Survey on sound environment in classrooms during school hours for hearing impaired students

Transcription

1 Survey on sound environment in classrooms during school hours for hearing impaired students Keiko Nishizawa a, Tetsuya Sakuma b a,b Institute of Environmental Studies, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo , Japan a nishizawa@env.arch.t.u-tokyo.ac.jp; b sakuma@k.u-tokyo.ac.jp Abstract In order to investigate the relationship between the actual situations of sound environment and the hearing impaired students' impressions in classrooms, we performed a survey during school hours by measurements of sound levels and by questionnaires to the students. In the survey, we selected instruction rooms for hearing impaired students and normal classrooms for 3 different grades, and the measurements are done in the classrooms, their adjacent rooms and corridors. The questionnaires were distributed to not only the hearing impaired but also normal students just after classes, asking about the following impressions: intelligibility of hearing voices, distraction with noises generated by furniture dragging, air conditioning and transmitted from adjacent spaces, and requirement for silence in the classroom. The measured result showed that L Aeq ranged from 60 to 65 dba in the instruction rooms, and those in the normal classrooms for the 3rd and 9th grades were about 80 and 70 dba, respectively. The hearing impaired students pointed out distraction with all kinds of noises in the instruction rooms, while not only they but also the normal students evaluated the dragging noise to be most distracted in the normal classrooms. In this survey, the hearing impaired in the elementary school required more silent classrooms, and this requirement was also pointed out by the normal students in the elementary school more keenly than the junior high school. 1. INTRODUCTION In Japan s educational system, in many cases hearing impaired students attend normal classes with occasional special teaching in hearing impaired classrooms, which are provided at more than 700 schools in Japan. However, we do not have concrete design guidelines for the instruction rooms for hearing impaired classes. Some acoustic measures should be taken in these instruction rooms, but the actual situation is unclear because they are rare cases in classrooms. In a previous report [1], we indicated the differences in acoustic performance between various instruction rooms, and teachers pointed out acoustic issues for students hearing in instruction rooms that do not conform to the recommended values in the acoustic guidelines [2,3]. The current survey emphasizes students attitudes; in order to understand the actual acoustic situations for the hearing impaired during school hours, we measured sound levels in the rooms used by hearing impaired students, the adjacent rooms and corridors, and

2 executed questionnaires asking about the intelligibility of voices, distractions from furniture dragging and air-conditioning noises, noises transmitted from adjacent spaces, and the requirement for silence in the classroom. 2. OUTLINE OF THE SURVEY 2.1 Features of rooms Tables 1 and 2 show the features of the rooms under investigation. We selected two instruction rooms on account of acoustic performance, normal classrooms where the hearing impaired students attend classes in three different grades. Figure 1 shows the plans of the instruction rooms and the normal classroom. 2.2 Method of the survey Measurement of sound levels Sound level meters were set up one meter from the corner in the rooms, and at the halfway points in the corridors between the rooms. We measured noise levels during one school hour, repeated two or three times in the instruction rooms and the normal classrooms. Moreover, we measured air-conditioning noise levels in unoccupied rooms. Questionnaires for students Questionnaires asking about the impressions of generated noises were distributed after one school hour to students and teachers. Table 3 shows the contents of the questionnaire. Normal students in the normal classrooms also completed the questionnaire, while, in the instruction rooms, only one hearing impaired student answered for the individual teaching style. Entrance Waiting room Corridor Corridor Corridor Steel partition Room a Test room Room b2 Room b1 Room c, d, e Room A Room C, D, E Figure 1:Plan of rooms Table 1:Features of instruction rooms Room Number Grade Floor Wall Ceiling Area Height RT *1 Adjacent corridor of students of students rooms A 1 3rd Plastic tile Paint Plaster board 25m 2 3.0m 0.4s B 1 6th Carpet Cloth Perforated 27m 2 2.5m 0.6s 30(b1) 35 50(b2) *1: Arithmetic average in 500-2kHz D r

