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

Nagata Acoustics News 98-10iNo.130j
Issued : October 25, 1998

Oita Prefecture's New Multi-use Cultural Center Opens at "Oasis Hiroba 21"

by Chiaki Ishiwata

Ongaku no Izumi Hall
Grand Theater
September 1, 1998 marked the opening of a new type of multi-building complex intended to lead Japan into the next century. Named "Oasis Hiroba 21," the complex is located eight minutes by foot from Oita Station. It contains not only the new Cultural Center, but also the local offices of the Japan Broadcasting Corporation, a new hotel: Dai-ichi Hotel Oita Oasis Tower, and commercial and office space. The promoters of this new complex expect Oasis Hiroba 21 to serve as a resource for--and supplier of--cultural activities and information as we enter the 21st century. The complex's name was devised by Oita Prefecture's Governor Hiramatsu, who created it from the first letters of the words Oita Asia Sekai International Square. Of these five words, only one is a Japanese word -- "sekai", meaning "world".

The Cultural Center project began as a proposal submitted to a competition for proposed uses of a large parcel of centrally located land that was left empty when the Oita Prefectural Hospital moved to a new location. Nagata Acoustics cooperated in the submission of the proposal for the Cultural Center, providing design, project management, and measurement expertise for the acoustical engineering and ventilation system requirements. The architectural design was done by Nikken Sekkei Ltd. and the construction contractor was a joint venture of Fujita Corporation and other firms.

The new multi-use Cultural Center has a large and medium-size hall, a rehearsal studio, and nine large, medium, and small practice rooms. In addition, the Center has rooms intended for use as meeting and conference facilities. From this mix of facilities, it is easy to see that the Center's steering committee wanted not only to provide a venue for performances by top-class domestic and international artists, but also aimed to create a facility that will support local cultural activities and offer these local activities a location where they, too, can perform and demonstrate their creativity.

<< The Cultural Center's Grand Theater >>

The large hall, christened "Grand Theater," holds an audience of 1966 seats and is a multipurpose, shoebox-shaped hall designed with an emphasis on concert performances, but also with the expectation that it will be used for operatic and theatrical stagings as well. To this end, we equipped the hall with portable standing reflection panels and a three-sided stage. Because the desirable reverberation times for concerts, theatrical performances, and lectures or other speaking engagements vary widely, we designed an installation that can be adapted to the differing needs of each of these kinds of events. Even within the genre of musical concerts, the desirable stage set-up varies depending on the size of the ensemble that will be performing. Our adjustable stage also enables the stage to be customized to the needs of different performing group sizes. The hall's adjustable reverberation is controlled by the ribbed design element in the hall's upper walls. Behind the ribbed section of the walls, we installed a sound-absorbing layer of glass wool that can be raised or lowered. Because the glass wool is behind the visible ribbed walling, adjusting the reverberation time by raising or lowering the glass wool does not alter the visual design aesthetics of the hall. The hall's reverberation time is approximately 2 seconds (at 500 Hz), when the glass wool absorption layer is not in use, and is 0.2 seconds shorter when the glass wool is in place.

<< The Cultural Center's Ongaku no Izumi Hall >>

The Center's second hall, named Ongaku no Izumi Hall, seats an audience of 710 persons and is designed primarily for musical performances and, in particular, the performance of chamber music. (The Japanese word izumi is a beautifully poetic word, for which the nearest English translation is "wellspring". Thus, this hall's name means "the musical wellspring".) However, this hall is also equipped with apparatus that adjusts the reverberation so that it may be used for lectures and other speaking engagements, giving it some characteristics of a multipurpose hall. In this hall, the ceiling has reflection panels that can slide into a housing when they are not needed, and the side wall reflection panels can also be rotated to change the hall's reverberation time. When the reflection panels are deployed, the reverberation time in this hall is approximately 1.8 seconds (at 500 Hz). This hall has also been equipped with a curtain behind the ribbed back wall of the stage so that adjustments can be made to the acoustics on stage. This enables the hall to better customize the stage for use by ensembles of different sizes and combinations of instruments.

