Objective evaluation of chamber-music halls in Europe and Japan

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, IACC(E), the where binaural quality index BQI equals [1-IACC(E3)]; 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.     

Computer model investigations on the balance between stage and pit sources in opera houses

The acoustical balance between the singer on the stage and the orchestra in the pit is typically found inside an opera house. The competition of the two sources is crucial, since in an opera the singer and the orchestra are performing at the same time. This topic of balance is receiving increasing attention in recent years, but several aspects are still to be clarified. The aim of this work is twofold: firstly the procedure for the acoustical qualification of the balance between the singer and the orchestra is investigated and secondly the means of controlling the balance at the design stage or during renovations is considered. For both tasks the study was conducted in a group of opera houses modelled within an acoustical CAD program. As regards the qualification of the balance this investigation compares the directional characteristics of two loudspeakers and of a dodecahedron omnidirectional loudspeaker in the emulation of a soprano during simulated room acoustics measurements. It is shown that, in order to emulate a soprano singer, the directional characteristics of the source on the stage are quite important. The control of balance was also studied and the work reserves a special emphasis to the case of historical opera houses. In fact, when such theatres are refurbished, the range of possible architectural interventions is often limited to the orchestra pit only, due to the heritage nature of the hall which prevents from any substantial change in the area of the forestage. For this reason it is important to investigate the effectiveness of such limited interventions in the pit, and this is done here by a detailed study of the effects on balance of some major changes of the orchestra pit only.     

Acoustical design of the Tokyo Opera City (TOC) concert hall, Japan

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.     

Relation of acoustical parameters with and without audiences in concert halls and a simple method for simulating the occupied state

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.     

A scale value for the balance inside a historical opera house

In the framework of opera house acoustics, the term "balance" refers to the acoustical competition between the singer on the stage and the orchestra in the pit. The mechanism allowing the operatic singers to be heard over the orchestra has to do with their skill in enhancing the vocal emission by a peculiar use of the formant frequencies. This vital factor is sensed by the listeners and, apart from the obvious sound power ratio of the stage and the pit sources, is the main cue that helps to formulate a subjective impression of the balance. To achieve its objective qualification, two calibrated sound sources can be placed on the stage and in the pit, respectively, and their sound level difference is measured at the listeners' seats. The scope of this work is to investigate the relationship between the subjective impression and the objective indicator of the balance and to develop a scale value for the parameter in the case of a historical opera house. For this scope a set of acoustical data from the Teatro Comunale in Ferrara will be used to create synthetic sound fields with controlled conditions of the balance between the stage and the pit. This methodology employs an anechoic piece for soprano (with piano accompaniment) and is implemented in a dead room equipped with an acoustical rendering system. The sound fields are used to investigate the appropriate balance values by means of listening tests. The results of the scaling exercise show that a suitable range of values can be extracted and that the sound from the stage and the pit is perceived as balanced when the loudness difference between the two is comprised within -2.0 dBA and +2.3 dBA.     

SUBJECTIVE PREFERENCE FOR SOUND SOURCES LOCATED ON THE STAGE AND IN THE ORCHESTRA PIT OF AN OPERA HOUSE

The present study investigates whether the subjective preference theory can be applied to the sound field in an opera house. Paired-comparison tests were conducted to obtain scale values of subjective preference. As the source locations of the music on the stage and in the orchestra pit were moved, listeners were asked to give their acoustical preference. The acoustical factors at each listening position were obtained from the interaural cross-correlation function and binaural impulse responses measured at each listening position. The relationship between the scale values of subjective preference and orthogonal acoustical factors (LL, IACC, τ_IACC, Δt₁ for the pit source, Δt₁ for the stage, T_sub for the pit source, and T_sub for the stage source) was determined by using factor analysis, which shows that the preference theory is applicable. Total scores obtained from factor analysis and measured scale values are in good agreement.     

座位数在音乐厅和歌剧院计算中的作用

在对Leo Beranek著《音乐厅和歌剧院》一书中所提供的80余所音乐厅和歌剧院声学参数的测定结果数据分析的基础上,经过简单的数学处理和简化,提出一些个人见解:强度因子G和座位数N的关系;对于N小于和等于2000的音乐厅,空场早期衰变时间EDT等于空场混响时间。文中给出在N＜ 2000的情形下空场EDT的计算。座椅数是决定厅堂容积的出发点,由此做出两个厅堂的初步设计实例。      

ON THE TESTING OF RENOVATIONS INSIDE HISTORICAL OPERA HOUSES

Due to the large number of historical opera houses in Italy, many theatres have been renovated in the past, but still more will undergo major restoration in the near future. Unfortunately in this context, the quality and protection of acoustics is rarely considered as an issue of its own. As a consequence, the renovations are hardly ever accompanied by proper scientific and technical support. In this paper, the acoustical impact of works inside the Teatro Municipale “R.Valli” in Reggio Emilia, including the restoration of the main hall and the construction of a new acoustic shell, will be dealt with. Surveys were held in the theatre before renovation and were repeated with identical procedure and instruments after its completion. By means of a comparative analysis of the architectural project and of acoustical data, the impact of major changes in the theatre can be predicted. It is shown that this approach can help in drafting an operational scheme for safeguarding the acoustics of historical opera houses.     