3 Table 2:Features of normal classrooms Room Number Grade Floor Wall Ceiling Area Height RT *1 Adjacent corridor of students of students rooms C 31 3rd Plastic tile Paint Plaster board 61m 2 3.0m 0.8s D 22 6th Plastic tile Paint Plaster board 63m 2 3.0m 0.9s E 28 9th Flooring Paint Plaster board 58m 2 3.0m 1.0s *1: Arithmetic average in 500-2kHz Contents Intelligibility of hearing voices Furniture dragging noise Air conditioning noise Noise from adjacent room Noise from corridor Requirement for silence Table 3:Contents of the questionnaires Choices 1:Intelligible 2:Somewhat unintelligible 3:Unintelligible 2:Somewhat distracted 3:Very distracted 2:Somewhat distracted 3:Very distracted 2:Somewhat distracted 3:Very distracted 2:Somewhat distracted 3:Very distracted 1:Require more silence 2:Not require more silence D r 3. RESULTS AND DISCUSSIONS 3.1 Intelligibility of voices Figure 2 shows equivalent continuous and percentile noise levels during each school hour, and Figure 3 shows the reverberation time. Table 4 shows the impressions in the instruction rooms, Figure 4 shows the results in the normal classrooms. A black triangle denotes a teacher s impression and a square is a hearing impaired student s impression. The RT in Room A is beyond 0.4s (The mean value in 500 and 1kHz) recommended by Architectural Institute of Japan (AIJ) [2] and in the normal classrooms the values are beyond 0.6s. L Aeq ranged from 60 to 65 dba in the instruction rooms, and unintelligibility was not noted frequently. On the other hand, L Aeq ranged from 74 to 84 dba in Room C (group work style) and ranged from 67 to 72 dba in Rooms D and E (lecture style). From 20% to 40 % of the students noted unintelligibility in Room C, while only 10% did so in Rooms D and E. This result suggests a relationship between intelligibility and teaching style or students grades. A-weigted SPL (dba) Room A Room C Room D Room E 1st 2nd 3rd 1st 2nd 3rd 1.2 4th 5th 6th 1st 2nd 3rd 4th Figure 2: Noise levels during school hours 1st 2nd 3rd L 5 L eq L 50 L 95 Reverberation time (s) Octav e band center f requency (Hz) Figure 3:Reverberation time AIJ recommendation for normal classroom AIJ recommendation for instruction room A B C D E

4 Table 4:Evaluation of intelligibility in instruction room Room A 1:Intelligible 1:Intelligible 2nd / Arithmetic 1:Intelligible 1:Intelligible 1:Intelligible 2:Somewhat unintelligible 1st / Free talk 1:Intelligible 1:Intelligible 2nd / Free talk 2:Somewhat unintelligible 1:Intelligible 3rd / Free talk 1:Intelligible 1:Intelligible Room C Room D Room E 1:Intelligible 2:Somewhat unintelligible 3:Unintelligible Figure 4:Evaluation of intelligibility in normal classroom 3.2 Furniture dragging noise Table 5 shows students impressions in the instruction rooms, and Figure 5 shows the results in the normal classrooms. student noted distractions in, which is carpeted. In Japan, used tennis balls are often used as measures to prevent dragging noise. This can be effective, particularly in a normal classroom with plastic tiles or flooring, Figure 6 shows an example. In Rooms C and E, which have not adopted any measures against furniture dragging noise, from 20% to 40% of the students noted a distraction. On the contrary, in Room D, which used tennis balls, under 20% noted. However, in the 4th school hour, when the tennis balls were tentatively removed, 50% of students noted a distraction. Table 5:Evaluation of dragging noise in instruction room Room A 2nd / Arithmetic 2:Somewhat disracted 2:Somewhat disracted Room C -No measures 1st / Free talk 2:Somewhat disracted 2nd / Free talk 2:Somewhat disracted 3rd / Free talk 2:Somewhat disracted Room D -Use of tennis balls (* removed tentatively) Room E -No Measures 2:Somewhat distracted 3:Very distracted Figure 6:Tennis balls used to prevent dragging noise Figure 5:Evaluation of dragging noise in normal classroom

