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

Nagata Acoustics News 02-6 (No.174)
Issued : June 25, 2002

Oizumi Gakuen "Yumeria Hall" Opens

by Toshiko Fukuchi

At Oizumi Gakuen, a suburban stop on the Seibu Ikebukuro train line, the area near the train station suffered from narrow, winding streets overloaded with traffic congestion. To remedy the situation, a municipally led project began several years ago to construct an underpass thoroughfare beneath the station and renovate nearby buildings. The entire project will complete in Autumn 2002, but the underpass and the building at the station's north exit are a step ahead of this date and already finished.

<< Yumeria Hall Project Overview >>

Oizumi Gakuen Yumeria Hall, the new, Nerima Ward-sponsored hall located in the "Yumeria 1"-named building at the station's north exit, opened in February 2002. This cozy and endearing concert hall seats an audience of 176 persons and occupies the fifth through seventh floors of Yumeria 1's 10-story structure.

The name "Yumeria," which is being used not only for the north exit building and the concert hall, but also for the entire redevelopment area, was selected from names entered in a public contest. The name derives from a combination of the Japanese word for dream: "yume," and the English word "area."

The project architect was I.N.A. Shin-kenchiku Kenkyujo and the general contractor was Toda Kensetsu. Nagata Acoustics' contribution began at the early stage of supporting the architect in developing the conceptual design and continued with participating in the construction management and conducting the post-construction acoustical evaluations.

<< Combating External Noise & Vibration, and Inter-room Sound Transfer >>

Surrounding the building that is Yumeria Hall's home are all the sounds and noises associated with railroads and train stations, from the warning bells and clanging of the railroad crossings and the noise of trains stopping and starting and express lines whooshing by, to the noise of the roads and commerce close to the station. Additionally, there is now the new underpass thoroughfare that cuts under the station at a point directly behind Yumeria 1. From a sound isolation perspective, it would be difficult to call this a very desirable location for a concert hall.

The concert hall's neighbors inside Yumeria 1 also posed sound isolation challenges. Among the building's tenants are pachinko parlors as well as banks and offices. Some of these occupants produce noise that must be kept out of the concert hall, while for others, problems would arise if sound from the concert hall transferred into their spaces. For all these reasons, we defined isolating the hall from external noise and vibration, and preventing sound transference between the concert hall and other spaces in the same structure as two major objectives of this project's acoustical design.

<< Strategies to Achieve a "Quiet" Concert Hall >>

To ensure an excellent level of quietness for Yumeria Hall, we used a nested, or box-in-box hall design that combined a layer of anti-vibration elastic material inside a fixed sound isolation layer. We also isolated the hall from possible noise and vibration generated on the floor immediately above the hall by giving that floor a vibration-isolating design using rock wool. We chose this approach since we had no way of foreseeing what kind of business might become the tenant immediately above the hall.

Because Yumeria 1 is a reinforced concrete structure with a steel-frame, for the concert hall's walls we did not use poured concrete. Rather, we had the hall's walls constructed of several bonded layers at the core of which is glass-wool matting sandwiched on both sides by prefabricated lightweight boards. On the outer sides of each sheet of board are two layers of panel board, one 21mm. (0.82") thick and one 12.5 mm. (0.49") thick. This design strategy achieved a sound isolation performance level exceeding 90 dB (at 500 Hz) between both the hall and adjacent rooms and between the hall and rooms on upper and lower floors.

Prior to the hall's opening, we tested the sound isolation performance level of the walls by playing loud music through the hall's speakers and beating on Japanese drums in the hall, while listening for sound transference in adjoining and nearby rooms. Our tests confirmed that there is no sound transference even at louder than 90 dB. In addition, the hall's HVAC system and interior noise level measures an exceptionally quiet NC-15 or lower and, even in the quietness of this space, there is zero intrusion of noise from outside the hall.

<< Deciding the Hall's Purpose >>

Because the Seibu Ikebukuro train line serves several neighborhoods and communities with performing arts colleges, including Musashino Music University, and because this is also a part of Tokyo where many musicians live and own homes, Nerima Ward indicated from the project's inception that the ward's intention was to sponsor the design and construction of a concert hall. As the design plans took shape, the desired scope of music for which the hall could be used grew from only classical music to include jazz concerts and other genres. However, allowing for these multipurpose-hall type uses was incorporated into the design only to the extent that they did not negatively impact the room's concert hall functionality. Fundamentally, the focus on a venue for acoustic (non-amplified) music performance remained a consistent goal throughout the project.

