Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 14-02 (No.314)

Issued : February 25, 2014

[ Japanese Version ]

Hirosaki Community Center Celebrates Gala Reopening and 50th Anniversary

By Chiaki Ishiwata

The Elaborate Doncho (
The Elaborate Doncho ("Drop Curtain") Entitled
"Princesses Sending Up Falcons" by Shikō Munakata

The Hall Configured With New Acoustical Shell
The Hall Configured With New Acoustical Shell

Copies of the Original
Copies of the Original "Retro" Chairs in the Lobby

As readers may recall from my article in our March, 2013 newsletter, shortly before its 50th anniversary Hirosaki Community Center, in Aomori Prefecture, closed its doors for a major renovation. The work completed on time and the center reopened immediately after New Year's on a snowy January 5, 2014. Local Hirosaki residents and people who participated in the project walked across the snow-covered park grounds to the community center for the unveiling of the renovated hall's Nishijin-ori drop curtain and a concert that used the new acoustical shell to commemorate the center's reopening and showcase its acoustics.

Mayekawa Associates, Architects & Engineers, the firm that designed the original building, served as the architect for the renovation project. A local joint venture of Horie Gumi and others was the general contractor. Nagata Acoustics collaborated on the acoustical design and managed implementation of the acoustical specifications.

<< Renovation Goals >>

The Hirosaki Community Center renovation project came about as a result of the city's 2010 proposed "Hirosaki City Historical Beautification and Renewal Plan". The community center was one of the buildings designated as having historical value and the decision was made to preserve and maintain it.

In addition to repairing the parts of the building that had aged and doing seismic and other structural upgrades, the renovations aimed to improve the usability of the hall for both audiences and performers. The audience seats were replaced with new, wider seats and the number of dressing rooms were increased. Energy-saving features and new, state-of-the-art stage equipment were installed. Throughout all of the planning and implementation the project also prioritized preserving and restoring Mr. Maekawa's original architectural design.

<< The Renovation's Acoustical Objectives and Implementations >>

Hirosaki Community Center's hall enjoyed a favorable reputation even before the renovation. Therefore, the basic objective for the hall's renovations was to maintain the already well-loved and familiar acoustics of the original hall. The original hall's acoustical consultant was Prof. Emeritus Kiyoteru Ishii of Tokyo University.

We kept untouched the hall's original wood veneer side walls, with their distinctive protrusions and indentations. The important renovation points of the hall were as follows:

  • refurbishing the ceiling above the audience seating (while retaining its original shape);
  • exchanging to new audience seating (making each seat wider and changing the angle of the seat back for improved comfort); and
  • designing and installing a new acoustical shell

The new acoustical shell has an electric motor to deploy and retract it, replacing the old, manually operated shell. Also, the new acoustical shell rear section is positioned more towards the rear of the stage to accommodate larger configurations of performing ensembles. Because we changed the shape of the acoustical shell, we used computer simulations to determine the best shape to preserve the acoustics of the original hall. Other than this, its original room shape wasn't changed.

Changing the audience seating could affect the sound-absorbing characteristic of the hall. To preserve the hall's original acoustics while making this change, we began by measuring and comparing the sound-absorbing properties of both the old and the new seating. To adjust the hall for this change, we removed some of the glass wool installed in the hall before renovation where the ceiling meets the side walls.

In addition to the hall renovations, the project included sound isolation improvements to the lobby and upper floor of the adjacent administration building where the large conference room is often used as a rehearsal room. We evaluated the existing drywall, non-bearing wall between the lobby and the large conference room as well as the sound isolation properties of the door to the conference room and provided new specifications.

Also, when the old interior finishes were removed and we could see the concrete framing and floor slab that serve as the basic sound isolation structure, we specified needed repairs and directed that gaps be closed around no longer used underground piping and conduits. All of these measures improved the sound isolation performance of the structure between the lobby and upper floor, and the large conference room.

<< Space Constraints and Sound Isolation >>

The project renovations included increasing the number of dressing rooms and multipurpose use space, replacing and increasing the quantity of electrical transformers, and adding an elevator. Because the center is located on Hirosaki Castle Park land increasing the footprint of the center was not an option and all of these renovations were accomplished within the space constraints of the original structure.

From the sound isolation perspective, we took into consideration the structural and space limitations plus the operational needs of the center. We specified the addition of the thickness of the floor slab in order to prevent solid borne noise from transformer vibrations. We also added soundproofing mounts, brackets and fittings to strengthen the sound isolation properties of the building machinery installations. We considered the acoustical implications of every aspect of the renovations and kept the hall protected from noise and vibration generated by new equipment and other renovations to the building.

