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A favorable reverberation time in concert halls is a fundamental issue for room acoustic design, and various recommendations have been suggested so far. Nevertheless, one must track back more than half a century when it comes to systematic subjective experiments on this topic. In this study, binaural room impulse responses (RIRs) measured with a dodecahedral loudspeaker in concert halls, where orchestra concerts are regularly held, are used. First, signal processing is applied to RIR to equalize the dodecahedral loudspeaker response as flat and broad as possible within the audible frequency range. Then, anechoic recordings of music by piano and violin, excerpts from cadenzas, are convoluted with the equalized RIR. Next, subjective experiments are conducted to seek favorable reverberation times. Reverberance and clarity were judged by 16 music experts. From this research, the favorable reverberation times RTM (octave band average for 500 and 1000 Hz) for piano and violin solos are from 1.2 to 2.0 s and 1.8 to 2.4 s, respectively. However, the clarity index C80,3 (octave band average for 500, 1000, and 2000 Hz) needs to range from 0 to 2.4 dB and −1.6 to 0.7 dB, respectively, to meet the optimum reverberance for piano and violin. [ABSTRACT FROM AUTHOR]

Access to the original Lascaux cave, a UNESCO World Heritage site famous for its 18 000 year old paintings, has been restricted since 1963. In 2016, an accurate facsimile, Lascaux IV, was designed and built. In the original cave, Lascaux I, classical contemporary room acoustics measurement systems could not be used. However, it has been possible to perform simplified measurements in a few minutes. Similar measurements were made in Lascaux IV once completed. The data provide a unique insight of the acoustic behavior of the Lascaux cave: it shows that the two caves, the original and the copy, have similar acoustical characteristics. In both cases, in the famed Hall of Bulls, the impulse response is smooth, reverberation time is relatively long, and speech intelligibility is fair; this environment is suitable for the ceremonies that presumably took place there. Because of the precision of the copy, Lascaux IV could be used as a 1/1 scale-model of Lascaux I. Therefore, sophisticated acoustical tests could be undertaken in Lascaux IV to help specialists in their archeological investigations. For example, resonances could be precisely documented to explore the potential relationship between parietal painting positions and echoes or sound effects that may have been used in ritual ceremonies. [ABSTRACT FROM AUTHOR]

Objective acoustical parameters for halls are often measured in 1-octave bands with mid-frequencies from 125 to 4000 Hz. In reality, the frequency range of musical instruments is much wider than that, and the fundamentals of the lower notes of bass instruments are contained in 31.5 or 63 Hz bands. Overtones of fundamentals in these bands fall in 125 Hz band. This report presents subjective experiments designed to determine to what extent the overtones in 125 Hz band and higher bands influence the loudness sensation of the components in 63 Hz band. In the experiments, the 125 Hz and higher components of the musical tone are used to act as a masker against the lower component used as a maskee. The threshold of the difference between G(125 Hz) and G(lower band) that just enables one to hear the fundamental tones in the lower band is determined. Masked loudness of 63 Hz sinusoidal tone caused by partial masking noise with higher frequencies was determined based on a similar procedure to the masked loudness-matching function. The result indicates that the difference in loudness of low tone will not be noticeable even if G changed by ±2.5 to ±3 dB, at least when there are other accompanying instruments. [ABSTRACT FROM AUTHOR]

The early reflections in the room impulse response are usually defined as those observed within the initial 80 ms after the arrival of the direct sound, after which time the sound field is called reverberant. This number was chosen from measurements of other functions in a limited number of halls. In order to give an objective foundation to this time separation and to establish a physical indicator for it, a new method is proposed that defines a “transition time tL,” which is the time at which the energy correlation between the direct plus initial sound and the subsequent decaying sound first achieves a specified low value. For various halls this number is shown and its relevance as a new parameter is discussed. [ABSTRACT FROM AUTHOR]

The tangential plane approximation (TPA) is introduced to investigate the spherical wave reflection from smooth concave cylindrical walls, and as a practical calculation scheme, asymptotic expression of the reflected sound from that surface with a relatively large dimension is derived. The physical condition under which TPA holds is derived for the spherical wave incidence; moreover, the essential properties of the reflected sound from the curved walls, which cannot be treated by the geometrical acoustics, are discussed through the numerical calculation for infinitely long cylinders. A formula of the reflection factor of the two-dimensional curved surface is obtained for the purpose of the room acoustical design. This formula coincides with that based on the geometrical acoustics when the frequency is infinitely high. [ABSTRACT FROM AUTHOR]

