Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 09-11 (No.263)

Issued : November 25, 2009

[ Japanese Version ]

Inagi City's " i " Plaza Cultural Center Opens

by Fumiaki Sakamaki

" i " Plaza exterior

Floor layouts
Floor layouts

" i " Plaza Hall interior with
stage sound reflection panel system in place

" i " Plaza Hall audience seating seen from the stage

On Sunday, October 18, 2009, a delightful and clear Tokyo autumn day, the community of Inagi City celebrated the long-awaited opening of " i " Plaza, a new multipurpose cultural center. The opening celebration included an inaugural concert by NHK Symphony Orchestra solo concertmaster Masafumi Hori conducting select leading members of the orchestra in performances of chamber music compositions. After years of waiting for the realization of this cultural center in their community, many local residents, from seniors to young children, flocked to the cultural center on its opening day.

<< The " i " Plaza Project Location, Scope and Financing >>

Inagi City, located about 15 miles southwest of central Tokyo, is part of the Tama Region suburbs that experienced rapid population growth as they developed into commuter communities in the 1970s. Traditionally, orchards and vineyards farmed in this area gave it a reputation for producing flavorful pears and grapes. In recent years, Inagi City has earned fame as the hometown of the club Tokyo Verdy of the Japan Soccer League.

The trip to " i " Plaza from Tokyo's Shinjuku Station takes about a half hour on the Keio Sagamihara Line to Wakabadai Station. The cultural center is located a brief, two-minute walk from the bus circle in front of the station. Near Wakabadai Station, numerous construction sites with condominiums or athletic facilities in various stages of completion greet the eye, visible evidence of the building development underway in Inagi City.

The planners of " i " Plaza envisioned the new cultural center as a place where residents of neighborhoods in the vicinity of Wakabadai will "gather, interact and learn from each other." The new cultural center is Inagi City's sixth facility for cultural activities. The center's layout has multiple uses and a separate area for each use. The Hall Area has the 410-seat " i " Plaza Hall and a studio large enough to accommodate up to 40 persons for music practice, rehearsals and similar uses. The Lifelong Learning Area includes a conference room and gallery space. The Children's and Youth Area has a playroom, creativity spaces and other rooms for young people. In addition to these facilities, the building also houses a library and the Wakabadai Branch of the Inagi City municipal administrative offices.

A consortium of private companies used the PFI (Private Finance Initiative) model to finance the " i " Plaza project. The participating companies included the architectural firm AXS Satow Inc., the construction company Matsui Kensetsu, JTB Communications Inc., and Keio Setsubi Service. Together, they formed the Inagi-shi Bunka Center Service Corporation to plan and implement the project. AXS Satow Inc. developed the architectural design and a joint venture of Matsui Kensetsu and Ohishi Construction Co. served as the general contractor. Nagata Acoustics provided acoustical consulting services during all phases of the project.

<< Acoustical Room Design of " i " Plaza Hall >>

With an interior inspired by Wakabadai's "satoyama" woodlands, and a one-level, sloped floor design, the " i " Plaza Hall acoustical room design provides a multipurpose hall venue with the priority on acoustics for music performances. We chose the shoebox configuration as the basis for our acoustical room design, because this shape would easily enable us to achieve our acoustical objectives for music performances.

In our room acoustical design, we focused attention on achieving the objective of sufficient room spatial volume. We raised the proscenium opening to be 10 m. above the stage and gave the ceiling a gentle and smooth downward slope that extends to the rear of the auditorium from the ceiling's highest point at the proscenium (where the ceiling meets the stage sound reflection panels). As a result, the auditorium's air volume per seat equals a generous 11 cu. m., which is large for a hall of this scale. When hall patrons sit in the audience and look up toward the ceiling, they will almost certainly be impressed by how high this ceiling is.

In order to design the shape of the hall's roof so that early sound reflections would be distributed effectively throughout the audience seating area, Nagata Acoustics used computer simulations to study and determine the ceiling's shape. For the stage reflection panels, our design included partial use of perforated panels backed by glass wool, implemented with the aim of balancing the reflection timing of the early reflections by somewhat diminishing reflections from sounds that reach the panels soonest. In addition, to promote sound diffusion in the hall, for the lower portion of the stage reflection panels and the audience area sidewalls, we specified the use of ribbed surfaces that have random variations in both the size and spacing of the ribs.

The ribs along the audience area sidewalls create a visual interior design element evocative of rows of tree trunks, complementing the architect's desire to use imagery of the Wakabadai "satoyama" woodlands. Likewise, the random assortment of subdued, autumn-colored hues used to upholster the audience seating evokes imagery of fallen leaves carpeting a woodland floor.

The hall's reverberation time measures 1.5 seconds (at 500 Hz, with the hall fully occupied), an appropriate amount of liveliness for the primary intended use of non-amplified music concerts. Also, the perceived sense of the hall's acoustics gives the impression of a space with an even somewhat longer reverberation time.

