4.2. Room acoustics, listening and speech intelligibility
Most pupils spend a great proportion of the school day learning by listening: listening to both their teachers and each other. The speech needs to be audible, undistorted, and accessible for learning and well-being.
The amount of audible and undistorted spoken information reaching a listening pupil will depend on the acoustic properties of the room and the pupil’s position within the room.
The National Deaf Children’s Society (NDCS) have created information and resources about listening and creating good listening environments (see further reading).
There are three main challenges to speech intelligibility in the classroom: noise, reverberation, and distance.
Noise is defined as any unwanted sound that competes with the sound signal that the listener needs or wants to listen to. In the classroom, speech is the signal. Noise is measured in dB. Higher noise level reduces the signal-to-noise ratio (SNR), (see sub-section 3) and masks speech sounds in the speech signal (see sound strength sub-section 3).
Noise may be generated inside or outside the room.
Examples of inside noise: ventilation or heating systems, fans, chairs being moved, students, or activities within the room.
Examples of outside noise are traffic, neighbouring classrooms, and grass cutting.
Outside noise may enter a classroom through windows, doors, gaps around them, or through the structure of the building.
A low background noise level will aid speech intelligibility and reduce the teacher’s vocal strain as they will not need to increase the intensity of their voice in order to be heard clearly above the background noise.
As background noise rises, speakers raise their voices and make vocal changes so that their voices are heard. In turn, others raise their voices to be heard and the noise within the room increases. This is known as the Lombard effect.
Children are more likely to find noise annoying, so the control of noise within the room is important.
Reverberation is sound that persists after the sound from the source has stopped. Sound, reflected from surfaces, continues to travel around the room when there is little or no absorptive material. Poor speech intelligibility occurs when reflected sound accumulates and masks direct sound. Reverberated sounds may have intensity and frequency differences from the original soundwaves depending on the absorbent properties within the room, affecting speech clarity and making communication challenging. Early reflections enhance the speech signal by arriving at the listener’s ear quickly and adding to the direct speech sound. Late reflections arrive at the listener’s ear much later than direct speech, overlapping speech sounds, and impairing speech intelligibility.
The intensity of the speech signal diminishes the further away the listener is from the speaker. Direct sound levels decrease 6 dB each time the distance from the sound source is doubled. This is known as the inverse square law.
Considerations for QToDs
Background noise can be measured with a sound level meter or an app on a compatible phone or device.
Smaldino, J.J. and Flexer, C. (2012). Handbook of Acoustic accessibility: Best practices for listening, learning and iteracy in the classroom. https://amzn.eu/d/h7T2cbt
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