, dependent on the type of room and the adjacent space.
Research has shown that good acoustic conditions have a significant effect on educational outcomes; BB93 is intended to ensure that pupils are not hindered by high noise levels or by not being able to clearly hear the teacher. Enhanced guidance is also provided to support children with additional needs, which includes not only hearing impairments, but also sensory processing disorders such as Autism, and those for whom English is a second language.
BREEAM is an environmental assessment method which is used to certify a variety of building types, including offices, schools, and prisons. Credits with varying numbers of points are awarded for compliance with various environmental aspects, with the overall score leading to a rating such as “Excellent”, “Very Good” etc.
There are two credits available for acoustics. Up to three points are available under HEA05, relating to noise levels, acoustic privacy, and room acoustics. A further credit is available under POL05 where noise emissions from plant to the surrounding environment are appropriately controlled.
BREEAM is the most commonly used assessment method in the UK, but other standards such as WELL are also becoming popular.
BS4142 sets out a methodology for assessing the impact of industrial and commercial noise on nearby noise sensitive properties. It is commonly used to assess the potential impact of proposed building services plant as part of a planning condition, but can also be used to investigate complaints, or to look at the potential impact of existing commercial and industrial noise sources on proposed residential development.
BS4142 includes a number of corrections for the character of the sound being assessed, taking into account that sound with distinctive characteristics is subjectively more disturbing. It also includes consideration of the context of the situation; for example, an additional industrial noise source in an area already exposed to industrial noise may be more acceptable than introducing an industrial noise source to an area where previously there was none.
It is typical for a BS4142 assessment to be required to support planning applications where new items of plant are proposed, or where new housing is proposed in an area affected by industrial or commercial noise.
BS5228: Code of practice for noise and vibration control on construction and open sites describes methods of assessing the impact of construction noise and vibration on sensitive receptors.
There are no fixed limits for noise, but guidance is provided on “Best Practicable Means” to control both noise and vibration. Where a significant impact is predicted, contractors may be required to measure noise and vibration during construction and demolition, and to limit the periods during which the greatest impacts occur.
These standards are used to assess the effect of vibration on people in buildings, predict the likelihood of adverse comment, and consider whether cosmetic or structural damage to buildings is likely to occur. They are used in a variety of situations, for example where new buildings are proposed close to an existing source of vibration such as a major road or rail line, but also where infrastructure works such as tunnelling may affect occupants of existing buildings.
BS8233: Sound insulation and noise reduction for buildings is most commonly encountered when considering the effects of noise on residential developments. The standard sets appropriate levels within a dwelling during both the day- and night-time periods, and a noise survey of the external levels is used during the design stage to assess the glazing and façade construction needed to control noise breaking into the proposed building. This assessment methodology is also used to determine whether a building can be naturally ventilated with open windows, or whether an alternative means of ventilation is required.
The standard also contains guidance on appropriate noise levels within a variety of commercial building types, as well as guidance on speech privacy between noise sensitive spaces.
Code of Practice on Environmental Noise Control at Concerts
The Code considers noise from large-scale music events at outdoor venues, and is primarily used for venues where music occurs for no more than 12 days per year – for example festival sites, or sports arenas used for occasional music events.
Criteria are presented for acceptable noise levels at noise sensitive properties, dependent on the type of venue and the number of events held per year. The guidance also recommends that when events continue beyond 23:00h, music should be inaudible within residential premises.
Guidance is given on appropriate licencing conditions, and noise control methods.
Control of Noise at Work Regulations
The Noise at Work Regulations set ‘action values’ dependent on the level of noise to which employees are exposed. This can be considered both in terms of daily and weekly exposure, to take into account different working patterns. Where the lower action level is met, hearing protection must be made available to employees. At the upper action level, employers must ensure that hearing protection is used.
The regulations also put a duty on employers to take all reasonable steps to reduce noise at source.
The decibel, written dB, is the unit by which sound levels are expressed. A level of 0dB is near total silence; a normal conversation may be around 60dB, a rock concert may be above 100dB.
Decibels often cause confusion as they add logarithmically -two noise sources of 40dB added together results in 43dB, not 80dB! As a rough guide, the smallest change in noise levels that humans can detect is typically around 3dB. Something which seems subjectively ‘twice as loud’ is likely to be around 10dB higher.
Acoustics – where 2+2 really does equal 5…!
Health Technical Memorandum 08-01: Acoustics sets out acoustic criteria for new healthcare developments. It includes acoustic criteria for speech privacy between rooms, noise levels in rooms both from building services and from external sources, and impact sound from rooms above. Specific guidance is given for audiology facilities.
The guidance also covers refurbishments and temporary healthcare premises, and the control of noise and vibration during construction.
NPPF / NPSE
The National Planning Policy Framework (NPPF) and Noise Policy Statement for England (NPSE) together set out guidance on the suitability of planning conditions, and the planning intent for noise including environmental noise, neighbour noise, and neighbourhood noise.
The policy aims to avoid significant impacts on health and quality of life, and where possible contribute to the improvement of health and quality of life. The NPSE provides some context, describing ‘effect levels’ at which noise may lead to changes in behaviour. This ‘noise exposure hierarchy’ can be used to assess the potential impact of noise and whether further steps to control it are required.
ProPG: Planning & Noise (Professional Practice Guidance on Planning & Noise) – New Residential Development is intended for use for new residential developments on land exposed to transportation noise. The guidance proposes a two-stage approach; an initial site risk assessment to be carried out before any planning application is made, and a full assessment where four key elements are considered in detail to produce an Acoustic Design Statement.
The Acoustic Design Statement must demonstrate consideration of good acoustic design (including providing adequate ventilation and avoiding overheating), compliance with noise levels in dwellings and external amenity areas, and the consideration of any other relevant issues.
Reverberation time (RT) is a measure of how quickly sound decays, but in layman’s’ terms it can be considered as how subjectively ‘echoey’ a space is. For example, a church or cathedral typically has a long reverberation time, while a recording studio would typically have a very short reverberation time.
A shorter RT is desirable for speech, for example in offices or classrooms, while a longer RT can support music. Often where a space is considered ‘too noisy’, for example a busy bar or restaurant, control of reverberation can help.
Reverberation is dependent on the quantities of acoustically reflective and acoustically absorptive (‘soft’) finishes within a room – for example, a room with carpet will sound very different when you take that carpet up. In acoustic design, the quantity, specification and placement of acoustically absorptive surfaces, as well as surfaces which diffuse (scatter) sound, can be used to optimise conditions for the proposed use.
Sound insulation is the term used when talking about how much sound passes from one space to another. There are two types. Airborne sound insulation relates to noise such as speech and music, and is relevant when designing both walls and floors. Impact sound insulation is considered in the design of floors and ceilings, and relates to the control of noise from (typically) people walking on the floor above being heard in the space below.
This is sometimes referred to as ‘soundproofing’, but it is important to understand that nothing is ever truly soundproof! The key is to control noise transfer to within an acceptable level, based on the typical activities which will occur in the spaces under consideration.