PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Effect of sound absorption on children’s behavior in daycare
rooms: a field experiment with installation of temporary soundabsorption.
Keiji KAWAI1
1

Kumamoto University, Japan

ABSTRACT
We have been investigating the effect of sound absorption for children in child daycare rooms and the results
demonstrated a mitigating effect of bustling atmosphere in the rooms and an improvement of word
intelligibility of children. In this study, we attempt to find behavioral change of children in acousticallyabsorbed daycare rooms by a field experiment with installation of temporary sound absorption. The
experiment was conducted in two actual daycare centers in Kumamoto City, Japan. Three mixed age (3-5years old) groups in a center were observed during the teacher’s announcement in the daily morning meeting
and a 1 year old group in another center was observed during being read a picture book by the teacher. The
observation was performed with video-recording for 6-10 days and sound absorbing cloths were attached tothe ceiling for 2-4 days in the days. The reverberation time without absorptive cloths was 0.65-0.90 s, as thedaycare rooms did not have any sound absorptive surface, and it was reduced to 0.4-0.5 s with absorption.
The observation period was 60 second from the beginning of the activity, cut from the recorded video bychoosing parts without particular disturbing events such as someone’s entering the room. Then the video wasdivided into 1 second segments and the ratio of the segments in which the face of a child was directed at theteacher was defined as concentration time ratio (CTR). Then the individual CTR was compared by theabsorption conditions. The result showed that the CTR of two groups out of four was significantly higher
with sound absorption. Though there were several limitations, the result supported the effect of soundabsorption.
Keywords: sound absorption, child daycare, concentration, classroom acoustics

1. INTRODUCTION
It is widely recognized that child day-care rooms require optimum acoustic condition as children
from 0 to 5 years old are supposed to be in the period of developing their listening and language skill
as a WHO guidelines (1) or other political documents (e.g.2) state. Several studies examinedinterference of poor acoustic condition with noises and reverberation on the speech intelligibility ofelementary school pupils and found younger pupils were more affected in the poor conditions (3,4).
It is highly possible that speech intelligibility of preschool children is more affected by acoustic
condition than pupils while we could not find the evidence for this. Thus in the previous study (5,6)
we attempted experiences that investigated pre-school children’s listening skill under interference ofnoise and reverberation. The results indicated greater effect of acoustic condition on young children’slistening than on that of pupils or adults. Such a loss of speech intelligibility as indicated in theprevious studies may cause a loss of concentration of children in verbal communications. Thus in thisstudy, as a further step of investigation of the effect of good acoustic quality by sound absorption on
preschool children, a field experiment was performed in which children’s listening to teacher’s talking
in the conditions with and without sound absorption were observed in actual kindergarten classrooms.
This paper is a revision of our paper in the proceedings of Internoise 2018 (7) and about a half of thedata in this paper came from the same experiment. The procedure of analysis was revised to be more
rigorous and reproducible and all the data were re-analyzed.
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kkawai@kumamoto-u.ac.jp

2. Experiment
2.1 Experimental rooms
The experiment was carried out in three actual classrooms with the cooperation of two childdaycare centers in Kumamoto city region. Dimension of the rooms is shown in Table 1. Room 1 andRoom 2 are daily used by three mixed year groups (Group A, B and C) of 3–5 year old children byturns for various kind of activity such as meeting, lunch, free playing, being read picture books byteacher, and so on. Room 3 is a home room of a 1 year old group (Group D). In these rooms, children’sconcentration in listening to teacher’s talking was observed in the conditions with and without
temporary installation of sound absorptive materials.
The original surface material of these rooms was not sound-absorptive such as gypsum boards,
glass windows or wooden floor, reflecting the situation that sound absorption for children’s room isstill not popular in Japan. Two reverberation conditions in the experiment were this original condition
and that with additional sound absorption by polypropylene fiber cloth with 4.5 mm thickness (Mitsui
Table 1 – Dimensions and acoustic characteristics of rooms for experiment.
without absorberwith absorber
Floor area Height Volume Surface Absorber
Room
RT STI- STI- RT STI- STI(m)(m3)
area (m2) area (m2)(m2)
1m 3m(s)†1 1 m 3 m‡2 (s)Room 1141
2.5352418
59.40.65 0.85 0.74 0.44 0.91 0.82
Room 21472.5368
418
80.4
0.90 0.82 0.72 0.51 0.91 0.80
Room 3632.6
163
213
41.0
0.73 0.77 0.70 0.39 0.87 0.80
†1Average over 500-2k Hz band. ‡2 Actually 3.5/3.1/4.0 m in Room1/Room2/Room3, respectively.

