Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 10-10 (No.274)

Issued : October 25, 2010

[ Japanese Version ]

Theatre Opens in Osaka, Osaka Shinkabukiza Uehonmachi's "Yufura"

By Chiaki Ishiwata

Yufura exterior Photo:YASUHIRO INAZUMI
Yufura exterior

This past summer, Japan's weather hit record high temperatures. Nevertheless, the weather's feverish temperatures paled in comparison to the "theatre fever" generated in Osaka by the opening of the new Osaka Shinkabukiza Theatre in Uehonmachi's Yufura multi-use complex.

From 1958 until June, 2009, Osaka's Theatre fans attended performances at Namba's iconic former Shinkabukiza Theatre, designed by architect Togo Murano in the style of Japan's 16th century Momoyama Period and located in Osaka's Namba Ward. After half a century, with the theatre's stage equipment mostly outdated and showing signs of wear-and-tear, Osaka Shinkabukiza Theatre organization evaluated the theatre's needs and other circumstances, and then decided to boldly "leap" into a new era by moving to a new structure in a new location.

The Osaka Shinkabukiza theatre held a last performance in the old theatre in June, 2009, and then suspended performances to prepare for the move to its new home. In August, 2010, the theatre completed its move and took up residence at its new location in the Yufura multi-use complex.

On September 3, the theatre began a series of performances to inaugurate the new hall by Kabuki performance. The offerings included festive and Celebratory Kabuki dances such as "Sanbaso" and "Renjishi", as well as play episodes and other pieces with congratulatory meaning performed by members of the Omodaka acting house, which has a long association with the Osaka Shinkabukiza Theatre. In true Osaka style, the audience quickly warmed to the new venue and showed its willingness to continue the tradition of occasional shouts of approving feedback to the performers on stage with the informal atmosphere of Osaka's Kabuki compared to Tokyo's "Ginza Kobikicho" style.

Osaka Shinkabukiza Theatre main and balcony seating seen from the stage Photo:YASUHIRO INAZUMI
Osaka Shinkabukiza Theatre
main and balcony seating seen from the stage

<<Overview of the Yufura Project >>

Kintetsu Corporation owns the Yufura property and planned the complex with Osaka Shinkabukiza Theatre as the building's main attraction. The corporation celebrated its 100th anniversary this year and has strong ties to Osaka as one of the city's two private railway companies. Kintetsu Corporation had its original office location in the same Uehonmachi section of Osaka's Tennoji Ward as the Yufura complex and the specific site of the complex uses land adjacent to Kintetsu Uehonmachi Station where the former Kintetsu Theatre once stood.

Yufura's first five floors house shopping and restaurant space. The fourth and fifth floors also have offices and other support rooms for Osaka Shinkabukiza Theatre. The entire sixth floor is dedicated to Osaka Shinkabukiza Theatre, and the theatre's main entrance is on this level. From Yufura's seventh floor upward, the building divides into two separate towers, one taller than the other. The seventh floor of the lower tower provides additional space for Osaka Shinkabukiza Theatre. The taller tower has seven additional floors of office space, for a total of thirteen floors.

Osaka Shinkabukiza Theatre has three audience seating levels (a main level and two balconies). The total seat count of 1,453 is slightly less than the occupant capacity of the old Osaka Shinkabukiza Theatre, but each seat of the new theatre has larger dimensions than the seats in the old theatre and some first balcony seating has especially generous proportions. From the last row of seating to the foot of the stage measures just 20 m. (66 ft), a measurement that ensures a feeling of intimacy with the performance taking place on stage, even for patrons seated in the last row.

New Osaka Shinkabukiza Theatre has an updated stage design and all-new stage equipment, including a circular, revolving stage instead of the sliding stage mechanism of the old location's theatre. In addition, to maximize the theatre's adaptability for wide range performances, the "hanamichi" stage extension can be dismantled.

Nihon Sekkei Kansai Branch created Yufura's architectural design and the Obayashi Corporation was the project's general contractor. Nagata Acoustics served as the Theatre's acoustical consultant for all phases of the theatre portion of the project, from design through project completion.

<<Room Acoustical Design of the Theatre >>

Osaka Shinkabukiza Theatre interior seen from a balcony seat
Osaka Shinkabukiza Theatre interior
seen from a balcony seat

Osaka Shinkabukiza Theatre's inaugural performance calendar typified the kinds of performances that will be held in the theatre on a regular basis. Most performances will be entertainment shows that feature a specific actor, actress, singer or commercial theatre performing group. Therefore, our room acoustical design began with the premise that performances will use the theatre's sound system to project sound to the audience. Our room design objectives included limiting the liveliness of the room's acoustics' while at the same time prioritizing clarity of sound and sufficient sound volumes to support the feeling of intimacy between the stage and the audience.

