Applied Ergonomics 38 (2
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The main scope of this work was to study the acoustical
time was calculated.
The school project is named Standard 023. It has four
countries such as Brazil, France, Germany, United Kingdom
ARTICLE IN PRESSand the USA. Limiting levels to the indoor background noise
are shown in Table 1 (ANSI S12.60, 2002; Building Bulletin 93,
2003; Karabiber and Vallet, 2003).
0003-6870/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.apergo.2006.10.001
Corresponding author.
E-mail address: paulo.zannin@pesquisador.cnpq.br (P.H.T. Zannin).quality of classrooms in Brazilian public schools. In order
to evaluate the acoustical quality of classrooms, three
acoustical parameters have been investigated: background
noise level, reverberation time and sound insulation.
Teachers and pupils have also been interviewed with the
purpose of evaluating the level of satisfaction of users of
the classrooms.
As the classrooms studied were built lacking any
absorbent materials in their interior, simulations have been
performed of the placement of absorbent materials on the
ceiling. The simulated materials were gypsum, plywood
and perforated ply wood. Their influence on reverberation
classrooms separated by a central circulation corridor and
it measures 7 7 3.1m. The walls separating the corridor
and the classrooms have a ventilation opening and
permanent illumination through glassy bricks. The max-
imum capacity of each classroom is for 40 pupils.
3. Background noise
Background noise is one of the parameters that affect the
acoustical comfort of classrooms. There are established
recommendations limiting background noise in severalr 2006 Elsevier Ltd. All rights reserved.
Keywords: Acoustic comfort in classroom; Reverberation time; Background noise; Sound insulation; Acoustic simulation; Subjective evaluation
1. Introduction
The acoustical conditions in classrooms appear to have
attracted worldwide attention. Good acoustics is an
indispensable requirement for verbal learning and therefore
vital to all knowledge-based societies (Karabiber and
Vallet, 2003).
2. Description of the classrooms
The school under study has been built by the Secretary
of Education of Parana´ State, in its capital Curitiba,
located in southern Brazil. In the last 8 years 400 public
schools have been built in Parana´, with an investment of
approximately USD$ 168 million.classrooms.Techn
Objective and subjective
comfort in
Paulo Henrique Trombetta Za
Laborato´rio de Acu´stica Ambiental, Industrial e Conforto Acu´stico, U
Centro Polite´cnico, Bairro Jardim das Am
Received 11 January 200
Abstract
The acoustic comfort of classrooms in a Brazilian public school h
measurements of background noise, reverberation time, and sound
quality of the classrooms. Results have shown that teachers and
neighboring classrooms as the main sources of annoyance inside
placement of perforated plywood on the ceiling, for reductionin , Carolina Reich Marcon
ersidade Federal do Parana´, Departamento de Engenharia Mecaˆnica,
s, CEP: 81.531-990, Curitiba, PR, Brazil
ccepted 23 October 2006
been evaluated through interviews with 62 teachers and 464 pupils,
sulation. Acoustic measurements have revealed the poor acoustic
pils consider the noise generated and the voice of the teacher in
e classroom. Acoustic simulations resulted in the suggestion of
reverberation time and increase in the acoustic comfort of the007) 675–680
l note
aluation of the acoustic
lassrooms
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ARTICLE IN PRESS
plie4. Reverberation time
Reverberation time is an important parameter that
interferes with the acoustical quality of a classroom. It is
strongly dependent on: (1) room volume; (2) the sound
frequency in the room, and (3) the total sound absorption
in the room (Harris, 1994). Many national and interna-
tional recommendations include reverberation time limits,
Table 1
Background noise limits
Country Noise
descriptor
Year of the
definition
Classroom Library
Brazil LAeq 1987 40–50 35–45
France LAeq 2002 38 33
Germany LAeq 1987 30–40 30–40
USA LAeq 2002 35–40 35–40
Table 2
Recommendations for reverberation time RT (furnished, unoccupied
rooms)
Country Reverberation time (s)
Brazil 150pVo300m3, 0.5pRTp0.7 (for
500–1000–2000Hz)
France Vp250m3, 0.4oRTo0.8 (for 500–1000–2000Hz)
V4250m3, 0.6oRTo1.2 (for 500–1000–2000Hz)
Germany 0.8oRTo1.0 (for 500–1000–2000Hz)
USA Vo283m3, RT ¼ 0.6; 283m3oVp566m3,
RT ¼ 0.7 (for 500–1000–2000Hz)
P.H.T. Zannin, C.R. Marcon / Ap676as shown in Table 2 (ANSI S12.60, 2002; Building Bulletin
93, 2003; Karabiber and Vallet, 2003).
