Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS


News 12-10 (No.298)

Issued : October 25, 2012

[ Japanese Version ]

Tokyo Metropolitan Theatre Reopens after Major Renovations

By Akira Ono

Pre-renovation set-up for orchestral concerts (sound reflection panel system height*: 15 m.)
Pre-renovation set-up for orchestral concerts
(sound reflection panel system height*: 15 m.)

Pre-renovation set-up for concerts that use the pipe organ (sound reflection panel system height*:19 m.)
Pre-renovation set-up for concerts that use the pipe organ
(sound reflection panel system height*: 19 m.)

Additional set-up added by the renovations (sound reflection panel system height*: 16 m.)
Additional set-up added by the renovations
(sound reflection panel system height*: 16 m.)

* Heights are measured vertically
from 3 m. above the front edge of the stage floor.

For the past year and a half, Tokyo Metropolitan Theatre, located in Tokyo's Ikebukuro district, has been closed for large-scale renovations. In September, 2012, with the renovations completed, the venue reopened as a venue for concerts, plays, experimental theatre and other performing arts.

Nagata Acoustics' newsletter first featured this facility in the September, 1990 issue, shortly before the theatre's 1991 opening. Thereafter, every 18 months or so, we had reason to share something new about Tokyo Metropolitan Theatre with our newsletter readers. (These articles precede the 1997 start of the English language newsletter.) Commentaries about the facility and how it was being used kept this facility in Tokyo's cultural spotlight. Dr. Nagata penned most of the comments in our newsletter, offering his usual frank and unadulterated ideas and opinions.

<< Overview of This Renovation's Starting Point and Objectives >>

When we began the requirements phase of the renovation project we discovered that some aspects of the venue that were criticized when it opened have become well-loved features of the facility. On the other hand, some features that the original venue's decision makers strongly requested were not being used at all, while other functionalities had average reputations and usage rates.

The key objectives of this renovation included increasing the hall's safety features for both performers and audience patrons, improving the facilities' ease of use by performers and technical stage professionals and making high quality changes to enhance the venue's real and perceived value.

<< Concert Hall Renovations >>

The 1,999-seat Concert Hall is Tokyo Metropolitan Theatre's Main Hall. The project's renovations in this space focused on three interior changes:

  • Improve the overhead sound reflection panel system to a more desirable configuration by changing the shape of the sound reflection panels and adding an additional height configuration.
  • Add sound-diffusing ribbing to the wood walls near the stage.
  • Replace the oak (nara) wood stage floor with cypress (hinoki) wood.

Prior to this renovation, the stage's overhead sound reflection panel system could be set to a height of either 19 m. (62 ft) or 15 m. (49 ft) (measured vertically from the front edge of the stage). The lower height was provided based on the notion that this height would provide the best acoustics for orchestral concerts. However, from the time of the hall's opening in 1991 until the time this renovation began, the sound reflection panel system was rarely, if ever, set to the 15 m. (49 ft) height. Instead, the system was left at the higher height even when the pipe organ was not played during a concert.

Our investigation revealed three main reasons why the sound reflection panel system was kept at the higher height. Some hall employees thought that being able to see the pipe organ made the hall look more like a concert hall. Others thought that the higher setting was the "real" setting and still others were uninformed that the sound reflection panel system's height can be customized to the performance genre.

In the years before this renovation, when large orchestras played in the hall with the sound reflection panel system set at its higher height, the sound had a pleasingly spacious feeling. The performing musicians of most orchestras that played in the hall also said that they preferred the higher height. Therefore, we took the opportunity of this renovation to add a third height option of 16 m. (53 ft) that both keeps the pipe organ visible and puts the height of the sound reflection panel system just 3 m. (9.8 ft) lower than the full 19 m. (62 ft) height. Now, orchestral concerts can have improved acoustics while keeping the pipe organ visible.

Both the sound-diffusing ribbing on the side walls and cypress stage floor are upgrades that improve the quality of the hall's acoustics. We initially proposed these items during the planning and design of the venue's original project. For this renovation project, we again proposed these upgrades as measures that would positively impact the quality of the concert hall's acoustics and, this time, these two upgrades were included in the project scope.

