Room acoustics design of classrooms

In classrooms in which consideration has not been given to room acoustics, sound often reflects strongly off the walls, ceilings and floors. This leads to a sustained echo which impairs comprehension of speech and raises the sound level in the room.

As a result, the lessons are only partly comprehensible, or can be followed only with great effort. Students become tired more quickly, and their performance suffers. A number of studies have shown that under exposure to noise, memory performance deteriorates by more than 20%.

In louder teaching situations in particular, an increase in the sound level caused by the echo has appreciable consequences: it forces the speaker to speak louder, which in turn increases the noise exposure even further. This increase in volume by the speaker, referred to as the Lombard effect, increases the noise exposure further still, and can result in an extremely unpleasant exposure situation for all involved. High noise levels during lessons may give rise to stress reactions among the teaching staff; these can be detected, for example from the heart rate. At the same time, a classroom with unfavourable acoustic properties also places considerably greater stress upon the voices of the teaching staff, which in turn may cause health problems.

Such problems can be avoided by acoustic design measures in the classroom. Aspects of acoustic design are described in DIN 18041, Acoustic quality in small to medium-sized rooms (in German only). According to this standard, the reverberation time in the 125 to 4,000 Hz octave bands is the decisive parameter for evaluation of a classroom's acoustics. The reverberation time is the time required for the sound to decay by 60 dB. It can be reduced by the fitting of sound-absorbent materials to walls, ceilings and floors. Fitting of materials to the ceiling is generally the preferred measure, and often suffices.

The IFA provides a room acoustics calculator for classrooms which calculates the reverberation times in the 125 to 4,000 Hz octave bands and the corresponding tolerance limits to DIN 18041, and outputs them in graphical form. The structure of the program is straightforward: only the room dimensions need be entered for an estimation of the reverberation times, which can easily be compared to the requirements of DIN 18041 by the simultaneous display of the upper and lower tolerance limits. The program is also able to calculate the effect of absorbers on the ceilings and walls of the room, enabling room-acoustic measures to be planned.