1. Research at Heriot-Watt University (Edinburgh)
This study was carried out by scientists at Heriot-Watt University and was initiated by the British government. The aim of the study was to examine the impact of poor classroom acoustics on students and teachers.
Research methodology
The study was conducted in 70 classrooms, both old and modern schools, over three years in the late 1990s (the study itself was published in 1999). The objects of observation were children aged 5 to 11, in classes with and without acoustic ceilings.
Ecophon was asked to participate in the study and install acoustic ceilings in a subset of classrooms to enable comparisons between acoustically untreated and treated classrooms.
The researchers measured noise levels, reverberation times, and speech intelligibility. They also interviewed students and teachers and examined their behavior.
results
The research results clearly show that high performance acoustic ceilings have a positive impact on the quality of education. They:
• Reduced background noise levels
• Reduced reverberation time
• Improved speech intelligibility
• Created a sense of well-being
• Changed student attitudes and behavior
• Contributed to improved test scores in acoustically treated classrooms
• Created a better working environment for students and teachers
The researchers also found that most of the disturbing noise comes from sources within the classroom (students, ventilation, etc.) rather than external sources.
Reverse Lombard Effect
Another important and at first somewhat surprising effect was the "Lombard inverse effect." The Lombard effect is that people tend to speak louder in noisy environments in an attempt to be heard. This leads to a gradual increase in the sound level in the room.
The inverse Lombard effect works exactly the opposite. In a quiet room, people tend to speak more quietly, as they do not need to speak loudly to be heard. This is also known as the "library effect".
In the Heriot-Watt study, an example from an elementary school in Ratmore illustrates this phenomenon well. When comparing sound levels in classrooms with and without acoustic ceilings, where children sat quietly, a classroom with an acoustic ceiling was 3 dB quieter. This is what one would expect from a purely technical point of view.
But when the students spoke, the noise level in the acoustically finished classroom was 10 dB lower than in the untreated room. A decrease in noise level of only 3 dB could be explained by a physical decrease in noise level due to its absorption by the ceiling, so that the remaining 7 dB of decrease was due to quieter behavior of students. Reducing the sound level by 10 dB is perceived as a halving of the sound volume, so this effect is very important.
2. Research from the University of Bremen
The following groundbreaking research was carried out by specialists from the University of Bremen. Here, the researchers examined the effects of poor acoustics on the teaching and learning environment, with additional emphasis on psychological and physiological phenomena such as stress levels and concentration.
The study was divided into three parts and was conducted in the late 1990s and early 2000s, and became the largest field study in school acoustics at the time, covering 570 teaching units, 28 classes and 5 schools.
Research methodology
Similar to the Heriot-Watt University study, this study followed the classic AB comparison principle, where data was collected in acoustically untreated classrooms and compared with corresponding data in classrooms after they were finished with class A acoustic ceilings.
The researchers measured room acoustics, including classroom noise levels and teachers' heart rates, to assess the correlation between acoustics, noise levels with different teaching methods, and student and teacher concentration and stress levels.
results
The research team found a number of interesting results. The study found that the teaching style in schools is shifting from a lesson in the form of a lecture, where the teacher speaks and the children listen, to a style that encourages children to communicate and work in pairs and in groups under the supervision of the teacher. In acoustically untreated classrooms, this change in teaching style resulted in an increase in overall noise levels. This would seem logical, since more people speak during group work than when the teacher speaks in front of the class.
However, after the classes were acoustically processed, the sound level actually dropped when the class was switched to group work or work in pairs. The noise level in the classroom was lower during group work than during lecture-style teaching. This was another example of the inverse Lombard effect.
The difference in level during group work in the classrooms before and after the installation of the acoustic ceiling was 13 dB, which is even higher than in the Heriot-Watt study. (See Figure 1). About 10 of this 13 dB is due to the inverse Lombard effect, and 3 dB is due to the actual absorption of sound waves by the acoustic ceiling.
Overall, the study suggests that schools looking to move from a traditional, lecture-based teaching style to a more group-oriented teaching style can actually reduce overall classroom noise levels, provided that classrooms are acoustically sound.
Less stress and tension in teachers' voices
The second interesting finding from the study was that the teacher's heart rate matched the noise level in the classroom. As the sound level rises, the heart rate rises as well. Heart rate is a recognized indicator of stress levels, which means that researchers have found a clear correlation between noise and stress levels. Comparing the HR data before and after setting the acoustic ceiling, a clear improvement could be seen. The teachers' heart rate dropped by as much as 10 beats per minute.
The improved acoustics also meant that teachers didn't have to strain their voices to be heard.
Better concentration among schoolchildren
The researchers also found that sound levels in acoustically untreated classrooms increased throughout the day. The noise level during the last lesson of the day was more than twice as high as during the first lesson (12-13 dB higher SPL).
This is because poor acoustics cause fatigue and students lose focus during the day, which in turn makes them noisier (more movement, whispering, etc.).
