Title means "Quietness", "Comfortable Sound" and "Excellent Acoustics"

Nagata Acoustics News 00-05 (No.149)
Issued : May 25, 2000

Big Heart Izumo Hall

By Akira Ono

Big Heart Izumo
Recently, when the conversation in Japan turns to new architectural achievements and successes, many of the buildings that are most discussed have addresses in the mountainous San-in region of the country, located in central Japan to the west of Kyoto. In our March 2000 News, we featured the new Taisha Bunka Place, located in Izumo's neighbor town, Taisha-cho, and there is a new Shimane Prefecture Museum of Art, as well as the new Chubu Teiju Center designed by the firm of Cesar Pelli. (This last project will be completed in March 2001.) In addition to the merits of these buildings, their location in the central part of Japan helps put them in the spotlight because they are easily accessible to the judges of architectural awards and others involved in architectural and building professions. Big Heart Izumo, the subject of this article, is yet another new San-in region structure currently receiving acclaim and attention in Japan.

Big Heart Izumo opened in December 1999 at the JR Izumo Train Station's west entrance, in Izumo, Shimane Prefecture. The building has already been featured in a number of architectural magazines and both the building's functional content and its architectural design have been the subject of detailed analyses and evaluations. Here, I wish to introduce the project from my perspective as the acoustician in charge of Big Heart Izumo's acoustical design.

<< A Novel, Integrated Approach to Foyer and Hall Design >>

Usually, concert hall visitors find three spaces as they arrive at their destination: first a lobby, then a foyer and then the concert hall. But Big Heart Izumo's architect, Kazuhiro Kojima, of the firm of Coelacanth and Associates, designed a space intended to break down the border between foyer and hall.

If we stop and think about it, there is no necessity for a concert hall to be visually separated from its foyer. At the completed Big Heart Izumo, visitors to the facility find that the foyer is located at the rear of the hall's side balcony. The stage is visible to guests in the foyer and sound from the hall carries over into the foyer. This brings the atmosphere of the hall's performance into the foyer and gives the foyer added appeal.

However, from an acoustical perspective, the balcony's rear wall plays an important role in delivering sound reflections to the hall's audience, so it would not be okay to totally eliminate the wall between the foyer and the hall. Our acoustical design documents for Big Heart Izumo provided for the implementation of a reflective curtain, such as is used in opera houses, between the foyer and the hall, but the facility's architect was not happy with this solution. He continued to withhold approval even as the installation of the hall's interior was being completed. Finally, I met with Mr. Kojima at the construction site so that we could come to an agreement this portion of the hall. As we stood just a few feet from the rear of the balcony and foyer, with our subject matter in plain view, I obtained his accommodation to erect a reflective surface made of glass that would only be deployed where its presence contributes significantly to the sound reflection needs of the hall.

<< Balancing an Architectural Design and Acoustical Requirements >>

In Japan, some critics of recent hall construction decry the growth of many similar-looking halls throughout the country. They apparently blame the architectural similarity of these halls on restraints imposed by acoustical considerations and take the extreme position that "not every town and city needs a hall with fine acoustics." But this kind of thinking only exists in the minds of some planners and other decision makers and commentators who may well be out of touch with the true wishes of a community.

For the residents of the communities where a hall is built, the functionality of the hall is of major importance, irrespective of whether the hall is visually and architecturally noteworthy or not. Every project deserves the best effort that I can put forth to give the hall excellent acoustics, within the many and diverse constraints and conditions that may exist. I believe that this should be an objective of all of the designers who contribute to the construction of a hall.

In the Big Heart Izumo project, I had several opportunities to hear first hand the desires of the people of Izumo, because workshops were held for this very purpose. The workshops were open to the public, and we were able to explain to the community all of the significant aspects of the dramatically different combined foyer-and-hall architectural design. Through the workshop process, we achieved the community's understanding of what would be possible acoustically given the selected architectural design. We were also educated, as many members of the community expressed their ardent desire for a hall with excellent acoustics. We knew that this is a region with very musically active communities; nevertheless, the desire and expectation of excellent acoustics were stronger than we anticipated. In the case of Big Heart Izumo, not only did architect Kojima's unique vision come to fruition, but the project also strove to satisfy the will of the community for high acoustical standards. As a result, to a certain degree, we achieved this latter goal as well.

