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

Room acoustic conditions of schools, a church, and a residential
premise for hearing impaired people
Cheol-Ho JEONG,1 Wan-Ho CHO,2 Ji-Ho CHANG,2 Sung-Hyun LEE,3Chang-Wook KANG,4 Jin-Gyun PARK5
1Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark, Denmark.
2Division of Physical Metrology, Korea Research Institute of Standards and Science, Daejeon, Korea
3Department of System Dynamics, Korea Institute of Machinery & Materials, Daejeon, Korea
4Department of Special Education, Kangnam University, Korea
5Oticon Korea, Seoul, Korea

ABSTRACT
It has been known that hearing impaired people need more strict room acoustic requirements than normal
hearing people for verbal communications. Therefore, several design guidelines exist, such as a maximum
reverberation time of 0.4 s in classrooms, signal to noise ratios (SNR) higher than 15 dB, and ambient noiselevels lower than 35 dBA. We measured noise levels and room impulse responses of 12 rooms in two schools
for hearing impaired children, a dormitory apartment with 3 rooms, and a church mainly for the hearing
impaired in the Republic of Korea and extracted room acoustic parameters. Subjective reverberance andquality of verbal communication and well-being are obtained through questionnaires and interviews withhearing impaired students.
Keywords: Classrooms, church, dormitory, hearing impaired people, reverberation time, speech clarity, noise

1. INTRODUCTION
Hearing impaired people have more challenges in verbal communication under noisy and bad
acoustic conditions. Effects of reverberation and noise on the intelligibility of sentences have beeninvestigated, e.g., see Ref. (1). In room acoustics, speech transmission index (STI) derived from themodulation transfer function is normally used to describe the combined effect of noise andreverberation on speech intelligibility. Using STI, it was found that for hearing-impaired subjects
every 3-dB hearing loss for speech in noise (elevation of the speech-reception threshold in terms ofS/N ratio relative to the speech-reception threshold for normal-hearing subjects) can be compensatedfor by an increase of 0.1 in STI. For classrooms, this increase can be obtained by reducing thereverberation time significantly (2). Since many hearing-impaired subjects have hearing losses forspeech in noise larger than 3 dB, Plomp and Duquesnoy concluded that the hearing impaired needmuch lower reverberation times and lower background noise level than the normal hearing (2).
The American Speech-Language Hearing Association (ASHA) published “Guidelines foraddressing acoustics in educational settings,” that called for background noise levels not to exceed 30
dBA, reverberation times not to exceed 0.4 seconds, and an overall teacher signal-to-noise ratio (SNR)of larger than 15 dB (3). Generally, these specifications were confirmed by the American National
Standards Institute (ANSI) by publishing “ANSI S12.60-2010 Acoustical Performance Criteria,
Design Requirements and Guidelines for Schools/Part 1: Permanent Schools” that, based on the roomsize, recommends that background noise level not to exceed 35 dBA, reverberation time (RT) not toexceed 0.6-0.7 seconds, and a SNR of +15 dB (4). The latest Danish Building Regulations publishedin 2018 (BR18) also set out a similar reverberation time limit of 0.6 s for classrooms and learning
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rooms (5). The only exceptions are rooms for singing and music, smaller than 250 m3 , for choral andacoustic music, which can have reverberation times up to 1.1 s. Several room acoustic studies also
concur with the building recommendations. Bradley concluded that optimum reverberation times of
0.4 s to 0.5 s for classrooms with a uniform background noise level of 30 dBA using subjective test
and theoretical prediction of U50 (6). Yang and Hodgson also found some useful speech intelligibility
scores for normal hearing and hearing impaired people, in two different signal to noise (SNR)
conditions, 0 and 5 dB (7).
Many studies have reported that these acoustic requirements are rarely fulfilled in reality. For
example, McCroskey and Devens found that the recommended acoustical conditions had beenachieved in only one classroom out of nine investigated (8), and Crandell and Smaldino reported thatnone of the 32 classrooms they studied met recommended criteria for noise le vels (9). Only 9 rooms
out of 32 satisfied for reverberation in another study (10).
We have investigated two schools, one church and one dormitory for hearing impaired people in
the Republic of Korea and compared to the previously recommended acoustic conditions. We haveconducted ISO 3382 measurements for objective quantification of room acoustic conditions (11). A
questionnaire and individual/group interviews were supplemented to strive to search for a meaning
correlation between the objective parameters and subjective responses.

2. Rooms
2.1 Two schools
Seoul National School for the Deaf (SNSD) was founded in 1913, having 95 students enrolled
covering kindergarten to high school classes. Another school for hearing impaired children in Seoul,Seoul Samsung School (SS), was founded in 1957, with 109 students enrolled, covering from akindergarten to high school. These are two large schools for hearing impaired children in Seoul, Korea.
Five classrooms in SNSFD and seven classrooms in SS were measured.
2.2 Church
Youngnak chuch of the deaf is a relatively big church mainly for hearing impaired people, foundedin 1946. Its dimensions are approximately 23 m, 17 m, and 4 m, ending up with a volume of 1564 m 3.
2.3 Dormitory
Nongawon dormitory (founded in 1957) is a residential facility, where 34 hearing impaired people
live. Three people share an apartment, which has a living room, bathroom, kitchen, and threebedrooms. One apartment was measured.