In order for many early sound reflections from the ceilings and the walls to reach all of the audience seating within 50 milliseconds, we studied the best height and angled surfaces to use for the ceiling and the architectural team adopted the specifications we provided. The surface of the theatre ceiling, which has recessed spotlights and other, built-in stage lighting equipment, slopes toward the rear of the theatre and its surface has accordion-like folds. (The peaks and valleys of the ceiling's surface may not be visible in the photos that accompany this article.)

For the theatre's wall treatments, we suggested having sound diffusing protrusions and recessed elements that would prevent echoes, not for sound-absorption. To meet these requirements, the architects developed a design reminiscent of Japanese folding screens. The visible surfaces of the theatre's walls are finished with a simple paint coating. The gold color chosen for the walls combines well with the matte black finish of the ceiling to create a very chic and appropriately dramatic interior.

<<Sound Isolation Design >>

Because the new theatre was planned as part of a multi-use complex, a key focus of our acoustical design was sound isolation between the theatre and other occupants of the building. Because the installation of sound isolation walls can be complicated and requires precise implementation of specified tolerances, we advocated the use of reinforced concrete for the structure. However, to accommodate the project's schedule constraints, the project decision-makers implemented a steel structure, creating unfavorable conditions from the sound isolation perspective.

The rotating stage mechanism in the machine pit Photo:YASUHIRO INAZUMI
The rotating stage mechanism in the machine pit

Balancing the disadvantage of the use of a steel structure, on this project we had the benefit of a clear understanding of how the building's commercial occupants planned to use their spaces and we also had the opportunity to research and measure the levels of sound generated during performances in the former Shinkabukiza Theatre. Using these inputs, as well as cost and space considerations, we developed the theatre's sound isolation plan.

For the main audience seating area, the stage and the below-stage "naraku" space, we used a floating floor design. We installed multi layer's gypsum board walls supported by the floating floors to create a structural sound isolation system. In addition, we specified that the hollow steel columns used in the theatre's construction be filled with concrete to inhibit the occurrence and transfer of secondary solid borne sound.

Stage equipment and mechanisms such as height-adjustable risers and the rotating stage that is a favorite of Kabuki and commercial theatre productions also tend to cause solid borne noise problems. Our sound isolation design also developed strategies in anticipation of this kind of noise. In particular, because the rotating stage mechanism uses a circular rail on which steel wheels of the same kind used for electric trains ride, the mechanism generates significant noise and vibration. The wheels weigh several tons and, when the rotating stage moves, the experience for a person in the machine pit below the stage can be likened to the sensation of a railroad train running directly overhead.

As part of our design work we observed and measured the noise and vibrations generated by similar rotating stages already in operation in other theatres. We also set noise and vibration targets consistent with levels that would not interfere with use of the commercial spaces below Osaka Shinkabukiza Theatre. For the rotating stage's fixed slab, we specified a heavier thickness than manufacturers typically use, and we installed a floating floor that uses anti-vibration rubber for the machine pit's floor. As a result of these measures, movement of the rotating stage floor is practically undetectable by people on the floors below the theatre.

Two months after Osaka Shinkabukiza Theatre's opening, the theatre continues to make entertainment headlines, most recently for the performance by Gakt. In November, Japanese "enka" singer Saburo Kitajima will perform at the theatre.

Unlike the atmosphere at a classical music concert, at Osaka Shinkabukiza Theatre, patrons can laugh and cry, giving full expression to the passionate emotions evoked by the performances on stage. This author invites you to check the Osaka shinkabukiza Theatre schedule and experience a performance there the next time you visit Osaka.

Osaka Shinkabukiza Theatre's home page is http://www.shinkabukiza.co.jp/.
Uehonmachi Yufura's home page is http://www.yufura.jp/.

Understanding Stage Sound Reflecting Panel Systems - Part 4

By Nobuhiko Hattori

Computer simulation showing initial sound reflections
Computer simulation showing initial sound reflections

Computer simulation showing secondary sound reflections
Computer simulation showing secondary sound reflections

In the March, 2010 issue of this newsletter, I completed my discussion of storage methods for sound reflecting panel systems and shared some related examples. In this article, I will turn my attention to the acoustically significant specifications of the configuration of the panels and their physical weight and related properties.

