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Apr 1982

Volume 71, Issue S1, pp. S1-S113

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back to top Session J. Architectural Acoustics II and Speech Communication II: Speech Intelligibility in Rooms
Invited Papers
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Predicting and measuring speech intelligibility in rooms (A)

T. Houtgast and H. J. M. Steeneken

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S19-S19 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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A well‐known concept—the Modulation Transfer Function MTF—which has only recently been adapted to the field of room acoustics, can successfully be used for predicting or measuring speech intelligibility in rooms. The MTF in room acoustics characterizes the quality of sound transmission between two points in a room by specifying the reduction of the original fluctuations in the signal (more specifically, the reduction of the modulation depth as a function of modulation frequency), brought about by interfering noise and/or reverberation. The relevance of this approach for speech intelligibility has been verified by a large‐scale international test: it was found that the results of the MTF analysis (in which an MTF is converted into a single index, the Speech Transmission Index STI) relate well with the mean results of various intelligibility tests for different languages. The accessibility of the MTF approach for architects and acousticians has been substantiated by (1) the development of a calculation scheme for predicting the STI from the design specifications of a room and (2) the development of specific equipment for measuring the STI in actual conditions.
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Room acoustics for the hearing impaired (A)

R. Plomp and A. J. Duquesnoy

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S19-S19 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Experiments have shown [A. J. Duquesnoy and R. Plomp, J. Acoust. Soc. Am. 68, 537–544 (1980)] that the Speech Transmission Index (STI), derived from the modulation transfer function, can be used to describe the combined effect of noise and reverberation on speech intelligibility by hearing‐impaired subjects. Every 3‐dB hearing loss for speech in noise (elevation of the speech‐reception threshold in terms of S/N ratio re speech‐reception threshold for normal‐hearing subjects) can be compensated for by an increase of 0.1 in STI. For an auditorium or classroom, this increase can be obtained by reducing the reverberation time with not less than 58%. Since many hearing‐impaired subjects have hearing losses. for speech in noise larger than 3 dB, we may conclude that they need very low reverberation times.
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Speech intelligibility in rooms (A)

Howard G. Latham

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S20-S20 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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This paper reviews developments in the science of speech intelligibility in rooms, and discusses the need for further work. Over the last 60 years, knowledge on this subject area of auditorium acoustics has been ascertained by observation and experiment, critically tested, systematized, and brought under a set of general principles. Objective indices are now available for measuring and predicting speech intelligibility in rooms without the need for traditional subjective testing procedures. Thus a more widespread application of intelligibility criteria in auditorium design is to be expected in future work. Parallel with the developments in objective and subjective measurement techniques, the computer prediction of reflection patterns in rooms has been developed so that speech intelligibility levels can now be ascertained during design, and acoustic faults remedied before construction commences. However, further work is needed to establish a valid basis for speech intelligibility design criteria based on objective measurements. To this end, a catalog of subjective and objective measures of speech intelligibility could be determined for a set of conditions in well‐known auditoria. The result would be a relative scale of intelligibility values for use by practitioners. [Work supported by the SERC, United Kingdom.]
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Sentence perception in noise (A)

Lois L. Elliott

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S20-S20 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Previous research has shown that normal children and older people have greater difficulty understanding sentences presented in a multitalker babble than do listeners in the 17–50 year age range. Recent work demonstrates that normally hearing children with speech‐production disorders and normally hearing learning‐disabled adults may demonstrate poorer speech perception than normal age mates. Since everyday listening situations often involve signal‐to‐noise levels comparable to the experimental levels, these data should be considered in design of school classrooms and home environments. [Supported, in part, by NSF, NIH, and BEH.]
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Listening devices in auditoriums for listeners with perceptual problems (A)