5 3.3 Air-conditioning noise Table 6 shows heating system and air-conditioning noise level. Table 7 shows the impressions in the instruction rooms, and Figure 7 shows the results in the normal classrooms. Noise level in is close to 35 dba, which is the maximum level recommended by AIJ [2], and hearing impaired student still noted a distraction. In the normal classrooms, all noise levels are beyond 40 dba. From 20% to 40% of the students noticed the noise in Room E, while, in Room D, about 10% out of them did. L Aeq during school hours in each room was about 67 dba (Figure 2), so it suggests a relationship between a distraction and the heating system or placement of equipment. Table 6:Heating system and air-conditioning level Class Normal Room A B C D E Heating system Fan heater Air conditioner Fan heater Fan heater Air conditioner Place for equipment Floor Ceiling Floor Floor Ceiling Noise level (dba) Recommended level(dba)[2] Table 7:Evaluation of air-conditioning noise in instruction room Room A 3:Very distracted 2nd / Arithmetic 3:Very distracted 1st / Free talk 2:Somewhat distracted 2nd / Free talk 2:Somewhat distracted 3rd / Free talk Room C Room D Room E 2:Somewhat distracted 3:Very distracted Figure 7:Evaluation of air-conditioning noise in normal classroom 3.4 Noise from adjacent rooms Figures 8 and 9 show L Aeq in the rooms hearing impaired students use and their adjacent rooms. Table 8 shows the impressions in the instruction rooms, and Figure 10 shows the results in the normal classrooms. Figure 11 shows the air-borne sound insulation performance. Compared with AIJ recommendation [2], the sound insulation performance in Room A is very low, and both teacher and hearing impaired student noted a distraction every school hour. In, the performance between B and b2 is beyond D-45, but hearing impaired student still noted a distraction. In the normal classrooms, the sound insulations performances are under D-40. In Room C (group work style), L Aeq rose to 84 dba and 40% of the students noted a distraction. On the contrary, in Room D (lecture style), L Aeq ranged from 65 to 72

6 dba and just 10% of students noted a distraction. This result also suggests a relationship between a distraction and teaching style or students grades. A vs. a B vs. b1 B vs. b2 C vs. c D vs. d L Aeq in adjacent room (dba) L Aeq in adjacent room (dba) L Aeq in instruction room (dba) Figure 8:L Aeq in instruction rooms and their adjacent rooms Figure 9:L Aeq in normal classrooms and their adjacent rooms L Aeq in normal classroom (dba) Table 8:Evaluation of noise from adjacent room in instruction room Instruction room Adjacent room Room A Room a *1 1st Arithmetic Play 2:Somewhat distracted 2:Somewhat distracted 2nd Arithmetic Play 2:Somewhat distracted 3:Very distracted 3rd Japanese language Play 3:Very distracted 3:Very distracted Instruction room Adjacent room Room b1 *2 or b2 *3 2nd Free talk b1:utterance on reading 1:Not disracted 3:Very distracted Free talk b2:free talk 1:Not disracted 2:Somewhat distracted 3rd Free talk b1:utterance on reading 1:Not disracted 3:Very distracted *1:Emotional disturbance class(6th) *2:Speech impaired class(3th) *3:Speech impaired class(6th) Room C Adjacent room: Room c (Normal/3rd) Room D Adjacent room: Room d (Normal/6th) A-a B-b1 B-b2 C-c D-d 2:Somewhat distracted 3:Very distracted Figure 10:Evaluation of noise from adjacent room in normal classroom Figure 11: Air-borne sound insulation performance between rooms AIJ recommendation for instruction room AIJ recommendation for normal classroom