When the hall stage is configured with a stage curtain instead of sound reflection panels, the hall's reverberation time measures 1.1 seconds (at 500 Hz, with the hall fully occupied). This reduced reverberation time provides the appropriate acoustical environment for the hall's use as a multipurpose venue.

<< Listening to " i " Plaza Hall's Inaugural Concert >>

On the day of the hall's inaugural concert, I listened to both the dress rehearsal and the gala concert. During the rehearsal, I sensed that the ensemble's musicians were still in the process of testing and learning about the hall's acoustics. As I listened to the rehearsal, I confirmed my initial impressions of a hall with warm acoustical tones and appropriately lively reverberations.

The inaugural concert included talks and commentary from the stage interspersed with the music performances, creating a casual, "at home" feeling. The NHK Symphony Orchestra members lived up to their reputation and delivered a wonderful performance. I was especially delighted with the strong presence of the contrabass. The concert program featured Schubert's "Die Forelle" ("The Trout") and other popular compositions. The audience clearly enjoyed every minute.

The " i " Plaza Hall calendar has a lineup of famous artists, such as violinist Mariko Senju and pianists Yukio Yokoyama and Hiroko Nakamura. The hall will also be used for performances and events by community members. It seems poised to become an integral part of the daily cultural life of adults and young people, a hall they can access easily, whether on the way home from school or work. I look forward to " i " Plaza Hall's success and hope that when you are in Tokyo, you will have the opportunity to attend a concert in this new hall.

The Inagi City " i " Plaza Hall's home page is http://www.iplaza.inagi.tokyo.jp/.

Understanding Stage Sound Reflection Panels - Part 2

by Nobuhiko Hattori

In our August, 2009 newsletter, I wrote about the basic considerations that underlie acoustical consultants' decisions when designing stage sound reflection panels for multipurpose halls. In this article, I will discuss how storage location influences the performance characteristics of stage sound reflection panels, with reference to examples of specific halls.

<< Methods of Storing Stage Sound Reflection Panels >>

The anticipated priority uses of a multipurpose hall, plus architectural and construction project considerations and constraints determine the stage surface area and fly tower dimensions of each multipurpose hall. The stage surface area and fly tower dimensions differ from hall to hall and, therefore, the storage method of the stage sound reflection panels must also be designed and adapted to the specific hall situation.

Fig. 1 Cross-section illustrations of a stage and sound reflection storage method options
Fig. 1 Cross-section illustrations of a stage
and sound reflection storage method options

Fig. 1 shows the three possible locations for storing stage sound reflection panels, with (A) illustrating storage in the ceiling area above the stage, (B) illustrating storage at the stage rear and (C) illustrating storage below the stage floor. In the 1950s, when stage sound reflection panels became regularly included features of multipurpose hall stages, most designs stored the panels from rigging in the flytower space above the stage, that is, using the method of illustration (A). However, as the kinds of performances and events staged in multipurpose halls became more diverse, and as the amount of stage equipment and lighting equipment suspended from flytower rigging increased, lighting and theatre consultants increasingly claimed the flytower space for their needs, making it difficult to locate the stage sound reflection panels above the stage. To solve this design issue, storage locations (B) and (C) started to be adopted.

In practice, primarily considering the hall's expected priority of uses and its size, those options (A), (B) and (C), or some combination of these locations are selected as the stage reflection panels' storage location. In the remainder of this article, I will discuss the advantages and concerns of locating the stage sound reflection panels either above the stage or on the same level as the stage in an off-stage location at the rear or side of the stage.

<< Storing Stage Sound Reflection Panels above the Stage >>

When stage sound reflection panels are stored above the stage and above the stage wings, the panel system is designed so that it can be separated into sections for storage. Typically, the system of panels is divided into the section used above the stage, the sections for the sides of the stage and the section for the stage rear. This design approach continues to be the most prevalent choice for the storage location of stage sound reflection panels and the mechanism for making them movable between the storage location and the stage.

When the panels are stored in the same space used for stage rigging and lighting equipment and because storing the panels above the stage involves suspending the panels, the weight and thickness of the panels cannot exceed certain limitations. In addition, to protect the panels from colliding with each other during setup and take-down activities, clearance space is allotted between the panels, creating gaps between panels. The gaps remain even when the panels have been correctly set in place for use during a performance. These gaps act as sound absorbing elements, diminishing the efficacy of the panels in reflecting sound to the audience and back to the stage. And still worse, gaps in the stage sound reflection panels reduce the ability to create a significant difference in reverberation time between use and non-use of the stage sound reflection panel system. By constructing stage sound reflection panel systems without sections, or by reducing the number of separate sections, concerns about the panels colliding and being damaged can be minimized and the disadvantageous acoustical effects of gaps alleviated.

