Education is an important area of room acoustics as poor classroom acoustics can negatively impact the learning and teaching process.
Research has shown this impact may lead to a lower skill level compared to an individual who benefited from an acoustically treated classroom*. A lower skill level can result in a diminished earning capacity and salary, causing significant economic loss to an individual.
The cost of providing a quality acoustic environment is not significant compared to the potential ongoing economic loss suffered by a student. A good acoustic environment within educational facilities should not be compromised by the initial higher cost of construction as this is far outweighed by the immediate and long-term benefits to students.
Teachers and students can overlook acoustic impediments that affect learning outcomes. Children and adults perceive speech intelligibility differently, adult perceptions of speech intelligibility can be better than children’s. Therefore the adult experience in this area cannot be relied upon when assessing student experience and understanding.
Children under the age of 13 are still developing word recognition and comprehension, and many children come from homes where English is not the first language.
Speech intelligibility is reduced in a space with long reverberation times. In situations where there are both high background noise levels and long reverberation times, the combined effect is negative for people with and without normal speech, language and hearing ability.
*A cost-benefit analysis of providing a ‘sound’ environment in educational facilities: Deb James, Matthew Stead, David Clifton-Brown and David Scott, The Australian Acoustical Society, Freemantle, 2012
CLASSROOM DESIGN CONSIDERATIONS
Designers should focus on controlling background noise levels, reverberation times and signal to noise ratios to improve the acoustic environment of schools.
- A spoken voice level at least 15dB above the background noise level throughout the room
- Background noise levels of 30-40dBA, or less when unoccupied
- Overall sound levels (consisting of teaching voice and student voice) no greater than 65-70dBA throughout the room
- Sound absorbing materials, placed to minimise reverberation to less than 0.4s in primary teaching spaces and 0.6s in secondary teaching spaces, requiring at least 40% absorptive treatment on the ceiling
- A Speech Transmission Index STI > 0.6 in open plan teaching and study spaces
- In the case of students with special hearing requirements: Reverberation time of 0.4 seconds or less, Signal to noise ratio of greater than 20dB
ACOUSTIC TREATMENTS FOR CLASSROOMS
- Children’s vocal output average frequency range is 250 – 300Hz
- Acoustic treatments need to be able to capture a reasonable percentage of sound at those frequencies otherwise a percentage of the vocal sound at those frequencies will reverberate in the classroom and this will reduce speech intelligibility.
- The physics of sound dictates that in order to absorb sound in the speech ranges then absorptive treatments need to be at thicknesses of 50mm or at an absolute minimum 25mm. There are many thin high frequency absorbers currently used in schools that cannot provide the levels of absorption required to provide acoustically fit for purpose teaching spaces. These materials make excellent pin-boards with a high frequency sound absorptive benefit
- The AAAC guideline for classroom acoustics states: Sound absorbing materials, placed to minimise reverberation to less than 0.4s in primary teaching spaces and 0.6s in secondary teaching spaces, requiring at least 40% absorptive treatment on the ceiling
- Each subject specific room requires differing acoustic treatments so that the room can be fit for purpose for the given activity
- Rooms that have audio visual equipment and amplification systems need to have acoustic surfaces that enhance the amplified sound:
- Music rooms
- Manual arts and crafts rooms
- Kindergarten rooms
Subject specific rooms will all likely have differing shapes, ceiling heights floor and wallcoverings etc.
- Place music rooms away from general classrooms and other quiet rooms
- Design ceilings to a minimum height of 4.5m, the instrumental sound quality is improved with higher ceilings
- Install quiet or passive ventilation systems
- Allow each student at least 2.5 square metres of space for band rooms and 1-2 square metres for chorus rooms
- Allow for diffusive surfaces in performance spaces
- Allow for absorptive surfaces in teaching spaces
- Ensure that walls, ceilings, doors and windows are constructed to control sound transmission and flanking transmission from one space to another
- Seating should be upholstered
- Seating array should be steeply pitched
- Human bodies also affect sound quality in theatres. The acoustic designer will design the theatre so that no matter how many seats are occupied or not the sound quality will remain intelligible
- The acoustic designer may specify variable acoustic treatments such as drapery and movable panels which can be rearranged to optimise the acoustics to suit audience numbers and the activity
- Background noise levels should be kept below NC35
- Reverberation times should be kept at around 0.6 seconds
- Lecture theatres require both reflections and absorption
- Reflective materials could be the plasterboard finishes used for wall and ceiling lining
- Absorptive treatments from acoustic panels
- Provide sound absorptive surfaces along the edges of the ceiling
- For large halls, reflective surfaces should be placed to the front and centre of the room ceiling to enhance the speech intelligibility of the speaker at the back of the hall
- In smaller theatres use hard smooth sound-reflecting material above the speaker to create sound reflections, the back wall of the theatre should be completely sound absorptive
- Sidewalls should have 30% absorptive coverage
Due to this complexity in room acoustic design, Instyle highly recommends engaging an acoustic consultant at the earliest stage of the design process.