Urban noise and classroom acoustical conditions in the teaching‐learning process

Intern. J. Environmental Studies, 1998, Vol. 56, pp. 41-59 © 1998 OPA (Overseas Publishers Association) N.V.Reprints available directly from the publisher Published by license underPhotocopying permitted by license only the Gordon and Breach Science

Publishers imprint.Printed in India.

URBAN NOISE AND CLASSROOMACOUSTICAL CONDITIONS IN THETEACHING-LEARNING PROCESS

MARIO RENÉ SERRA* and ESTER CRISTINA BIASSONI

Centro de Investigaciones. Acústicas y Luminotécnicas (CIAL),Ciudad Universitaria, Agencia Postal 4, 5000 Córdoba, Argentina

(Received 8 August 1997)

The main parameters to determine general acoustical conditions in regard to verbalcomprehension in classrooms are studied. The results showed that the general acousticalconditions of the surveyed noisy classrooms were not suitable for academic purposes,according to the suggested requirements for that kind of activity. The youngest groupsexhibited lower performances than the older one, according to their classroomsacoustical characteristics.

Keywords: Acoustical conditions classrooms; background noise; reverberation time;intelligibility

INTRODUCTION

Research has consistently shown that urban noise affects the quality oflife and activities of people, adults and children, even though aspassive observers.

With regard to children, a number of studies suggest that noise,both in the home environment and at school, may have an effect onsome of the academic skills they are expected to acquire [1].

The Acoustical and Luminotechnical Research Center of theNational University of Cordoba, Argentina, has carried out severalstudies in relation to the effects of urban noise on the inhabitants of

*Corresponding author.

41

42 M. R. SERRA AND E. C. BIASSONI

Cordoba city [2 - 4] and on the teaching-learning process of childrenand adolescents [5-10].

As it is known, the main source of urban noise is traffic noise, whichmasks speech due to the components of the frequencies involved [2, 3].In Cordoba city, many school buildings are located close to heavy andnoisy traffic streets; this constitutes an important component ofenvironmental noise in classrooms.

Schools are established to promote learning, which is principallyacquired by human voice utterance and listening skills. Acoustics isone of the most important physical properties that determine how wellthe school buildings can serve their primary function [11]. Inappropri-ate noise levels in school environments can be the reason of difficultiesin the normal development of the teaching-learning process [12] andone of the most damaged aspects is verbal communication [12-17].

When speech intelligibility i.e. the percentage of a verbal messageunderstood by the listener, is near perfect, it is very unlikely thatacoustical conditions would be detrimental to academic achievement[18].

The main parameters for determining general acoustical conditionsof an enclosure for locution are sound level of background noise andreverberation time.

The effects of background noise per se on speech intelligibility arewell recognised, [5, 8, 9, 19, 20] when noise and reverberation interactwithin educational environments they impair communicative efficiency[21, 22].

In educational environments, the sound level of backgroud noiseshould be under 50 dBA to allow for normal speech communication,and the intelligibility percentage should not be lower than 95% [23].Reverberation time for theoretical classes and normal listening pupilsshould be between 0.8 and 1.0 second [24].

Children and older adults require enhanced acoustical signals tounderstand speech as compared with youngsters. Normal-hearingchildren and children with a variety of disabilities who are presumed tohave normal hearing, require enhanced acoustical signals in order tounderstand, not just to hear, speech [25]. Hence they are also moreadversely affected by high environmental noise and reverberantconditions [26]. Lower reverberation time allow for higher backgroundnoise levels without impairing intelligibility [18].

URBAN NOISE 43

The Acoustical Society of America (ASA) has received muchinformation regarding children's ability to perceive and understandspeech in a classroom environment. This information has beenvigorously investigated by the audiology profession. The ASA, inresponse to this updated information, has established a task force todefine new acoustical standards for classrooms [25].

Our study consists of both acoustical measurements, noise levelsand reverberation time in classrooms affected and not affected byurban noise, of two leading schools of Cordoba city, Argentina, andspeech intelligibility tests performed by groups of pupils of suchschools. Comparisons among the main acoustical parameters mea-sured and speech intelligibility scores performed, taking into accountthe age of the subjects, were the purpose of the study.

METHOD

1. Working Places

Two schools (School No. 1 and School No. 2) located close to heavyand noisy traffic streets, were chosen for the present study.

Previously to the experiences with subjects, a series of statisticalnoise levels measurements inside each school were carried out. As aresult, the two noisiest classrooms, affected by urban noise, and thequietest one, located in the interior of the building and not affected bysuch noise, were selected as study places for experimental and controlsituations respectively.