<< Deployable Stage Reflection Panels with Additional Seating >>

Stage reflection panels
The stages of most multipurpose halls have stage reflection panels that are deployed on stage or kept housed depending on the acoustic requirements of each performance. Typically, these panels are stored behind or above the stage area. At Big Heart Izumo, the wings store scaffold-like, vertically raised additional seating that can be deployed to the central area of the stage. When this on-stage seating is deployed, the audience seating surrounds the performance area. In addition, because the hall also has overhead reflection panels that hang from the ceiling, when the on-stage seating is deployed the hall's configuration becomes virtually a rectangular space.

When the on-stage seating is deployed, this seating area connects without additional apparatus to the same level of the hall's fixed balcony, enabling hall attendees to walk between these two seating areas with ease. The space between the deployed on-stage seating and the fixed balcony is nearly seamless, having been precisely adjusted to within centimeters. This configuration provides hall audiences a delightful sense of oneness and connection to the performers on stage. This configuration can also be implemented to stage performances of works such as Luigi Nono's "Prometeo," for which the composer specified that some of the performers be situated in several locations on a balcony surrounding the main audience area.

<< Strategies to Attenuate Railroad Noise and Vibration >>

* Noise Attenuation
Big Heart Izumo's stage-side exterior wall is only 10 m (33 ft) from the tracks of the JR Railroad. Prior to construction, we calculated that if the building's walls were to be constructed of glass, the noise level inside of the hall would exceed NC-30.

In order to attenuate noise penetration through the hall's exterior glass walls, we suggested to the architect that the railroad-side of the stage's fly tower be constructed of a double layer of reinforced concrete. This double layer of reinforced concrete would provide the attenuating affects of a thick anti-noise wall. Accordingly, the architect designed the large, black-colored fly tower to extend out horizontally and overhang the glass exterior walls of the building's foyer and hall.

* Vibration Attenuation
Regarding vibration from passing trains, we measured the project site prior to construction and, from the peak vibration level of the ground (experienced when trains were moving directly past the site), we calculated that this would translate to a vibration level of approximately NC-25~30 on the stage of the proposed hall. In this kind of environment, our usual strategy is either: (1) to embed attenuating material in the structural foundation of the building where it is in direct contact with the ground; or, (2) to use a floating foundation for the hall. However, both of these options entail large additional construction costs.

When the client weighed the low frequency of passing trains and the project's total available construction budget against the additional costs required to attenuate the possible vibration, the client decided not to implement any construction-based, anti-vibration remedies. After the completion of the facility's construction, we measured vibration in the hall. Under peak conditions of a train passing directly past the hall, vibration registered at most NC-27. This vibration came almost entirely from vibration from the ground below the building. Vibration from the double-layer glass walls of the building was negligible.

<< A Small Design Element that Makes a Big Difference >>

Throughout Big Heart Izumo, the repeated use of a small, yet exceptionally well-wrought design element adds pleasure to the eyes of all who visit the building. The hall asked one of Japan's premier industrial and graphics designers, Mr. Hiromura, to design the signage used throughout Big Heart Izumo. Mr. Hiromura is famous in Japan for developing a brand of clothing and housewares-related merchandise named Mujirushi-ryohin (literally "non-branded good merchandise." It is well known that Japanese consumers are attracted by designer-name brands. Mr. Hiromura's lack of a designer name on his "no-brand" brand, which used the natural colors of fabrics and other simple styling elements, developed a strong following and became a fashion statement of its own.) Mr. Hiromura is also the graphic designer for the Kioi Hall Kioi Symphonietta's concert advertising materials.

At Big Heart Izumo, signs for "reception area" and "loading entrance," as well as for the restrooms appear on the doors to these areas using a distinctive logo design created by Mr. Hiromura. Instead of the usual acrylic or metal signage on which room and area designations are printed using a screen printing process, the unique calligraphic designs are painted directly on the glass and other portions of the respective doors.