The room acoustical parameters reverberation time, RT; early decay time, EDT; clarity, C80; time gravity, Tg; bass ratio, BR; strength, G; initial time delay gap, ITDG; interaural cross-correlation coefficient, IACCE, the where binaural quality index BQI equals [1-IACCE3]; and stage support, ST1 were measured in 18 major chamber-music halls in Austria, Germany, the Netherlands, Czech Republic, Switzerland, and Japan, employing procedures in accordance with ISO 3382 (1997). In combination with the architectural data, the intrinsic objective parameters for the acoustics of chamber-music halls and their variation range were examined. The results of these studies reveal four pertinent orthogonal parameters: RT, G, ITDG, BQI. General design guidelines for a chamber-music hall are presented. [ABSTRACT FROM AUTHOR]

Four methods are explored for predicting the reverberation times in fully occupied halls for music as related to the sound absorption by their audiences. The methods for providing audience absorptions include two that use reverberation chambers, namely, the ISO 354 method (and other similar standards) (ISO) and Kath and Kuhl's method (K & K) [Acustica 15, 127-131 (1965)], and two that use average data from halls, i.e., Beranek's method (COH) [Concert and Opera Halls: How They Sound (Acoustical Society of America, Melville, NY, 1996)], and the average audience power-per-seat absorption which in practice is multiplied by the number of seats (ΔA). These methods are applied to the calculation of reverberation times in six existing halls, fully occupied, and the results were compared with actual measurements. The COH method was best for predictions over the entire frequency range. The K & K method showed the highest accuracy at mid-frequencies. Both the ISO and the K & K methods yielded wide differences for the measurements in the 125- and 250-Hz bands. The ΔA method was as good as the COH method when the measurements for the six halls were averaged, but showed a wide spread in the predictions around the average because it does not consider the degree of upholstering of the seats. It was hypothecated by the authors that the principal reasons for the ISO and K & K discrepancies at low frequencies were (a) differences between the degree of sound diffusion in actual halls and that in reverberation chambers, and (b) lack of information on the mechanisms of absorption of sound by people seated side-by-side in rows, particularly for near-grazing incidence sound fields. First, this article explores the sound diffusivity in a reverberation chamber and in the halls using CAD models. A probability density function of the incident angles of the sound rays that impinge on the audiences is defined and was measured for each case. Using a unique method, the sound absorption coefficient of each portion of the body and chair in a seated audience was determined in an anechoic chamber as a function of the incident angle of a sound wave. With adjustments from these findings, the K & K method can be made to equal the COH method in accuracy at all frequencies. Its forte is that it can be used for the determination of the sound absorption of occupied chairs from measurements of a limited number in a reverberation chamber. © 2001 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Five acoustical parameters-reverberation time RT, early decay time EDT, clarity C80, strength G, and interaural cross-correlation coefficient IACC-were measured using identical procedures with and without audiences in six concert and opera halls. Reverberation times without audiences were measured in 15 additional halls using the same measuring techniques as for the six halls above, but for full occupancy the data were taken from musical stop chords at symphonic concerts. This paper shows that in all halls (1) the occupied RT can be predicted from the unoccupied RT using a linear regression equation, y=a-b exp(x), within acceptable limits, at low- and mid-frequencies. It is also shown for the six halls that (2) occupied C80's are predicted accurately from unoccupied values by the newly proposed equation; (3) G's with and without audiences are highly correlated by a first degree linear regression equation; and (4) IACCs have nearly the same value in both occupied and unoccupied halls. As a separate subject, the successful use of a cloth covering for seats in a concert or opera hall to simulate the occupied condition has been developed. © 2001 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The Tokyo Opera City concert hall seats 1632, volume 15 300 m3, and reverberation time, with audience and orchestra, 1.95 s. As part of the design process, measurements on CAD computer and 1:10 wooden models of the hall and full-sized materials samples were conducted over a 5-yr. period. The hall in plan is rectangular. The ceiling is a distorted pyramid, with its peak 28 m above the main floor and nearer the stage than the rear of the hall. This unique shape was analyzed on the models so that all interior surfaces combine to distribute sources on the stage uniformly over the seating areas and to yield optimum values for reverberation time (RT), early decay time (EDT), interaural cross-correlation coefficient (IACCE3), bass ratio (BR), initial-time-delay gap (ITDG), strength (G), and sound diffusion index (SDI) [for definitions see L. Beranek, Concert and Opera Halls: How They Sound (Acoustical Society of America, Woodbury, NY, 1996)]. On the long ceiling facing the stage, Schroeder QRD diffusers provide diffusion, eliminate a possible echo, and strengthen lateral reflections. Performers and critics judge the acoustics excellent. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Architect Takahiko Yanagisawa's preface explains his approach to the design. The NNT opera house seats 1810, its volume is 14 500 m3, and its reverberation time, with audience, is 1.5 s (proscenium curtain open). Measurements on CAD computer and 1:10 wooden models and full-sized materials samples were conducted over a 7-yr. period. The main floor is almost rectangular, the three balconies have modest fan shape in plan, although the balcony facia at each level create a rectangular shape. The unique design has a large curved reflector in front of and above the proscenium and six curved reflecting surfaces at the front ends of the three side balconies to form, in combination, an 'acoustic trumpet.' These surfaces, along with the balcony faces and the shaped ceiling, distribute the singers' voices uniformly over the seating areas from a large portion of the large stage at sound levels that easily override the orchestra in the pit. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The room acoustical parameters, reverberation time RT, early decay time EDT, clarity factor C80, bass ratio BR, strength G, interaural cross-correlation coefficient IACC, and initial-time-delay gap ITDG [definitions in Hidaka et al., J. Acoust. Soc. Am. 107, 340-354 (2000) and Beranek, Concert and Opera Halls: How They Sound (Acoustical Society of America, New York, 1996)], were measured in 23 major opera houses under unoccupied conditions in 11 countries: Argentina, Austria, Czech, France, England, Germany, Hungary, Italy, Japan, The Netherlands, and the USA. Questionnaires containing rating scales on the acoustical quality of 24 opera houses were mailed to 67 conductors, 22 of whom responded. The objective measurements were analyzed for reliability and orthogonality, and were related to the subjective responses. Presented are (a) the rankings of 21 opera houses each rated by at least 6 conductors for acoustical quality as heard by them both in the audience areas and in the pit; (b) relations between objective room acoustical parameters and subjective ratings; (c) findings of the most important of the parameters for determining acoustical quality: RT (or EDT), GM, ITDG, [1-IACCE3], texture (appearance of reflectrograms in the first 80-100 ms after arrival of the direct sound), a lower limiting value for BR, and major concern for diffusion and avoidance of destructive characteristics (noise, vibration, echoes, focusing, etc.); (d) the differences between average audience levels with and without enclosed stage sets; and (e) the differences between average levels in audience areas for sounds from the stage and from the pit. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