After the completion of the renovations in September, we are hearing favorable comments about the effects of these changes. After a pre-opening performance in the hall, I asked Maestro Tatsuya Shimono for his impressions of the acoustics in the renovated hall. He replied that the hall's acoustics have always been superb and now the hall's sound has gained some additional mildness. The violin players said that they find it easier to play in the renovated hall, but some of the wind musicians commented that they have more difficulty hearing the string instruments. As orchestras acclimate themselves to the changes in the hall, I'm hopeful that these wind musicians will join the many others who have only positive words for the changes accomplished in this renovation project.

<< Background to the Playhouse Renovations >>

The Playhouse has 834 seats. When the Playhouse opened in 1991, the Japanese theatre world criticized it, saying that it was a difficult space in which to perform. In our September, 1991 newsletter (available in Japanese only) Dr. Nagata addressed these criticisms, including making recommendations for ways to remedy the source of the criticisms. One of the most categorical of his recommendations was for the Playhouse to hire an artistic director and change this theatre from a rental facility into the home of a repertory theatre company.

Now, more than a decade later, playwright Hideki Noda serves at the helm as the venue's Artistic Director. He served as the representative stakeholder to the Playhouse renovation, providing the renovation planning team the requirements and requests for the changes he wanted to see achieved. As a result, the Playhouse has been transformed by its Artistic Director into a theatre where the resident repertory company produces and stages its own productions. Dr. Nagata's recommendations have become a reality and the theatre now has the right infrastructure to drive its success.

<< Highlights of the Playhouse Renovations >>

Criticism arose about the Playhouse after its opening because of patrons in some seats had difficulty clearly hearing the performers on stage. We believed that the horseshoe shape of the hall was at the root of this problem because this shape can cause the undesirable phenomenon of sound focusing and, even though the original hall plans called for implementation of a sound system that would counterbalance the sound focusing, the implementation did not sufficiently address the problem.

The renovation project included a total makeover of the Playhouse interior, changing the style from formal elegance to a trendy, casual atmosphere that features brick walls and exposed concrete. For the rear brick wall, we specified an openwork pattern and we installed sound absorbing material behind the brick across the entire rear wall. The uneven surface of the brick wall serves to diffuse sound, benefitting the acoustics of the Playhouse.

<< Theatre East and Theatre West >>

On the basement level, Tokyo Metropolitan Theatre has two small halls. Before the renovation, one hall was a multipurpose hall and one was a black box theatre. On the recommendation of Artistic Director Noda, the renovations changed the multipurpose hall into a second black box theatre. The successful result has been a full calendar of bookings since the halls reopened and reservations far into the future.

Tokyo Metropolitan Theatre's Playhouse and Concert Hall have also been well-received and well-used since the completion of the renovations. The focus of the theatre is it repertory theatre offerings under the direction of Artistic Director Noda. Also, the non-profit performing arts and cultural organization Tokyo Creation Project has made Tokyo Metropolitan Theatre its main venue and has many exciting events planned for both children and adults.

I am glad that the post-renovation Tokyo Metropolitan Theatre has a full calendar and that favorable comments by both performers and audiences demonstrate the success of this project.

For more information about Tokyo Metropolitan Theatre, visit its website at http://www.geigeki.jp/.


Harbin Concert Hall 1/10 Scale Model Testing-on site in Harbin City, China

By Fumiaki Sakamaki

Audience seating
Audience seating

Stage
Stage

In Harbin City, the capital city of Heilongjiang Province-the northernmost province in northeastern China-construction is progressing on the new Harbin Concert Hall (also featured in the April, 2011 issue of this newsletter). Harbin Concert Hall will have a 1,200-seat main hall and a 400-seat small hall and is expected to become the cultural destination of the city's Qunli New Development Zone.

<< Overview of the Main Hall >>

The building that houses the main hall and small hall has an exterior façade that uses glass extensively to create an image of ice crystals. Portions of this glass façade also serve as sections of the main hall's interior upper side walls. The main hall interior has an arena configuration with seating surrounding the stage on all sides. Chandeliers are hung across a large center area of the main hall's ceiling . An Italian pipe organ is planned to be installed at the front of the stage.

