Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS


News 09-08 (No.260)

Issued : August 25, 2009

[ Japanese Version ]

Iwaki Performing Arts Center "Alios" Celebrates Its Grand Opening

by Masaya Uchida

Fig.1  Alios exterior with mid-size theater at far right
Fig.1 Alios exterior with mid-size theater at far right

Fig.2  Stage view of proscenium configuration with full-width stage of 14.5 m. (48 ft)
Fig.2 Stage view of proscenium configuration
with full-width stage of 14.5 m. (48 ft)

Fig.3  Audience seating of proscenium configuration with full-width stage of 14.5 m. (48 ft)
Fig.3 Audience seating of proscenium configuration
with full-width stage of 14.5 m. (48 ft)

Last year, we devoted most of the Nagata Acoustics May and June 2008 newsletters to the new Iwaki Performing Arts Center "Alios" and its completed Phase 1, which included a large hall and small theater. Phase 2, which houses a mid-size theater, completed construction at the end of 2008. Thereafter, the center spent four months training staff and testing operational procedures and processes, culminating in the center's grand opening in May, 2009.

Iwaki Alios' 1,705-seat large hall, the mid-size theater with seating capacity of 500 to 687 seats (depending on the configuration in use), the 233-seat small theater, the two rehearsal rooms and four studios are now fully operational. In this article, I will focus on introducing the Phase 2 mid-size hall to our readers.

<< The Mid-size Theater's Many Configurations >>

The mid-size theater's design provides an abundance of configuration variations that can be set up depending on a performance's needs. The basic configuration has a proscenium and a full-width stage of 14.5 m. (48 ft). Alternative configurations include a proscenium stage with a 10.9 m. (36 ft) stage width, a podium configuration with audience seating in front of and behind the stage, a thrust stage configuration, a Noh theater configuration and a Kabuki theater configuration with a "hanamichi" stage section along the left side of the audience seating.

To effect the numerous configurations of the mid-size theater, the theater's design combines floor portions that can be raised and lowered, modular side-frame units that house the side loudspeakers and side lighting, modular seating sections that include first floor and balcony seating in each module, and lighting and proscenium bridges that can be adjusted both vertically and horizontally depending on the configuration. The modular frame and seating units are equipped with pneumatic systems that make these large and heavy structures easy to move.

We often participate on projects that have theaters with variable configurations. Compared with these other theaters, however, the Alios mid-size theater represents an unprecedented scale of flexibility and number of configurations within a single theater space.

  Fig.4  Plan of mid-size theater (configured with proscenium and full-width stage of 14.5 m. (48 ft) (upper part) and of 10.9m (36ft) (lower part))
Fig.4 Plan of mid-size theater (configured with
proscenium and full-width stage of 14.5 m. (48 ft)
(upper part) and of 10.9m (36ft) (lower part))
Fig.5  Cross-section of mid-size theater (configured with proscenium and full-width stage of 14.5 m. (48 ft))
Fig.5 Cross-section of mid-size theater
(configured with proscenium and
full-width stage of 14.5 m. (48 ft))

<< The Mid-size Theater's Room Acoustics >>

Fig.6  Podium configuration
Fig.6 Podium configuration

Fig.7  Thrust configuration
Fig.7 Thrust configuration

Fig.8  Audience seating module being moved into place
Fig.8 Audience seating module
being moved into place

Fig.9  Side framing module
Fig.9 Side framing module

Fig.10  Sound booth with window opened fully to 2.7 m. (9 ft)
Fig.10 Sound booth with
window opened fully to 2.7 m. (9 ft)

A key objective for the mid-size theater was that each member of the audience, sitting in any seat of the theater, should be able to clearly hear the non-amplified spoken lines of actors. We satisfied this objective by obtaining effective sound-reflecting surfaces in our room acoustics design, which uses a combination of sound-reflecting elements. We tilted the angle of the portion of ceiling that is above the audience seating and we used cylindrical tiles with a sound-diffusing finish along the audience seating sidewalls. Also, we installed sound-reflecting surfaces below the fixed lighting bridge that hangs above the audience seating area as well as at the eaves of the upper portion of the third-floor balcony.