2. Subjects

The subjects of study were the pupils attending classes in the selectednoisiest classrooms daily, in both schools.

In School No. 1, with two scholastic levels, the noisiest classroomswere: one section of high school level, a freshman year with 30 pupils,and the other, one section of elementary level, 4th grade, with 44pupils. The age of the students ranged between 13-14 years for thehigh school and 9-10 years for elementary level.

In School No. 2, with only elementary schooling, the noisiestclassrooms were two sections of 4th grade A and B with 31 and 30pupils, respectively, between 9 and 10 years old.


3. Acoustical Measurements

Noise Levels

According to the source, sound stimuli inside the noisy studiedclassrooms can be classified as follows:

a. Natural classroom noise.b. Noise coming from the rest of the school.c. Noise coming from outside the school, namely "urban noise".

In the present study, in the experimental situation, the sound stimulifrom "a" were strictly controlled and from "b", in general, weremasked for "c". Hence the third type of sound source was principallyheard inside the classrooms during the trial, coming through thewindows, some them left open as usual during springtime.

In the control situation, there was no urban noise and the soundstimuli from "a" were also strictly controlled. Hence only theuncontrollable noise coming from the rest of the school was heardduring the trial.

Statistical measurements of noise levels were carried out in eachclassroom, while the pupils performed an intelligibility test, using amodular precision sound level meter 2331 type from Briiel & Kjaer,with BZ 7101 type module.

Environmental noise was measured during the pauses of verbalstimuli presentation, in order to avoid sound overlapping.

Reverberation Time

Reverberation time was measured in each selected classroom withoutpupils present using an automatic measurements system form Bruel &Kjaer (2231 + BZ 7108 + 4224 + 2318).

4. Material

An intelligibility test was applied with two parallel forms A and B forexperimental and control situations, respectively. It involved lists ofmeaningless monosyllabics and disyllabics, monosyllabic and bisylla-bic words and sentences and considered each group as a subtest, inorder to find out the effects of classroom acoustical conditions on eachof them.

URBAN NOISE 45

To avoid experimental variations during the reading of the verbalitems, they were previously recorded on magnetic tapes, performed inan Anechoic Chamber, in order to obtain a "neutral" record. So, whenthey were played back during the experimental and control situations,each classroom imposed its own acoustical patterns on the verbalstimulus.

Items were recorded with a pause between each statement to givesubjects enough time for writing them down on a special answer sheet.During pauses, the classroom environmental noise was measured.

For reproducing the verbal stimulus in each classroom, its soundlevel was adjusted to the teacher's normal voice level. In the case of thefreshman group of a high scholastic level, an average was thatproduced by several teacher's voices. A high quality electroacousticchain system for reproducing the test material was used.

5. Experimental Procedure

Both groups of pupils of each school worked in two differentsituations:

a. Experimental: Each group performed the intelligibility test, FormA, in its own noisy classroom.

b. Control: Each group performed the intelligibility test, Form B, inthe classroom not affected by urban noise of its own school.

By this way, it was possible to compare the intelligibility testperformance among the three sections of elementary 4th grades,working under different acoustical environments, and one section ofthe high school level freshman group.

All measurements and experiments were carried out in the springcharacterised by warm weather in our latitude.

DATA ANALYSIS AND RESULTS

1. Noise Levels

For the statistical distribution analysis of the sound levels measuredduring the pauses of verbal stimuli the percentile L50 was used whichrepresents the exceeded level during 50% of the observation period, so


as to describe the average noise level for each subtest. Values areshown in Table I.

2. Reverberation Time

The reverberation times measured in each selected classroom areshown in Figure 1.

3. Intelligibility Test

The percentage of correct answers for every subtest from each groupof pupils was considered, taking into account the noise-signalrelationship according to the place of each child with regard to thesignal emission and urban noise inmission.

After a data descriptive study, ANOVA for repeated measurementswas applied in order to find the differences between the groups ofpupils, comparing both experimental and control situations in eachsubtest. The results obtained are shown in Tables II and III.

Figures 2, 3, 4, 5 and 6 represent the mean value plus and minus twostandard errors for each subtest by comparing experimental andcontrol situation, for showing scores deviations of the four groups ofpupils: Freshman Year, experimental situation (F.Y.- Exp. Sit.);Freshman Year, control situation (F.Y.- Cont. Sit.); 4th Grade,experimental situation (4th G.-Exp. Sit.); 4th Grade, control situation(4th G.-Cont. Sit.); 4th Grade A, experimental situation (4th G.A-Exp.Sit.); 4th Grade A, control situation (4th G.A-Cont. Sit.); 4th Grade B,experimental situation (4th G.B- Exp. Sit.); 4th Grade B, controlsituation (4th G.B- Cont. Sit.).

