Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 09-07 (No.259)

Issued : July 25, 2009

[ Japanese Version ]

"Suzu no Né" Hall Opens in Shinshu's Azumino, Japan's Snow Country

by Satoru Ikeda

"Suzu no Né" Hall's
stage set up with the orchestra shell

"Suzu no Né" Hall's
stage with a stage curtains in use

At the foot of the Japan Alps, in Matsukawa Village, in the part of Japan's Shinshu region known as Azumino, the new multipurpose cultural exchange center "Suzu no Né" Hall opened in May 2009. Matsukawa Village (administratively part of Azumi-gun in Nagano Prefecture) has a population of about 10,000 and is a farming community nestled amidst several rivers, including the Takase and Hodaka rivers. Matsukawa Village also has name recognition in Japan as the home of the Azumi-bushi style of "min-yo" (a traditional folk genre of accompanied singing), the location of Chihiro Art Museum Azumino and the village of the bell crickets.This region boasts some of Japan's most stunning natural vistas, with the snow-capped Japan Alps peaks rising in the background and the verdant farmland of Azumino stretching from the village to the foot of the mountains. Here a visitor can fully experience the satisfaction of being in the midst of nature's bounty.

The JR Oito Line stops at Shinano Matsukawa Station in the village. All of the village's public facilities can be found nearby in the same part of the village. One building houses the village's administrative offices and another building has the health and welfare center. There is also a public auditorium and a school. The new cultural exchange center joins these structures on a site adjacent to the village's administrative office building.

<< Overview of the Project and Programming Processes >>

"Suzu no Né" Hall includes a flat-floored, multipurpose hall with removable tiered seating, a rehearsal room, a corner gallery, a library, quiet study rooms, general use rooms, a kitchen and support rooms. The firm of Atelier Ryu created the building's architectural design and the construction company Hashiba Technos Co., Ltd. built the facility.

Eight years ago, in 2001, a planning committee was established in preparation for the design and construction of this cultural exchange center. The following year, a committee formed to make more specific and detailed decisions. Thereafter, project participants and village residents participated in workshops and hearings to discuss and scrutinize the plans for the new facility, with Matsukawa Village community members taking the lead during this phase of the project.

According to local community members, the committee participants began meeting regularly during the project's planning phase and continued to meet until the completion of construction. The scope of these meetings' discussions included both the physical aspects of the building's design and layout, and also the day-to-day operation of the facility.

Matsukawa Village thoroughly researched the kind of new hall that would best suit the community. The committee charged with this task considered the use patterns of the existing public auditorium, the music and theater activities of elementary and middle school students and groups, the kinds of gatherings and events held in the community, and the desire need for a space suited to light exercise classes. The intended uses became associated with the following requirements: a high standard of acoustical performance characteristics for concerts and recitals; a theater configuration and stage equipment for drama productions; a configuration and equipment for cinema showings; and, a flat-floor configuration for a variety of gatherings and light exercise classes. Nagata Acoustics made these requirements the key objectives of our acoustical room design.

<< "Suzu no Né" Hall's Room Acoustical Design >>

View of
View of "Suzu no Né" Hall's
tiered seating and hollow concrete block sidewalls

"Suzu no Né" Hall was designed without a proscenium and with a simple configuration that has an end stage and a flat floor. The hall has a single balcony level and theater grid along the sidewalls and rear of the hall. In the hall's compact size, the removable tiered seating for 198 persons plus 52 individual chairs are fit. The interior sidewalls of stacked hollow concrete blocks and the arches of wood panel strips that extend from the hollow concrete block sidewalls up to and across the ceiling create a strikingly dramatic interior design.

In this hall, the open configuration of the end stage establishes the sense of unity between the audience and the stage. But this configuration must be provided the basis for adapting the hall to its multiple purposes. For classical music performances and other music genres that do not use amplification, we provided a large, on-stage orchestra shell that folds out symmetrically from its center and, at the stage wings, we installed rotating doors that hide the stage curtain. As a result, we obtained effective sound reflections from the stage. To adapt the acoustical conditions for speaking engagements and drama performances, we installed a stage curtain at the front of the stage and retractable sound-absorbing curtains along the theater grids at the left and right sidewalls. These curtains dampen the hall's sound reverberations to provide an appropriate acoustical environment for plays, lectures and other speech-based events.