<< The Old Suginami Koukaido's Sound Reflection Panels Storage Design >>

Photo 1 Old Suginami Koukaido
Photo 1 Old Suginami Koukaido

The old Suginami Koukaido (built in 1957) in Tokyo was one of the first multipurpose halls in Japan to have a true stage sound reflection panel system. The system included a fixed sound reflecting surface at the rear of the stage, a two-section set of panels above the stage that could be stored in the ceiling above the stage, and rotatable panels at the sides of the stage. pace between the two sections of the overhead stage sound reflection panels was used for stage lighting. The old Suginami Koukaido stage can be seen in Photo 1.

The rotatable stage sound reflection panels at the sides of the stage served a dual purpose. In addition to providing sound reflecting surfaces when in their closed position, in their rotated, open position they provided stage entrance and exit paths for people and objects and they masked off-stage areas from the audience. Rotatable sound reflection panels continue to be a frequent design choice for stage side walls when a hall will be primarily used for the performance of non-amplified music and in small scale halls with stages that lack depth from front to rear.

As can be surmised from the completion date of the old Suginami Koukaido, the sound reflection panels type (A) are a design approach that has been used for decades. While they continue to be a design option, they have certain disadvantages. Specifically, because the sound reflection panels storing above the stage at that time must be constructed of relatively thin materials, they absorb low frequency sounds. Also, the gaps between the panels absorb high frequency sounds. These two deficiencies reduce the ability to achieve a significantly different reverberation time for the two different setups (one being when the panels are set in their closed position to create sound reflections and the other setup being when they are set at an open angle to achieve a lower reverberation time).

<< Storing Stage Sound Reflection Panels in an Off-stage Area >>

Photo 2 Hyogo Prefecture Performing Arts Center
Photo 2 Hyogo Prefecture Performing Arts Center

Photo 3 Aubade Hall
Photo 3 Aubade Hall

Photo 4 Mechanism using large L-shaped brackets
Photo 4 Mechanism using large L-shaped brackets

Photo 5 Iwamizawa City Civic Center
Photo 5 Iwamizawa City Civic Center

The method of storing a stage sound reflection panel system behind or at one side of the stage in a space reserved for this purpose, as shown in Photo 2, is a method used when the sound reflection panel system is constructed as an integrated stage shell that cannot be readily taken apart. Alternatively, to reduce the amount of off-stage space needed for the sound reflection panel system, the system is often built as several three-sided segments that can be nested one inside the other, as shown in Photo 3.

Sound reflection panel systems stored behind or at one side of the stage typically use railings as the mechanism to slide the sound reflection panel system into place on stage.This system may affect the lighting and theatre consultants' ability to freely determine the location of the stage rigging and lighting equipment above the stage.

Because these sound reflection panel systems are constructed without gaps, they avoid the sound absorption problems inherent to suspended panel systems. Also, stage sound reflection panel systems stored behind or at the side of the stage can be made of heavy materials that eliminate the problem of the panels absorbing low frequency sounds. However, with stage sound reflection panel system designs that use the space-saving technique of dividing the system into nested three-sided segments, the shape of the overall stage sound reflection panel system becomes constrained.

For conditions in which the off-stage area does not have sufficient space for the stage sound reflection panel system, the system may be folded and stored in the upper portion of the backstage area. In this kind of a design, mechanisms that use large L-shaped bracket devices, such as those shown in Photo 4, push the stage sound reflection panel system into place on stage. This storage method eliminates the need for rails on which to slide the reflection panels. Also, the system can be designed without gaps between the panels and the space above the stage is preserved for lighting and other theater rigging equipment. The disadvantages of this design are limitations on the weight of the materials used to make the sound reflection panels and possible unevenness in the overall system's surfaces where the panels are repeatedly folded and unfolded.

<< Iwamizawa City Civic Center's Sound Reflection Panels Storage Design >>

At Iwamizawa City Civic Center (completed in 2003), the hall's stage has stage ceiling sound reflection panels and side sound reflection panels that fold up for storage and that form an integrated system with the sound reflection panels at the rear of the stage. As can be seen in Photo 5, this folded storage design achieves the two goals of using minimal storage space and raising the storage location to a height above the stage floor, alleviating the possibility of interference with the movement of people and objects to and from the stage. In this design, when setting in place the stage sound reflection panels, the system is moved into place along rails at the right and left sides of the stage. In addition, the number of panels that are unfolded at the ceiling and sides of the stage can be varied as shown in Fig. 2, enabling the system to create two different stage sizes to suit different instrument configurations of music ensembles.

This concludes my discussion of this article's topics. In my next article, I will discuss the topics of stage sound reflection panels stored below the stage floor and other, less-standard kinds of sound reflection panel systems.

  Fig. 2 Stage sound reflection panel system setup variations-1    Fig. 2 Stage sound reflection panel system setup variations-2    Fig. 2 Stage sound reflection panel system setup variations-3 
Fig. 2 Stage sound reflection panel system setup variations

Nagata Acoustics Inc.

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[ Japanese Version ]