The results of this study showed that:

a. The general acoustical conditions of the surveyed classrooms arenot suitable for academic purposes, specially the noisy classrooms,according to the suggested requirements for that kind of activity.

b. Such acoustical conditions in classrooms can dramatically affectthe speech intelligibility.

c. The youngest groups exhibited lower performances than the olderone, according to their classrooms acoustical characteristics.

Schools

Classrooms

~~"~\^^ Noise

Stimuli ^~~- - -^^

TABLE I L50 values measured

School No. 1

Freshman Year 4th

in each studied

Grade

With Without With WithoutUrban Noise Urban Noise Urban Noise Urban Noise

classroom of both schools

School No.

4th Grade A

2

4th Grade B

With Without With WithoutUrban Noise Urban Noise** Urban Noise UrbanNoise**

MonosyllablesDisyllabicsMonosyllabic WordsBisyllabic WordsSentences *

68 dBA69 dBA68 dBA70 dBA74 dBA








* The intelligibility test was performed by the different groups of pupils always at the same time. Due to the extent of the test, the last subtest with sentences wasperformed at midday when the traffic density increased and so did sound levels inside the classrooms.** The classroom used for control situation was the quiest of the School No. 2.

3.5

2.5 T-

1.5

0.5

• —

- • • '

SCHOOL No 2- 4th Grade A

SCHOOL No 2- 4th Grade B- Control Classroom

SCHOOL No 1- Freshman Year- 4th Grade- Control Classroom

125 250 500 1000

FREQUENCY (Hz)

2000 4000

FIGURE 1 Graphical comparison of the reverberation times in each studied classroom.

TABLE IIsituations

School No. 1: Intelligibility percentage mean of the two groups of pupils in the five subtests, comparing experimental and control

Pupil Groups

Intelligibiiity~~Test

Test Situation ExperimentalSituation

Freshman Year

ControlSituation

F ExperimentalSituation

4th Grade

ControlSituation

F

MonosyllabicsDisyllabicsMonosyllabic WordsBisyllabic WordsSentences

88.4080.3380.8389.6385.37

93.1791.3094.0396.5797.70

4.77"10.97"13.20"6.93**12.33"

p< 0.0001p< 0.0001p< 0.0001p< 0.0001p< 0.0001

86.8675.2373.8686.2980.73

91.4889.2391.1194.5796.14

4.61"14.00*17.25*8.27"15.41*

j?<0.0001*p< 0.0001*p < 0.0001p< 0.0001* D < 0.0001

TABLE IIIsituations

School No. 2: Intelligibility percentage mean of the two groups of pupils in the five subtests, comparing experimental and control

