Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 12-05 (No.293)

Issued : May 25, 2012

[ Japanese Version ]

Orix Theater Opens (Formerly Osaka Koseinenkin Kaikan)

By Nobuhiko Hattori

Starting in 1968, and for more than 40 years thereafter, Osaka music fans flocked to Osaka Koseinenkin Kaikan for (mostly pop-music) concerts. On April 8, 2012, this venue, now privatized, renamed and renovated, reopened as Orix Theater. The inaugural concert featured a program of classical music.

The theater's stage prior to the renovation
The theater's stage prior to the renovation

New Orix Theater stage
New Orix Theater stage

New Orix Theater audience seating area
New Orix Theater audience seating area

<< History of the Theater and Scope of the Renovation Project >>

During the second half of the 20th century Japan built seven public multipurpose halls known as "Koseinenkin Kaikan" across Japan, one in each of the following cities: Sapporo, Kanazawa, Tokyo, Nagoya, Osaka, Hiroshima and Fukuoka. Eventually, these public halls became financially unsustainable and, during economic downturns, the government sold them to private companies. In the case of Tokyo Koseinenkin Kaikan and Aichi Koseinenkin Kaikan (in Nagoya), the new owners tore down the halls and replaced them with buildings for other purposes.

In the case of Osaka Koseinenkin Kaikan, Orix Real Estate Corporation purchased the property and developed a plan that gave different fates to each of the old facility's two wings. While the wing that housed a performing arts hall (1,100 seats) and rental spaces for weddings, assorted community classes and other private events was demolished and now in process of construction replacing with condominiums, Orix decided to renovate and partially add to the wing that contained the main hall (2,400 seats), back-stage dressing rooms and a green room.

<< The Plan to Add Concert Hall Programming >>

Prior to the renovation, the main hall venue was used mostly for popular music concerts. As part of the renovations, Orix requested that the new acoustical design be appropriate for classical music concerts and opera as well. Therefore, within the constraints dictated by the existing structure being renovated, we focused our work on achieving the best possible acoustics for classical music concerts.

Kume Sekkei Co., Ltd. designed for the renovation of the property's main hall wing. Nagata Acoustics provided acoustical consulting services from the design phase of the renovation project through the project's completion. Highlights of our work included the room acoustical design, noise abatement improvements and new loudspeakers for the sound system.

<< Room Acoustical Design >>

For classical music concerts, a hall stage's system of sound reflection panels should provide abundant early sound reflections and contribute to the hall's long reverberation time. In the old Osaka Koseinenkin Kaikan, sound reflection panels were hung between the stage and the ceiling above it, but they created a steep angle from the stage to the audience ceiling and the system had many gaps between and around the reflection panels. As a result, the main floor seating, in particular, received few early sound reflections. In addition, at some point in the past, the management of Osaka Koseinenkin Kaikan had replaced the seats' original upholstery with a material that negatively impacted the length of the hall's reverberation time. In the old hall, there was hardly any difference between the reverberation time of the hall when configured with its sound reflection panel system and when configured with its stage curtain. The old Koseinenkin Kaikan, though a multipurpose venue, was unsuitable for classical music concerts.

The old hall's interior had attractive side walls of porcelain tiles that the owner and renovation team wanted to retain in the design of the new Orix Theater, so we focused our acoustical design on renovating the stage sound reflection panel system and changing the shape of the ceiling to create a more gentle slope (as shown in Fig. 1). As a result of these changes, we successfully increased the amount of early sound reflections that reach the first floor audience seating.

For popular music concerts, Orix Theater retracts and stores its stage sound reflection panel system and we kept the venue's pre-renovation, short reverberation time for this configuration. For classical music concerts, we designed a stage configuration with a new system of sound reflection panels. Our goal for this new system was to achieve the longest possible sound reverberation time.