<< Acoustically Significant Sound Reflecting Panel System Specifications >>

When configuring or adapting a multipurpose hall for classical music concerts, the hall's fly tower, stage wings and other large open spaces above or around the stage need to be temporarily partitioned from the stage so that sounds generated on stage can be made to reflect to the audience seating areas. Storable sound reflecting panel systems provide this physical separation between the open areas around the stage and the stage. Designing and engineering an effective sound reflecting panel system requires consideration of numerous inputs as well as acoustical engineering experience and skill.

Photo 1: Sakura Hall Owada Cultural Center, Shibuya

Photo 1: Sakura Hall
Owada Cultural Center, Shibuya

For example, the tilt or angle of the sound reflecting panels affects the coverage area that the sound reflections will reach. Also, the height of the sound reflecting panels affects the delay time of the sound reflections. In addition, the surface treatment of the sound reflecting panels and their weight affect the strength of the sound reflections and the hall's reverberation time. Therefore, for non-amplified music performances in multipurpose halls, the configuration, surface treatment and weight of the sound reflecting panels play as important a role in creating the desired acoustical environment as do the ceiling above the audience seating and the hall's sidewalls.

<< Sound Reflecting Panel Shapes for Secondary Reflections >>

Before computer simulation technology came into use, acoustical engineers used two-dimensional representations of sound reflections as the basis for their sound reflecting panel designs and primarily developed panel systems that could reflect initial sound reflections with a brief delay. Nowadays, we use computer simulations that enable us to study the three-dimensional distribution of not only initial sound reflections, but also secondary and tertiary sound reflections as well. Accordingly, our design objectives focus on achieving the best delay times compared with the original direct sound.

For example, at Owada Cultural Center's Sakura Hall, which will open this fall in Tokyo's Shibuya Ward, initial sound reflections reach the stage and audience with uniform distribution from a combination of the ceiling above the audience and sound reflecting panels suspended from the ceiling. Additionally, the suspended sound reflecting panels and sound reflecting panels at the rear and sides of the stage have a gentle angle that makes them effectively reflect secondary sound reflections.

Because the stage and front rows of multipurpose halls tend to receive only a few early sound reflections, at Sakura Hall we installed eave-like sound reflecting surfaces to produce secondary sound reflections that have a short delay compared with the original direct sound and that reach the stage and front row seating. Also, we added sound diffusing elements below the eave-like sound reflecting surfaces that are closest to the stage, to prevent the possibility of the sound reflecting panels producing overly strong sound reflections in the direction of the musicians on stage.

<< Sound Reflecting Panel Systems with Minimal or No Gaps >>

Photo 2: Obvious gaps characterize this older hall's sound reflecting panel system.
Photo 2: Obvious gaps characterize
this older hall's sound reflecting panel system.

The gently angled sound reflecting panels at Owada Cultural Center's Sakura Hall provide one example of the important role played by the shape of sound reflecting panels in effectively distributing sound reflections in a hall. Likewise, minimizing or eliminating gaps between panels and at the perimeter of sound reflecting panel systems significantly affects the effectiveness of the system in achieving the desired acoustical results.

Gaps can occur between overhead panels or between panels set up at the sides and rear of a stage or between the sound reflecting panel system and the stage's proscenium frame. These gaps may intentionally be included in a panel system's design to ensure sufficient clearance between portions of the system so as to prevent sections of the system from interfering with each other or banging against each other during setup and dismantling.

Alternatively, gaps may result from design constraints, a situation more likely to have been accepted on projects of the past. For example, in older halls we see stage equipment designs that interfere with the sound reflecting panel system by locating a drop curtain between the proscenium and the overhead sound reflecting panel. Sometimes, stage lighting batons have been interspersed with overhead sound reflecting panels, or gaps have been left between sound reflecting panels at the sides of a stage so that performers can enter and exit the stage between the panels. These situations can cause wide gaps of up to two meters between sections of a sound reflecting panel system. An example of a hall stage with wide gaps in the sound reflecting panel system can be seen in Photo 2.

When a sound reflecting panel system has gaps, some of the sound the performers generate on stage escapes through the gaps at the sides or above the stage, resulting in fewer sound reflections. Also, if the use of the sound reflecting panel system changes a hall's reverberation time, gaps may also reduce the ability of the sound reflecting panel system to significantly lengthen the halls reverberation characteristic.

