Audience Area Research Articles

Acoustic measurement of Shakespeare’s Globe Theatre, London

In the late 1960’s, Sam Wanamaker initiated the reconstruction in London of the theatre built for William Shakespeare’s company of players in the late 16th century. The theatre was built in the traditional manner to be as faithful to the original as surviving documentation allows, and has a circular auditorium with an open roof. The theatre was opened for performances in the summer of 1997. An acoustic survey of the theatre has been carried out. Measurements have been made of reverberation time (RT), early decay time (EDT), clarity index (C50), definition (D50), and rapid speech transmission index (RASTI) within the theatre’s auditorium. Various source positions were chosen on the stage after consultation with voice coaches and actors at the theatre, and receiver positions were chosen to provide uniform coverage of all the major audience areas. The results of these measurements indicate that, despite the theatre’s open-air construction, the amount of early energy provided to most audience areas results in reasonable levels of speech intelligibility, although achieving an adequate speech sound level is more of a problem. This is clearly exacerbated by the theatre’s open-air design, and its position in central London under the main flight path to London’s Heathrow Airport. The reverberant characteristics of the auditorium are generally within acceptable limits for modern theatres.

CAAD—Computer aided architectural and acoustical design

The computer program ‘‘AUDIO’’ is intended to encourage architects to include (integrate) the room acoustics study in the architectural design from its very beginning, by using in both ways, interactively, the same computer descriptions (AUTOCAD environment) of the room. The main stages of the design are: first: – first architectural variants: – 2-D acoustical comparison, improvement of the room shape in plan, longitudinal, and transversal sections; second: – architectural 3-D model: – 3-D detailed shape analysis, proposed absorbtion characteristics of room bound- aries; third: – architectural details and specifications: – proposals for finishings and materials, taken from the database of the program. In both 2- and 3D stages the program is based on a very performant ray-tracing method. Entry: – room boundaries taken from the architectural model and internally processed (boundary area, volume), audience area, sources (characteristics and location), acoustical processing: – in almost real time, the complete history of impingements (collisions), that is almost statistical, – output: graphic representation of first 2–4 reflections, equal contours on the audience surface of up to ten chosen parameters, (reverberation time, sound level, clarity, spatial impression, lateral efficiency, time gravity point...), detailed impulse response, reverberation time, and the same ten parameters for any reception point.

New subjective and objective data on 20 opera houses of the world

Acoustical measurements have been made in opera houses of Europe, Japan, the United States, and Argentina using the same equipment: dodecahedron loudspeaker, stretched impulses, and monaural and binaural sensing devices. The measuring positions were 3 on-stage and 2 in-pit for sources, and 8 to 17 in audience areas for sensors. Quantities measured as a function of frequency were reverberation time RT, early decay time EDT, clarity C80, deutlichkeit D, time gravity Tg, early to reverberant energy ratio as a function of cutoff time C(t), strength G, interaural cross correlation IACC, IACCE, and IACCL, stage support ST1 and ST2, initial-time-delay gap ITDG, and reflectograms. International opera conductors were contacted by mail to rate 20 opera houses, with satisfactory responses. An attempt is made to correlate the objective data with the subjective ratings. Early results indicate that IACCE3 and ITDG are definite indicators. Others seem important in a certain type of opera house.

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.

Measurements of orchestra acoustics. How reflecting surfaces influence ‘‘Klangfarbe’’ and the possibility of playing in time

When investigating room acoustics, and also stage acoustics, most concern is often based on ‘‘how much energy arrives in the time interval between time x and,’’ and not on how these reflections are distributed within that time interval and how that affects the Klangfarbe and rhythmic conditions. The stage acoustics of the Oslo Concert Hall was measured (MLS) with and without the orchestra on the stage, and with different settings of reflecting surfaces to achieve a better ‘‘ensemble’’ feeling (TOR measurements: Through Orchestra Response). Reflecting surfaces above, behind, and to the side of the orchestra were examined, with a questionnaire for each musician and a number of tonemeisters in the audience area. Similar measurements of the stage acoustics were done also in several European halls on the tour of the Oslo Philharmonic Orchestra/ Mariss Jansons including Gasteig/Munich and Musikverein/Vienna. For further analysis of the ability of playing in time, measurements were done in the Hall for the Norwegian Radio Orchestra, with analysis of both orchestra tutti and multichannel recording situations. The paper analyzes the aspects of playing together in an orchestra, and especially how different placements of reflecting and diffusing elements affect the Klangfarbe and rhythmic conditions, both for the orchestra and the audience.