<< The Gala Reopening of Hirosaki Community Center >>

For the renovated hall, a Kyoto Nishijin tapestry vendor reproduced the original hall's drop curtain using the same weaving techniques as were used for the original curtain. The hall's Steinway grand piano was shipped to Germany where it received a complete overhaul and was then returned to Hirosaki. Even the technical team of employees was reinstated to their positions in the renovated and renewed hall.

At the reopening ceremony, local musicians performed a program of works chosen to showcase the hall's acoustics. Attendees welcomed the hall's well-loved acoustics back into their midst. After the official ceremony, the residents of Hirosaki showed their joy and appreciation for the hall's reopening by joining in numerous events.

Compared with a teardown-and-rebuild approach to community center renewal, renovating an existing structure typically presents some inconveniences both during the project and in terms of what can be achieved. Preservation and renovation are surely not the best choice for many situations. In the case of Hirosaki Community Center, there's a clear connection between this building of notable design and the community's pride and warm fondness for preserving the legacy of the building, its interior spaces and its acoustics. The decision to renovate was a wise choice for the building and the city.

Taichung Metropolitan Opera House Celebrates "Topping Out" Milestone

By Nobuhiko Hattori

On January 16, 2014, the Taichung Metropolitan Opera House project reached the important "Topping Out" milestone, marking completion of the building's frame. In our January, 2009, April, 2010 and September, 2012 newsletters we introduced readers to earlier stages of this project designed by architect Toyo Ito & Associates. Construction began about 4 years ago.

<< Progress at the Project Site >>

Playhouse interior as of Jan. 2014 (The photo shows the left side of audience section seen from the stage.)
Playhouse interior as of Jan. 2014
(The photo shows the left side of audience
section seen from the stage-right.)

When I arrived a few days before the ceremony, work was being completed on the building's 6th floor. The opera house will have 2 levels below ground and six levels above ground. The building is still surrounded by scaffolding so it's not yet possible to see the entire exterior. From the top floor, the design's distinctive, 3-dimensional catenoid shapes could be seen rising upward toward the sky. The completion of framing was imminent.

The project's use of catenoid shapes in the design of the main structure made the production of rebar and its installation on-site extremely time-consuming. The pouring of concrete also required extra effort. As the framing work progressed and the workers gained experience in the unique aspects of the project the pace of construction noticeably increased.

Inside the building, the 2,000-seat Grand Theatre and 800-seat Playhouse are both still open to the sky, but the catenoid shapes that surround them are virtually complete. In particular, the scaffolding that filled the Playhouse has been temporarily removed, making the dynamic feeling of the catenoid shapes visible to the eye. After the interior finishings and audience seating are installed, the Playhouse interior will take on a different look than it has today. As the accompanying photo shows, now the space has exposed catenoid surfaces and the strong presence of light streaming through the open ceiling-an image for the moment that will be gone once the ceiling and roof are installed.

<< Topping Out Ceremony >>

Topping Out Ceremony
Topping Out Ceremony

For the first few days after my arrival, Taichung's weather had a nip in the air, but on the day of the ceremony the weather was perfect, with clear skies and the temperature above 20 °C (68 °F). The Taichung mayor and architect Toyo Ito, as well as many other dignitaries and people involved in the project, plus representatives of the media attended the event.

After opening speeches and prayers, a gold-colored steel beam-bearing the signature of each and every person present-was raised through the air and into place, successfully completing the ceremony. Firecrackers punctuated the event and added to the excitement.

<< On-Site Acoustical Work Will Peak in the Future >>

The catenoids represent the largest part of this project's construction. Now that the work to build them is coming to an end, I expect that the remaining work to complete the project will proceed quickly.

During this trip I participated in meetings about the Grand Theatre's HVAC system and about the below ground anti-vibration and sound isolation construction work. I saw installation of the below-ground equipment conduits and anti-vibration hangers in progress. The peak of Nagata Acoustics' on-site work for the project's acoustics will soon be approaching.

Sound Diffusion and Sound Scattering

By Kosuke Suzuki

From sometime around 2009, the growing popularity of Twitter has led to increased use of the word "diffuse", in connection with the spread of information. Before then, the intransitive verb "diffuse" was originally used mostly in natural science references about the process of energy transfer to a state of equilibrium. These days, the use of "diffuse" as a transitive verb has become common and not just in discussions of information technology and social networks in Japan. I hear and read my colleagues and others in the field of acoustics now speak of "sound waves diffused" by obstructs and I think this creates ambiguity around the meaning of the term "diffuse".

We use the word "diffusion" repeatedly in this newsletter's articles. For example, in one 1999 article we have "the interior finishing materials and sound diffusion of the concert hall" (Japanese only) and in 2009 Dr. Nagata wrote three articles on "The Effects of Diffusion on Room Acoustics". Also, just last month we had an entire article on the topic of "Diffusion in Sound Fields and Hedgehog Visualizations". In this article, I wish to clarify what we mean by "diffuse" and "diffusion".

