Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 13-02 (No.302)

Issued : February 25, 2013

[ Japanese Version ]

New Yamanashi Prefectural Library

By Akira Ono

view of a interior
view of a interior
view of a interior
view of a interior
view of a interior
Several views of the interior

On November 11, 2012, the new Yamanashi Prefectural Library opened across from the North Entrance of JR Kofu Station. Mr. Hideyo Noguchi of the architectural firm Kume Sekkei created the building's architectural design. Nagata Acoustics worked with him on many past projects and we enjoy the vitality and creativity he brings to every design and collaboration. His architectural designs typically include aspects that pose acoustical design challenges. Nevertheless, or perhaps because of the interesting challenges we encounter in our collaborations with Mr. Noguchi, we always look forward with pleasure to working with him. As the Acoustical Consultant on the recently completed Yamanashi Prefectural Library project, we again found ourselves engaged in the acoustical design and sound isolation needs of a very interesting and unique architectural design.

<< A Blending of Lively Sound and Silence >>

We generally think of libraries as quiet environments where even normal conversation may be discouraged. However, the planners of Yamanashi Prefectural Library identified the goals of having a welcoming atmosphere, being a destination where residents feel at ease and becoming a place where people expect to see friends and neighbors. In response to these programming objectives, Kume Sekkei proposed a design that blends the two concepts of "Lively Sound" and "Silence". Specifically, the architectural design begins with a large space that has a lively atmosphere and where people can see others engaged in various activities and conversations. In the midst of this space, the design adds rooms that are quiet oases where silence can be found.

By creating a space where people feel encouraged to come for conversation and active interaction, the design revitalizes the meaning of a library. In addition to being inspired only by the words found between the covers of books or on computer screens, the library becomes a place where people can inspire each other directly through conversation and activities. The library's planners also took into consideration that the building is located at the north entrance of JR Kofu Station, the side of the station with low foot traffic. By creating an upbeat and lively atmosphere in the new library, the planners hoped to encourage use of the new facility.

<< Overview of the Facility >>

The overall plan of the library interior combines two basic areas into a whole that has an open plan feeling. One area is a large space where people can meet and simply hang out and a second area has bookshelves and books. Within the overall open plan are glass-enclosed "silent" rooms for library users who want to read or study in a quiet environment. The library also has four glass-enclosed activity rooms on the first floor and two glass-enclosed rooms on the second floor that can be reserved and rented for a fee.

For two of the rental activity rooms, we implemented a special sound and vibration isolation structural design so that both of these rooms can even be used for music practice without disturbing other library users in the silent rooms and main conversation and reading areas. The second floor also has a 200-seat multipurpose hall with transparent glass walls and an anti-vibration and sound isolation structural design. Library users standing outside the hall can see the activity or event happening in the hall and the level of sound and vibration isolation sufficiently prevents transfer of sound and vibration beyond the hall's glass walls. The library's other large meeting room is a flat-floored event space that accommodates up to 500 people. In the four months since the library's opening, this event space has hosted well-known speakers for a variety of lectures and symposia, drawing many people to the area.

<< Quietness in the Reading Area >>

During the project's planning and design phases, the blending of the area intended for lively sound and the more quiet reading area raised concerns about the level of noise that would transfer from the lively sound area and be audible in the reading area. As part of our acoustical room design, we evaluated the size of the space, interior surface materials and the design of the book stacks, taking into consideration their sound absorbing properties and the benefit that each material would provide to the acoustics.

In addition, we simulated the estimated sound level in the new library by setting up loudspeakers in the lobby of the old Yamanashi Prefectural Library, playing recorded sound through the loudspeakers and measuring the sound transmitted into the book stacks and reading area. Using the data we gathered for the sound attenuation from the old library's lobby to its reading area, we were able to predict the level of sound that would be audible in the reading area of the new facility.

<< The New Library's Utilization and Sound Levels in the Facility >>

When I recently visited the new library, I saw numerous middle school and high school students seated at the library's desks and reading books or working on homework. At many of the tables designed for four people to sit, I observed students talking in small groups. Because of the library's spacious, open plan dimensions, when I walked a few steps away from any of these tables, the sound levels of the conversations diminished sufficiently that I could no longer distinguish the content of what was being said. The sound level was sufficiently low that it would not disturb me if I was reading at a nearby table.