The new sound reflection panel system uses a mechanism and design that minimizes gaps between the panels. Our only option for a location to store the sound reflection panels was the stage fly tower, which remained mostly the same size before and after the renovation project. This constraint of limited storage space motivated us to find a solution that both fits the fly tower space and minimizes the possibility of gaps between the panels. In the sound reflection panel system we designed, the front side panels are set in place by sliding them forward (towards the audience) from the center side panels after the system descends from the fly tower.

Fig. 1: Cross section view
Fig. 1: Cross section view

In addition to the new sound reflection panel system, we also improved the sound reverberation time by making changes to the seating upholstery. We decided to reuse the pre-renovation seats and change the upholstery of the seat surfaces and the front portions of the seatbacks. In addition, to reduce sound absorption by the seats' upholstery, we affixed a laminate material to the rear portions of the seatbacks of the two balcony tiers' seats, which have higher backs than the main level seats.

Fig 2: Reverberation characteristic of Orix Theater  (with sound reflection panels in use)
Fig 2: Reverberation characteristic of Orix theater
(with sound reflection panels in use)

Our strategies to obtain the maximum reverberation time for the classical music concert configuration resulted in our increasing the sound reverberation time from 1.6 seconds to 1.9 seconds (at 500 Hz). In a fully occupied hall, we achieved a (calculated) reverberation time of 1.5 seconds which, while not quite the reverberation time of a hall built exclusively for classical music concerts, does represent a valuable improvement on the order of 0.2 seconds compared with the pre-renovation hall's reverberation characteristic.

Another focus of our room acoustical design addressed the conspicuous long path echo heard in the pre-renovation hall whenever the sound amplification system was used. This undesirable phenomenon especially affected performances by inexperienced singers who found it difficult to adjust to the condition and performers were known to warn one another about the "Osaka Koseinenkin Kaikan echo". As part of the renovation, we gave the rear wall of the audience seating area a sound absorbing surface and eliminated the disturbing long path echo from the acoustics of Orix Theater.

<< Noise Abatement Design >>

The HVAC system of the pre-renovation hall produced a noise level of between NC-25 and NC-31. In addition, transformers in the electrical room adjacent to the hall produced noise. Together, these two sources produced noise unacceptably loud and distracting for a classical music concert environment.

The renovation plan included reuse of the pre-renovation HVAC equipment, but we replaced the ductwork with anti-vibration and sound-dampening duct materials and we also redesigned the quantities and locations of the silencers . Our design resulted in the HVAC system's noise level being reduced to a level of NC-20. In addition, to isolate the sound of the transformers as well as other external noise, we upgraded the anti-vibration materials installed around the transformers and we also upgraded sound proofing doors around the hall stage and the electrical room.

<< Renovation Plan for the Stage Sound System >>

Prior to the theater's renovation, the stage had a proscenium loudspeaker and side speakers at each of the left and right sides of the stage. The proscenium speaker had not been replaced in 30 years. Because of its inadequate sound volume and sound quality, this speaker was no longer usable. Instead, the old hall relied entirely on the two stage side speakers that Koseinenkin Kaikan's management had updated about 10 years before the start of the Orix renovation project.

Unfortunately, differences could be heard between the sound quality of the left and right side speakers. Also, the amplified sound of the left and right side speakers, with their different sound qualities, overlapped at some audience seating locations, while the sound speaker coverage simply missed other audience seating locations.

From this starting point, we developed a renovation plan for the stage sound system using the same type of loudspeakers as the pre-renovation stage side speakers. We installed a new loudspeaker at the center of the proscenium, replaced the side speakers with new units, increased the number of speakers at the left and right sides of the stage, revised the placement angles and adjusted the entire sound system for optimal performance.

<< Inaugural Concert >>

Orix Theater celebrated the opening of the renovated venue with a classical music program featuring Maestro Akira Miyagawa and Maestro Tatsuya Shimono conducting the New Japan Philharmonic Orchestra. Maestro Miyagawa created a program with the city of Osaka as its theme and included a live talk session with the audience. Maestro Shimono performed Beethoven's Seventh Symphony. Both performances filled the new theater with energetic and festive music that made the evening truly a gala event.