<< A Cultural Exchange Center Suited to Japan's Evolving Demographics >>

Japan's population continues its trend of aging combined with low birthrates. Cultural exchange centers such as "Suzu no Né" Hall can offer communities a venue for activities that span the generations and bring together local residents of all ages. As a member of the project team for the Matsukawa Village Cultural Exchange Center, I will be very pleased if "Suzu no Né" Hall becomes a frequent destination for both young and old. I have strong confidence that the hall will fulfill this important role.

The Effects of Diffusion on Room Acoustics -2

by Dr. Minoru Nagata, Founder of Nagata Acoustics

When a sound source emits sound inside a room, sound reflections from the walls and ceiling mix with the emitted sound to form a sound field that is unique to the conditions that formed it. The term "diffuse sound field" refers to a condition our minds can imagine of a sound field with the maximum possible degree of diffusion. Reverberation theory began by relying on the assumption of this diffuse sound field ideal condition. In recording studios and concert halls, where it is considered desirable to promote the dispersion of sound reflections, a variety of sound diffusion structures have been implemented, beginning with polycylinders and evolving to an assortment of other shapes, as I described in last month's newsletter. In this month's article, I will discuss the effects of sound diffusion from the acoustical room design perspective.

<< How Sound Diffusion Eliminates Howling >>

In last month's newsletter, I mentioned that the polycylindrical diffusers used in U.S. recording studios a half-century ago improved the ease of locating recording microphones in a studio. The journal article on polycylinders that I cited included graphs, reproduced here as Fig. 1, that depict the change in transmission frequency characteristics caused by interference of direct and reflected waves between two points in a studio before and after the installation of polycylinders.

Fig. 1: Interference between direct and reflected waves for convex and flat panels <sup>1)</sup>
Fig. 1: Interference between direct and reflected waves
for convex and flat panels1)

Fig. 2: Polar distribution characteristics of reflected wave for convex and flat panels <sup>1)</sup>
Fig. 2: Polar distribution characteristics of reflected wave
for convex and flat panels 1)

In general, when a pure sound is emitted in a room, interference occurs between the direct sound and the sound reflected off the surrounding walls and ceiling, and this interference causes changes in the level of sound waves at a sound receiving point (a microphone). The interference occurs because the direct sound and the reflected sound have different propagation lengths, with the reflected sound arriving later than the direct sound, and because of phase differences between the direct and reflected sound. When frequency of the sound are gradually shifted, the waves overlap or cancel each other to varying degrees depending on the sound wave frequencies, resulting in changes in the level of the sound waves at a sound receiving point.

Sound reflections propagated off a flat surface have specific directivity, concentrating in the manner shown by the dotted line in Fig. 2. However, sound reflections off a curved surface travel in the manner shown by the solid line in Fig.2. That is, the reflections spread out widely in many directions. Because curved surfaces diffuse the sound reflections, this lessens the interference between the direct sound and the sound reflections, as indicated by the smaller decibel fluctuation range (shallower peaks and valleys) of the curved panel's graph in Fig. 1. As a result, the location of a microphone in the room has less of an effect on the level of the receiving signal at the microphone and, therefore, the location of microphones can be changed with less effect on the signals' tone colors.

In indoor spaces, some fluctuation of the interference level between direct and reflected sound cannot be avoided. When using sound amplification devices, as the output sound pressure level continues to be increased, at certain frequency the undesirable phenomenon known as "howling" inevitably occurs. These frequencies are the decibel peaks shown in Fig. 1. Any change to the height of the peak, for example, even lowering the peak by 3 dB, increases the stability of the amplification device significantly. In the Nagata Acoustics June, 2008 newsletter article about Iwaki "Alios" Performing Arts Center, our sound system acoustical consultant mentioned that our specifications for the Large Hall's sound diffusers play a role in mitigating interference. Alios' Large Hall has a long reverberation time, but we eliminated the likelihood of howling interference. The sound diffusers cause the room to have a more uniform sound field and it is precisely for this reason that they play a role in eliminating howling.

<< Sound Diffusion and the Sound Absorption Coefficient >>

The sound absorption coefficient of a material is defined using the following formula, where α is the material's sound absorption coefficient, "I" represents the intensity of the incoming sound, and "R" represents the intensity of sound reflected off the material:

α = (I-R)/I = 1-R/I .......... (1)

In thinking about the material's sound absorption characteristics, the specific conditions of how the sound comes in contact with the material must be considered. That is, if the sound wave's direction is perpendicular to the material or at a different angle, or if it glides along the surface of the material, this condition will obviously affect the absorption or reflection of the sound by the material. It is equally obvious that in a typical room it would be impossible to verify the condition of contact of every sound on every surface of the room. Therefore, for purposes of determining the sound absorption coefficient of a material, the sound absorption coefficient definition includes the assumption that the sound comes into contact with the material from all directions (random incidence).