<< Yumeria Hall's Shape and Dimensions >>

Yumeria Hall's width measures nine meters (29.5 ft) wall-to-wall for the audience seating section and the hall's length is 23 m. (75 ft) from the rear wall of the stage to the wall at the far end of the audience seating. The ceiling height is 9.5 m. (31 ft) at its highest point, and the floor slope beneath the audience seating is slightly steeper than usual for this otherwise traditional shoebox-shaped hall.

We determined Yumeria Hall's width and length dimensions to fit within the already pre-determined surface area dimensions of the Yumeria 1 building. That the result was such a rectangular shape so appropriate for a concert hall was a lucky coincidence.

As for the hall's ceiling height, high ceilings are desirable in concert halls because of the role they play in creating long reverberation times. In Japan, most halls that are planned for a portion of a multi-story building are allotted just two stories, in part, perhaps, because many of these halls are intended to be designed as multipurpose halls. When a hall uses only two stories of a building, its maximum ceiling height cannot extend much above seven meters (23 ft). However, for the Yumeria Hall project, we knew from the outset that the client desired a concert hall, and we were able to reserve a three-story space for its use. The 9.5 m. (31ft) ceiling that we achieved represents a high ceiling for a hall of Yumeria Hall's scale.

<< Yumeria Hall's Room Acoustics >>

Because of space constraints, we were unable to design the walls around Yumeria Hall's stage area and audience seating area with folds and other variations that would enhance sound diffusion. Instead, we adapted to this constraint by covering much of the side walls' surface area with wood ribbing in order to soften the sound reflections from these surfaces.

In order to accommodate a greater variety of performer configurations, programs, and non-concert performances, we installed deployable curtains at the upper portions of the side walls of the audience seating area as well as at the rear wall of the stage. These curtains enable adjustments to be made to the hall's reverberation time. While the adjustable reverberation-time range measures only 0.1 seconds, the difference between when curtains are deployed and when they are retracted is easily discernable to the human ear. The hall regularly deploys the curtains for programs such as those that feature traditional Japanese comedians and storytellers. At 500 Hz, the hall's reverberation time is 0.9 seconds with the curtains retracted and 0.8 seconds with them deployed.

<< Yumeria Hall's Opening and Ongoing Operations >>

On February 1, 2002, Yumeria Hall held its inaugural ceremonies featuring a performance by Nerima Ward resident and acclaimed violinist Teiko Maehashi. The hall's reverberation time may not be as long as some other venues, but the hall produced amply abundant sound and tone enjoyed by the entire audience. In particular, the fine nuances of Ms. Maehashi's playing and the influence of her breathing were conveyed to audience members seated in even the audience rows farthest from the stage, providing a kind of listening experience impossible in larger halls.

In addition to Yumeria Hall, Nerima Ward runs the Nerima Cultural Center, located across from the Nerima train station. The cultural center's facilities include a large, 1,498-seat hall and a medium-size, 592-seat hall. Oizumi Yumeria Hall was designed to complement these two halls and will offer the ward's performers the previously unavailable option of booking a small local hall. The ward's two larger halls will continue to attract more commercially oriented events and performances, while Yumeria Hall will be the stage for more intimate programming that will likely reflect the close ties of the performers to the surrounding Nerima Ward communities. To encourage local use of Yumeria Hall, the ward set the hall's rental rates well below the rates for comparable halls in other sections of Tokyo. The cost to rent the hall from 9:00 AM to 10:00 PM on a Saturday, Sunday or holiday costs just 50,800 yen (US$417). Yumeria Hall's reasonable rates and its close proximity to mass transit combined to make this new hall immediately popular, as I hear that the hall is already almost entirely booked through the end of the year.

Yumeria Hall can be contacted directly at +81-3-5947-2351. The hall's address is 29-1, Oizumi 1-chome, Nerima Ward, Tokyo.