<< Sound Isolation Issues in the Oita Prefecture Cultural Center >>

The focuses of our sound isolation design for the Cultural Center included primarily: (1) ensuring that the sounds of the large and medium-sized halls would not be heard in the other hall and; (2) ensuring that sounds from the practice rooms below the large hall were isolated. The Center's Grand Theater and Ongaku no Izumi Hall have different ceiling heights, but are located side by side. Keeping in mind the likelihood that these halls will be used simultaneously, we installed an acoustical expansion between the halls. In addition, we installed an anti-vibration, sound-insulating layer beneath the floor of Ongaku no Izumi Hall and behind its walls.

Both the rehearsal studio and the practice rooms of the Center are partially situated directly below the Center's large hall. In order to ensure that sound from these facilities will not be heard in the large hall, we planned special sound isolation upgrades and implemented anti-vibration and sound-insulation structural techniques throughout this part of the Center.

<< Opening Ceremonies Match the Center's 21st Century Outlook >>

The Cultural Center's opening ceremonies were a fitting testimonial to its dedicated mission of providing an arts venue for the 21st century. The opening ceremonies featured a performance by junior high school pianists and a chorus, certainly representative of the Center's future performers and audience.

Beginning October 18, 1998, the local arts festival will be in full swing, and the Center's halls will also begin a seven-month long series of concerts and events to inaugurate the hall, including orchestral, chamber music, opera, and a variety of inaugural activities that will continue through April 1999. We join with the Center's organizers and staff in wishing them much success as a cultural oasis, where the people of Oita Prefecture will gather to enrich their lives through the performing arts.

20th International Conference of the ISO
(International Society of Organ Builders)

by Dr. Minoru Nagata

The initials ISO usually refer to the International Organization for Standardization, but the ISO that is the subject of this article is the International Society of Organ Builders. This Society, referred to as the ISO by those who know it, holds international conventions bi-annually, and just finished hosting its 20th International Convention, from August 16 to August 22, 1998. This year's convention was based at the Cite Internationale Universitaire de Paris, located at the southern tip of metropolitan Paris, with some events taking place at other locations in and around the city.

According to literature provided by the ISO, 200 persons from 19 countries attended the ISO 20th International Convention. Germany was the most represented country, with 53 persons attendees.

The convention's program provided for a full week of activities. From Monday to Friday, I visited organs at churches in Paris and its environs, where I listened to and observed the organ installed in each location. I also attended an hour-long demonstration on the voicing of French reed pipes. On Saturday, the last day of the convention, I joined a 14-hour-long tour of churches in the French suburbs. For the entire week, my waking hours were truly steeped in organ listening, observation, and study.

During the weekdays, I left my hotel daily at 8:15 in the morning and, following the directions in my convention program, rode the Paris subways and navigated the necessary transfers to arrive at the specified church by the program's designated start time. Each day's program followed the same pattern: First a speaker would talk about the organ of the church. The talks were given in English, in German and in French. Next, the organist was introduced, followed by a performance of approximately 30 minutes. After the performances, there was time to observe the organ at close range. The convention organizers provided a helpful program book that documented in a well-presented manner the history of each organ's specifications, manufacture, and repair or renovation, as well as the organ builder's name, information on the organist for each performance, and titles of the works performed.

Our first little trip was on Monday, August 17. We traveled by bus to the town of Houdan, 35km west of Versailles. There we visited Saint Jacques Saint Christophe Church and my heart fairly swooned at the organ's gracious, rich sound as it enveloped the sanctuary where we listened to it. Later, I discovered that with the exception of two or three of the churches we visited, almost all of the churches chosen by the convention shared this same kind of luxuriant sound, sustained by the rich reverberations of the church's high ceilinged spaces. The organ at the church in Houdan dates back 250 years, and is said to be a famous instrument now sought after for use in recordings and other projects. Somewhat ironically, the organ balcony had a maximum weight limitation of five persons, indicating a lapse in the protective care being extended to this instrument despite its high value.

Over the course of six days, I visited some 25 locations and listened to as many mini-recitals. Among our stops were the chapel at Versailles; Saint Clotilde Church, where Cesar Franck was our performing organist; Messiaen's Saint Trinite Church, and Notre Dame Cathedral, where Olivier Latris performed for us. It was truly a week in which I enjoyed to the fullest the refined timbres of the French organ.