Anna K. Nábělek

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S20-S20 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Acoustic criteria for auditoriums have been developed for listeners with normal perceptual skills. In consequence, these criteria applied to room acoustics may not be good enough for listeners with perceptual deficiencies. Perceptual problems are usually associated with congenital or acquired hearing losses, but also, elderly listeners who might have only slightly less acute hearing then their younger counterparts find listening in some auditoriums very difficult. Three parameters contribute to such problems: sound pressure level too low, speech‐to‐noise ratio too low, and reverberation too long. When acoustic conditions become unsatisfactory, many listeners cease attending lectures, art performances, etc. In some communities loss of elderly listeners might consist of a significant reduction in public support of drama theaters or concerts. The so‐called “group amplification systems” or “listening devices” can provide help for listeners with perceptual problems. The main principle of such devices is to pick up the signal close to the source and deliver it directly to the listener's ears. In such a way the signal can be individually amplified and delivered without background noise and reverberation. The following systems which are presently in use will be discussed: (1) hard wired, (2) induction loop, (3) amplitude modulation, (4) frequency modulation, and (5) infrared. All these systems will be discussed for the use of listeners with and without hearing aids. [Work supported by NIH.]
Contributed Papers
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Determining speech intelligibility in industrial environments (A)

John G. Powell and Louis C. Sutherland

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S20-S20 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Application of the speech transmission index to determination of speech intelligibility in indoor industrial environments is described. Equations suitable for engineering use are presented. The effects of reverberation in the direct field of the speech source are accounted for. Presbycusis effects are included in the equations, allowing, for example, calculation of the source level required for 95% of the 40‐year‐olds to attain 97% speech intelligibility. The effects of high ambient noise and hearing protection devices are also described. Effective room volume is required in the calculation. In a building cluttered with machinery, pipes, etc., the effective volume may be a fraction of the physical volume, or one or more of the classical six surfaces may be missing. A practical method of measuring effective volume is described.
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Sensitivity of predicted effectiveness of a paging system to design criteria (A)

Louis C. Sutherland, Constantine Glaretas, and John G. Powell

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S21-S21 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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The expected effectiveness of an industrial paging system for presentation of emergency messages has been evaluated in terms of sentence intelligibility (SI). The evaluation was based on the Speech Transmission Index concept developed by Houtgast and Steeneken [J. Acoust. Soc. Am. 67, 318–326 (1980)]. Changes in SI were evaluated for 17 paging system locations with nominal signal‐to‐noise ratios ranging from −21 to +15 dB and reverberation times ranging from 0.3 to 1.6 s. The change in signal level required to achieve a design goal of 90% and 97% SI was evaluated as a function of (1) the average age of the listeners (30 or 40 years), (2) the percentage (50% or 90%) of this age group who would achieve the desired SI, and (3) the number of message repetitions. The primary result is to point out that the influence on required signal level of message repetitions was found to be at least as important as the other factors. This influence is not included in the usual engineering methods for evaluating communication systems. Conflicts between alternate prediction models for the effect of message repetition according to current signal detection theory and earlier experimental work are considered.
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Predicting speech intelligibility in rooms (A)

J. S. Bradley

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S21-S21 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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The pioneering work of Lochner and Berger [e.g., J. Sound Vib. 1(4), 426–454 (1964)] has provided a basis for measuring and calculating speech intelligibility in rooms in terms of a ratio of useful early sound to detrimental late arriving sound and background noise. In the present work their results are used in an image sources computer model to predict speech intelligibility in rooms. The calculation procedure is discussed and the influence on speech intelligibility of room geometry, room surface sound absorption properties, and background noise levels are investigated. Comparisons are made with speech intelligibility calculations based on the modulation transfer function approach.
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Panel discussion (A)

Ira J. Hirsh

J. Acoust. Soc. Am. Volume 71, Issue S1, pp. S21-S21 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Future uses for automatic speech intelligibility assessment of indoor spaces such as offices, factories, restaurants, and theaters will be discussed. Panelists will include some of the invited speakers and, also, distinguished guests.
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