Acoustical remodeling of a large fan-type auditorium to enhance sound strength and spatial responsiveness for symphonic music

The Grand Theater in the Sejong Performing Arts Center in Seoul, Korea is a proscenium hall with 3022 seats. Originally built in 1978, the Grand Theater was remodeled in 2004 to provide variable reverberation time (RT) using a sound system. Recently, a second remodeling was scheduled to enhance the hall’s acoustic quality, especially its RT, sound strength (G) and binaural quality index (BQI = 1-IACCE3), based on architectural acoustic analysis. In the remodeling plan, the wall covering and chair materials were changed to produce longer RT and higher G. For the remodeling design, side balconies were added to the first and third floors to provide lateral reflections to the audience area. The orchestra shell and various ceiling/wall reflectors were planned to provide more early reflections to the audience area. To verify the design, the effects of these structures on the sound pressure levels and spatial parameters of early sound in the audience area were investigated by open-type 1:10 scale model measurement. In addition, the acoustical qualities of the remodeled hall were evaluated using computer simulations and 1:50 scale model measurement. The results show that G was improved by 5 dB and BQI by 0.24, whereas the occupied RT at mid-frequencies became variable from 1.47 to 2.24 s.     

Speech transmission performance and the effect of acoustical remedies in a dome

For the purpose of improving speech transmission performance in a dome space, the acoustical properties in a dome having a diameter of 20 m were examined. The acoustical properties measured evenly on the floor of the dome were evaluated both objectively and subjectively and the interrelationship of the objective measures and subjective measures were also examined. Then, on the basis of the results of the study, simplified acoustical remedies were applied to the dome to improve speech intelligibility and the effect of the remedies was also examined. The following findings were obtained from this investigation.(1) The speech transmission performance in the dome space without treatment by absorptive materials varies greatly with the locations of sound sources and observation points: a range of 0.17-0.59 for RASTI value and a range of 30-97% for speech intelligibility test results. (2) There are peculiar observation points at which speech transmission quality is very high due to a considerable sum of the energy arriving in the first 0.06 s after the arrival of the direct sound. (3) Of all the measured acoustical parameters, RASTI, EDT in 1 kHz band, early-to-late arriving sound energy ratio, and Ts corresponded well to the speech intelligibility test scores. (4) Rubber tiles, cotton canvas 12 m in length, and glass wool board, are effective in improving speech intelligibility remarkably due to increased sound absorption and the diffusion effect.     

Orthogonal acoustical factors of a sound field in a bamboo forest.

To investigate the acoustical quality of a sound field in a bamboo forest, acoustical measurements were conducted to obtain orthogonal acoustical factors of the sound field. These results are compared with previous results for a sound field in an ordinary forest [H. Sakai, S. Sato, and Y. Ando, J. Acoust. Soc. Am. 104, 1491-1497 (1998)]. The IACC, which is defined as a maximum value of the normalized interaural cross-correlation function between signals at the ears, was 0.07 (4 kHz) and 0.16 (2 kHz) at positions 20 and 40 m from the source, respectively. These values are much better than those in the previously investigated forest. The measured subsequent reverberation time Tsub was up to 1.5 s in the frequency range above 1 kHz at the position 40 m from the source. For certain music sources with higher frequency components, therefore, sound fields in a bamboo forest have excellent acoustic properties.     

Characteristics of train noise in above-ground and underground stations with side and island platforms

Railway stations can be principally classified by their locations, i.e., above-ground or underground stations, and by their platform styles, i.e., side or island platforms. However, the effect of the architectural elements on the train noise in stations is not well understood. The aim of the present study is to determine the different acoustical characteristics of the train noise for each station style. The train noise was evaluated by (1) the A-weighted equivalent continuous sound pressure level (L_Aeq), (2) the amplitude of the maximum peak of the interaural cross-correlation function (IACC), (3) the delay time (τ₁) and amplitude (?₁) of the first maximum peak of the autocorrelation function. The IACC, τ₁ and ?₁ are related to the subjective diffuseness, pitch and pitch strength, respectively. Regarding the locations, the L_Aeq in the underground stations was 6.4 dB higher than that in the above-ground stations, and the pitch in the underground stations was higher and stronger. Regarding the platform styles, the L_Aeq on the side platforms was 3.3 dB higher than on the island platforms of the above-ground stations. For the underground stations, the L_Aeq on the island platforms was 3.3 dB higher than that on the side platforms when a train entered the station. The IACC on the island platforms of the above-ground stations was higher than that in the other stations.     

Nonlinear response in evaluating the subjective diffuseness of sound fields

Tests were conducted to determine which horizontal reflection angles are most effective in stimulating subjective diffuseness for a listener in a room. Paired comparison tests were carried out where subjects were asked to judge in which of two sound fields they perceived more diffuseness. Results show that the most effective horizontal angle depends on the frequency of the one-third-octave-band noise, as is indicated by the interaural cross correlation. The remarkable finding in this investigation is that the scale value of subjective diffuseness may be formulated in terms of the 3/2 power of the magnitude of interaural cross correlation (IACC) and that the scale value does not vary with the frequency of the bandpass noise source.     