300

1800

Polypropylene fiber cloth @ 4.5 mm(Mitsui Chemical Inc. TAFNELTM)

Figure 1 – Attachment of sound absorber
1.0

Reverberation time [s]

0.8

0.6

0.4
Room 1 without/with absorption
Room 2 without/with absorption
Room 3 without/with absorption

0.20.01252505001000 2000
Frequency [Hz]4000

Figure 2 – Reverberation time by installation of sound absorber7105

1470014700
Children

Teacher

9800

Play area

Play area
7000

10000

ChildrenShelves
Teacher

10000

Teacher

Shelves
ChildrenRoom 3

Room 2

Room 1Figure 3 – Layout of rooms for experiment
Chemical Inc. TAFNELTM). The cloths were attached on the ceiling with 300 mm back air thickness
at the center (Figuge-1). Figure 2 and Table 1 show the reverberation time and STI obtained from
impulse response measurements using time stretched pulse method before and after installation of thesound absorbers. The original reverberation time of each room in 500–2000 Hz band was around 0.65s, 0.90 s and 0.73 s, and the average absorption coefficient estimated by Eyring’s formula was 0.20,0.14 and 0.17, respectively. The short reverberation time in Room 1 was considered to be due to someextent of absorption by the open shelves in which children’s personal belongings such as clothes andbags were put. By the installation of the sound absorbers, the reverberation times were reduced tobelow 0.6 s, which is the target value for playrooms of preschools in the WHO guideline (1), andaverage absorption coefficient increased to 0.28, 0.24 and 0.31 in Rooms 1, 2 and 3, respectively.
2.2 Behavioral observation
We selected teacher’s speeches in morning meetings in Room 1 and Room 2 and those of reading
aloud a picture book in Room 3 as target activities for the observation. The morning meeting was held
every day and children sat on the chair and listened to the teacher who told them about the activities
and schedule of the day. Teacher’s reading a picture book aloud to children was performed also every
day in the morning as a kind of morning meeting for 1 year old children. The room layout is illustrated
in Figure 3.
Each observation time began at the moment the teacher began speaking when everyone became
concentrated to the teacher after the teacher calmed the freely playing children by calling them andplaying music by an organ and so on. A video camera was set in front of the children and a microphone
was hung above the children recorded the activities. Also two experimental staff observed theactivities to check any events that might affect children’s concentration.
The experiment was carried out from December 2017 to February 2018 in Room 1 and Room 2and in January and February 2019 in Room 3. Group A, B and C had around 40 children and GroupD had 19 children but number of children varied due to absence. The number of children attended andthe days with and without sound absorber of each of the groups are shown in Table 2. The number ofdays of observation were 6-10 and the order of changing absorption conditions differed depending on
the groups. The detail is indicated in Table 2 and Figure 4.
There are limitations, as follows, concerning with the quality of the experiment due to the limited
possibility of control in the actually running daycare centers and there had to be considered in theanalysis. 1) There were two or three homeroom teachers for each groups and the teacher speaking in
the meeting changed on the days with and without absorption in the cases of Group A, B and C. This
Table 2 – Sound absorption condition of observation

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Group

Number ofattended children

RoomA27-39

B

Number of observation daywith absorberwithout absorberRoom 22428-38Room 1

34C

26-41

Room 2

44

D

11-16

Room 337

point is considered to be a major flaw of this experiment because the concentration to the speech could
be affected by the skill of teachers. This point is discussed later. The teacher of Group D was the same
throughout the days. 2) Children were not the same among the days of observation because of absence.
3) Children’s attention could be affected by the factors other than acoustics but it was not possible tocontrol actually, and so on.
2.3 Analysis
The observations was performed on the video recordings. The starting point of observation was set
at the beginning of the teacher’s speech because the teacher had called all the children’s attention tohim/her at that moment. The observation time period was 60 seconds of the speech for each of themeetings. When an event that interrupted the speech or children’s concentration occurred, such as achild of late arrival coming in, the period of interruption was omitted and the 60 seconds were selectedfrom other than interrupted period.
Thus obtained videos of 60 seconds for observation was divided into one second segments and thedirection of the face of each of the children was observed by pausing the video play every one second.
We judged a child to be concentrated to the speech when his/her face was directed to the teacher,which was due to the quality of the video not enough to observe eye directions precisely. Each of theone second segments was coded into 1: concentrated, 0: not concentrated, x: unable to judge becauseof the face hidden by other children or other reasons. Then the ratio of the number of 1 to the numberof 0+1 was defined as concentration time ratio (CTR). The CTR of each of the attended children wasanalyzed. Since the children sat on different chairs day by day, each of the children on the video wasidentified over all the days of observation, by the cooperation of the teachers, in order to compare theCTR individually by the change of the absorption conditions.