<< Diffuse vs. Scatter >>

Let me begin by summarizing how the use of the term "diffuse" entered the vocabulary of acoustics. At the beginning of the 20th century, W. C. Sabine posited the concept of a "diffuse sound field" for use in his statistical calculations. This appears to be the origin of use of the word "diffuse" in the context of acoustics. Sabine defined "diffuse sound field" as a room where (either in a transient state or in a state of equilibrium) the acoustic energy is uniform throughout the room and where there is an equally probable propagation of sound from all directions at all points in the room. Any theory that relies on the existence of a diffuse sound field is known as a statistical acoustics.

Because actual collected data is essential to validating a theory, acoustical engineers and researchers at universities, research institutes and companies in many countries have attempted to create a diffuse sound field. The scale and shape of a room, its finishes and the nature of the sound source, together with other factors seem to determine the degree of sound diffusion in a room. While this knowledge has not led to creating a diffuse sound field, some of the many trial-and-error attempts led to the creation of rooms called "reverberation chambers" that are used for experiments and testing.

Not only building a room, but also placing objects on or near the walls, hanging these elements in mid-air, or setting up rotating fans were also measures for the trial-and-error attempts. We refer to these elements as "diffusers". In acoustics, a "diffuser" causes sound waves to be reflected in various directions. That is, a "diffuser" might be said to "scatter" the sound waves. Acoustical engineers expect that this activity of the sound waves will increase the sound diffusion in the room.

<< Quantitative Evaluation of "Scattering" >>

Topping Out Ceremony
Figure of Reflected Waves

How much "scattering" is then needed for more "diffusion"? The degree of sound wave scattering that an object causes can be measured. ISO recognizes two methods of obtaining this data. ISO-17497-1:2004 defines the "scattering coefficient" and ISO-17497-2:2012 defines the "diffusion coefficient". The 2004 standard expresses-as a numerical value-the probability that reflection components are nonspecular. The adoption of this value for geometric acoustical simulations was a driving force for the early publication of this standard.

The 2012 standard expresses the uniformity of reflections' directionality for each incident angle of sound waves. Even though this value is named "diffusion coefficient", it refers to the reflection properties of objects. The use of the word "diffusion" for this value is causing confusion for the international professional acoustics community. For example, among Japanese researchers, more than one translation of the term is being used. In my opinion, instead of using various semi-accurate translations, the best course is to quote the original English ISO phrase "diffusion coefficient".

<< Quantitative Evaluation of "Diffusion" >>

Now that we can know the degree of sound wave scattering that a room configuration causes, measurement of the extent to which a room approaches a diffuse sound field based on the sound wave scattering characteristics of the room is wanted. Unfortunately, while this topic has been the focus of research for more than 50 years, none of the academic, institutional research or corporate communities has yet found an accurate way to quantitatively express the closeness of an acoustical space to a diffuse sound field. A variety of evaluation methods have been proposed by numerous researchers around the world and, while each methodology may have aspects that attract support, they all have shortcomings that prevent them from achieving universal acceptance. Instead, various quantitative methods continue to vie for adherents. For example, in 1953, Thiele proposed a measure called "directional diffusion"; in 1968, Makita and others published a method using a ratio of horizontal to vertical mean energy; in 1971, Koyasu and others proposed a surface diffusivity index (SDI); in 1997, Nelisse suggested use of a standard deviation of the acoustic pressure field; in 1998, Kawakami and others proposed the curvature index of reverberation curves; in 2002, Tomiku and others proposed use of the difference between spatial correlation values in reverberation room and the theoretical value (DSC); and in 2010, Hanyu suggested a measure succinctly entitled "Diffusion Time".

<< Mindful use of the word "Diffuse" >>

While the definition of a diffuse sound field ignores how sound is actually waves in media, we know that statistical acoustics has practical applications for easy, if rough, calculation of the characteristics of noise transfer and the sound fields of rooms. Further, when a sound field has objects that scatter sound, even if it is difficult to quantify the degree of diffusion, we often find qualitatively that the presence of the scattering objects brings the state of the room closer to that of a diffuse sound field than when the objects are not present. Because of these experiential results, use of the verb "diffuses" seems to have become common in this context.

Sound fields tend to some extent of diffusion naturally. In addition, certain conditions in a room can cause sound waves to scatter, but conditions in a room do not directly cause more or less diffusion. Therefore, we should be cautious in our use of "diffuse" to describe the condition of a room and "scattered" to describe the characteristics of sound reflections. In particular, the phrases "sound diffusing wall" should be reserved for materials from which sound reflects uniformly in all directions regardless of the angle of incidence and, when referring to walls that scatter sound, we should use "textured" (or "rough" or "uneven" wall surface). Careful use of these terminologies will increase understanding among both professionals and our clients.

Nagata Acoustics Inc.

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E-mail: info@nagata.co.jp

[ Japanese Version ]