From experimental data in concert and opera halls, absorption coefficients were determined for audience seating, unoccupied and occupied, of different constructions, and for gypsum, wood, plaster, and concrete interior surfaces of various thicknesses and densities. A total of ten halls were involved in the bare hall (before seats were installed) analysis, yielding 'residual' absorption coefficients, i.e., coefficients for those areas not including the areas to be covered by the seating. In ten halls reverberation times were measured after installation of the seats (unoccupied) and in seven of these halls at concerts with seats fully occupied. The seating absorption coefficients are presented for 'acoustical' audience areas, i.e., with a 0.5-m-wide edge around each seating block. The results are compared with the data of Appendix 5 in Beranek [Concert and Opera Halls: How They Sound (Acoustical Society of America, Woodbury, NY, 1996)]. The sound absorption data presented for interior surfaces and audience areas should permit more accurate estimation of reverberation times as a function of frequency for large halls during the planning stage. © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Relations are determined between one of the important subjective attributes of concert hall acoustics, the apparent source width, ASW, and three acoustical measures, interaural cross-correlation coefficient IACCE, LFE, and strength factor G. Although these measures previously have been found to correlate with ASW, their relations with it have not been examined sufficiently, especially in respect to their frequency characteristics. Herein, ASW's are directly determined for electronically reproduced musical sound fields with extensive ranges of values for IACCE and LFE. Investigated as parameters are angles of incidence, the time delay difference between a pair of symmetric early lateral reflections, and the number of early lateral reflections. These studies indicate the relative efficacy of IACCE and LFE for determining ASW under conditions that are realistically encountered in concert halls. The results were compared with measured IACCE's, LFE's, and also the strength factor G's in existing concert halls. It is concluded that the arithmetic average of [1-IACCE]'s at 500, 1 k and 2 k Hz combined with the strength factor Glow of the sound field at frequencies below 250 Hz are physical measures highly correlated with the subjective rank ordering of concert halls and that they cover the effects on ASW of the entire octave-band frequency range from 125 to 4 k Hz. © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Subjective ratings of acoustical quality in concert halls were determined from interviews of conductors, musicians, music critics, and informed listeners during which they were asked to judge the quality of the acoustics and to rank the order of those halls each knew. Subjective ratings on 34 halls were divided into three principal groups: excellent, very good, and less good. No bad halls were studied. The use of the interaural cross-correlation coefficient (IACC) and lateral efficiency (LF) as correlates with the subjective ratings were analyzed in depth. In order to make IACC sensitive to quality ratings, a multi-octave-band average was developed, based on Blauert et al. [Acustica 59, 292 (1986)] and on a subjectively derived set of equal apparent source width (ASW) contours that showed the 0.5-, 1.0-, and 2.0-kHz octave bands to be of equal and principal importance to ASW. This IACC3 was divided into two components, IACCE3, integrated over the first 0.08 s after arrival of the direct sound, and IACCL3, integrated over 0.08-1 s. Subjective judgments were also performed to determine the effects of increased sound levels of symphonic music at frequencies above or below 355 Hz on ASW. It was found that changes in the low-frequency levels (GL) made greater changes in ASW than changes in the high-frequency levels (GH). Because the difference between the low- and high-frequency levels in real halls does not exceed ±5 dB and because both are inversely related to [EDT/Volume], it suffices to measure GL. Thus IACCL3 and GL appear valuable for determining ASW and the degree of sound-field diffusion in the frequency range from 100 to 3000 Hz for symphonic music in concert halls. The measured quantity [1-IACCE3] alone was found to separate exactly the 17 concert halls for which data were available into three category groups. The constituents of these three groups were the same as those determined from the interviews. The measured lateral fraction (LF) for the 24 halls for which data were available was also compared to the subjective groupings. The average measured values of LF for these halls covered a small range and there were so many overlaps among halls when separation of the halls into three rating groups was attempted that LF was judged not to be suitable for rating the acoustical quality of occupied concert halls. © 1995 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The New National Theater (NNT) project containing three halls started with an open international design competition in 1986 and ended with a grand opening October 10, 1997. The architect is Takahiko Yanagisawa. The opera house, the core of the NNT facility, has a seating capacity of 1810, a volume of 14 500 m3, and a reverberation time with full audience of 1.5 s (stage curtain open). Various model experiments, using a CAD model, 1:10 scale model, and full-sized materials samples, were conducted over a 7-year period. As a result, the main floor has an almost rectangular shape, three-layered balconies have a modest fan shape, and the balcony fronts at each level create a rectangular shape. The overhang of each balcony is minimized to take visibility requirements into consideration. The unique design has a large curved reflector in front of the proscenium and over the orchestra pit and curved reflecting surfaces at the fronts of each of the side balconies to reflect the singer's voices uniformly from a large portion of the tremendous stage. The balcony fronts, the side walls, and the ceiling also augment the reflections from those surfaces. The unoccupied values are: EDT=1.6 s, C80(3)=2.4 dB, [I-IACCE3]=0.66m and bass ratio=1.1. [ABSTRACT FROM AUTHOR]

