Archives of Acoustics, 42, 3, pp. 527–532, 2017
10.1515/aoa-2017-0056

Comparison of Two Types of Combined Measures, STI and U50, for Predicting Speech Intelligibility in Classrooms

Young-Ji CHOI
Kangwon National University
Korea, Republic of

The present study reports on the speech intelligibility as measured by speech transmission index (STI) and useful-to-detrimental sound ratios ($U_{50}$) in university classrooms. Acoustic measurements were made in 12 quietly occupied university classrooms. The measured impulse responses of the classrooms were used to determine the modulation transfer function, $m(F)$, for the STI calculation according to IEC 60268-16. $U_{50}$ values were determined from both signal-to-noise ratios (SNR) and $C_{50}$ values. The mean STI and frequency-weighted $U_{50}$ values for the 12 occupied classrooms were strongly linearly related. The results showed that classrooms with $U_{50}$ values of about +0.5 dB correspond to STI values of 0.60, indicating ‘good’ acoustical conditions for speech intelligibility. The results illustrate that the $U_{50}$ measure can be a more practically useful means of assessing and understanding room acoustics conditions for real speech communication in active classrooms.
Keywords: speech intelligibility; speech transmission index; useful-to-detrimental sound ratios; classrooms
Full Text: PDF

References

ANSI S12.60 (2004), Acoustics performance criteria, design requirements, and guidelines for schools, American National Standards Institute, New York.

ANSI S3.5 (1997), American National Standard Methods for Calculation of the Speech Intelligibility Index, American National Standards Institute, New York.

Bradley J.S. (1986), Speech intelligibility studies in classrooms, Journal of the Acoustical Society of America, 80, 846–854.

Bradley J.S. (2011), Using room acoustics measures to understand a large room and sound reinforcement system, Proceedings of the Institute of Acoustics, 33.

Bradley J.S., Bistafa S.R. (2002), Relating speech intelligibility to useful-to-detrimental sound ratios, Journal of the Acoustical Society of America, 112, 27–29.

Bradley J.S., Reich R., Norcross S.G. (1999), On the combined effects of signal-to-noise ratio and room acoustics on speech intelligibility, Journal of the Acoustical Society of America, 106, 1820–1828.

Choi Y.J. (2016), Effect of occupancy on acoustical conditions in university classrooms, Applied Acoustics, 114, 36–43.

DIRAC room acoustics software version 6.0 (2014), Brüel & Kjær, Denmark.

Hodgson M. (2002), Rating, ranking, understanding acoustical quality in university classrooms, Journal of the Acoustical Society of America, 112, 568–575.

Hodgson M., Nosal E.-M. (2002), Effect of noise and occupancy on optimal reverberation times for speech intelligibility in classrooms, Journal of the Acoustical Society of America, 111, 931–939.

Hodgson M., Rempel R., Kennedy S. (1999), Measurement and prediction of typical speech and background noise level in university classrooms during lectures, Journal of the Acoustical Society of America, 105, 226–233.

IEC 60268-16 Edition 4.0 (2011), Sound system equipment. Part 16: Objective rating of speech intelligibility by speech transmission index.

ISO 3382 (2003) Acoustics. Measurement of the reverberation time of rooms with reference to other acoustical parameters.

Nijs L., Rychtáriková M. (2011), Calculating the optimum reverberation time and absorption coefficient for good speech intelligibility in classroom design using U50, Acta Acustica United with Acustica, 97, 93–102.

Sato H., Bradley J.S. (2008), Evaluation of acoustical conditions for speech communication in working elementary school classrooms, Journal of the Acoustical Society of America, 123, 2064–2077.

Schroeder M.R. (1981), Modulation transfer functions: Definition and Measurement, Acustica, 49, 179–182.

Yang W.S., Bradley J.S. (2009), Effects of room acoustics on the intelligibility of speech in classrooms for young children, Journal of the Acoustical Society of America, 125, 922–933.




DOI: 10.1515/aoa-2017-0056

Copyright © Polish Academy of Sciences & Institute of Fundamental Technological Research (IPPT PAN)