Presented on Wednesday 13 March, 2013
Classroom Acoustics, BB93 and the
NDCS Acoustics Toolkit
Richard Vaughan, Customer Support Manager Connevans Ltd
Including some information produced by: Arthur Boothroyd, PhD, Distinguished Professor Emeritus, City University of New York; Scholar in Residence, San Diego State University
DfES Building Bulletin 93
(search for BB93 under "publications")
Quote from the introduction:
"The constructional standards for acoustics for new school buildings, as given in Section 1 of this document, are required to be achieved under the Building Regulations. This represents a significant tightening of the regulation of acoustic design in schools, to reflect a general recognition, supported by research, that teaching and learning are acoustically demanding activities. In particular, there is a consensus that low ambient noise levels are required, particularly in view of the requirements of the Special Educational Needs and Disability Act 2001 for integration of children with special needs in mainstream schools."
Part E of the Building Regulations gives the following guidance:
"In the Secretary of State's view the normal way of satisfying Requirement E4 will be to meet the values for sound insulation, reverberation time and internal ambient noise which are given in Section 1 of Building Bulletin 93"
The Building Regulations and hence the requirements of BB93 only apply in England
and Wales. They apply to both LEA maintained schools and independent schools.
BB93 standards: Three main acoustic measurements
- Internal ambient noise
- Reverberation time
- Sound insulation
BB93: Indoor ambient noise in unoccupied space
The indoor ambient noise level includes noise contributions from:
- External sources outside the school premises (including, but not limited to, noise from road, rail and air traffic, industrial and commercial premises).
- Building services (eg; ventilation systems).
The indoor ambient noise excludes noise contributions from:
- Teaching activities within the school premises, including noise from staff, pupils and equipment within the building or in the playground. (Noise transmitted from adjacent spaces is addressed by the sound insulation requirement.)
- Equipment used in the space, eg; machine tools, computers, overhead projectors etc. However these noises should be considered in the design process.
- Rain noise; however it is essential that the noise is consiered in the design of lightweight roofs and roof lights.
Indoor ambient noise BB93 standards
Upper noise limits given for different spaces, including:
- General teaching spaces: 35dB LAeq,30min
- Classrooms designed specifically for use by hearing impaired students (including speech therapy rooms): 30dBA LAeq,30min
- Reverberation time (RT60) is the time taken for the sound level to drop by 60 dB after the source is turned off.
- A classroom with a long reverberation time will cause syllables to be prolonged so that they overlap and hence degrade speech intelligibility.
- Long reverberation times occur in large rooms with hard wall and ceiling surfaces. Adding acoustic absorption and reducing the ceiling height will reduce the reverberation time and will improve speech intelligibility.
Reverberation time BB93 standards
Maximum reverberation times given for different spaces, including:
- Primary school general teaching areas: <0.6s
- Secondary school general teaching areas: <0.8s
- Classroom designed specifically for use by hearing impaired pupils (including speech therapy rooms) <0.4s
Defined under three categories in BB93:
- Airborne sound insulation between spaces.
- Airborne sound insulation between circulation spaces and other spaces used by students
- Impact sound insulation of floors
Sound insulation BB93 Standards
- Complex to measure/calculate
- Defined in terms of:
- Minimum weighted BB93 standardized level difference, DnT (Tmf,max),w
- Minimum sound reduction index Rw and minimum Dn,e,w-10lgN
- Maximum weighted BB93 standardized impact sound pressure level LnT (Tmf,max),w
BB93 Chapter 6: Acoustic design & equipment for pupils with special hearing requirements
- "Sound insulation must be of a hight standard, with the lowest background noise levels possible to ensure that a good signal to noise level is achieved."
- "Shourt reverberation times are also critical in ensuring that sound does not build up when the class are working in groups."
- "Care must also be taken to ensure that the level of low frequency noise is kept to a minimum. For many people with impaired hearing, low frequency noise can have a devastating impact on speech recognition, masking many important speech sounds ... "
Includes information about FM systems, soundfield systems and other technology.
"Classrooms are not the only places where hearing impaired children interact. It is often overlooked in school design, but critical learning and interaction takes place outside the classroom and if hearing impaired children are to be fully included, attention should be given to all areas of the school where children might be expected to interact with others."
Typical problems encountered in (old build) schools
- High ceilings
- Hard surfaces
- Poor insulation between spaces
NDCS Acoustic Toolkit
Or contact NDCS directly ...
Provides advice and guidance to schools and local authorities to help them:
- create a better learning environment to improve the attainment of all childfren and particularly those who are deaf;
- prepare their Accessibility Plans and Disability Equality Schemes as required by the disability and special needs legislation;
- meet their "anticipatory" duties under the Disability Discrimination Act;
- develop their asset management plan;
- involve pupils in the development of their plans and schemes.
The first section is aimed at non specialists in schools:
- an overview of factors affecting school listening environments
- a brief introduction to acoustics
- surveys which are simple to conduct which will help identify problem areas within schools
- practical suggestions to improve listening environments.
The second section is mainly aimed at specialists (education audiologists, teachers of deaf children, acoustic consultants or acoustical engineers):
- build on the information schools have collected
- explore in more detail any major problems
- identify possible solutions.
Section 1 - Schools
- Noise surveys:
an introduction to noise surveys, pupil interviews, preliminary
surveys, practical suggestions
- Reverberation times
- Speech intelligibility:
an introduction to speech intelligibility, pupil questionnaires
- Assistive listening devices in the classroom
personal FM systems, classroom soundfield systems
Section 2 - Professionals
- Noise surveys:
survey data collection, data collection sheets, worked examples
- Reverberation times
calculating reverberation times, using the spreadsheet and data
collection sheets, reverberation times survey - worked example,
data collection sheets, producing graphs
- Speech intelligibility:
measures of speech intelligibility, setting up the room for speech
testing and using the AB word list, worked example
Tools and equipment
Reverb kit £250 ex VAT