Objective measures were investigated as predictors of the speech security of closed offices and rooms. A new signal-to-noise type measure is shown to be a superior indicator for security than existing measures such as the Articulation Index, the Speech Intelligibility Index, the ratio of the loudness of speech to that of noise, and the A-weighted level difference of speech and noise. This new measure is a weighted sum of clipped one-third-octave-band signal-to-noise ratios; various weightings and clipping levels are explored. Listening tests had 19 subjects rate the audibility and intelligibility of 500 English sentences, filtered to simulate transmission through various wall constructions, and presented along with background noise. The results of the tests indicate that the new measure is highly correlated with sentence intelligibility scores and also with three security thresholds: the threshold of intelligibility (below which speech is unintelligible), the threshold of cadence (below which the cadence of speech is inaudible), and the threshold of audibility (below which speech is inaudible). The ratio of the loudness of speech to that of noise, and simple A-weighted level differences are both shown to be well correlated with these latter two thresholds (cadence and audibility), but not well correlated with intelligibility.

1.
ASTM E1130-02, “Standard Test Method for Objective Measurement of Speech Privacy in Open Offices Using Articulation Index,” (ASTM International, West Conshohocken, PA).
2.
ANSI S3.5-1969, “American National Standard Methods for the Calculation of the Articulation Index,” (ANSI, New York, NY).
3.
ANSI S3.5-1997, “American National Standard Methods for Calculation of the Speech Intelligibility Index,” (ANSI, New York, NY).
4.
W. J.
Cavanaugh
,
W. R.
Farrell
,
P. W.
Hirtle
, and
B. G.
Watters
, “
Speech privacy in buildings
,”
J. Acoust. Soc. Am.
34
,
475
492
(
1962
).
5.
R. W.
Young
, “
Re-vision of the speech-privacy calculation
,”
J. Acoust. Soc. Am.
38
,
524
530
(
1965
).
6.
M. D. Egan, Architectural Acoustics (McGraw-Hill, New York, 1988.)
7.
F.
Santon
, “Intelligibilité de la parole masquée et rôle de la direction de la source masquante,” “
The Intelligibility of Speech and the role of the Masking Source Direction
Acustica
61
,
67
74
(
1986
).
8.
IEEE recommended practice for speech quality measurements
,”
IEEE Trans. Audio Electroacoust.
17
,
227
246
(
1969
).
9.
A. C. C.
Warnock
, “
Acoustical privacy in the landscaped office
,”
J. Acoust. Soc. Am.
53
,
1535
1543
(
1973
).
10.
C.
Speaks
,
B.
Parker
,
C.
Harris
, and
P.
Kuhl
, “
Intelligibility of connected discourse
,”
J. Speech Hear. Res.
15
,
590
602
(
1972
).
11.
W. O.
Olsen
, “
Average speech levels and spectra in various speaking/listening conditions: A summary of the Pearson [sic], Bennett, & Fidell (1977) report
,”
Am. J. Audiol.
7
,
1
5
(
1998
).
12.
ANSI S12.2-1995 (R1999), “American National Standard Criteria for Evaluating Room Noise,” (ANSI, New York, NY).
13.
ISO 532-1975, “Acoustics—Method for calculating loudness level,” (ISO, Geneva, Switzerland).
14.
ISO 7029-1984 (E), “Acoustics—Threshold of hearing by air conduction as a function of age and sex for otologically normal persons,” (ISO, Geneva, Switzerland).
15.
H.
Tachibana
,
Y.
Sonoda
,
K.
Iwamoto
,
S.
Kuwano
, and
S.
Namba
, “
Validity of arithmetic average of sound pressure levels in octave bands as a loudness index
,”
J. Acoust. Soc. Jpn. (E)
14
,
197
204
(
1993
).
16.
ORIGIN User’s Manual Version 5,” Microcal Software Inc., 1997.
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