Pupil Groups

~~~~~~-~^^_JTest SituationIntelligibiliiy~~~~-~~-^^^Test - ^ ^

MonosyllabicsDisyllabicsMonosyllabic WordsBisyllabic WordsSentences

ExperimentalSituation

(%)

79.7466.9070.4577.7469.39

4th Grade

ControlSituation

(%)

89.8189.9089.0691.2692.55

A

10.06"23.00"18.61"13.52"23.16"

F

p< 0.0001p < 0.0001p< 0.0001p< 0.0001p <0.0001

ExperimentalSituation

(%)80.6072.2373.0780.7777.57

4th Grade B

ControlSituation

(%)89.4086.9387.7391.6391.83

F

8.80" p< 0.000114.70"/> < 0.000114.67"/) < 0.000110.90"p< 0.000114.27" p< 0.0001

95

90

85

75

70

65

60

1I

5

2

TI

II

F.Y.Exp.Sit.

F.Y.Cont.Sit.

4th G.Exp.Sit.

4th G. 4th G.ACont.Sit. Exp.Sit.

GROUPS

4th G.ACont.Sit.

4th G.BExp.Sit.

4th G.BCont.Sit.

FIGURE 2 Mean value plus and minus two standard errors, comparing experimental and control situations of the four groups of pupils forMonosyllables subtest.

100 T -

90

85

80

75

70

65

60F.Y. F.Y. 4th G. 4th G. 4th G.A 4th G.A 4th G.B 4th G.B

Exp.Sit. Cont.Sit. Exp.Sit. Cont.Sit. Exp.Sit. Cont.Sit. Exp.Sit. Cont.Sit.

GROUPS

FIGURE 3 Mean value plus and minus two standard errors, comparing experimental and control situations of the four groups of pupils forDisyllabics subtest.

II I

1

T1

1

1

T

i

100

95

90

85

80

75

70

65

60

T

I

{

I

7

I

F.Y.Exp.Sit.

F.Y.Cont.Sit.

4th G.Exp.Sit.


GROUPS

4th G.ACont.Sit.

4th G.BExp.Sit.

4th G.BCont.Sit

FIGURE 4 Mean value plus and minus two standard errors, comparing experimental and control situations of the four groups of pupils forMonosyllabic Words subtest.

100

95

85

80

75

70

65

60

Ii

i5

Ii

0

F.Y.Exp.Sit.

F.Y.Cont.Sit.

4th G.Exp.Sit.


GROUPS

4th G.ACont.Sit.

4th G.BExp.Sit.

4th G.BCont.Sit

FIGURE 5 Mean value plus and minus two standard errors, comparing experimental and control situations of the four groups of pupils forBisyllabic Words subtest.

100

95

90

85

3O 8 0

u

70

65

60

ri

T

<>

T<>

F.Y.Exp.Sit.

F.Y.Cont.Sit.

4th G.Exp.Sit.


GROUPS

4th G.ACont.Sit.

4th G.BExp.Sit.

4th G.BCont.Sit

FIGURE 6 Mean value plus and minus two standard errors, comparing experimental and control situations, of the four groups of pupils forSentences subtest.


CONCLUSIONS AND DISCUSSION

The physical measurements results of noise levels and reverberationtimes revealed that the general acoustical conditions of the foursurveyed noisy classrooms were not suitable for academic purposes.Because of the intelligibility test results, there were reasons to believethat such acoustical conditions were serious drawbacks for speechcomprehension, specially among the younger pupils.

In all the cases, in experimental situations with the worst acousticalconditions, the intelligibility percentage reached was significantly lower(p < 0,0001) than in control situation with best acoustical conditions,although not always perfect. On the other hand, the performancevariability was higher in experimental than in control situation.

In any case, the intelligibility mean percentage reached 95%, as ISOStandard suggests for educational environments, was too low in somecases. In control situations, the intelligibility mean percentage reached95%, or was near to that value only in a few cases, according to thecharacteristics of the classrooms.

Comparing the four groups studied, in experimental situations, theoldest one (freshman - high school level - School No. 1) exhibitedthe best performance in the intelligibility test in the noisiest classroom,but with reverberation times lower than those of School No. 2.

The younger group of the same school (4th grade - elementarylevel), had a lower performance than the former group in a classroomwith the same reverberation time, but less noisy.

The two groups from School No. 2 (4th grader - sections A and B -elementary level) had lower performances than their peers of SchoolNo. 1, working in apparently noisy classrooms, but with higherreverberation times. From these two groups, section A had the lowerperformance, and the highest noise levels and reverberation times.

In general, the youngest groups exhibited lower performances thanthe older one, according to their classrooms acoustical characteristics.

The low performance of the four groups in sentences, even thoughthis kind of verbal stimulus are the easiest ones to understand, mightaccount for the significant increase in the background noise levelsduring this subtest (see Tab. I).

URBAN NOISE 57

With regard to the quiet classrooms, they exhibited better acousticalconditions, although that from School No. 2 was no so suitable asdesired.

Reverberation and environmental noise in a classroom may notentirely impair understanding, but the results of this study stronglysuggest that room acoustical conditions cannot remain as an ignoredvariable in the educational field.

This research under representative daily listening conditions showedthat the acoustical environment in classrooms can affect theintelligibility of speech. As new concepts and new vocabularies areintroduced continually in educational settings, the distortion in a noisyand highly reverberant environment may hinder the mastery of theseconcepts. Extraneous noise in classroom plus inappropriate reverbera-tion times influence the youngsters ability to cope with newinformation. The effect of a given intruder noise level becomes moredisruptive to speech as reverberation time is prolonged.

Noise and reverberation, like signals competition, do affect anddegrade the speech intelligibility of groups of listeners to a differentextent. Speech intelligibility decreases with either increasing noise orreverberation, and the adverse influence of each one of the variablesisolated is further increased by the introduction of the other factor.

The degradation of a classroom acoustical environment may turnunderstanding speech more difficult for younger children than forteenagers and adults. There are studies suggesting that the perfor-mance and speech discrimination of school-age children under suchconditions are reduced when compared to those of young people oradults [5, 18, 27], as in the present study.

Consequently, both variables need to be controlled if optimalcommunication and comprehension are to be achieved in educationalareas.

Ackno wledgements

The authors would like to thank leading staff of the two schools, wherethe study was carried out, for letting us work there, and to teachersand pupils who participated in this study, for their important help.


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URBAN NOISE 59

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Urban noise and classroom acoustical conditions in the teaching‐learning process