Takayuki Hidaka

Interaural cross‐correlation, lateral fraction, and low‐ and high‐frequency sound levels as measures of acoustical quality in concert halls

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.

Relations among interaural cross-correlation coefficient (IACCE), lateral fraction (LFE), and apparent source width (ASW) in concert halls

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, ASWs 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 IACCEs, LFEs, and also the strength factor Gs 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.

Objective and subjective evaluations of twenty-three opera houses in Europe, Japan, and the Americas

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), G(M), ITDG, [1 - IACC(E3)], 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.

Sound absorption in concert halls by seats, occupied and unoccupied, and by the hall’s interior surfaces

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.

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 C80s are predicted accurately from unoccupied values by the newly proposed equation; (3) Gs 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.

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.

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

The TOC Concert Hall, called ‘‘Takemitsu Memorial’’ in honor of the late composer Toru Takemitsu, was opened September 10, 1997. With a seating capacity of 1636 and a volume of 15 300 m3, the hall is sized to cover the musical range from recitals to orchestral concerts. The plan is rectangular in shape but, by request of the architect Takahiko Yanagisawa, the ceiling is a distorted pyramid, with its peak nearer the stage than the rear of the wall. This unique shape had to be analyzed using a CAD model and a 1:10 scale model so that all interior surfaces would be adjusted in shape and absorption to yield optimum values for RT, EDT, IACCE3, surface diffusion, initial time delay gap, and loudness [Beranek, Concert and Opera Halls (ASA, New York, 1996)]. To provide a better ensemble condition for the musicians on stage and to provide early reflections to several other regions, a square canopy, almost 10 m on a side, is suspended above the stage. The pyramidal ceiling has diffusing elements added to simulate c...

Mechanism of sound absorption by seated audience in halls

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 Kuhls method (K & K) [Acustica 15, 127-131 (1965)], and two that use average data from halls, i.e., Beraneks 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 (AA). 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 AA 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.

Mechanism of sound absorption by seated audiences in concert halls

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 OperaHalls , 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 predicti...

Relations between the apparent source width (ASW) of the sound field in a concert hall and its sound pressure level at low frequencies (GL), and its inter‐aural cross correlation coefficient (IACC)

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 phys...