For the interior walkways and on the stairs we installed a material made from rubber chips. As a result, the sound of footsteps does not create any disturbance at all. In the reading area, the only sound I noticed was the ambient noise from the HVAC system. In Japan, consumers often read in the aisles of large bookstores. I realized that the aisles and bookshelves of a bookstore and a library's book stacks basically serve the same function. In either situation, some ambient sound does not impede readers from finding the books they want to read.

The new library appointed author Takashi Atoda to be its new Chief Librarian. As a young man, Mr. Atoda worked in the National Diet Library and he has vivid memories from that period of his life. He says "What people do in a library is really important. It's not just a place where we rent books for free." The new Yamanashi Prefectural Library's design intentionally promotes interactions and conversations among the people who come to use it. I look forward to the leadership of this new Chief Librarian who agrees that this is the way a library ought to be.

The URL of the Yamanashi Prefectural Library website is https://www.lib.pref.yamanashi.jp/.

Acoustical Design Legacies and Lessons of Older and Bygone Halls - Part 6
-Past and Present Uses of Resonators in Acoustical Designs-

By Dr. Minoru Nagata, Founder of Nagata Acoustics

Fig. 1: Basic design of a Helmholtz resonator device
Fig. 1: Basic design of a Helmholtz resonator

Fig. 2: Pocket resonator
Fig. 2: Pocket resonator

Fig. 3: Plan view of a reverberation chamber
Fig. 3: Plan view of a reverberation chamber

Fig. 4: Reverberation time ranges in a reverberation chamber
Fig. 4: Reverberation time ranges
in a reverberation chamber

Fig. 5: Schema of a perforated panel backed by an air space
Fig. 5: Schema of a perforated panel
backed by an air space

If you hold a soda glass bottle or milk bottle to your ear, or blow across the top of such a bottle, you will hear particular frequencies of sound resonating. The Helmholtz resonator is a device that combines an air cavity with a narrow opening to make use of this sound phenomenon for various applications. There are records of a bronze urn tuned to the Greek scales that was found buried below the seating floor of one of the ancient Greek outdoor playhouses. When it was found, its resonating frequencies were still clearly discernible[1]. Writings from the middle ages record in detail that Scandinavians embedded urns of varying shapes and sizes in the walls and ceilings of their churches to dampen the churches' reverberations[2]. In Japan, records show that below the wood floors of some Noh playhouses earthenware pots were placed with their openings set in various directions, though the reasons for this practice are not entirely clear[3].

In the later part of the 20th century, acoustical consultants and others again took to installing resonators in buildings, primarily in halls where there was a desire to increase the sound reverberations. The resonators served as sound reverberation enhancing devices. The resonator portions of the devices were embedded in hall ceilings and the generated sound resonances were collected through microphones and reproduced sound back into the halls via loudspeakers[4].

Fig. 1 shows a simple vibrating resonator design. The mass "M" of the air in the neck exhibits vigorous vibrations due to the force of repulsion from spring "K" of the air cavity (the springiness of the air cavity). In addition, when the energy of the sound field and the reciprocal action are taken into consideration, radiation resistance (R1) of the emitting air at the opening of the device and friction resistance (R2) around the air cavity must also be kept in mind. In order to increase the amount of emitted energy, R1 must be greater than R2. Because the value of R1 is inversely proportional to the area of the opening, small resonators with small openings are not effective for sound absorption.

The development of pocket resonators provided a useful sound absorption alternative. As shown in Fig. 2, the design is a pipe with one end closed. The length of the pipe is λ/4 and λ represents the wavelength. This pocket resonator can be used effectively to control booming of small volume spaces.

In the years before signal processing technology made it possible to develop commercially viable reverberation enhancing devices, we built reverberation enhancing devices by starting with an "ideal" reverberation chamber with pocket resonators to absorb the low frequency sound. In addition to installing pocket resonators, we also affixed 45 cm. squares of glass wool blocks in the corners of the chambers to increase the range of sound frequencies that would be absorbed (Fig. 3). I first tried this design in a reverberation chamber of Nihon Educational Television. Afterwards, I implemented this design at NHK Broadcasting Center. Fig. 4 shows the possible ranges of reverberations in a room of this design.

At the rear wall of the old (long gone) NHK Hall, we installed blocks of 4 resonators each of which had a different resonance frequency[5]. Examples of halls that used embedded bottles in some part of the walls are Tokyo Cathedral and Victor Company of Japan, Ltd's studio at Aoyama, Tokyo. When these facilities opened, their acoustical designs were widely discussed, but no records remain about the sound absorbing effectiveness of the resonator designs used. The chart shown in Fig. 4 is the only extant data from that period.