Regarding the mid-size theater's reverberation time, one significant factor is that some of the room configurations have seating where other configurations have portions of the stage. To address this variable condition, we dispersed the placement of sound-absorbing material on the stage sidewalls so that the entire theater space has a uniform sound reverberation characteristic. When set up with a proscenium stage and full stage width of 14.5 m. (48 ft), the theater's reverberation time measures 1.0 seconds (at 500 Hz, unoccupied).

<< Sound Isolation and Noise Prevention Design >>

As discussed in the May 2008 newsletters, in the Alios structural design we implemented acoustically effective expansion joints between the large hall's wing and the central lobby part of the structure, and likewise between the lobby part of the structure and the mid-size hall's wing. Additionally, we used anti-vibration and sound-isolating structural designs for each room in the lobby part of the structure, because this portion of Alios is sandwiched between the large hall wing and the mid-size theater wing. As a result of these measures, we achieved a sound isolation performance level that enables all of the rooms to be used simultaneously without the sound from any one or more of the rooms disturbing the concurrent events and performances in other rooms.

In the mid-size theater, a displacement ventilation system was installed both to alleviate the possibility of HVAC currents causing the theater curtain to sway and to accommodate the numerous seating arrangements of the several configurations. The quietness rating inside the mid-size theater measures NC-22.

<< The Mid-size Theater's Stage Sound System Design >>

In designing the mid-size theater's sound system, we recognized the need for a system that would adapt seamlessly when the theater is set up in its different configurations. For this reason, we installed main loudspeakers in both the proscenium bridge (which can be moved forward and backward as well as raised and lowered) and in the modular side-framing unit. We only designed the use of portable speakers mounted to batons for the podium configuration, which has the audience seating set up inside the area otherwise reserved for the stage. We decided that, for all configurations other than the podium configuration, instead of providing portable main speakers that would need to be rearranged and adjusted for each configuration, a large amount of setup time and labor would be saved by embedding separate sets of main speakers within the proscenium bridge or side-frame modules of the configurations. This design preserves more setup time for the creative aspects of sound checks.

Like our speaker design for the Alios large hall sound system, we did not enclose the mid-size theater's speakers in hard walls. For the proscenium and side-frame speakers, we covered the speakers entirely in acoustically transparent netting and affixed opaque, light-blocking cloth on their rear surfaces. We left the auxiliary speakers as is, without any coverings. Even before we began fine tuning the sound system, the mid-size theater's sound system delivered the same kind of natural and clear sound that also characterizes the large hall's sound system.

As for other aspects and components of the mid-size theater's sound system, we basically aimed for the same kind of integrated operability that we achieved for the large hall's sound system. Also, we designed the mid-size theater's sound booth to have a three-panel window that measures 2.7 m. (9 ft) wide and can be fully opened to the interior of the theater.

<< Alios' Strong and Diverse Programming for the Local Community >>

Iwaki Alios has many performances scheduled on its calendar, but the programs that may be most worth mentioning are the workshops and off-site events being aggressively planned by Iwaki Alios' management. Alios runs participatory workshops in percussion, acting, dramatic script reading, dance and back stage observation. The off-site events include programs at local venues, such as public halls, churches, temples, gymnasiums, schools and nursery schools.

The workshops and off-site events make it easy for the general public to become involved with Iwaki Alios programming, either because the event is at a convenient location or because of interest in the workshop. When local residents participate in the workshops, they will also likely want to perform at Alios and they will more likely enjoy the professional concerts. Friends and relatives of the workshop participants will attend the amateur performances and, in turn, they will also become interested in Iwaki Alios' programs and events. Thanks to this innovative programming approach, Iwaki Alios already shows great vitality and is in no danger of becoming an underused, hollow box. I look forward to continuing to hear about Alios' thriving programs and event planning.

home page is http://iwaki-alios.jp/



Understanding Stage Sound Reflection Panels - Part 1

by Nobuhiko Hattori

Photo 1: Stage with stage curtain configuration
Photo 1: Stage with stage curtain configuration

Photo 2: Stage with stage sound reflection panels configuration
Photo 2: Stage with
stage sound reflection panels configuration