(a)
(b)
(c)
Figure. 1. Photos of the measured rooms (a) SNSD, (b) Youngnak church, (c) Nongawon dormitory.

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3. Methods
3.1 ISO 3382 measurements
Room acoustic conditions were measured according to ISO 3382 (11). Due to small volumes of themeasured rooms and limited time, it was not always possible to make 12 source-receiver combinations
as suggested in ISO 3382. For Youngnak church, reverberation time T 20 and STI are of main concern.
For the dormitory and classrooms, only T20 is presented.
3.2 Questionnaire
A questionnaire was distributed to collect the users’ acoustic satisfaction regarding reverberation,
speech clarity, and external/internal noise. All the questions were rated on a 5 -point scale andanswered in December 2018.
3.3 Interviews
Hearing impaired people usually receive a lot of questionnaires and tend not to take them very
seriously. As the two schools cover a broad age range from kindergarten to high school, it was decided
to interview with the pupils who use the measured classrooms as of May 2019, assuming that theresults of which would make a better correlation to the objective measurement than the questionnaireresults. Individual interviews are known to more precise so we tried to avoid group interviews for tworeasons. First, the interview results could possibly be biased by certain strong opinions in a groupinterview. Second, the interviewee are hearing impaired children, who might face even bigger
challenges in group conversations, e.g., lack of concentration and difficulties in conversing in a biggroup. However, we ended up with a group interview in one classroom (High school 3-2) at SS due
to limited time allowed. The interviews were conducted only in SS in May 2019.

4. Results
4.1Classrooms

4.1.1 Objective measures, T20 CPFPQKUGNGXGNU
All the classrooms measured turn out not to comply with the ASHA limit of 0.4 s as shown in Fig.
2. In general, SNSD has longer reverberation times than SS. In SS, the reverberation time graduallychanges from 0.45 s to 0.61 s as shown in Fig. 2 (bottom). The noise levels in occupied conditions
vary from 31 dBA to 42 dBA.
4.1.2 Questionnaire and interview results
No good correlation is found between T 20 and subjective speech clarity in Table 1 conducted in SS.
Here the subjective speech clarity ratings [5, 4, 3, 2, 1] mean [Extremely good/Perfect, Good, Normal,Bad, Extremely bad]. Moreover, the subjective rating of every classroom is higher than 3, although
the reverberation time of every room is longer than the ASHA limit.
We could speculate some reasons. First, the reverberation time change is not large enough, only
varying from 0.46 to 0.61 s. Second, the number of respondents is small and also varies withclassrooms, from 3 to 8 people. Third, the ages of the respondents vary from 10 to 18 . Particularly,
younger students enrolled in the elementary school have difficulties understanding the question about
the speech clarity and seems not experienced to evaluate the acoustic quality. Perhaps they do nothave a decent reference/experience on good acoustic conditions with cochlea implants and hearing
aids. Although many eventually answered that the speech clarity was ‘Perfect’, they spent a lot of time
understanding the sentence of questions clearly and therefore the teachers repeated the same questions
several times. We asked an additional question if they could perceive any acoustical difference indifferent spaces, and most of them answered negatively; 63% answered ‘No’ and the rest answered‘Rarely’. This potentially indicates that they might not understand the question correctly. While
younger students used the high scores (4 and 5) in the speech clarity question, older students (18 yearsold) could use a wider score range and therefore the room High 3-2 has the lowest mean and largest
spread.
Potential reasons for the good rating might be a small number of students in the class and shortdistance from the teacher. Many rooms have dimensions of 4.8 m (D) × 6.3 m (W) × 2.7 m (H) andthe distance from the teacher was mostly within 2 m (shortest 1.3 m, longest 3.0 m).

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(a)

(b)
Figure. 2. Reverberation time T 20 (a) SNSD, (b) SS.
Table. 1. Reverberation time T 20 and subjective speech clarity results in SS.
ScienceEle 6-1

Ele. 5-2

Ele. 5-1

High 3-1

High 3-2

Mid. 1-1

Octave-band
averaged T20 (s)

