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Speechless in the Classroom

The size and shape of a classroom affects the loudness and intelligibility of speech depending on the distance between teacher and pupils.

Sound Decay Graph in a Typical ClassroomAt a distance of 1 metre, the sound level of normal speech is about 60 dB. However, each doubling of the distance reduces the sound level by 6 dB. For a pupil sitting 2 metres away from the sound source, the signal is 54 dB and at 4 metres, the signal is only 48 dB.

Typical background sound levels in a classroom are about 60 db, so a teacher needs to raise their voice level above this by about 15 dB. A suitable sound pressure level is about 75 dB to be heard distinctly, this level maybe difficult for many teachers to maintain all day. If a teacher remains at the front of the class, sound levels at the back could easily be lost in the background noise by the end of the day.

A microphone, amplifier and multiple speakers can boost the sound level and distribute it more uniformly in the classroom especially if ceiling speakers are used or speakers mounted on the side walls.

Class discussions may also benefit from additional microphones (or passing a microphone from pupil to pupil) so that everyone can hear and contribute.

An amplifier system needs to be designed especially for classroom use as the construction and size of a classroom is very different to the rooms in normal houses

Voice amplification is only a partial solution if the building design is poor for sound. The amplified sound may well interfere with teaching in adjacent classrooms if interior walls do not perform well as an acoustic barrier.

Useful links
Sound reinforcement equipment
Birth of a Classroom Speaker System David Edis-Bates

About the Author

David Edis-Bates, C.Eng MIET spent more than 30 years in export related communication, IT and electronics activities around the world. He lived in Taiwan for 4 years in the late 70’s and in China since 2004. He taught part time in further education for several years in the UK and is currently CEO of EdisAV doing more of what he enjoys doing most.

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