Renovations and Acoustical Design - Part 3:
Noise Abatement Renovations

by Satoru Ikeda

There are two distinct kinds of work that can be considered renovations for the purpose of noise abatement. One kind of noise abatement renovations addresses sound isolation needs and the other kind addresses noise created by HVAC or other equipment associated with a hall or other facility. Examples of both of these kinds of renovations can be found among the projects discussed in past issues of this newsletter.

As we repeatedly caution, because achieving an excellent level of sound isolation performance depends to a large extent on the decisions made relating to a building's structural design, post-construction renovations for this purpose are not only difficult to implement, but usually produce only limited sound isolation performance improvements. For these reasons, it is most important that sound isolation needs be considered and addressed during the basic design stages of a project.

For renovations that aim to reduce or eliminate equipment noise, technological advances have made effective noise-canceling devices and anti-vibration apparatus commonly available. However, when one tries to use these new technologies in a renovation project, space constraints and other difficulties frequently create obstacles that make these kinds of projects as difficult and prone to limited success as renovations for sound isolation purposes.

<< What Causes the Need for Noise Abatement Renovations? >>

Typically, noise abatement renovations begin as a complaint or claim resulting from one of two possible causes. Either the purpose and intended uses of the structure defined during its original planning do not match how and for what purposes the facility is actually used, or, the noise-related performance levels of the building and/or its equipment have deteriorated due to age, dirt build-up, etc.

<< Obstacles to Noise Abatement Renovation Implementation >>

Even when the cause of the noise can be clearly identified, planning a remedial renovation involves numerous considerations, such as determining the renovation method, defining project scope, setting a schedule for on-site construction work, and estimating and approving the project budget. These questions often do not have simple answers. Therefore, while potential clients often approach us to discuss their needs for noise abatement renovation work, the problems associated with this kind of renovation attempt mean that most of potential projects do not come to fruition. The extremely small number of implemented noise abatement renovation projects indicates and reflects how difficult these projects can be.

<< Why Sound Isolation Strategies Are Critical to Initial Project Plans >>

Most of the sound isolation complaints from multipurpose cultural facilities concern sound transference between rooms. The problem locations might be two halls or between a hall and a rehearsal room or practice room, or between some combination or subset of these locations and rooms and spaces that serve other purposes. A sound isolation problem can arise at a hall already in operation or at a brand-new hall, but when the problem concerns a hall that has been in operation for some time, it almost always occurs for one of two reasons. Either the content of performances or the ambient environment outside the hall, or both, has changed since the hall was planned and built. The sound isolation performance requirements planned and designed into the hall's original specifications no longer meet the hall's needs.

If a problem during the physical construction of a project were to affect sound isolation performance, the problem would be discovered during the acoustical testing and evaluations conducted upon completion of the construction phase. In such a situation, the problem will be resolved before the project is accepted by the client. It is exceedingly rare for a problem of this nature to escalate into a claim from the client after the hall opens and is in operation. Therefore, when a client requests renovation work to remedy a sound isolation problem, the problem almost always stems from something other than the project's physical construction.

Remedial sound isolation renovations do often have their origins in the planning and design phases of projects. Concessions may have been made at the time of site selection or in limiting the project budget. Or how the facility would be utilized may have been only vaguely defined, or problems uncovered during the planning and design phases may have been tabled for future consideration and resolution. These kinds of factors become the seeds from which client claims and complaints can grow. While sound isolation performance can be improved and enhanced after a facility is completed and in operation, that there are limitations to what can be achieved at such a late stage.

<< Pre-renovation Evaluation of Noise Abatement Needs >>

In developing a noise abatement renovation plan, one necessary task is to determine the true sound isolation and quietness performance requirements. To this end, we research and analyze both the characteristics of the facility and how it is actually used, from an on-site perspective. Equally important, we determine the limitations of the physical structure and its existing equipment and whether these create constraints on achieving the newly calculated, desired sound isolation and quietness performance levels.

For renovations focusing specifically on sound isolation performance improvements, the initial steps toward planning a renovation project also include on-site listening evaluations performed by the acoustician and determination of the physical sound-transfer paths. Additionally, it is also important to balance the evaluation of overall sound isolation performance level goals with individual elements that contribute and influence the sound isolation performance level. These factors may include the sound isolation performance level of interior walls and doorways, the influence of sound transference from corridors and the contribution to the sound isolation problem of small gaps in the physical structure and solid-borne sound transference from fixed objects in the facility.