To determine a material's sound absorption coefficient, a sample of the material is placed in a reverberation chamber (which, by definition, has rigid, sound-reflecting walls) and the change in reverberation time is computed. ISO standards specify reverberation chamber shapes and volumes, as well as the dimensions of the sample material and its placement in the chamber for sound absorption coefficient testing. In Japan, reverberation chambers must also comply with JIS standards published by the Japan Industrial Standards Committee.

Fig. 3: The diffusion structures in the reverberation chamber
Fig. 3: The diffusion structures
in the reverberation chamber

Returning now to our topic of sound diffusion, let me point out that the sound field diffusion conditions in reverberation chambers pose a problem that affects the accurate determination of sound absorption coefficients. To correct the reverberation chamber results to better account for the effects of diffusion panels, the test setup may include multiple curved diffusion panels of the type shown in Fig. 3 randomly suspended in the reverberation chamber, or sound reflecting panels may be rotated in the chamber, or other methods may be used to gauge the effect of sound diffusion on the measurement of the material's sound absorption coefficient.

Fig. 4: The relationship between the suspended diffusion panels and the sound absorption coefficients <sup>2)</sup>
Fig. 4: The relationship between the suspended diffusion panels
and the sound absorption coefficients 2)

Fig. 4 shows the relationship between the numbers of diffusion panels used in a reverberation chamber during testing and the sound absorption coefficient values obtained, as published by the JIS Committee in connection with its formulation of the JIS method for the measurement of sound absorption coefficients. This JIS testing used glass wool boards of 50 mm thickness and density of 25 kg per cubic meter, the most commonly used sound absorbing material in Japan. In this graph, the "y" axis shows the measured sound absorption coefficient and the horizontal graph lines represent the results with different numbers of diffusion panels (each panel being 90 cm x 180 cm).

As the graph shows, when glass wool of 50 mm thickness (the most popular sound absorbing material used today) is used in a room that has good sound diffusion, the sound absorption for mid-range and high frequencies can approach 100%. However, as the number of panels used decreases, the sound absorbing performance also diminishes.

In the graph of Fig. 4, the condition most unlike a good diffusion condition is the condition of zero ("0") diffusion panels combined with directional loudspeakers emitting sound in a plane parallel to the sound absorbing material. This test condition matches the situation of having sound-absorbing material only at the surface of a room's ceiling, a situation often seen in conference rooms and offices. Indoor athletic facilities also often have sound absorbing material solely on the ceiling.

In athletic facilities (when set up with audience seating), as well as in concert halls and theaters, even if the ceiling has a sound-reflecting surface, the audience seating on the floor of these rooms is a large, sound-absorbing surface. The sound absorbing effect of hall audience seating differs from the computed values obtained in a reverberation chamber for the sound absorption coefficient. For example, when a gym's sound absorption design uses sound absorbing material only on the ceiling, the actual measured conditions in the facility may differ markedly from the design's target sound absorption values. Many an acoustical consultant has struggled with the unfortunate situation of great disparity between sound absorption design calculations and the measured results.

I admit having a memory of my own encounter with this problem shortly after I began work at NHK Technical Research Laboratory. Mr. Norio Ohga, (who later became president and CEO of Sony Corporation) hired us to design a sound absorption solution for a conference room. In those days, we were both still young men at the start of our careers. At the time, mineral fiber dressed board had just begun to be imported to Japan and I designed the installation of this material on the conference room ceiling. However, in calculating the conference room's needs, I relied on the product catalog's sound absorption coefficient values, which had been computed using reverberation chamber testing. When the conference room's post-installation measurement results were very different than what I had expected, I concluded that there must have been a problem with the sample tested in the reverberation chamber. I recall that small project as if it happened yesterday, and with the embarrassment of how I was still wet behind the ears.

From the perspective of our day-to-day interaction with sound diffusion, unless you are inside a cathedral-like structure with a very high ceiling and stone interior walls, most of the spaces that we experience have some in-between level of sound diffusion. In Europe, the Bonn Beethoven Hall's acoustical design intentionally aimed to create a diffuse sound field by placing sound diffusing structures on all of the walls and the ceiling, but I for one have not heard accolades about this hall. I think it fair to conclude that, across the 500 or more years of classical music history, this music genre has been nurtured in spaces with neither extreme surfeit nor deficit of sound diffusion, but rather some sound diffusion level in-between the two extremes.