Acoustical design and the characteristics of Sapporo Concert Hall

Sapporo Concert Hall, with 2008 seats in the large hall and 453 seats in the small hall, was opened on July 4, 1997. Both halls were designed for classical music, the large one mainly for orchestral music and the small one for chamber music and recitals. The large hall was designed with the concept of the surrounded stage and ‘‘vineyard steps’’ seating arrangement like Philharmonic Hall in Berlin and Suntory Hall in Tokyo. The emphasized points in acoustical design were as follows: (1) Effective use of the ‘‘vineyard steps’’ walls which were introduced into the audience area to provide the effective early reflections; (2) installation of the big sound reflectors suspended above the stage area to provide the effective early reflections to musicians and audience around the stage; (3) introduction of heavy material, 150-millimeters-thick concrete, into the main ceiling to get enough response in the low frequencies. The small hall was designed as a typical shoebox hall with narrow width and high ceiling. Acoustically tunable curtains were introduced to make the wide range of acoustical possibilities. The results of the acoustical design and its characteristics will be reported.

Acoustical design of Sumida Triphony Hall

The Sumida Triphony Hall was opened near Kinshityo JR station, located in the eastern part of Tokyo, in October 1997. The building contains two concert halls, the Main Hall, with 1801 seats, as the home of the New Japan Philharmonic, and the Recital Hall, with 252 seats. The Main Hall has a rectangular shape with the sloped ceiling rising at 12.5 degrees toward the back of the hall in parallel to the main floor and with two balconies around the main audience area. The reflecting panels were hung over the stage to help the ensemble for players. The shape was basically checked with the technique of computer simulation and the detail of the ceiling and the wall was studied by use of a 1/10th-scale model. An organ with 66 stops was installed at the front of the hall. The Recital Hall is a typical ‘‘shoebox’’ hall. In order to attenuate the vibration caused by railroad tracks, the vibration isolating barriers were embedded around a part of the outer walls of the building, and also the vibration insulating structure was adopted at the Main Hall partly and the Recital Hall entirely. The outline of acoustical design will be reported.

Early sound distribution in auditorium

It is known that the strength of the audience area of a hall is largely dependent on the early sound, i.e., the direct sound and the first reflections. They are varied not only with reverberation time, but also with the geometry of the room, the absorption arrangement of the room, and the location of the source and(or) the receiver. Results from digital simulation and field measurements in halls show that the attenuation rate of early sound with the distance between the source and the receiver is much larger than ordinary predictions. It is more rational in complying with the subjective judgment. Therefore it should not be ignored in the acoustical design of a hall.

Subjective experiment on the effect of hall response on a violin player in a simulated sound field

In order to investigate the effect of hall response on players, a subjective test was performed in an artificially simulated sound field in an anechoic room. By referring to the data obtained in actual concert halls, the sound field was modeled and synthesized by using 14-channel reproduction systems: 12 channels for the ambient reverberation using simple digital reverberators, and two channels for late reflections from the rear part of the audience area using real time convolvers. In the test, the reverberation was fixed and the level and delay time of the late reflections were changed in three steps, respectively. Under each condition, the subject, a professional violinist, imagining that he/she was playing on a stage, played various pieces in a variety of playing styles and responded to questionnaires. As a result, it has been found that favorable stage conditions for a player differ as to the style of playing; solo, with piano, with orchestra, and in a quartet, and that the late reflection from the audience area is, to some extent, necessary in order to get ‘‘hall reaction.’’

Measured effects of orchestra shells

The effects of adding orchestra shells or modifying orchestra shells were measured in six different concert halls varying in volume from 3000 to 32 000 m3. Early, late, and total sound levels were seen to increase with the addition of an orchestra shell. Effective orchestra shells were found to increase total sound levels by up to 2 dB at mid‐frequencies in audience areas of halls. Average changes to measured clarity could be larger. The measured increases in sound levels varied with location in the halls, and in several cases sound level increases were greatest towards the rear of halls. In one case, adding an orchestra shell was found to decrease low‐frequency levels due to a shift of the seat dip attenuation. On‐stage, larger effects were measured. Support values increased by as much as 5 dB with the addition of an orchestra shell. Partial changes to shells generally produced much smaller effects. In audience seating areas the effects of partial changes and adjustments to orchestra shells were usually less than estimated just noticeable differences in the measured quantities.