0.43

0.49

0.49

0.51

0.54

0.64

0.66

Questionnaire

3.9

3.3

3.5

3.7

4.4

4

3.8

Interview

4.5

4.5

5

4.6

5

3.6

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4.2 Church
The reverberation time T 20 in the church is shown in Fig. 3, including the 63 Hz octave band. The
mean reverberation time is 0.74 s averaged across the frequency bands. This reverberation time cannot
meet the ASHA limit, but compared to other worship places, the reverberation time is much shorter,and this might be a reason for a satisfactory subjective speech clarity rating.
The average of STI values in 13 source-receiver combinations was found to be 0.69 with a standard
deviation of 0.03, meaning a good speech communication quality. This value corresponds to thequalification scale “C” of high speech intelligibility according to IEC 60268-16 (12). Note that thesame standard states that modern churches typically have a nominal STI value of 0.58 (Category “E”).
Therefore, it is concluded that this church has a better speech indelibility than other modern churches,but no data are found regarding church acoustics for hearing impaired people.
The noise level in an unoccupied condition is quite stable over the church, varying from 33 dBA
to 35 dBA. With an open window, 39 dBA is measured. The unoccupied noise level satisfies the ANSI
recommendation, but not the ASHA recommendation.
The church was subjectively rated as fair-to-good in terms of speech clarity (mean speech clarity
rating of 3.3) and not disturbing in terms of noise annoyance (mean noise annoyance rating of 1.6).
Here the subjective noise annoyance ratings [5, 4, 3, 2, 1] mean [Extremely annoying, Annoying,
Slightly annoying, Not disturbing although noise heard, No noise heard]. The subjective ratings arein line with the objective room acoustic parameters.

4.3 Dormitory
The reverberation time in the dormitory Nongawon is shown in Fig. 4. The longest reverberation
time was found to be 0.76 s averaged across the measurement points and frequency bands in the livingroom, as it the largest room volume and connected to the kitchen. The big bedroom has an averaged
T 20 of 0.49 s and the small bedroom has a T 20 of 0.41 s.
Unoccupied noise levels are found to be 34-38 dBA, which is close to what is recommended by
ANSI and ASHA, although this is not a classroom. The speech clarity was evaluated as fair-to-good(subjective score of 3.3) and noise annoyance was rated as slightly disturbing (noise score of 2.3).
They commented that chair dragging noise, computers, and conversation during night wereparticularly annoying.

Figure. 3. Reverberation time T 20 in Youngnak church. The error bar means the standard deviation.

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Figure. 4. Reverberation time T 20 in Nongawon rooms.

5. CONCLUSIONS
The acoustic conditions of several rooms for hearing impaired people in the Republic of Korea aremeasured and presented. In the two schools measured, no classroom could satisfy the reverberation
time requirement of 0.4 s. The correlation between the reverberation time and subjective speech clarity
is poor, and it is difficult to obtain reliable subjective responses for several reasons. The noise level
was measured to vary from 31 to 42 dBA in occupied conditions, while the recommendation was given
for unoccupied conditions.
The church has a reverberation time of 0.74 s averaged across the frequency and 13 source -receiver
combinations and a mean speech transmission index of 0.69. As it is a worship space, the acoustics
could be much more reverberant than as it is. According to IEC 60268-16, this church has a higher
speech intelligibility than typical modern churches. The unoccupied noise level seems proper for theintended use.
The dormitory has no acoustic design guideline. The reverberation time in the living room islongest as 0.67 s, and the speech clarity is evaluated as fair-to-good. The noise in the dormitory isslightly disturbing with main sources of chair dragging noise and computer noise.

ACKNOWLEDGEMENTS
The authors acknowledge all the administrators of the two schools, Nongawon dormitory,
Youngnak church, who allows us to measure the rooms and collect the questionnaire. The authors also
thank to all the participants in the questionnaires and interviews, and to Hye Min Byun, Sin Sung
Baek, and Youngrok Heo, from Oticon Korea, who helped us during ISO 30082 measurements,questionnaires and interviews.

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REFERENCES
1. Duquesnoy AJ, Plomp R. Effect of reverberation and noise on the intelligibility of sentences in cases ofpresbyacusi, J. Acoust. Soc. Am. 1980;68:537-544.
2. Plomp R., Duquesnoy AJ. Room acoustics for the hearing impaired J. Acoust. Soc. Am. 1982;71:S19.
3. American Speech-Language Hearing Association (ASHA). Guidelines for addressing acoustics ineducational settings. 2005.
4. American National Standards Institute (ANSI) S12.60. Acoustical performance criteria, design
requirements and guidelines for schools. 2010.
5. BR18, Danish Building regulation, http://bygningsreglementet.dk. 2018.
6. Bradley JS. Speech intelligibility studies in classrooms. J. Acoust. Soc. Am. 1986;80:846-854.
7. Yang W, Hodgson, M. Arualziation study of optimum reverbereation times for speech intelligibility fornormal and hearing-impaired liste ners in classrooosm with diffuse sound field J. Acoust. Soc. Am.
2006;120:801-807.
8. McCroskey F., Devens J. Acoustic characteristics of public school classrooms constructed between 1890
and 1960. Proc Noise Expo, National Noise and Vibration Control Conference; 1975, OH, USA 1975, p.
101–103.
9. Crandall CC, Smaldino JJ. Classroom acoustics for children with normal hearing and with hearing
impairment, Lang. Speech Hear. Serv. Sch. 2000;31:362–370.
10. Crandall CC. Classroom acoustics for hearing impaired children, J. Acoust. Soc. Am. 1992;92:2470.
11. International Standard Organization (ISO) 3382-1. Acoustics - Measurement of room acoustic
parameters - Part 1: Performance spaces. 2009.
12. International Electrotechnical Commission (IEC) 60289-16. Sound system equipment - Part 16:
Objective rating of speech intelligibility by speech transmission index. 2011.

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