First, a prediction of the sound absorption of seated audiences in four concert halls was made by three methods. Employed were: reverberation chamber data obtained at the laboratory by the Kath and Kuhl method [Acustica 15, 127 (1965)] and the ISO-354 method on similar seating, and average absorption coefficients derived from RT data in 15 halls with three levels of upholstered seating [Beranek, Concert and Opera Halls, Acoustical Society of America, Woodbury, NY, 1996]. For each of the four halls, the residual absorption coefficients were determined from actual measurements (''residual'' meaning that due to all surfaces other than the seating). When the coefficients from the three methods and the measured residual coefficients were substituted in the Sabine equation, the K&K method gave the best prediction above 500 Hz and the Beranek method below 1000 Hz. In order to explain the large differences between K&K/ISO and actual hall measurements at the lower frequencies and to construct a method for predicting RTs in halls from reverberation chamber data, the difference in diffusivity in large concert halls and a reverberation chamber was examined. The incident angle distribution of sound rays onto a seated audience was determined by computer simulation and the oblique incident absorption coefficients of seated audiences were measured in an anechoic room. These findings were then employed to explain the large discrepancy. [ABSTRACT FROM AUTHOR]

The concept of knowledge-based architectural acoustics is proposed showing a prototype of an intelligent system for room acoustic design as a practical example. The system is composed of two major subsystems, an acoustic field simulator and an expert system for room acoustics. The principal objective of the system is to assist acoustic designing. This system can also be used for training acoustic designers and for evaluating both design policies and design parameters to represent the physical characteristics and subjective aspects of sound fields, such as spaciousness and definition. The field simulator is utilized effectively by refining the calculation algorithms and checking whether the performance coincides with actual fields. The validity of the design parameters is examined by listening to the output sounds of the field simulator. Some examples of the system's performance on rooms with simple shapes are shown, and the principle of evaluating subjective design parameters is indicated. [ABSTRACT FROM AUTHOR]