3. RESULT

Concentration time ratio (%)

As an overview of the result, Figure 4 indicates the individual distribution of CTR by date and theabsorption conditions. The CTR distributed widely and the median were 70-95 %. An obvious high
CTR by sound absorption was only seen for Group C. It is seen for every group that rather low CTR,
such as less than 60%, were relatively fewer with sound absorption than without absorption, while
this was statistically significant only for Group C (p=0.003 by chi-square test).
Next, individual CTR was compared between the absorption conditions. Since not many children
100

100

80

80

60

60

40

40
2020GroupAConcentration time ratio (%)

0 20/12 21/12with100

23/1

24/1 25/1
without26/1

Group B01008080

60

60

40

40

20

75%
medianmean25%

20
Group C018/12 20/12 21/12 22/12 22/1 25/1 26/1
withoutwith

12/12 13/12 14/12 16/12 15/1 17/1 18/1 19/1
without
withGroup D
021/1 22/1 23/1 24/1 25/1 28/1 30/1 1/2 4/2 5/2
withwithout
without

Figure 4 – Individual distribution of concentration time ratio by date and absorption conditions

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GroupA

Table 3 – Binomial test on the effect of sound absorption
N of children who
N of children indicating
Probability of occurrence byexperienced bothbetter CTR underbinomial distribution assuming
absorption conditions
absorptive condition
equal probability
34
210.11B37

180.63C41

370.00D

19140.03

attended all the days of observation, the children who experienced both of the absorption conditionsat least one day each were selected for the comparison (Table 3). Among them, number of children
whose CTR was higher under the condition with sound absorption was counted. Then with ahypothesis that the ratio of these children is expected to be 50 % if there was no effect of soundabsorption, the probability of occurrence of actual number of the children of higher CTR withabsorption was calculated. The result was that more than 50 % of children other than Group B
indicated higher CTR with absorption, with Group C as the highest at 90 %. The probability bybinomial test was significantly low for Group C and D, and Group A showed rather low probabilityof 0.11. The result of Group B with no difference between the absorption conditions might be reasonedby that the meeting of Group B was held in Room 1 with relatively low reverberation originally.
As mentioned before, the teacher of each of Group A, B and C was different between the absorption
conditions and therefore an interpretation of the result that these differences came from the different
communication skill of the teachers can not be rejected. However the CTR was considered to beaffected either way by the teacher’s skill but the result was consistent with the expected effect ofsound absorption. Though a weak verification, we examined the teacher on the video and could not
find much difference of communication skill which might cause a difference in Group C. Also theteacher of Group D was the same throughout the experiment. As a whole, though with several
limitations, it is considered that an evidence of the effect of sound absorption on the children’sconcentration was obtained.

4. CONCLUSIONSIn this study, concentration of children aged 1 and 3-5 years old to teacher’s speech in the acoustic
conditions of temporal installation of sound absorption was examined through behavioral observation.
Though there were several limitations of experiment due to the limited control over the situation in
the actually running daycare centers, the result indicated an increase of concentration with soundabsorption and this can be regarded as an evidence of the benefit of good speech intelligibility bymeans of acoustic design. On the other hand, this is the first attempt and contains lot of points toimprove for further studies, such as detailed activity planning with teachers, variation of activity, highresolution camera and so on. Though field experiments in actual daycare center has various limitations,accumulation of studies, even with limitations, should be needed to clarify the effect of acoustics onchildren.

ACKNOWLEDGEMENTS
We wish to thank the children and teachers of Jozan Kindergarten and Sakurambo Nursery for
their cheerful and helpful cooperation in this experiment. This work was supported by JSPS
KAKENHI Grant Number 16H03274.

REFERENCES
1. WHO, “Guidelines for Community Noise” (1999)
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design standards and guidelines”, p.33 (2016)
3. J. S. Bradley, H. Sato, “The intelligibility of speech in elementary school classrooms”, J. Acoust. Soc.
Am., 123, 2078–2086, (2008).
4. A. Astolfi, P. Bottalico, G. Barbato, “Subjective and objective speech intelligibility investigations in7108

primary school classrooms” J. Acoust. Soc. Am., 131, 247–257, (2012).
5. K. Kawai, K. Harada, “Experimental measurements of word intelligibility of pre-school children underacoustic interferences of reverberation and background noise” J. Acoust. Soc. Am., 141(5) Pt. 2, 3482,(2017).
6. K. Kawai, M. Otaku, “Experimental investigation of effect of background noise and reverberation onlistening comprehension of pre-school children” Proc. of Euronoise 2018, (2018).
7. K. Kawai, R. Yoshidome, S. Masumoto, “Effect of sound absorption on children’s concentration tolistening to teacher’s speech in a child daycare room” Proc. of Internoise 2018, (2018).

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