Only a narrow range of frequencies can effectively be absorbed using resonance technology, making the application of this sound phenomenon difficult to apply to typical hall projects. Today, the prevailing sound absorption design technique uses perforated panels backed by a layer of air (as shown in Fig. 5). This design effectively absorbs low frequency sound in halls and other indoor spaces.

[1][2]: P.V.Brüel, "Sound Insulation and Room Acoustics", p218-219, Chapman & Hall, 1951
[3]: Tokura and Matsuura, "The Acoustics of Noh Playhouses", Acoustical Society of Japan Research Committee Papers, AA-70-14, 1970
[4]: P.H.Parkin, "Assisted Resonance", p169, Applied Science Publishers Ltd., 1975
[5]: Minoru Nagata, "Acoustic Design of a New Echo Chamber with Variable Reverberation Characteristics.", Journal of the Acoustical Society of Japan, p433-441, Volume 23, No. 6, 1967

Dr. Nagata Appears in Necessary Conditions For Professionals Of The Most Advanced Age

Reviewed by Ryoichi Wada

The second, sequel volume of the popular book Professionals Of The Most Advanced Age Tell How They Do It recently became available. The first volume was published in December, 2010 and its popularity led to the preparation of a second volume with more interviews of academics, musicians, chefs, sports professionals, literary and cultural critics and pundits and even a hostess of a bar.

This second volume includes a chapter about Nagata Acoustics Founder and Executive Advisor Dr. Minoru Nagata. The interview with Dr. Nagata traces the course of his career from his earliest attraction to "sound" as a field of endeavor, through his years at the NHK Technical Research Laboratories, to his establishment of Nagata Acoustics and his current involvement with the professional world of acoustical engineering and acoustical consulting. The chapter also includes some of Dr. Nagata's philosophical thoughts about "sound".

The Book

The target audience of the book is my demographic, that is, young professionals who are still on the trajectory toward the peaks of their careers. As a member of the target audience, I found the style of this book appealing because the text of each interview retains the speaking style of the person interviewed. Through each writing style, the reader learns something about the person being interviewed. Also, as each professional recounts the story of the experiences that led to that person's high level of professionalism, the retelling includes comments about the historical and social situation of particular years. The professionals' insights into the times through which they've lived offers fascinating reading. Some readers might find some of the chapters lacking in sufficient substance. I think the book is an easy read without convoluted ways of stating the ideas being presented and without resorting to words that would send some readers to the dictionary.

The book's cover has the subtitle "If you can achieve this, for your entire life you can earn your daily bread doing work you love!" In the current economic climate, with the TV and news media clamoring about the difficult job market, it may be an exaggeration to claim that we can learn from this one volume how to find truly satisfying work that will last a lifetime. But here's what I did learn. If a person thinks about what is going on around him, he can learn and gain expertise by watching others. Also, a person develops expertise by doing. Said another way, experience builds character and expertise.

When the people interviewed in this book experienced adversity or a setback, they remembered to keep a positive outlook. In addition, more than any other quality, these professionals all have a strong curiosity streak and minds with "antennas" that treasure every opportunity to learn. If there's a new food or cuisine to try, or something to experience or a new idea they encounter through reading or that they hear in the media or from someone they know, they pursue it not out of a sense of obligation but out of a natural drive to better themselves. This drive propelled each of them to be thriving professionals into the later years of their lives. At least, when I'd read the last page of the book, that is the impression that stayed with me.

The people interviewed for this book have surely earned great respect from others engaged in the same profession. The reason they have earned the respect of their peers is not because they are old in years. It's because of the way they continue to better themselves. These professionals stay in the forefront of their professions, using the "antennas" of their minds to stay attached to the trends and ideas of their chosen fields. The real way to read this book is not to see it as a collection of the words and thoughts of old people, but as a book about how to stay interested and engaged in the world. When read this way, there's much to discover in the pages of this book.

The book is Necessary Conditions For Professionals Of The Most Advanced Age, by Tokuma Shoten Investigative Reporting Team, published in Japan by Tokuma Shoten, ¥1,400

Nagata Acoustics Inc.

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E-mail: info@nagata.co.jp

[ Japanese Version ]