Speech intelligibility in Swedish forests

Regular paper

Jonas Christensson

Saint-Gobain Ecophon

Tuesday 2 june, 2015, 11:40 - 12:00

0.9 Athens (118)

For thousands of years we have developed our hearing in an outdoor environment full of natural sounds, as babbling brooks, wind from trees, bird songs and human voices. The problem is that students and teachers spend a major part of their time indoors, in a sound environment with very few natural sounds. The effect is problem for students to understand what the teacher is saying and voice problems for teachers. It´s important that teaching places provide good speech intelligibility for listeners and good speak comfort for speakers. Being able to listen without effort is important for good learning and we know that bad room acoustics is a burden that impedes learning and affect teacher voice health. A good example is the Swedish forests where we can talk to each other over long distances without having to raise our voice. I have made several listening tests in the forest and also measured the sound reflections in different forests. The results are interesting and I mean that “forest acoustics” should be the goal in terms of acoustic conditions in our schools. My presentation will focus on why the forest acoustics provides so good speech intelligibility, and which acoustic parameters what are interesting to measure. Many national sound standards put requirements on room acoustics in classrooms. One requirement is reverberation time, according to ISO 3382-2, and it´s often evaluated with T20. Unfortunately this is a very blunt measure, because we start T20-evaluation first after the sound pressure level dropt 5 dB. This “waiting time” is often quite long and it´s a problem because we miss a lot of important information from the early part of the decay curve. Therefor I mean we have to add C50 according to ISO 3382-1, to control if the room acoustics is good enough for teaching.

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