Lateral low‐frequency components of reflected sound from a canopy complex comprising triangular plates in concert halls

Applying the diffraction integral of Rubinowicz, the transfer functions (TFs) for reflection by canopy panels of various shapes were calculated. Numerical calculation of TF shows that the optimum interior angle of an isosceles triangle giving a flat response lies between 90° to 120°. And, the use of a number of canopy panels above both sides of a concert hall helps to control lateral low‐frequency components for the audience area, and produces a small value of interaural cross correlation (IACC). It is interesting to observe that the interior angle of the triangular panels composing the canopy in the Tanglewood Music Shed falls in the optimum range. The TFs of large triangular panels suspended in front of the top of the proscenium arch in Fujita Hall, a concert hall designed by us, indicate the existence of relatively strong low‐frequency components of reflection from lateral directions to a listener at the front section of the hall. Further, higher frequency components of the reflections tend to arrive near to the median plane of each listener.

FUJITA HALL 2000 with adjustable IACC and reverberation time.

FUJITA HALL 2000 is a multipurpose auditorium seating 2001 persons with a shape similar to that of the Symphony Hall in Boston. Reverberation time (RT) can be adjusted from 1.4–2 s. This hall has lattice-structured double walls and ceiling, each of which amounts to about half of the total area of the wall and ceiling, respectively. The other half of them consists of highly diffusing surfaces. For a drama setting of the hall, RT is shortened by drawing absorbent curtains behind the lattice walls and adding a number of absorbent material boxes on the lattice ceiling. These sound absorbers are removed for a concert setting. This hall has a canopy comprised of triangular panels as in Tanglewood Music Shed. It consists of stage and audience canopies that are suspended over the stage and in front of the top of proscenium arch, respectively. The stage canopy provides balance between orchestra and soloist, confluence, and clarity of music inside the hall. The audience canopy [T. Nakajima, Y. Ando, and K. Fujita, J. Acoust. Soc. Am. Suppl. 1 88, S185 (1990)] provides not only SPL uniformity but also strong lateral low-frequency components in the audience area. The setting of such canopies also changes the IACC of the hall.

Concert Hall Acoustics—1991

Acoustical design of concert halls began with Wallace C. Sabine who developed the reverberation equation and advised on Boston Symphony Hall (1900). Little additional information was learned in the next half‐century. The use of reflecting panels in large spaces was introduced in halls with acoustically adverse shapes between 1953 and 1959. Next followed an understanding of sound absorption by audiences in different densities of seating, the initial‐time‐delay gap, and the value of lateral reflections. The London Royal Festival Hall and New York Philharmonic Hall confirmed the importance of those findings and revealed additional design requirements for reflective panels and sound diffusion. Extensive subjective studies, both in actual halls and in laboratories with electronically produced acoustical environments, were performed in Göttingen and Berlin (Germany), England, Denmark, Japan, and Canada. Those studies, when combined, revealed five orthogonal subjective attributes of concert hall quality: reverberance, loudness, envelopment, intimacy, and bass balance. These, in turn, are related to the objective quantities: initial and subsequent reverberation times (RT); cubic volume and audience area; lateral reflections and diffusion; initial‐time‐delay gap and subsequent reflections in the first 50 ms after arrival of the direct sound; and the slope of the initial RT versus frequency curve between 125 and 2000 Hz. An additional important subjective attribute is related to the physically measured ratio of the reflected energy in the sound field during the first 50 ms and that after 50 ms. Concert halls built since 1975, principally in Europe, United States, and Japan, constitute a “laboratory” for confirmation of those subjective attributes and related objective parameters.