7 3.5 Noise from corridors Figures 12 and 13 show L Aeq in a chosen room and the corridor. Table 9 shows the impressions in the instruction rooms, and Figure 14 shows the results in the normal classrooms. Figure 15 shows the air-borne sound insulation performance. Room A is located in front of the entrance (Figure 1) and L Aeq in the corridor rose to 75 dba, with both teacher and hearing impaired student noted a distraction. In, the performance is almost over D-35, nevertheless hearing impaired student noted a distraction. In the normal classrooms, the performance of Room C is over D-20, AIJ recommendation [3], but 40% of the students noted a distraction when L Aeq rose to 68 dba in the corridor. Room A Room C Room D Room E L in corridor (dba) Aeq L Aeq in corridor (dba) L Aeq in instruction room (dba) Figure 12:L Aeq in instruction room and the corridor L Aeq in normal classroom (dba) Figure 13:L Aeq in normal classroom and the corridor Table 9:Evaluation of noise from the corridor in instruction room Room A 3:Very distracted 2nd / Arithmetic 2:Somewhat distracted 1: Not distracted 2:Somewhat distracted 1st / Free talk 2:Somewhat distracted 2nd / Free talk 3:Very distracted 3rd / Free talk 3:Very distracted Figure 15:Air- borne sound insulation performance between room and corridor A B C D E AIJ recommendation for normal classroom Room C Room D Room E 2:Somewhat distracted 3:Very distracted Figure 14:Evaluation of noise from the corridor in normal classroom

8 3.6 Requirement for silence Table 10 shows students impressions in the instruction rooms, and Figure 16 shows the results in the normal classrooms. student required more silence in providing architectural specification considered on acoustics (Table 1). In the normal classrooms, 50% of students in 3rd and 6th grades required more silence. On the other hand, 30% at 9th grade required silence. One of the reason is supposed to the difference in L Aeq (Figure 2). Although L Aeq in Rooms D and E are almost the same, the requirement for silence was pointed out more keenly in Room D. In Room E the teacher was practically the only person who talked during school hours, while, in Room D the students communicated actively with the teacher. This result suggests a relationship between teaching style or students grades and requirement for silence. Table 10:Requirement for silence in instruction room Room A 2:Not require more silence 1:Require more silence 2nd / Arithmetic 1:Require more silence 2:Not require more silence 1:Require more silence 2:Not require more silence 1st / Free talk 1:Require more silence 1:Require more silence 2nd / Free talk 2:Not require more silence 1:Require more silence 3rd / Free talk 2:Not require more silence 2:Not require more silence Room C Room D Room E 1:Require more silence 2:Not require more silence Figure 16:Requirement for silence in normal classroom 4. CONCLUSION In this survey in order to understand actual acoustic situation for hearing impaired students, we measured sound levels and executed questionnaires asking about the impressions of generated noises during school hours. As the results, following matters were clarified. In the instruction room without consideration on acoustics, a distraction was pointed by the hearing impaired student at all items. Especially, noise from adjacent room frequently distracted both the student and the teacher. In Japan, it is an usual case to use a normal classroom without acoustic consideration as a instruction room, but it can cause hearing impaired interference with hearing. On the other hand, in the instruction room considered on acoustics, hearing impaired still pointed a distraction except intelligibility although the performance meets AIJ recommendation as an instruction room. That is the important matter to think over at design of instruction room. Regarding to the normal classrooms, acoustic qualities are under AIJ recommendations except air-borne sound insulation between room and corridor. Not only hearing impaired students but also normal students indicated distractions. Dragging noise is pointed out most frequently as a distraction in rooms without measures. At the present tennis

9 balls are adopted as an effective measure, however, consideration for dragging noise should be taken at furniture design. Regarding intelligibility, noise from adjacent rooms, and requirement for silence, at 3rd grade (group work style) distractions were pointed most frequently. This suggests relationships between distractions and teaching style or students grades. Air conditioning noise was indicated as a distraction frequently in case of 50dBA. However, relationship to heating system or placement of equipment is suggested, so further investigation should be conducted on relations between noise level and distraction. AKNOWLEGEMENTS We would like to thank the stuff of the elementary and junior high schools for the efforts on this survey. REFERENCE [1] K. Nishizawa, J. Munakata and T. Sakuma: Survey on acoustic environments for hearing impaired students at schools in Japan, Proc. 18th Int'l Cong. Acoust. (Kyoto), Vol.2, pp , [2] T.Fukuchi, K.Ueno: Guidelines on acoustic treatments for school buildings proposed by the Architectural Institute of Japan, Proc. 18th Int'l Cong. Acoust. (Kyoto), Vol.2, pp , [3] Edited by Architectural Institute of Japan, Standard of sound insulation performance and planning guide for architecture (second edition), 1997.