The direct application of Mr. Hiromura's designs to doors and glass may have been a cost-saving measure. But the liberal use of Mr. Hiromura's design work for the hall goes a long way to adding an artistic and distinctive touch in parts of the facility that would otherwise be purely functional, unadorned space. For example, the corridors on the second floor of the building are very plain and have a decidedly backstage look to them, except for Mr. Hiromura's distinctive signage. The signage makes this area of the building less stark and more friendly, which will make local performing groups and other members of the community more at ease when they use the hall. The signage truly matches Big Heart Izumo's overall architectural style and design. It is an excellent and cost effective way to make this hall a little bit more special for all who come here.

For more information on Big Heart Izumo, please call the hall directly at +81-853-20-2888.

Acoustical Design of Round Halls:
Tackling the Problem of Sound Focusing

by Keiji Oguchi

Circular and elliptical hall configurations are hall shapes that textbooks on room acoustics design warn us to avoid at all cost because they are likely to be troubled by occurrences of sound focusing. The prohibition extends not only to rooms that are circular or elliptical in their horizontal dimension, but to rooms with dome or vaulted ceilings as well.

Despite the prohibition, I know of a number of examples of such halls and Nagata Acoustics has recently worked on the acoustical design of halls that presented this very challenge. In this article, I will discuss some of these examples and methods for mitigating the sound focusing phenomenon.

<< Examples of Sound Focusing >>

At the center in a round room (that is, a room that is either circular in its horizontal dimension only, or spherical), delayed burst reflections is heard when hand clapping. These reflections come from circular wall or spherical ceiling at the same time. That is an occurrence of sound focusing. When we speak a few words at the center, our own voice sounds too loud, as if amplified.

<< Physical Characteristics of Sound Focusing >>

The echo diagram in the center
of a round room
The accompanying figure shows an echo diagram in a room where sound focusing occur. An influx of sound reflections is observed delayed from the direct sound. In some cases, the clump of sound reflections produced is larger than the original direct sound.

In circular rooms, even when the sound source is not in the center of the room, sound focusing frequently occur in the area of symmetry to the sound source. In addition, when the floor of the room is flat, the sound reflections that bounce off the floor exacerbate the sound focusing. This phenomenon is especially noticeable in empty round rooms in which desks, chairs and other planned fixtures and furniture have not yet been installed.

<< Historical Roots of Round Halls >>

If we trace the history of performance spaces back to ancient times, we find that the Greeks and Romans had amphitheaters. The audience seating in these theaters rose steeply in concentric circles around a central stage, called the "Orchestra," and, overhead, the theaters were open to the sky. Analyzing this configuration from an acoustical perspective, we understand that the sound emanating directly from the performers into the spherically surfaced configuration combined effectively with reflections from the stage floor to reach the audience.

In the 16th century, the flourishing of the English theater led to the construction of Shakespearean-style round theaters. These were also open-air theaters. In these theaters, three tiers of box seating surrounded flat, central audience pits. The audience in the three tiers of box seating probably added enough sound absorption and scattering characteristics to sufficiently mitigate occurrences of sound focusing in these round theaters.

<< Two Examples of Round Theaters in Japan >>

In Japan, there are several modern theaters-in-the-round. Nagata Acoustics served as the acoustical consultant for the ART TOWER MITO AMC Theater, which opened in 1990. We were also responsible for the acoustics of Shizuoka "GRANSHIP," the Shizuoka Convention and Arts Center completed in 1999. (See our News No. 138, June 1999 for an article on this hall.) Both of these halls are based on the Shakespearean theater configuration. In order to obtain the desired absorption and scattering characteristics for each of these round halls, we specified that the walls behind the balcony seating areas be made of brick openwork.

<< Round Concert Halls in Europe >>

In Amsterdam, the Concertgebouw's recital hall has an elliptical-shaped floor. In London, Wigmore Hall has a rectangular floor shape, but a barrel-shaped, vaulted ceiling arches across the shorter dimension of the hall. Royal Albert Hall, also in London, has both an elliptical-shaped floor and a dome ceiling.

