Classroom acoustics
The key components that create a classroom acoustic are:
- the room design
- the levels of background noise - internal/external noise IANL (indoor ambient noise level)
- the levels of reverberation
Reverberation times
It the room is reverberant, the sound reverberating or echoing around the room will have a poor effect on speech intelligibility and listening. Critical distance is the distance from the speaker in a room, where the speaker’s voice level is equal to that of the reverberation or sounds bouncing off hard surfaces. Beyond that, speech becomes less intelligible. Boothroyd’s research (2004 and 2012) investigates the characteristics of a range of speech sounds/critical distance and information on the physics of the human voice and the distances it remains intelligible within learning spaces.
Boothroyd, A (2004) ‘Room acoustics and speech perception’. Seminars in Hearing, Vol 25 pp155-166, New York: Thieme Medical Publishers.
Boothroyd, A.(2012) ‘Speech perception in the classroom’ in Smaldino, J.and Flexer, C. (ed.) (2012) Handbook of Acoustic Accessibility: Best Practices for Listening, Learning and Literacy in the Classroom. New York: Thieme Medical Publishers (ISBN 978-1-60406-765-1). This also gives more general information on the physics of classroom acoustics and contains more recent examples of the application of the physics of critical distance and pupils’ ability to hear clearly what is said to them in learning spaces.
Whitmal and Poissant(2009) investigated the effects of the distance between speaker and listener on the perception of speech of cochlear implant wearers.
Whitmal N.A. & Poissant S.F. (2009). ‘Effects of source-to-listener distance and masking on perception of cochlear implant processed speech in reverberant rooms’. Journal of the Acoustical Society of America, 126(5), 2556-2569.
Signal to noise ratio
A good signal to noise ratio is important if pupils are to have good access to speech and learning. The teacher’s voice at the pupils’ ears should ideally be at least 10dB above the background noise for hearing children and at least 15-20 dB for hearing impaired children. There are Apps available that will give an idea of decibel levels.
A study giving a practical consideration of signal to noise ratios in working classrooms was undertaken at Manchester University. It explains about Classroom Acoustics (p4) and Classroom Signal to Noise Ratio Measurement Methods (p6).
McCracken, W., Roberts, A. and Wilding, T. (2012) ‘Study of FM in Real World Settings’ Oticon Foundation
Classroom design
The size and shape of a room, whether it is enclosed or open plan, the height and slope of the ceilings, the number of windows and doors, the furniture and soft furnishings etc all influence the acoustics of a room. A small, square enclosed room, with a low flat ceiling and soft furnishings will have better room acoustics than a large open plan room with no absorbent materials.
Where the design of a classroom results in poor acoustic conditions then the installation of both sound insulation materials and sound field and personal radio aid systems can to greater or lesser extent overcome the problems of the noise and/or reverberation that is acting as a barrier to pupils hearing and learning. These palliative tools are discussed in more detail in the Interventions and Case Studies columns.