By definition, multipurpose halls serve as the venue for multiple event genres, from ceremonies, symposia and plays, to classical music concerts and other performing arts performances. A distinguishing characteristic of recent multipurpose halls is that their stages can be modified depending on the kind of event. Today's multipurpose halls have a proscenium stage configuration, with its clear delineation between stage and audience and a stage curtain for ceremonies, symposia and plays, and, these halls also have stage sound reflection panels that can be set up to modify the stage for classical music concerts. From the acoustical perspective, the stage sound reflection panels play a critical role in adapting a multipurpose hall to the appropriate acoustical characteristics for classical music performances. Most of this newsletter's readers may be familiar with the phrase "sound reflection panels", but you may not have thought much about the specific function of the stage sound reflection panels or how they work. In this series of articles, I will explain the basics of this important element of multipurpose halls and stage acoustical design, and I will introduce examples from actual halls to help explain some of the concepts I will present.

<< What are "Stage Sound Reflection Panels" ? >>

Stage sound reflection panels are sound reflection panels that are set up on stage to form a partial enclosure behind, at the sides and above orchestras, choruses and other ensembles or individual musicians who perform without sound amplification. At their most elaborate, a hall's system of stage sound reflection panels may include overhead panels, side panels at both stage right and stage left and panels at the rear of the stage, and the set up of the panels may be electronically controlled and operated and integrated with other stage machinery. At their simplest, a hall's stage sound reflection panels may be a set of freestanding panels that need to be carried from where they are stored and set in place on stage by the manual labor of stage hands. Between these two extremes exist a multitude of different stage sound reflection panel designs and implementations.

Photo 3.1: A simple stage sound reflection panel implementation     Photo 3.2: A simple stage sound reflection panel implementation
Photo 3: A simple stage sound reflection panel implementation

Both acoustical and stage design aspects of a multipurpose hall influence the design and size of a hall's stage sound reflection panels. The programming priorities of whether a multipurpose hall will be used primarily for classical music or for theater provide one key input to the design of the stage sound reflection panels. Other considerations include the desired reverberation characteristic for the hall and the availability of storage space in the locations around the stage where stage machinery will also be housed.


<< Why Do Multipurpose Halls Need Stage Sound Reflection Panels? >>

When a multipurpose hall's programming will include full-scale opera, ballet and drama performances, the design of the hall's stage area must plan sufficient space not only for the performance area, but also for storing the large number of props, scenery and stage installations that these performance genres require. For these genres, the space above the stage typically has a fly tower that extends upward to a height equal to about twice the height of the proscenium opening. The fly tower houses the drop curtain and stage curtain, rigging for stage lighting, related suspension devices and other lighting equipment. In addition, stages built for opera, ballet and drama typically have stage wings of 0.5 to 1.00 times the width of the proscenium opening at stage right and stage left of the stage's performance area.

In contrast to the stage design I just described, the design needed for classical music performances requires that the sound absorbing spaces of fly towers, stage wings and the back portion of the stage be closed off from the main portion of the stage. Instead of being surrounded by these open spaces, classical music performances require sound-reflecting surfaces that effectively reflect the music's sound both into the audience seating area and back to the performers.

Fig. 1: Stage cross section drawing indicating direction reflection panels move for storage
Fig. 1: Stage cross section drawing
indicating direction reflection panels
move for storage

With regard to the multipurpose hall's sound reverberation characteristic, the needs of classical music performances also differ from the requirements for speech-based events. In particular, to obtain clear speech for ceremonies and symposia, the hall's reverberation time needs to be relatively short, while for classical music performances the reverberation time should be longer to obtain the rich acoustics appropriate to this genre.

While classical music performances require a stage design and sound reverberation characteristic that is the opposite of what is needed for other events held in multipurpose halls, nevertheless, multipurpose hall projects typically include the requirement that the hall be adaptable for classical music concerts. Temporary portable and storable stage sound reflection panels provide a solution for this objective. For example, in the many multipurpose hall projects that have ceremonies and symposia as their primary use, and that also need the hall to be able to be used as a venue for classical music concerts, the stage can be transformed from a proscenium configuration into a space appropriate for classical music performances using the method illustrated by Fig. 1. Stage sound reflection panels can be set in place so that they close off the stage's fly tower, side wings and rear stage area for classical music performances. When the hall is used for ceremonies and symposia, the stage sound reflection panels are stored in the fly tower and stage wings.