Not only did the sound level decrease after the acoustic ceiling was installed, but it remained more or less constant throughout the day, as shown in Figure 3.
Thus, it can be assumed that lower noise levels allow students to stay focused and less prone to disturbance throughout the day.
3. Study at a school in Essex County, UK
The study was commissioned by the Essex County Council in the United Kingdom to determine whether the acoustics of hearing-impaired classrooms would have a positive impact on students and teachers with normal hearing.
This study assessed the impact on the educational process of various degrees of acoustic treatment of classrooms.
Research methodology
The study compared four different classrooms in a high school in Essex. The first classroom is a control room without any acoustic treatment. Three other classrooms met three different UK standards for school acoustics.
One was fitted with a perforated plasterboard suspended ceiling that meets the requirements of the BB93 high school standard.
In another class, a class A acoustic ceiling was installed with good sound absorption in the frequency range from 500 to 2000 Hz. This grade met the BB93 Hi standard for hearing impaired children in regular schools.
In the third classroom, additional absorption of low-frequency sound in the range of 125-4,000 Hz was provided. The premises were compliant with the BATOD (British Association of Teachers of Hearing Impaired Children) standard, a standard used in special schools for children with hearing impairments.
The researchers measured reverberation times and noise levels, monitored student and teacher behavior, and interviewed students, teachers, and panelists. The study was conducted in the form of a double-blind test, in which none of the respondents knew in which classroom particular acoustic conditions were created.
results
Research has shown a strong correlation between good acoustics (i.e. short reverberation times) and the perceived quality of the learning environment, for both students and teachers.
Teachers, students, and a group of acousticians, district council officials and other professionals filled out a questionnaire about acoustics in different classes, and the results showed very clearly that the better the acoustic treatment, the higher the grade was scored (see Figures 4 and 5).
The classrooms were distinguished by the following:
• There was no acoustic treatment in room MA5;
• A plasterboard suspended ceiling was installed in room Ma1 to meet the UK high school standard (BB93);
• A class A acoustic ceiling was installed in room Ma2, with improved performance in the frequency range 500-2000 Hz compared to the ceiling in room Ma1. This class met the standard for classrooms for hearing impaired children in mainstream schools (BB93 section 6);
• In room MA3, the most effective sound-absorbing solutions were installed, including absorbers of low sound frequencies impairing speech intelligibility. The class acoustical furnishings included class A sound-absorbing suspended ceilings with Extra Bass low-frequency absorbers additionally installed in the ceiling space.
Once again about the opposite Lombard effect
A clear improvement in acoustics in the study was that the background noise level was significantly reduced as the reverberation time became shorter. Reducing the reverberation time from 1.2 to 0.8 seconds, which is the difference between an untreated control room and a classroom with a plasterboard ceiling, reduces background noise by 9 dB. This is close to halving the perceived loudness.
The difference in noise level in the unprocessed class with the class with the best acoustics (where the reverberation time was 0.3 s) was more than 20 dB. This is of great importance.
From a purely technical point of view, halving the reverberation time results in a 3 dB reduction in noise. So only about 6 dB of the total sound reduction can be attributed to the physical sound reduction through absorption. The rest was due to the quieter behavior of the students. Once again, this was the opposite of the Lombard effect, which turned out to be the main reason for the decrease in sound levels.
Figure 6 shows how background noise levels are affected by room acoustics. The volume of the teacher's voice decreases when the acoustics in the classroom are better. There is no need to shout in a quiet room.
It is interesting to note that the background noise (caused by the students) decreased more significantly than the volume level of the teacher's voice. This led to an increase in the loudness-to-noise ratio (signal-to-noise ratio) by 10 dB (from 8 to 18 dB). So, not only has the room become quieter, it has also become much easier for the students to perceive the teacher's speech.
It should be noted that the main difference between classroom 3 (BB93 Hi) and classroom 4 (BATOD) was better low frequency absorption. This clearly shows how important it is in schools.
Reported positive effects of good acoustics include:
• Better sound localization. Teachers could easily identify who was causing the noise, which contributed to better classroom management;
• Reducing the number of repetitions;
• Better discipline, which means that teachers could take a more relaxed approach to classroom management;
• More effective group work in the classroom;
• Reduced stress and tension of the vocal cords in teachers.
4. Summarizing the research results
Taken together, the results of three studies clearly show the benefits of good acoustics in schools:
• Acoustic treatment of classrooms encourages calmer student behavior. The inverse Lombard effect was very clear in all three studies;
• Signal-to-noise ratio gets better, improving speech intelligibility;
• Teaching methods can be modified to allow students to take a more active part in learning through discussion and group work. It should be noted that a study by the University of Bremen showed that in rooms with good acoustics, sound levels were lower during group work than in classical lecture-style teaching;
• Teachers and students get a quieter work environment in which they feel more at ease;
• Pupils can maintain concentration for longer;
• Students' results are improving;
• The stress level of teachers is reduced;
• Teachers do not overextend their voices;
• Children with special needs and their teachers need really good acoustics.
