A suspended acoustic ceiling was installed in a Year 5 classroom in a Swedish middle school. No other changes were made to the acoustic environment. The teacher then measured how long it took for pupils to enter the classroom and settle down so that lessons could begin. These measurements were compared with those taken before the ceiling was installed.
The results are clear: Before the modification, it took an average of 2 minutes and 18 seconds until the teacher could start the lesson.
After the ceiling was installed, it took 1 minute and 17 seconds – a gain of about a minute, or 44 per cent, so almost half the time. Given that the pupils take their seats in the classroom 15 times a week, this means that effective learning time is extended by 15 minutes weekly.
Petra Lagerberg, supervisor Svante Granqvist and Sebastian Holm.
Plugging a knowledge gap
The study was conducted as part of a degree thesis in construction technology and design/economics. The supervisor, Svante Granqvist, emphasizes that his students took a serious and thorough approach.
“This was just a study of a single classroom, but the findings are so interesting that we have an incentive to perform further studies in a similar vein.”
Sebastian Holm, who conducted the study with Petra Lagerberg, explains that they discovered a knowledge gap in this field when preparing the study.
“No previous studies have combined objective acoustic tests like the Speech Transmission Index (STI) with a subjective listening test. So we added a test called Hagerman’s Sentences, where pupils had to listen to specially prepared sentences and write down what they understood. The various test results support one another, which lends scientific weight to the study.
Specific classroom requirements
Holm and Lagerberg conducted the study in a classroom of Year 5 pupils that met the specific requirements for the study to be valid.
“It’s important to have the right age group. Their hearing has to be sufficiently developed, so we didn’t want pupils who were too young. The lessons have to be measurable, with specific subjects and comparable conditions over time.”
Year 5 in the Swedish school system meets these requirements: a single class in a single classroom, but with subject-specific lessons in recurring time slots.
Another key factor was being able to link the findings to the action taken: installing a suspended acoustic ceiling.
“When an acoustic ceiling is installed, there are usually also changes to the ventilation system, which affects the acoustic environment. In this case, background noise was already at a good level, so we were able to link the changes specifically to the improved acoustics.
The following measurements and tests were performed before and after the acoustic ceiling was installed:
- Teacher’s timekeeping
- Hagerman’s Sentences: a listening comprehension test consisting of several meaningless sentences amid a certain amount of background noise
- Reverberation time: impulse measurements using wooden clapperboard
- Clarity 50: measurement in decibels (dB) of the sound energy in early reflexes
- Background noise levels: measured at weekends while school was empty
- Speech Transmission Index (STI): describes how well speech is transmitted from speaker to listener
- Survey: the same survey was used in a major study of speech intelligibility in Swedish classrooms
Easily defensible costs
The purpose of the study was to examine whether improving the acoustic environment in the classroom can yield socioeconomic benefits.
“I think we’ve shown that this leads to socioeconomic improvements. It’s a clearly measurable result that everyone can understand and use to defend the cost of installing an acoustic ceiling.”
The installation in this specific one-off case cost around EUR 8,500*, (over three times the cost of a typical new build classroom ceiling) including demolition and quit a lot of over time compensation due to the tight deadline. However, this is roughly equivalent to the annual cost of one pupil in the Swedish compulsory education system. If, over the ceiling’s lifetime, just one pupil avoids having to repeat a year thanks to the improved learning environment, even this one-off high costing ceiling has paid for itself.
I think the greatest benefit of the improved acoustics is that they can help you create a better, more harmonious atmosphere in the classroom and counteract exclusion.
According to Holm, it’s not only about short-term financial savings:
“You’ll have a calmer class with less stress and more focused pupils. I think the greatest benefit of the improved acoustics is that they can help you create a better, more harmonious atmosphere in the classroom and counteract exclusion.
“If you’re performing better, teamwork becomes easier. Everyone has a lot to gain from this.”
Improved acoustic environment is key
The study findings exceeded Holm’s and Lagerberg’s expectations.
The method for measuring the time taken for the class to settle down relied heavily on the teacher performing the measurements correctly.
“He understood exactly what was needed. He had performed similar measurements in the past and was very careful to measure the same way each time. One of the study’s strengths is that we took enough measurements for it to be statistically reliable.”
The study findings exceeded Holm’s and Lagerberg’s expectations.
“There was a really big improvement. I think the Lombard effect** was a big factor in the results. Noise generates noise – one person raises their voice, and then so does the next person, and so on. By reducing reverberation time, we reduce noise levels,” explains Holm.
Both before and after the modification, pupils were asked to fill in a survey on their perceptions of the acoustic environment in the classroom.
“This also indicates when there is an improved acoustic environment. The classroom is now perceived as a more pleasant space to be in,” says Lagerberg.
The study indicates that it’s easier for the teacher to connect with pupils, which should be of benefit throughout the lesson.
Benefit throughout the lesson
Granqvist believes the study makes it possible to calculate, in financial terms, the cost of poor acoustics in the form of lost teaching time.
“I also see it as an accessibility issue. Pupils with concentration difficulties, like ADHD, or for whom Swedish is a second language find it harder to learn in a noisy environment.”
Halving the time taken to get lessons under way is a big improvement, says Granqvist.
“But it’s not just about time. It also encourages the class to settle down of its own accord. That’s likely to spill over into the rest of the lesson. The study indicates that it’s easier for the teacher to connect with pupils, which should be of benefit throughout the lesson.”
Text: Lars Wirtén
Photo: Anette Persson and Image Source Limited
* When constructing a new building, the estimated installation cost will be significant lower, approximately EUR 2 500.
** Lombard effect: our tendency to raise our voice when the ambient noise level is high.