Like the Concertgebouw's recital hall, Wigmore Hall is also a recital hall. The small size of these round halls obviates the need for any special acoustical arrangements to prevent sound focusing. Wigmore Hall has a well-deserved, strong reputation as an excellent venue for the London debuts of chamber music ensembles. It may be that this hall does not suffer from sound focusing because the focal point of the vaulted ceiling is considerably above the plane of the audience seating.

In Royal Albert Hall, numerous circular reflecting panels hang from the ceiling. These serve the dual purpose of acting as an obstacle to the rather late sound reflections that emanate toward the audience from the dome ceiling and enhancing the hall's desirable and effective sound reflections.

<< Other Round Auditoriums >>

Examples of other uses of spherically configured auditoriums are planetariums and cinemas with dome ceilings. In these kinds of auditoriums, the ceiling is usually made of perforated metal material behind which we install sound-absorbing material such as glass wool. However, when using this technique for a planetarium and a cinema, caution is needed so that the perforated metal ceiling does not adversely interfere with the visual appearance of the projection of stars and the movies. Therefore the size of the perforations in the metal ceiling must not be too large. Because the functionalities of these spaces allow for only limited use of sound focusing remedies, these halls tend to produce very obvious sound focusing, depending on the location of the sound source. Fortunately, planetariums and dome-ceilinged cinemas use loudspeaker systems (not embedded in the dome ceilings) for sound amplification, ensuring that the entire audience can enjoy the planetarium presentation or movie soundtrack unhindered by the auditorium's sound focusing.

<< Strategies to Mitigate Sound Focusing in Round Halls >>

There are two categories of strategies for mitigating sound focusing in round halls. One category involves disrupting the smooth arc of portions of the circumference or curves of the round or spherical shape of the hall, so that the hall is no longer a "perfect" circle or sphere. The other kind of strategy involves adding some kind of sound absorbing and scattering treatment. Below are some recent Nagata Acoustics projects and details of the specific strategies we used to mitigate sound focusing.

Project Name


Size and Configuration

Sakurai Library Auditorium

Nara Prefecture

10.8m (35 ft)-radius circular floor and gently curved roof

Strategy: (1) Stepped gradations for the auditorium ceiling; (2) Suspended convex reflection panel at center of ceiling; (3) Retractable sound-absorbing curtains and blinds for the front portions of the glass sections of the auditoriumfs walls.

Sakurai Library Auditorium


Taisho Multi-use Facility Round Hall


10.5m (34 ft)-radius circular floor and open ceiling

Strategy: (1) Ceilingfs stage apparatus and fixtures, ducts and catwalks provide sound diffusion and absorption; (2) Use of square, spindle-like shaping of the walls to create sound-diffusing shape and intermittent use of sound-absorbing perforated board along wall surfaces.

Taisho Multi-use Facility
Round Hall


Osaka International Conference Center "Specialh Conference Hall


11.5m (38 ft)-radius circular floor and dome ceiling

Strategy: (1) Use of perforated aluminum panels for dome ceiling (paneling perforation ratio = 20%); (2) Addition of transparent sound-absorbing material on the inner side of the hallfs central ring-shaped chandelier.

Osaka International
Conference Center
"Specialh Conference Hall

<< Effectiveness of Strategies to Mitigate Sound Focusing in Round Halls >>

As readers will surmise from my use of the word "mitigate," the strategies discussed in detail above, and any strategy to address sound focusing in round halls, can only decrease the intrusiveness of the sound focusing, so that they do not adversely impact use of the hall from a practical perspective. The strategies cannot entirely eliminate or prevent sound focusing. In conference halls and auditoriums that rely on sound systems for sound amplification, the use of the sound system obviates some need for concern that sound focusing will adversely affect a room's use or the perceived sound quality of events and conferences.

While acoustics textbooks may always say "no" to circular and spherical rooms, clients and architects sometimes say "yes." Part of the role of the acoustical consultant is: (1) to understand that, in circular and spherical spaces, at least a minimum of sound focusing is inevitable; (2) to ensure that the space constructed has enough vitality and acoustical countermeasures to override whatever sound focusing may occur; and (3) to educate the client and gain the client's acceptance of this special characteristic of round and spherical halls.

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Nagata Acoustics News 00-05iNo.149j
Issued : May 25, 2000

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