Scale model experiments were executed for two concert halls and two opera houses which recently opened in Tokyo. Based on the geometrical acoustic analysis by using CAD model, effective room shapes were studied so as to minimize the extra labor at the scale model test. Then, 1:10 scale models made of wood and proper acoustical materials were constructed. Up-to-date digital signal processing technique was applied in order to improve the accuracy of the experiment. Also, several new ideas concerning the sound source, receivers, scale modeled seatings, and how to calibrate the air absorption were introduced, intended for the precise prediction of the room acoustical parameters. Thus, monaural parameters RT, EDT, C80, D, G, and ST, and binaural parameter IACC were measured in the scale models, and they were compared with those measured in real halls. The accuracy and problems of this method were discussed with the acoustical data found here. [ABSTRACT FROM AUTHOR]

Interaural cross-correlation coefficient (IACC) and lateral efficiency (LF) as correlates with subjective ratings [see companion paper, L. Beranek, ''Determination of categories of acoustical quality in concert halls'' (this session)] were analyzed. To make IACC sensitive to quality ratings, a multi-octave-band average was developed, based on Blauert et al. [Acustica 59, 292] and on a subjectively derived set of equal ASW contours that showed the 0.5, 1.0, and 2.0 octave bands to be of equal importance. This IACC3 was divided into IACCE3 integrated over first 0.08 s after arrival of the direct sound, and IACCL,3 same, 0.08 to 1 s. Subjective judgments were also made to determine the effects of increased sound levels of symphonic music at frequencies above and below 355 Hz on apparent source width ASW. IACCE3 and GL both appear important for determining ASW. The measured quantity [1-IACCE3] alone was found to separate the 17 concert halls of this study for which IACC data were available into the same three category groups as those determined from the interviews. Lateral fraction (LF) was found to extend over a very small range and there were so many overlaps among halls when separation into three rating groups was attempted that LF was judged not to be suitable for rating acoustical quality. [ABSTRACT FROM AUTHOR]

The interaural cross-correlation coefficient (IACC) has been shown to be an important measure, along with others, of the quality of acoustics in concert halls and opera houses [Schroeder et al., 1199 (1974); Ando, Concert Hall Acoustics (Springer-Verlag, Berlin, 1985)]. When measured in auditoriums with binaural heads (real or dummy) using an impulse source, means must be adopted to achieve accuracy and precision, and to select the type of impulse and processing methods to make IACC most useful in the prediction of acoustical quality. Subjects covered include: (1) type of impulse, (2) convolution signal, (3) integration limits, (4) directivity and positions of source in the hall, (5) parameters of head, (6) comparisons of measurements made with real and dummy heads, (7) value of torso, (8) measuring positions in hall, (9) comparison of measurements of IACC in halls with upholstered and nonupholstered seats, (10) comparison with IACC measurements made by other laboratories, and (11) some preliminary data on differences among IACCs measured in occupied and unoccupied halls. [ABSTRACT FROM AUTHOR]

The influence of GL (amplifier gain the low-frequency range below 355 Hz) and IACC on ASW was determined by psychoacoustic experiments with simulated concert-hall sound fields using anechoic symphonic music presented to subjects by multiple loudspeakers. ''Equal ASW curves'' were determined for 1/1 octave band filtered source signals with mid-frequencies from 125 to 4000 Hz. The ASW's for the upper four bands are found to be equal for the same IACC and SPL band values, indicating equal importance of those bands in determining overall ASW's. Combinations of GL's and IACCE3's (average of IACC's in the 500, 1 and 2 kHz bands) for wide-band musical source signals were determined that produced the same ASW's. The early sound was comprised of 2 to 11 early ''reflections'' and judgments were made with and without later reverberation. It was found that both larger values of GL and smaller values of IACCE3 result in larger values of the subjectively determined ASW's. It is shown that GL and IACCE3 jointly are physical measures of spatial impression in a concert hall and that, combined, they cover the frequency range from low to high frequencies. [ABSTRACT FROM AUTHOR]

Masked-threshold-level (MTL) and just-notice-level differences (jnld) are two of the most basic and important attributes of early reflection in a room's sound field because they are deeply related with necessary accuracy of sound field simulation and with subjective efficiency of early reflection. MTL and jnld of reflection were measured using a music source signal. Various types of sound fields that were composed of multiple reflections were tested. MTL of a reflection rises when an additional reflection is added because of the increase of masking by the additional reflection. The rise of MTL is larger than the energy summation low, which is basically the same as the addition of simultaneous masking. The rise of MTL influences jnld of reflection. The jnld becomes larger as the reflection level becomes closer to its MTL, and is expressed as a function of LT, which is the reflection level relative to its MTL. [ABSTRACT FROM AUTHOR]