Abstract: Most domestic and foreign acoustics standards and recommendations for the requirement of classroom acoustic environment focus on the mid-frequency range (500~1 000 Hz). The corresponding designs and installations, however, cause tremendous loads on both teachers and students. Experience from classrooms with optimized environments recommends specific absorption measures yielding an almost flat frequency characteristic of the reverberation time. The aim must be to help early lateral reflections from the room's boundaries to support the direct sound from a source according to ‘Haas effect’ and thus reduce ‘masking’ of the important higher frequencies by irrelevant lower frequencies. Some practical examples are presented which definitely support speech intelligibility with an amazing reduction of noise in all kinds of conversations in a room.