Speech intelligibility metrics that take into account sound reflections in the room and the background noise have been compared, assuming diffuse sound field. Under this assumption, sound decays exponentially with a decay constant inversely proportional to reverberation time. Analytical formulas were obtained for each speech intelligibility metric providing a common basis for comparison. These formulas were applied to three sizes of rectangular classrooms. The sound source was the human voice without amplification, and background noise was taken into account by a noise-to-signal ratio. Correlations between the metrics and speech intelligibility are presented and applied to the classrooms under study. Relationships between some speech intelligibility metrics were also established. For each noise-to-signal ratio, the value of each speech intelligibility metric is maximized for a specific reverberation time. For quiet classrooms, the reverberation time that maximizes these speech intelligibility metrics is between 0.1 and 0.3 s. Speech intelligibility of 100% is possible with reverberation times up to 0.4–0.5 s and this is the recommended range. The study suggests “ideal” and “acceptable” maximum background-noise level for classrooms of 25 and 20 dB, respectively, below the voice level at 1 m in front of the talker.

Topics
Human voice, Acoustic noise, Sound source perception, Speech intelligibility
1.
J. P. A.
Lochner
and
J. F.
Burger
, “
The intelligibility of speech under reverberant conditions
,”
Acustica
11
,
195
–
200
(
1961
).
Google Scholar
 
2.
H. G.
Latham
, “
The signal-to-noise ratio for speech intelligibility—an auditorium acoustics design index
,”
Appl. Acoust.
12
,
253
–
320
(
1979
).
Google Scholar
Crossref
Search ADS
 
3.
J. S.
Bradley
, “
Predictors of speech intelligibility in rooms
,”
J. Acoust. Soc. Am.
80
,
837
–
845
(
1986
).
Google Scholar
Crossref
Search ADS
PubMed
 
4.
T.
Houtgast
and
H. J. M.
Steeneken
, “
The modulation transfer function in room acoustics as a predictor of speech intelligibility
,”
Acustica
28
,
66
–
73
(
1973
).
Google Scholar
 
5.
V. M. A.
Peutz
, “
Articulation loss of consonants as a criterion for speech transmission in a room
,”
J. Audio Eng. Soc.
19
,
915
–
919
(
1971
).
Google Scholar
 
6.
T.
Houtgast
, “
The effect of ambient noise on speech intelligibility in classrooms
,”
Appl. Acoust.
14
,
15
–
25
(
1981
).
Google Scholar
Crossref
Search ADS
 
7.
J. S.
Bradley
, “
Speech intelligibility studies in classrooms
,”
J. Acoust. Soc. Am.
80
,
846
–
854
(
1986
).
Google Scholar
Crossref
Search ADS
PubMed
 
8.
J. S. Bradley, “Uniform derivation of optimum conditions for speech in rooms,” Report BRN 239 (National Research Council, Ottawa, Canada, 1985).
9.
M.
Hodgson
, “
UBC-Classroom acoustical survey
,”
Can. Acoust.
24
(
4
),
3
–
10
(
1994
).
Google Scholar
 
10.
M.
Hodgson
,
R.
Rempel
, and
S.
Kennedy
, “
Measurement and prediction of typical speech and background-noise levels in university classrooms during lectures
,”
J. Acoust. Soc. Am.
105
,
226
–
233
(
1999
).
Google Scholar
Crossref
Search ADS
 
11.
J. S.
Bradley
, “
Relationships among measures of speech intelligibility in rooms
,”
J. Aud. Eng. Soc.
46
,
396
–
405
(
1998
).
Google Scholar
 
12.
H.
Haas
, “
The influence of a single echo on the audibility of speech
,”
J. Audio Eng. Soc.
20
,
146
–
159
(
1972
).
Google Scholar
 
13.
F.
Aigner
and
M. J. O.
Strutt
, “
On a physiological effect of several sources of sound on the ear and its consequences in architectural acoustics
,”
J. Acoust. Soc. Am.
6
,
155
–
159
(
1935
).
Google Scholar
Crossref
Search ADS
 
14.
R.
Thiele
, “
Richtungsverteilung und zeitfolge der schallruckwurfe in raumen
,”
Acustica
3
,
291
–
302
(
1953
).
Google Scholar
 
15.
T.
Houtgast
,
H. J. M.
Steeneken
, and
R.
Plomp
, “
Predicting speech intelligibility in rooms from the modulation transfer function I: General room acoustics
,”
Acustica
46
,
60
–
72
(
1980
).
Google Scholar
 
16.
M. R.
Schroeder
, “
Modulation transfer functions: Definition and measurement
,”
Acustica
49
,
179
–
182
(
1981
).
Google Scholar
 
17.
T.
Houtgast
and
H. J. M.
Steeneken
, “
A multi-language evaluation of the RaSTI-method for estimating speech intelligibility in auditoria
,”
Acustica
54
,
185
–
199
(
1984
).
Google Scholar
 
18.
S. R. Bistafa and J. S. Bradley, “A comparative study of speech intelligibility metrics and the derivation of optimum reverberation time and maximum background-noise level for classrooms,” Report IR-778 (National Research Council Canada, Ottawa, Canada, 1999).
19.
H. Kuttruff, Room Acoustics (Elsevier Applied Science, London, 1991), pp. 114–123.
20.
H.
Niese
, “
Die messung der nutzschall-und echogradverteilung zur beurteilung der horsamkeit in raumen
,”
Acustica
11
,
201
–
213
(
1961
).
Google Scholar
 
21.
V. S. Mankovsky, Acoustics of Studios and Auditoria (Focal, London, 1971), pp. 75–79.
22.
V. O. Knudsen, Architectural Acoustics (Wiley, New York, 1932), pp. 373, 395–396.
23.
T.
Houtgast
and
H. J. M.
Steeneken
, “
A review of the MTF concept in room acoustics and its use for estimating speech intelligibility in auditoria
,”
J. Acoust. Soc. Am.
77
,
1069
–
1077
(
1985
).
Google Scholar
Crossref
Search ADS
 
24.
V. M. A. Peutz, “Speech perception and information,” in Proceedings of the 9th International Congress of Acoustics, Madrid, 1977, Vol. 1, p. 428.
25.
The Acoustical Society of America’s response to a request for information on acoustics from the Office of Technical and Information Services—Architectural and Transportation Barriers Compliance Board, 27 July 1998, The Acoustical Society of America, 2 Huntington Quadrangle, Suite 1 NO 1, Melville, NY 11747.
26.
J. S.
Bradley
,
R. D.
Reich
, and
S. G.
Norcross
, “
On the combined effects of signal-to-noise ratio and room acoustics on speech intelligibility
,”
J. Acoust. Soc. Am.
106
,
1820
–
1828
(
1999
).
Google Scholar
Crossref
Search ADS
PubMed
 
27.
H. F.
Kingsbury
, “
Review and revision of room noise criteria
,”
Noise Control Eng. J.
43
,
65
–
72
(
1995
).
Google Scholar
Crossref
Search ADS
 
28.
K. S. Pearsons, R. L. Bennett, and S. Fidell, “Speech levels in various noise environments,” Bolt, Beranek and Newman Inc. report to the U.S. Environmental Protection Agency, EPA Report 600-77-025, Canoga Park, CA (May 1977).
29.
M. Barron, Auditorium Acoustics and Architectural Design (E & FN SPON, London, 1993), pp. 418–419.
This content is only available via PDF.
© 2000 Acoustical Society of America.
2000
Acoustical Society of America
You do not currently have access to this content.