<< Hall Characteristics that Affect Stage Sound Reflection Panel Design >>

While the stage and sound reverberation conditions of a hall can be temporarily modified, obtaining the ideal conditions for every genre and kind of performance can still be difficult. For example, in multipurpose halls designed primarily for drama performances, the location in the fly tower to house the stage sound reflection panels is often the same space where the stage designer plans to store stage curtains, rigging and lighting equipment, resulting in a competition for the space between these conflicting design needs.

In large multipurpose halls intended primarily for classical music performances, the design requirements typically include the ability to vary the size of the stage depending on the concert program's music. The need for a variable size stage creates the requirement that the stage sound reflection panels also have a mechanism or means of being adapted to the various stage size options.

As can be understood by the above two examples, the specific situation of a multipurpose hall can create complex requirements for the stage sound reflection panels. Therefore, the design configuration and set-up methods of the stage sound reflection panels often play a critical role in achieving advanced levels of multipurpose functionality and excellent acoustical performance characteristics in multipurpose halls.

<< Acoustical Objectives of Stage Sound Reflection Panels >>

Photo 4: Steeply angled overhead stage sound reflection panel design
Photo 4: Steeply angled overhead
stage sound reflection panel design

Thus far, I have primarily discussed the requirement that stage sound reflection panels have mechanisms that make them portable on and off the stage. What other conditions, especially acoustically-impacting conditions, must the stage sound reflection panels meet? Fundamentally, the panels must meet specific shape and weight (density or mass in kg per sq. m.) requirements.

Regarding the stage sound reflection panels' shapes, they must be designed so that the sound reflections easily reach the audience. The appropriate shape partially encloses the stage, creates a sense of unity between the stage and the audience and propagates balanced sound reflections from the musicians on stage to the audience and among the musicians on stage as well.

The exact proportions and angle of the overhead and side stage sound reflection panels are also important. In the past, the overhead stage sound reflection panels were typically designed with a sharp slope that sent strong sound reflections early to the audience, as shown in the example of Photo 4. However, in current designs of multipurpose halls intended primarily for classical music concerts, we adopt the design methodology used when designing a concert hall and prioritize calculations of the delay times, densities and strengths of the sound reflections to the audience and the musicians on stage. As a result, we set overhead or ceiling stage sound reflection panels at a high height and give them a gentle slope. In addition, to promote sound diffusion, we design sound-diffusing protrusions or eaves in the side stage sound reflection panels. Photo 5 provides an example of this kind of design.

Photo 5: Stage sound reflection panel design with high ceiling and side protrusions
Photo 5: Stage sound reflection panel design
with high ceiling and side protrusions

Regarding the weight of the stage sound reflection panels, to effectively and consistently achieve sound reflections of even the low frequency sounds, the panels must be as heavy in weight as is practically feasible. In halls that have stage sound reflection panels constructed of thin, lightweight materials, even when the stage sound reflection panels are used, they vibrate and absorb the low frequency sounds, resulting in a short reverberation time characteristic for the low frequency sounds. (See Dr. Oguchi's article in our September, 2006 newsletter for further discussion about stage fly towers and sound absorption.)

Previously, damping sheets were sandwiched between layers of stage sound reflection panels to mitigate the panels' absorption of low frequency sounds while taking into consideration regulatory constraints concerning the weights of suspended objects. However, more recent designs use the same approach as for concert hall sound reflection panels that are installed above audience seating areas and along audience seating sidewalls. This design uses multilayered panels with weights of about 40 kg per sq. m.

I will end my overview of the background and basic design elements of stage sound reflection panel design here. In future writings, I will delve into specific examples of stage sound reflection panel storage methods, mechanisms for moving the panels and innovative designs to achieve specific acoustical conditions.


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

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Los Angeles, CA 90025, U.S.A.
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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 ]