Outside, in the park adjacent to Orix Theater, the cherry trees showed their full blossoms like a delicate paean welcoming Orix Theater's gala opening. When the concert ended, many of the audience patrons took a stroll in the park to savor the cherry blossoms and continue their enjoyment of the inaugural concert evening.

Orix Theater's home page can be found at http://www.orixtheater.jp/.

Acoustical Design Legacies and Lessons of Older and Bygone Halls - Part 3

-- Mr. Tsukuda's Slide Rule for Room Acoustics --

By Dr. Minoru Nagata, Founder of Nagata Acoustics

<< The Sabine Equation >>

The seemingly complex phenomenon of how sound reverberates in a room began to be deciphered towards the end of the 19th century. Harvard physicist W. C. Sabine defined reverberation time (RT) as the number of seconds required for a sound intensity to decay to one one-millionth of its original state. Sabine established that the reverberation time of a room can be calculated using the volume (V), which is a cubic meter (m3) value, the total surface area (S), which is a square meter (m2) value and the average sound absorption coefficient indicator, represented by the symbol "α". Eq. 1 shows Sabine's equation for this calculation.

Eq. 1 : RT=0.161V/Sα

The sound absorption coefficient α of a surface is an indicator that is calculated using the formula of 1 - r, where r equals the ratio of "R", the intensity of sound reflected from a surface, divided by "I", the intensity of incident sound that initially came in contact with the surface. That is, r = R/I. If a surface totally absorbs sound, then α = 1 and, if a surface totally reflects sound, then α = 0.

The average sound absorption coefficient α provides an indication of the degree of sound absorption in a room. For concert halls, the average sound absorption coefficient typically equals on the order of 0.2 to 0.25. For theatres, the coefficient is between 0.25 and 0.30, and for recording studios, the coefficient typically equals between 0.3 and 0.4.

In connection with the Sabine equation shown above, let me highlight its reliance on just 3 values (room volume (V), surface area (S) and average sound absorption coefficient (α) to easily calculate a room's reverberation time (RT). This equation has been a mainstay of hall and recording studio acoustical design and continues to be a widely used formula to this day. However, there's a problem with relying on the Sabine equation. The problem is that even in a situation where α= 1, meaning that sound is entirely absorbed, the reverberation time will not equal zero.

<< The Eyring Equation >>

To solve the problem of the Sabine equation, in 1930, C. F. Eyring presented the equation shown in Eq 2.

Eq. 2 : RT=0.161V/(-Sloge(1-α))

The difference between the equations of figures (1) and (2) is their denominators. Sabine's equation uses α for the denominator and Eyring's equation uses -loge(1-α). The resulting difference becomes larger as the value of α increases. For example, when α = 0.1, the difference is 5%, when α= 0.2, the difference is 12%, when α = 0.3, the difference is 19%, and when α = 0.4, the difference is 28%.

When I worked at NHK Technical Research Laboratories, NHK built its radio studios to have relatively dead acoustical environments of slightly greater than α = 0.3. Therefore, at NHK Labs we adopted the use of Eyring's equation to calculate the reverberation time of our acoustical designs, a practice that NHK continues to follow to this day. Nagata Acoustics also uses the Eyring equation.

By the 1960s, estimating and predicting room reverberation times became an integral part of the calculations we perform during our room acoustical design work. In order to use Eyring's equation, we needed to add the extra step of calculating the logarithmic function of -loge(1-α). At first, we relied on a reference book that even now is tucked away in some corner of a bookshelf somewhere in our office. This guide, entitled "Architectural Acoustics Handbook", by the Acoustical Materials Association of Japan (published in 1963 by Gihodo Shuppan) contains an article about reverberation time equations and has an "α" to "-loge(1-α)" conversion chart. The chart spans two full pages.