I was particularly impressed by the organ at a country church we visited late in the afternoon of the last day's "marathon" tour. This church is the Church of Notre Dame in Lorris, a Paris suburb. The organ in this church is the oldest of extant French organs, having been crafted in the early part of the 16th century. It's organ builder is unknown and the organ itself sat gathering dust for many long years until 1974, when it was refurbished. Unlike many reconstructed organs that undergo considerable transformation in the process of being repaired, the organ in the Lorris Church of Notre Dame retains 80% of its original pipes. In the sound of this organ I could hear the pristine artlessness and gentle "voice" of these pipes that weathered many years of silence and now produce music once again. But here, as well, I was struck by the deteriorated state of both the interior and exterior of the church building and a sense that this treasure might somehow be left behind as modernity progresses.

By attending this ISO Convention, I caused myself to question and express simple doubts as to the "true" primary factors that created the beautifully refined and graceful timbres I experienced for an entire week. Was it the sensibility and craftsmanship of the organ builders, the many years of aging of the instruments, the high, vaulted ceilings of the churches, the positioning of the organs midway between those high ceilings and the church floors, the reverberation times that easily exceeded 5 seconds, the gently subsiding nature of the reverberation of the lower registers, or a number of other factors? Ultimately, I wonder if the answer to this question lies in the delicate balance between the church spaces and the instruments, a harmony achieved over many years of "cohabitation" with one another. My week in Paris was an invaluable week of sound and harmony that I would never have been able to experience in my own homeland.

A Discussion of Stage Acoustical Reflection Panels

by Toshiko Fukuchi

When a new hall is completed and performers get their first taste of performing on its stage, sometimes their first impression is that they find it difficult to hear themselves. Or, in the case of an orchestra, sometimes their complaint is that the players in one section cannot hear the other instruments. If the hall has the appearance of having a very high ceiling, performers frequently attribute the cause of their difficulty to the ceiling's height. Some of the halls designed by Nagata Acoustics have also faced this challenge of performers' negative first impressions. Certainly, the height of a hall's ceiling is one factor that affects how performers will hear the sound they produce on stage. However, it is also our experience that,, after a time span of several years, performers' concern about a hall's ceiling height tends to diminish and eventually disappears.

It is a generally accepted acoustical engineering principle that comparatively strong early reflections from both ceiling and walls are the key to designing a stage on which performers hear themselves and their co-performers easily. Of course, performers' ability to hear themselves and each other is essential to their successfully achieving an ensemble, or tutti, performance. Early reflections refer to sound that is reflected back from walls and ceilings after a minimal time lapse of approximately 0.08 seconds.

<< The Larger the Hall the Less Early Reflections on Stage >>

At normal room temperatures, sound travels at 340m per second. Therefore, the lower a hall's ceiling, or the narrower the hall, the more abundant will be the early reflections heard on stage. However, when large contemporary concert halls are designed, higher ceilings tend to be favored as a means of increasing the total cubic volume of the hall, thereby enhancing the richness of the hall's sound. In addition, if a pipe organ is installed behind the stage, the ceiling must be built even higher. Under these conditions, it necessarily becomes more difficult to bring those valuable early reflections to the stage area. The larger the hall, the more likely is one to hear the kinds of performers' complaints mentioned in my opening paragraph above.

<< Early Reflections are Critical to Concert Hall Acoustical Design >>

When Nagata Acoustics engineers the acoustical design of a concert hall, we focus on the design options' early reflections in determining the shape of the hall. At the same time, we give full consideration to the necessity of having the early reflections heard on stage. When the height of a hall's ceiling is higher than what we would like it to be to achieve the best acoustics, we design suspended reflection panels in order to produce the early reflections needed on stage. In previous research on reflection panels in halls, I discovered that suspended reflection panels are used in a majority of halls that have ceilings 15m high and above.

<< Reflections Panels used in Triphony Hall >>

In the acoustical engineering process for Triphony Hall (opened in autumn 1997, in Tokyo's Sumida Ward), I responded to our client's request that the hall be adaptable for other-than-concert use by not including suspended reflection panels in my design. Keeping in mind that a ceiling of 15m height or higher would necessitate reflection panels, I designed a ceiling that slopes from the stage end of the hall to the back of the audience seating. This enabled me to limit the ceiling height above the stage. At the very back of the stage, the ceiling is only 12.5m high, and at the edge of the stage the ceiling height is just 15m. For a hall the size of Triphony Hall (1801 seats), which has a pipe organ installed at the rear of the stage, these ceiling heights are quite low.