5. Subjective evaluation
In order to evaluate the level of satisfaction of teachers
and pupils, users of classrooms of the Standard 023,
questionnaires have been elaborated, targeted to each of
the two groups. Sixty-two teachers and 464 students have
been interviewed. In the teachers’ questionnaire, some of
the questions had to be answered based on a scale,
according to the level of annoyance with respect to noise,
ranging from 0 (low score—not annoyed) to 6 (high
score—extremely annoyed). One of the questions to the
teachers was: ‘‘Which class activity is most affected by
noise?’’ The options offered were: lecture, understanding of
the contents explained by the teacher, individual reading,
and quizzes or examinations. Again using the 0–6 scale, the
teachers should indicate the degree to which each of these
activities were disturbed by noise in the classroom.
Afterwards, values attributed to each alternative were
added and divided by the number of interviewed teachers.
Figures with the outcome of the interviews are presented in
the Results and Discussion. The questionnaire presented to
the pupils contained questions similar to the ones posed tothe teachers. However, they were answered qualitatively,
not using an evaluation scale.
6. Measurement of the background noise, reverberation time
and sound insulation
Four classrooms built according to the Standard 023
have been evaluated. Reverberation time was measured for
the following situations: (1) empty classrooms; (2) class-
rooms with 20 students; (3) classrooms filled to their
maximum capacity, i.e. 40 pupils.
Background noise in the classrooms (closed doors and
open windows) was measured for the following situation
(see Fig. 1): (1) Measurement in room 03; room 01 with
normal ongoing class; rooms 02 and 04 with children in
silence, (2) Measurement in room 03; rooms 01, 02 and 04
with normal ongoing classes. Reverberation time was
measured following International Organization for Stan-
dartization—ISO 3382 (1997). In all situations room 03 has
remained empty and the other 3 rooms were filled to their
full capacity, with 40 pupils.
Background noise was measured in 10 positions around
the school. Measurements were taken during 5min for each
position. The equivalent sound level Leq, expressed in
dB(A), was measured in 5 positions inside each classroom.
Background noise was also measured in 3 positions inside
the classrooms and the measurement period was 5min.
The weighted apparent sound reduction index (Interna-
tional Organization for Standartization—ISO 140-4, 1998)
was measured for the wall separating the classroom from
the corridor. This wall has the door and glassy bricks.
The equipments used were from Bru¨el and Kjaer (2003):
(1) sound analyzer BK 2260, (2) sound amplifier 2271, (3)
sound source, (4) building acoustic software BZ 7204, (5)
building acoustic software Qualifier 7830, and (6) sound
level meter Mediator BK 2238. All measurements were
carried out under ideal meteorological conditions: no wind
and no rain.
7. Simulation of reverberation time
The classrooms studied here were built without any
acoustical treatment. Simulations have been performed
with different types of materials, and their influence on the
reverberation time was investigated. The materials tested
for the simulation were: (1) gypsum, (2) plywood, and (3)
perforated plywood.
8. Results and discussion
The school is located in the suburb of Curitiba, in an
area classified as residential according to the local
legislation. The local legislation establishes that the
external background noise for daytime (7:00 am–7:00 pm)
should not exceed 55 dB(A) (Zannin et al., 2002, 2003). The
d Ergonomics 38 (2007) 675–680mean equivalent sound level for background noise was
53.5 dB(A) and this means that the school is located in a