Photo 1: Tsukuda Slide Rule

Photo 1: Tsukuda Slide Rule
Photo 1: Tsukuda Slide Rule

<< The Tsukuda Slide Rule >>

I've written this long, technical preface to introduce an invention worth remembering. It's a calculation tool that measures a mere 150 mm (6 in.) long x 29 mm (1 in.) wide, and it contains all the information needed for the logarithmic calculation in the Eyring equation. Best described as a slide rule for room interior design calculations, we named the tool after its inventor, Mr. Tsukuda, and call it the Tsukuda slide rule (Photo 1).

My former colleague Mr. Harutoshi Tsukuda is an architect by training. He was slightly junior to me at NHK Labs, where he began his career in the Architecture Division. Around 1950, he changed assignments and joined the Technical Research Laboratories' Acoustical Research Department. Mr. Tsukuda was known among our colleagues for his deliberate, methodical work habits. For example, I remember that he tirelessly pursued the visualization of sound reflection paths to create ray-tracing diagrams that illuminated the content of the department's written reports.

To use the Tsukuda slide rule shown in Photo 1, one need merely slide the center bar of the slide rule, which has values of V/S, so that it aligns with the mark of V/S on the fixed portion of the scale, and the relation of the average sound absorption coefficient α and reverberation time RT values can be read. I still use my Tsukuda slide rule when studying the sound absorbing properties of surfaces in small spaces, such as residential music rooms. In addition, I can use the "m" (energy attenuation constant for sound traveling through air) at the left end of this tool to determine the humidity correction needed in a room. (This is especially important in large spaces.)

Mr. Harutoshi Tsukuda
Mr. Harutoshi Tsukuda

Unfortunately, I do not have documentation or instructions for the Tsukuda slide rule and my use of this tool is limited to the calculations I just described. Therefore, this completes my retrospective about it.

The Tsukuda slide rule became commercially available around 1960. About a decade later electronic function calculators came on the scene and the Tsukuda slide rule disappeared from market . In Japan, before World War II, we used the abacus. In the 1950s, a Japanese manufacturer produced the Tiger mechanical calculator. Desktop electronic calculators superseded this innovation and were in turn superseded by personal computers as the pace of technological innovation increased dramatically with each year and decade. Today, handheld electronic calculators collect dust in dollar discount stores, despite their minimal price. I thought that the phrase "slide rule" was obsolete, but I discovered that slide rules can still be purchased online.

"Organ Entertainment 5"Concert Planned for This July

By Toshiko Fukuchi

After last year's Great Tohoku Earthquake disaster required the cancellation of this organ concert, the organizers plan to hold the concert this summer, with the venue moved to Yokohama's Minato Mirai Hall. This summer's concert will be the 11th concert in this series, which dates back to a first concert held in 2004.

The concert will feature Mr. Ryoki Yamaguchi, the same organist who performed the previous concerts. The change of venue from Triphony Hall to Yokohama Minato Mirai Hall will add the novelty of the very different flavor of this hall's organ compared with the organ at Triphony Hall.

Minato Mirai Hall's organ, affectionately known as "Lucy", has exceptionally clear tones and the concert program of both classical music and movie soundtracks will be a concert sure to delight all attendees. This year, the organizers are trying something else new as well with the addition of some silent movies during the performance.

The concert date is a weeknight, but it may be the perfect opportunity to spend time near the port of Yokohama at the trendy Yokohama Minato Mirai Hall. If you're in the area this summer, please consider it.

The concert features Mr. Ryoki Yamaguchi, on July 30 (Monday) in the Yokohama Minato Mirai Hall Main Hall. Doors open at 6:30 p.m. and the concert begins at 7:00 p.m. Ticket prices are ¥2,500 (¥1,500 for students and seniors over age 65). For tickets, call +81-45-682-2000.

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 ]