Despite my best efforts, when the New Japan Philharmonic Orchestra tested out the hall under the baton of Maestro Seiji Ozawa, six months before Triphony Hall's scheduled opening, Maestro Ozawa's immediate initial comment was that he was having difficulty hearing the first violins. Then, of course, people immediately sought the cause of this concern by looking up at the height of the ceiling. After some discussion, we tested the installation of 17 temporary suspended reflection panels, and ultimately, we installed the 24 suspended reflection panels that are in use in the hall today.

The closer the reflection panels are to the performers, the stronger will be the early reflections. It is a no-brainer that this makes the playing conditions easier for the performers. Especially in the case of a new hall, the performers are not accustomed to the particular direction from which the hall's early reflections will reach them. This makes it all the more important to have strong early reflections that performers can easily hear. Consequently, if a stage is evaluated by performers for ease of hearing before they have spent some time to acclimate themselves to the new hall, it is almost a foregone conclusion that the evaluation will include a request for reflection panels to improve the sound on stage.

The reason that the administrators of Triphony Hall decided to proceed so quickly with adding reflection panels is probably due to the New Japan Philharmonic's franchise relationship with the hall (meaning that this orchestra will hold all of its subscription concerts in the hall) and to the hall's desire that the perfection of the hall's sound be an ongoing process of growth, rather than a static achievement that would not change after the hall's completion. Since installing the reflection panels, the hall has repeatedly used trial-and-error in an attempt to find the best heights for the panels. As of this writing, of the three rows of panels, the two posterior ones are set at a higher height than their original setting. I expect that Triphony Hall will be adjusting its reflection panels for some time to come.

<< How Long Does It Take to Become Accustomed to a New Stage? >>

Just how long does it take until performers become accustomed to the early reflections of a new hall's stage? The time frame seems to somewhat longer than one or two years, but cannot be estimated more precisely than to say several years. Often, some years after a hall opens, both audience and performers start to say that a hall's sound has changed and improved. They ask what measures were undertaken to make this happen. In fact, usually no action has been taken at all. While some of the perceived improvement may come from the structure's natural aging (as materials dry out, etc.), I think that the more significant change is that the performers (and audience) have become familiar with the hall's particular characteristics and sound. From an acoustical engineering perspective, far too many halls rush to add reflection panels before the hall is used for a sufficient period during which performers become familiar with it and therefore better qualified to evaluate its stage.

<< The Deliberate Approach of The Harmony Hall >>

The Harmony Hall, in Matsumoto City, has been open for more than 10 years, and its excellent acoustics enjoy an excellent reputation with audiences. Nevertheless, performers have repeatedly expressed their desire for reflection panels to improve the quality of sound on stage. In response, suspended reflection panels were installed last year. After the installation, tests were done to determine the best height for the panels. The performers who participated in the tests were all musicians familiar with The Harmony Hall. From the tests, we confirmed that adding the panels did aid performers in hearing themselves and co-performers more easily. We also found that the lower the panels were hung, the better became the hearing of performers on stage. However, as we worked with the musicians, performing many on-stage hearing tests with the panels hung at various heights, the performers they came to agree that setting the reflection panels high above the stage did not have a significantly negative impact on their efficacy. The overwhelming opinion of the audience was that setting the panels higher seemed to better preserve the excellent acoustics that they are accustomed to at The Harmony Hall.

I have been told that at one concert in this hall the reflection panels were suspended just seven meters above the stage, demonstrating to me the large range in personal preferences when it comes to the strength of early reflections performers wish to hear. In addition, this anecdote made me acutely aware of the danger in halls that are primarily rented out to impresarios and promoters, as time limitations may result in reflection panels being set according to performers' requests (so that they can hear themselves easily) without checking how those settings may impact on the sound heard by the audience.

The ability to hear oneself and other performers easily on a stage is the successful result of several factors, only one of which is the installation and setting of reflection panels. The use of tiered platforms and the configuration of the walls around the stage also play a role. The relative importance of each of these factors is as yet unclear--an aspect of acoustical engineering that awaits further study. And because, in the end, the evaluation of a stage also depends so heavily on the familiarity of the performer with that particular stage, this is truly a realm where art and engineering intersect. It is an issue not easily subject to objective resolution.

Nagata Acoustics News 98-10iNo.130j
Issued : October 25, 1998

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