From the start of our design process for the acoustical room design of the main hall, we included consideration of the audience seating's terraced walls, the angles of the glass façade and specifics of the ceiling's shape, using 3-dimensional computer simulations to determine the basic aspects of the hall's shape. After completing our computer-aided work, in April of this year we turned to detailed review and adjusting of the hall's configuration during a two-month testing phase in the 1/10 scale model of the hall built precisely to our design specifications.

<< Testing in the 1/10 Scale Model >>

We test in the 1/10 scale model primarily to check for echoes and, if we find an echo, to learn what is causing the echo and adjust the design of the surface(s) in question to eliminate the echo. We also use 1/10 scale model testing to collect impulse response data for comparison with data from existing halls and related physical indices in order to confirm the acoustical conditions of the space.

Inside the 1/10 scale model we install proportionally-scaled loudspeakers and microphones. Through these devices, we send sound into the model, record the sound and listen to the results. Because we can listen to these tests with our own ears, we can evaluate sound wave behaviors that are difficult to assess using computer simulations.

<< Testing How the Hall's Glass Elements Affect the Acoustics >>

For this project, in particular, we used the 1/10 scale model testing to check for echoes caused by the hall's unique glass surfaces. When we test for echoes in a 1/10 scale model, if we obtain a test result that might cause an echo condition, we analyze the wave pattern to find the specific location in the hall that could cause the echo and add either sound absorbing material or a sound diffusing element in the 1/10 scale model. Then we run the same test again to validate that we successfully eliminated the potentially echo-causing condition. We follow these steps for each test that produces a result suspected of causing an echo.

In the case of Harbin Concert Hall, our tests found that when certain sound waves came in contact with the hall's glass surfaces, wave patterns that could cause echoes resulted. We added proportionally scaled 1 mm.-thick pieces of rough-surfaced acrylic material inside the model to the model's glass walls and successfully eliminated the concerning wave patterns. We adapted our room acoustical design specification based on the knowledge gained through this testing process.

In addition, our 1/10 scale model testing revealed that the walls around the stage, while not causing echoes, were likely to produce undesirably strong reflections. To soften these reflections we prepared pieces of 1/10 scale ribbed sound diffusing elements, added them to the model and then tested the results to confirm that the change achieved the desired softening of the sound reflections' strength.

To understand the effect on the hall's acoustics of the ceiling chandelier, we conducted tests both before we added a scale model version of the ceiling chandelier to the 1/10 scale model and with the scale-model's ceiling chandelier installed. Based on our test results, we specified to the interior designer minor adjustments to the size of the chandelier and the manner in which they are suspended from the ceiling so that the chandelier provides effective sound reflections to the audience seating.

Excellent progress for the Harbin Concert Hall project continues at the construction site. The target date to complete the project is set for autumn, 2013.


Acoustical Design Legacies and Lessons of Older and Bygone Halls - Part 5
-Tokyo Bunka Kaikan Main Hall's Original Loudspeaker System-

By Dr. Minor Nagata, Founder of Nagata Acoustics

Photo 1: Tokyo Bunka Kaikan Main Hall
Photo 1: Tokyo Bunka Kaikan Main Hall

Photo 2: Opening in side wall for primary loudspeakers
Photo 2: Opening in side wall for primary loudspeakers

Photo 3: 2S-305 monitor loudspeaker provided by Mr. Tamon Saeki
Photo 3: 2S-305 monitor loudspeaker
(provided by Mr. Tamon Saeki)

Tokyo Bunka Kaikan, which last year celebrated the 50th anniversary of its opening, continues to this day to be a venue beloved by many classical music performers and concert patrons alike. The Main Hall and Small Hall each has an interior shape that is increasingly hard to find among concert halls. In particular, the main hall has a unique design on the two sides of its stage where outwardly curved concrete side walls rise with embellishments made of an abstract pattern of three-dimensional wood diffusing elements, creating a signature element of the hall's interior.

Tokyo Bunka Kaikan architect, Mr. Kunio Maekawa, conceived this stage design. Credit for specifying shapes and the concave depth of each wood shape belongs to Mr. Yasuo Makita, NHK Technical Research Laboratories' then lead acoustical design engineer for the Tokyo Bunka Kaikan project. Master sculptor, Mr. Ryokichi Mukai, interpreted the technical specifications into the Main Hall's artful walls (Photo 1). These three colleagues of mine are no longer with us, but their accomplishments and memories of them endure. It was an honor for me to work with them on this project.

