Sound absorption increases student performance at Polish school

In 2012, the primary school SP340 in Warsaw was completed. With 1,200 students, the 8,200 square meters comprises 29 classrooms, a number of language and common rooms, a canteen, an auditorium and a large gym. Soon it became obvious that the acoustic environment was intolerable.

The parents’ council, led by Robert Wojciechowski, took action and pushed the local government to finance an acoustic refurbishment. It was not an easy task. The parents’ council had to contact several instances and fight hard for their sake. But finally, after a meeting with the chancellor of the urban municipality of Warsaw in which the school is situated, it all changed.

“She has children of her own in the same age and understood what we were saying. She wanted the problem to be solved, and the door to change opened in a moment,” Robert Wojciechowski remembers.

Test rooms showed huge improvements

The key to the turning point was a small investigation into the acoustic conditions in the school that the authorities agreed to go through with.

“The results were horrible, even though the authorities tried to disguise the problem by presenting a 24-hour average of the sound values that had been measured. This paper became a weapon in our struggle,” Robert Wojciechowski says.

The parents’ council got in touch with Ecophon, who helped with facts about sound environment and noise. Ecophon and one other manufacturer also refurbished one classroom each as test rooms.

“The difference was huge. The children suddenly said that they could understand what the teachers were saying. The teachers did not have to scream anymore,” Robert Wojciechowski says.

Worse than a factory

After evaluating the test rooms, it was decided that the whole school should be acoustically refurbished. The project got a budget of 200 000 euro, and the tender was won by professor Andrzej Klosak’s consultancy Archakustik.

“The school acoustics were very bad. The sound pressure levels in the corridors during the breaks were higher than the acoustic regulations for factories,” Andrzej Klosak points out.

Andrzej and his team started with measuring the reverberation time in each room as they were furnished, to get the existing absorption levels. Then they created 3D-models for each room – modeling that turned out to match reality very well. The aim was to comply with the new Polish standard for room acoustics in schools that came into force 2018 – without covering more than 40% of the ceiling area with sound absorbent materials.

“There were two reasons for this. One was the limited budget. Second, this would have made it hard to comply with Poland’s national hygienic regulations for public and commercial buildings.”

One of the parameters in these regulations is the amount of air, measured in cubic meters of the room.

“The height of the rooms in this school was about 3 meters, which is the minimum height in the hygienic requirements. Adding a sound absorbing ceiling would reduce the ceiling height. We agreed with the authorities to use less than half of the ceiling area for absorbers. Then they would not review the hygienic conditions – something everyone involved wanted to avoid, as the school was built and planned for considerably less students than is the case,” Andrzej Klosak says.

Considerably improved acoustics

Despite these limitations, Andrzej’s team managed to get the reverberation time in the classrooms below 0.6 seconds. The speech intelligibility was also considerably improved, complying with the Polish standard of which Andrzej Klosak is one of the authors.

“We wanted a flat reverberation curve, without booming sounds. It is easy to absorb high frequency sounds, but you need to also absorb the low frequency sounds to avoid a strange feeling. That is why we used thick absorbers, but to a limited amount due to the reasons mentioned earlier.”

In the corridors and common rooms, the ceiling was higher and it was possible to cover most of the ceiling with sound absorbers. In the extremely nosy corridors, the early reverberation time (EDT) was reduced from a high 2.5 seconds to 0.5 seconds.

All the goals achieved

Andrzej Klosak is very satisfied with the outcome of the refurbishment.

“From an acoustical point of view, we achieved all the goals. The school is fantastic now. It was the first school in Poland to be acoustically refurbished in a scientific way.”

Robert Wojciechowski agrees and points out that the key is to get across the barrier of ignorance and political risk of not knowing the outcome of a public investment.

“In Warsaw only, nine schools have been refurbished now and two more are in the process. Other schools from all parts of Poland want to follow our example of how to do it and where to get the money. We have put a snowball in motion.”

A feeling of deep change

A survey, with 378 students and 40 teachers participating, confirmed a perceived feeling of deep change due to the improved acoustics.

• Teachers asked about students’ performance and behaviour, noticed positive changes in the level of concentration and pace of work, task fulfilment, short-term memory capacity, durability of memory, level of fatigue and aggression and, above all, level of speech intelligibility.
• When asked about their working conditions, they can see benefits in terms of less fatigue, lower vocal effort, reduced prevalence of hoarseness, headache and tinnitus, and a lower level of stress.
• Students asked about their own performance noticed better concentration, speech intelligibility and pace of work. They pointed out less incidences of aggression at school.
• Both groups pointed out higher students’ school achievements after the acoustic renovation of the building, but the teachers found stronger correlation. 76% of teachers stated that students’ school achievements were higher.

Text: Lars Wirtén