Computer simulation technique regarding distribution of early reflections for room acoustical design

The computer simulation technique is used to study the fundamental room shape of auditoriums, especially of concert halls, during the conceptual and schematic design phases in our acoustical design. The hardware of the computer simulation system consists of HP 9816 (CPU:68000, Memory: 1.25MB) and some output devices. The simulation software is based on the ray-tracing algorithm. In our computer simulation study of the room shape, the density, and the distribution of the early reflections on the audience area are observed. The omnidirectional and upper directional sound sources are assumed, and the early reflections after the arrival of the direct sound are calculated in following three time intervals, such as 0–30, 30–60, and 60–90 ms, respectively. This method has the advantage of easy modification of the room shape and visual explanation of the sound behavior in an auditorium. Then it becomes a very useful tool of our acoustical design, particularly during early design phases. On the other hand, it has the disadvantage of difficulty of treating curved surfaces.

Evaluation of Japanese speech intelligibility for the sound system of an auditorium by STI

Subjective hearing tests and STI measurements were carried out in a church and in six auditoriums. The relationship between the intelligibility and the directivity of the loudspeakers was studied for Japanese speech. In the church, the experiment was performed with four types of loudspeakers having different radiation directivity. At the point of 4*Dc (Dc is the critical distance) from the loudspeaker, STI was about 50%, and the intelligibility was found to be “fair.” STI measurements were successively carried out in six auditoriums with clustered loudspeaker systems designed to cover the audience area within 4* Dc. The results showed almost the same relationship between the STI and the ALcons given by T. Houtgast even for Japanese speech. Finally, the validity limits of STI as parameter for evaluating the performance of sound systems in auditoriums is discussed.

An investigation of the sound field above the audience in large lecture halls with a scale model.

Measurements of steady-state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was measured on a 1:10 scale model and was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats in the model was calculated by subtracting the direct field from the measured total field and was found to be dependent on the magnitude and particularly on the placement of absorption. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate depends strongly on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. These consequences are discussed with respect to prediction of speech intelligibility.

An investigation of sound pressure level predictions in large lecture halls

Measurements of steady‐state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was studied on a 1:10 scale model of a large lecture hall using the removable audience from the scale model. It was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats was studied by subtracting the direct field from the measured field in the model. It was found to be dependent on the magnitude and particularly on the placement of absorption in the room. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate strongly depends on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. The consequences are discussed with respect to prediction of speech intelligibility, and modifications are suggested for three current speech intelligibility prediction schemes.

A method to improve the listening conditions in audience areas shielded from the main volume of the hall

The listening conditions for audience located under deep balconies in halls can be improved through application of electronic systems providing a uniform distribution of the reverberant sound field. Such systems include microphones for pickup of reverberant sound in the main volume of the hall, electronic delays, and loudspeakers distributed above the audience area. Subjective listening tests during adjustments of actual installations indicate that the level of reverberant sound radiated from the loudspeakers must be approximately equal to the level of the reverberant sound from natural sources, at the same listening positions, for the systems to be acceptable and effective. Similar smaller scale systems are helpful to improve the listening conditions in sound control rooms with inadequate connections to the main volume of the hall.

A statistical analysis of audience sound absorption

The absorption produced by the audience in concert halls is considered a random variable. Beranek's proposal [L. L. Beranek, Music, Acoustics and Architecture (Wiley, New York, 1962), p. 543] that audience absorption is proportional to the area they occupy and not to their number is subjected to a statistical hypothesis test. A two variable linear regression model of the absorption with audience area and residual area as regressor variables is postulated for concert halls without added absorptive materials. Since Beranek's contention amounts to the statement that audience absorption is independent of the seating density, the test of the hypothesis lies in categorizing halls by seating density and examining for significant differences among slopes of regression planes of the different categories. Such a test shows that Beranek's hypothesis can be accepted. It is also shown that the audience area is a better predictor of the absorption than the audience number. The absorption coefficients and their 95% confidence limits are given for the audience and residual areas. A critique of the regression model is presented.

Acoustical design of the multi-purpose ‘Hjertnes’ hall in Sandefjord

‘Hjertnes’ is a typical multi-purpose hall primarily intended for concerts. A three-dimensional ray tracing computer program was used to provide a picture of the sound energy distribution on the audience area of the hall, various room shapes being investigated. This resulted in tilted side walls and a convex ceiling. Variable acoustics have been obtained through the use of movable ceiling absorbing and diffusing elements. In addition, a demountable orchestra enclosure has been constructed within the stagehouse. Control measurements of pulse response and reverberation time are reported.