<< The Main Hall's Loudspeakers >>

Each of the concrete side walls has two circular openings for air ventilation. Above the ventilation openings, at an apex midway between the two openings, each wall has two additional circular openings (indicated by the arrow in Photo 2). When Tokyo Bunka Kaikan opened in 1961, the Main Hall's primary loudspeakers were located behind these openings.

Each side wall had two pairs of loudspeakers. We installed standard 2S-305 monitor speakers, which NHK Technical Research Laboratories developed and Mitsubishi manufactured. Each of these 2-way speakers had a 30 cm. woofer and a 5 cm. tweeter.

For loudspeaker coverage to the seats at the rear of the first floor's audience seating, we embedded 3 pairs of 2S-305 loudspeakers in the ceiling above the first floor aisles. Also, on each level we installed additional speakers to ensure coverage at every audience seat. For these additional speakers we used single cone, 16 cm. diameter, sealed enclosure Diatone Mitsubishi P-62F dynamic speakers. We also embedded these speakers in the ceilings, installing 12 units per floor for a total of 72 units dispersed throughout the hall.

I recall that in addition to installing the 2S-305 units in the ceiling at the rear of the hall, we added means to pass the sound through a time lag device. However, the time lag device used a 76 cm. per second, endless-loop magnetic tape and the tape unfortunately tore quickly after being installed, rendering this innovation useless.

<< Tokyo Bunka Kaikan and the First Introduction of Feedback Stability Index >>

In the 1960s, we concentrated our sound system development efforts on microphones and monitor loudspeakers used during studio recordings. News about developments in the United States by JBL and Altec to design speakers for movie theatres did not reach us at that time. In hindsight, Japanese acoustical engineers and researchers, including me, might have turned our attention in those years from studio sound system needs to the sound system possibilities for performance halls. Had we done so, I wonder if our thinking might have illuminated a different approach to concert hall sound systems.

We designed and built Tokyo Bunka Kaikan primarily for unamplified performances of classical music, opera and ballet and it's true that we lacked strong interest in sound system features and equipment. However, we did implement a mechanism to prevent feedback.

Under certain conditions, when a PA (public address) system's amplifier is turned up, the unpleasant phenomenon known as feedback can occur with loudspeakers emitting unpleasant feedback noise instead of the desired amplified sound. During our sound system design for Tokyo Bunka Kaikan we developed a stability index for feedback and a way to measure it. Today, this mechanism is known as the "amplifier gain stability index".

Diagram 1: Set up for measuring an amplifier's maximum stable gain.
Diagram 1: Set up for measuring an amplifier's maximum stable gain.

<< The Amplifier Gain Stability Index >>

As shown in Diagram 1, to measure the maximum stable gain of an amplifier, a loudspeaker used as the sound source is set at a distance of 30 cm. in front of a PA system's microphone. (In a real application, the sound source would likely be a person speaking into the microphone.) For the input signal of this loudspeaker, pink noise and white noise signals attenuated by an octave and 3dB per octave, respectively, are used. The amplification level is raised and at a certain point oscillation (that is, feedback) occurs. Next, the amplification is constrained to 6dB below the point at which feedback occurs, pink noise is again input through the amplifier and the sound pressure level at the audience seating is measured.

In this set up, the distance between the microphone and loudspeaker is set at 30 cm. Normal conversation typically take place between two people who are about 1 m. apart. Therefore, when the sound pressure level of sound at the time it passes through the microphone exceeds -10dB, the amplified voice will have natural sounding volume.

<< Loudspeaker Changes Came Early to Tokyo Bunka Kaikan >>

In the decades since its opening, Tokyo Bunka Kaikan has undergone both large and small scale renovations. I recall that a replacement loudspeaker project was among one of the earliest of the hall's renovation projects.

Replacement loudspeaker systems come and go. In this article I wrote about the well-known 2S-305 speaker that did a good job as the hall's amplification system 70 years ago. I find it noteworthy that this vestige of the original sound system still shows its "face" tucked in away in a corner of the Main Hall where you and I might notice and remember it.



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[ Japanese Version ]