For more recently constructed halls, sound reflecting panel systems now include stage lighting and stage entrance and exit doors as part of the sound reflecting panel system. Recent designs also use innovations such as panels that can be folded instead of separated for storage and ways to reduce the clearances needed between panels to as little as 100 mm. in order to reduce the quantity and size of gaps in the sound reflecting panel system.

Photo 3: This recent hall's sound reflecting panel system has very minimal gaps.
Photo 3: This recent hall's
sound reflecting panel system has very minimal gaps.

These kinds of improvements in sound reflecting panel system design likely contribute to the trend in recent hall projects of providing the ability to vary the hall's reverberation time significantly through the use of a storable sound reflecting panel system. While the variable reverberation time trend of recent hall projects cannot be attributed solely to gap reductions in sound reflecting panel systems, the increase in the achievable reverberation time differences can at least partially be attributed to the use of panel systems that have fewer and more minimal gaps. As shown in the accompanying two graphs, sound reflecting panel systems of an older hall achieved a 0.2 - 0.3 second difference in reverberation time length, while the sound reflecting panel system of a recently built hall lengthened the hall's reverberation times by 0.4 - 0.5 seconds.

<<Surface Materials and Mass of Sound Reflecting Panel Systems >>

Reverberation times in an older hall
Reverberation times in an older hall

Reverberation times in a recently built hall
Reverberation times in a recently built hall

The materials and structure of the sound reflecting panels and, especially, their weight and density, also play a significant role in the panels' effectiveness. If thin board materials with low density (kg/sq. m.) are used, the boards will vibrate and absorb low-frequency sound. In particular, if such lightweight sound reflecting panels are used on a stage where the stage wings or fly tower provide insufficient sound absorption, the sound reflecting panels will produce the negative result of shortening the reverberation time of low frequency sound.

Because the acoustical environment for classical music concerts places high value on robust low frequency sounds and reverberations, the ideal surface materials and structure to use for a sound reflecting panel system are those that have the same density properties as the surface materials of the permanent ceiling and walls of the audience seating areas. Of course, achieving this ideal may be constrained by storage considerations for the sound reflecting panel system and the maximum allowable or practical weight for a system that will be repeatedly set up and dismantled.

When the materials used for the interior surfaces of the ceiling and sidewalls of the audience seating area cannot be used for the sound reflecting panel system, some panel system designers focus on achieving the maximum allowable weight for the system, or they may add a damping sheet of no more than 3 mm. thickness as a middle layer sandwiched between a visible and back panel layer. However, from both the architectural and acoustical perspectives, the most preferred sound reflecting panel designs reproduce the look and structural density (30 - 50 kg/sq. m.) of the hall's permanent interior surfaces, in addition to achieving the maximum allowable or practical weight.

The two halls used for the accompanying reverberation time graphs demonstrate the points I discussed above. The older hall's sound reflecting panel system was constructed of 9 mm. plywood, while the more recently built hall's system used 54.5 mm. gypsum board, three layers within. The older hall's system has gaps where the system meets the proscenium and also between the panels of the system. The reverberation times for each of these two halls can be seen in the accompanying graphs. Each graph shows the reverberation time measurements both with and without the sound reflecting panel systems in place.

In the older hall, when the sound reflecting panel system is not in use, the low frequency sounds have longer reverberation times and the system only lengthens the reverberation time of high and mid-frequency sounds by 0.2-0.3 seconds. By comparison, deploying the sound reflecting panel system in the recently built hall increases the reverberation time obtained for low frequency sounds and a wide range of frequencies have their reverberation times lengthened by 0.3-0.4 seconds, enabling the recently built hall to truly fulfill its role as a hall that can be configured for classical music concerts.

Nagata Acoustics Inc.

(Tokyo Office)
Hongo Segawa Bldg. 3F, 2-35-10 Hongo
Bunkyo-ku, Tokyo 113-0033, Japan
Tel: +81-3-5800-2671, Fax: +81-3-5800-2672

(LA Office)
2130 Sawtelle Blvd., Suite 308
Los Angeles, CA 90025, U.S.A.
Tel: +1-310-231-7878, Fax: +1-310-231-7816

(Paris Office)
75, avenue Parmentier
75011 Paris, France
Tel: +33 (0)1 40 21 44 25, Fax: +33 (0)1 40 21 24 00

E-mail: info@nagata.co.jp

[ Japanese Version ]