The effect of visual and auditory cues on seat preference in an opera theater

Opera performance conveys both visual and auditory information to an audience, and so opera theaters should be evaluated in both domains. This study investigates the effect of static visual and auditory cues on seat preference in an opera theater. Acoustical parameters were measured and visibility was analyzed for nine seats. Subjective assessments for visual-only, auditory-only, and auditory-visual preferences for these seat positions were made through paired-comparison tests. In the cases of visual-only and auditory-only subjective evaluations, preference judgment tests on a rating scale were also employed. Visual stimuli were based on still photographs, and auditory stimuli were based on binaural impulse responses convolved with a solo tenor recording. For the visual-only experiment, preference is predicted well by measurements taken related to the angle of seats from the theater midline at the center of the stage, the size of the photographed stage view, the visual obstruction, and the distance from the stage. Sound pressure level was the dominant predictor of auditory preference in the auditory-only experiment. In the cross-modal experiments, both auditory and visual preferences were shown to contribute to overall impression, but auditory cues were more influential than the static visual cues. The results show that both a positive visual-only or a positive auditory-only evaluations positively contribute to the assessments of seat quality.     

Analysis of Sabine and Eyring equations and their application to concert hall audience and chair absorption

Historically, two equations have been used for predicting reverberation times, Sabine and Eyring. A precise means is presented for determining Eyring absorption coefficients alpha(eyring) when the Sabine coefficients alpha(sabine) are known, and vice versa. Thus, either formula can be used provided the absorption coefficients for the Sabine formula are allowed to exceed 1.0. The Sabine formula is not an approximation to the Eyring equation and is not a shortcoming. Given low reverberation times, the ratio of alpha(sabine) to alpha(eyring) may become greater than 2.0. It is vital that, for correct prediction of reverberation times, the absorption coefficients used in either formula must have been determined in spaces similar in size and shape, with similar locations of high absorption (audience) areas, and with similar reverberation times. For concert halls, it is found that, when the audience area (fully occupied) and midfrequency reverberation time are postulated, the hall volume is directly proportional to the audience absorption coefficient. Approximately 6% greater room volumes are needed when choosing nonrectangular versus classical-rectangular shaped halls and approximately 10% greater volumes when choosing heavily upholstered versus medium upholstered chairs. Determinations of audience sound absorption coefficients are presented, based on published acoustical and architectural data for 20 halls.     

Subjective and objective assessment of acoustical and overall environmental quality in secondary school classrooms

A subjective survey on perceived environmental quality has been carried out on 51 secondary-school classrooms, some of which have been acoustically renovated, and acoustical measurements were carried out in eight of the 51 classrooms, these eight being representative of the different types of classrooms that are the subject of the survey. A questionnaire, which included items on overall quality and its single aspects such as acoustical, thermal, indoor air and visual quality, has been administered to 1006 students. The students perceived that acoustical and visual quality had the most influence on their school performance and, with the same dissatisfaction for acoustical, thermal and indoor air quality, they attributed more relevance, in the overall quality judgment, to the acoustical condition. Acoustical quality was correlated to speech comprehension, which was correlated to the speech transmission index, even though the index does not reflect all the aspects by which speech comprehension can be influenced. Acoustical satisfaction was lower in nonrenovated classrooms, and one of the most important consequences of poor acoustics was a decrease in concentration. The stronger correlation between average noise disturbance scores and L(A max) levels, more than L(Aeq) and L(A90), showed that students were more disturbed by intermittent than constant noise.     

Optimizating the seats surrounding the platform in a recital hall when considering source directivity

The influence of source directivity can be significant for solo and chamber music performances, particularly for arena type halls that have improved visual intimacy for the audience. Computer simulation was performed to analyze the possibility of optimizing the acoustical qualities of a 4000-m³ recital hall with a significant portion of seats surrounding the platform when considering source directivity. The effects of surface treatments, length-to-width proportion, seating arrangement and platform location were evaluated. Most acoustical parameters derived from a baritone singer source were categorized as one factor that can be best represented by 2-kHz band early sound strength G_E. Regardless of room proportion, front-back 2-kHz band energy difference derived from optimized models can be controlled within 4 dB, a value much smaller than the difference in direct component.     

音乐厅音质设计进展述评

本文对近年来音乐厅音质设计中若干问题的进展作一述评。（1）在已建立的众多独立音质参量基础上，如何作出大厅综合评价，就需要考虑到它们的互动性和贡献权，方法学将成为关键。（2）空间感已确认由声源视在展宽度ASW和听者环绕感LEV组成，对于影响两者的诸多复杂因素有了较深入研究，这声场中的细节又将如何与大厅设计相联系亦备受关注。（3）听众及座椅吸声这个老问题有了新的研究成果，对于空、满场的声学关系已积累了更多资料，使大厅音质的估算更为精确可靠。（4）常说扩散对大厅音质很重要，但其主观效应仍然处于玄虚状态，一些新的主观试听实验结果还不足以说明问题。