1) J.E.Volkmann, 'Polycylindrical Diffusers in Room Acoustical Design', J. Acoust. Soc. Am. 13, 234, (1942)
2) Guide of JIS - Architectural Acoustics, Acoustical Materials Association of Japan, (1979)

Stockhausen's "Gruppen" at Suntory Hall this August

by Akira Ono

"Gruppen," the work for three orchestras by Germany's contemporary music composer Karlheinz Stockhausen (1928 - 2007), will be performed by the NHK Symphony Orchestra on August 31, 2009 at Suntory Hall in Tokyo. The concert is part of Suntory Music Foundation's annual Summer Music Festival. This year, the festival commemorates the 40th anniversary of the establishment of Suntory Music Foundation. This will be the first performance of the work in Japan in 35 years.

Stockhausen was a composer who repeatedly brought fresh creativity to 20th century music, and his work has greatly influenced not only classical music composers, but also rock and jazz composers as well. When the Beatles were transitioning to a studio band and made their "Revolver" album, they adopted Stockhausen's technique for electrically processing new sounds that, at the time, could not be reproduced in a live concert setting. Perhaps not so coincidentally, on the cover of the Beatles' next album, "Sgt. Pepper's Lonely Hearts Club Band", Stockhausen's photograph appears as the fifth face from the left in the top row of the cover's montage artwork.

<< "Gruppen" Premiere Liner Notes Snub Classical Concert Halls >>

Stockhausen wrote "Gruppen" between 1955 and 1957, and the work premiered at Cologne's Koelnmesse International Exhibition Center in 1958. The premiere's liner notes describe the composer's intended spatial conditions for performing the work, stating that the venue should be a space with a flat floor where the stage and audience seating can be freely moved and relocated to create Stockhausen's specified layout. The liner notes also dismiss existing classical concert halls as inappropriate venues for "Gruppen" performances.

Stockhausen's layout for "Gruppen" performances places the three orchestras, each of which has the same instrument configuration, at the front, left and right sides of the audience around the audience. Stockhausen conceived "Gruppen" before the availability of stereo technology, yet he had the idea that by specifically placing the sources of a performance's sounds, he could hope to achieve the reality of sound directionality in the "Gruppen" performance space.

At the time when Stockhausen composed "Gruppen," concert halls mostly had the classical configuration of audience seating at one end of the hall and a stage with performers facing the audience at the opposite end of the hall. Understandably, Stockhausen found it difficult to imagine a concert hall where the sound envelops the audience. On the other hand, in the kind of warehouse-like space he specified, even if a performance could achieve sound directionality, it would be difficult to also ensure that the sounds from each of the three orchestras' instruments would carry fully and clearly throughout the audience.

<< 1996 City of Birmingham Symphony Orchestra "Gruppen" Performance >>

The 1996 performance of "Gruppen" by Conductor Simon Rattle and the City of Birmingham Symphony Orchestra can be seen on You Tube. A friend of mine who attended this performance in person described the experience as "like standing at the top of a geyser and hearing spurts of sounds coming out from one direction and then another direction."

<< This Summer's "Gruppen" Performance at Suntory Hall >>

The placement of three orchestras in Suntory hall
The placement of three orchestras
in Suntory hall

This summer's "Gruppen" performance at Suntory Hall will place the three orchestras as shown on the accompanying seating chart. The composer would have identified only the first floor center audience seating as appropriate seats. What Stockhausen could not have anticipated is a concert hall such as Suntory Hall that has excellent sound separation, and where we expect the sound clarity in the balcony seating to enable the "Gruppen" performance to be heard like a geyser spreading both to the right and the left throughout the hall.

Because the Suntory Hall performance will be an unprecedented attempt to bring "Gruppen" to a vineyard configuration concert hall venue, the concert organizers decided to perform the work twice for the audience. A portion of the seating will be left unsold and the audience will be encouraged to change their seats for the second performance so that they can experience "Gruppen" in two different seat locations. This consideration for music aficionado patrons is one of the enduring hallmarks of Suntory Hall. If you can be in Tokyo for this end-August performance, it is one you will surely not want to miss.

More information (in Japanese) about Suntory Music Foundation's and the Suntory Summer Music Festival can be found at: http://www.suntory.co.jp/culture/smf/summer/index.html

Nagata Acoustics Inc.

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[ Japanese Version ]