<< Sound Isolation from External Sources of Noise >>

Every hall has numerous large and small openings to the world outside, including, for example, a stage loading dock for large instruments and stage props, a stage entrance for performers, a front entrance for the audience, an emergency exit, and exhaust fume shafts and ducts, etc. In general, these kinds of openings have a neutral zone such as a loading staging area, corridor, front foyer or entranceway plus a double-layer sound isolation building component (such as a sound isolation door) separating the exterior of the building from the hall. However, depending on the exterior ambient noise levels at the time of construction, and for other reasons, some halls have only single-layer doors and separations.

Since two of the frequent reasons for sound abatement renovation requests are changes in the exterior ambient environment's noise level and changes in the required level of quietness within halls, the ideal response to these requests would be to create neutral zones in-between openings to the outside and the hall, and to install double-layer sound isolation elements. In some of these cases, however, we can achieve a high sound isolation performance level by simply installing a single sound isolation door where there was none previously.

<< Sound Isolation between Adjacent Halls and Other Rooms >>

When a facility has both a large and small hall and, in particular, when the halls are part of a multipurpose facility that also has rehearsal and practice rooms, space considerations often require the two halls to be placed one beside the other. Alternatively, the small hall is sometimes located on the floor below the large hall, directly underneath the large hall.

The designs for recently built halls tend to anticipate events that generate very loud sound, and they use strategies such as locating the two halls as far from each other as possible, implementing anti-vibration and sound isolation structural techniques and using expansion joints. However, in some older facilities, the two halls are located back-to-back on the same level, with a single concrete wall separating the rear walls of the two halls' stages or two halls may share a single loading dock entrance. Also, we find that for some halls that were built with one hall directly above the other, while the specifications require a double-layer concrete slab, a large percentage of the slab has openings for HVAC ducting.

<< Sound Isolation Improvements Often Not Good Enough >>

When two halls are placed in adjacent locations, the sound isolation performance level between the halls must be able to prevent transference of (midrange) sounds of at least 90 dB, but some halls can only isolate sounds up to 60-or-70 dB. Years ago, before loud sound volumes gained popularity, and when hall utilization was less frequent, the lower sound isolation thresholds may not have caused problems, but today, a 60-to-70 dB sound isolation performance level places a serious limitation on simultaneous use of adjacent halls.

If a hall currently has a sound isolation performance threshold of 60 dB, it is surely possible to strengthen the sound isolation performance to the 70 dB-level by adding a sound-isolating layer to walls and/or installing or adding sound-isolating doors and other coverings at hall openings. But to raise the sound isolation performance from 60 dB to 90 dB would require not only installing double-layer walls and double-layer slabs. It would also require major construction to give at least one of the two halls an anti-vibration, sound-isolating structure.

This is not to say that there are no sound isolation improvement success stories. One example of Nagata Acoustics' successful design and implementation of sound isolation improvement renovations is a project in which we satisfied the client's needs by adding a sound-isolating layer to the walls of an adjacent large and small hall, thereby increasing the sound isolation performance level from 67 dB to 78 dB (both measured at 500 Hz). For another client who wanted to convert space on the floor below a hall to new music practice rooms, we implemented a more robust renovation that raised the sound isolation performance to a high level in excess of 100 dB.

<< Hall Equipment Noise Abatement >>

Quietness is the "sine qua non" of a hall's reputation, and if sound isolation is critical to achieving excellent quietness, the role of HVAC noise abatement is equally significant. Typically, equipment-generated noise figures prominently in cases requiring HVAC noise abatement. We have measured multipurpose halls with noise as loud as NC-25, and some older halls measure as high as NC-30. In the past, the standard acceptable maximum value for a concert hall was NC-20. Now, however, the bar has been raised and clients expect multipurpose halls to achieve an NC-20-level of quietness, and concert halls require NC-15 or lower.

Equipment other than the HVAC system also contributes to noise within a hall. Transformers create an annoying hum and strong outdoor winds can make exhaust ducts whistle. The most prevalent examples of transformer problems come from an electrical equipment or lighting controls room near a hall. In these situations, the transformers generate the most conspicuous of noises. It disturbs the human ear even when it occurs at an NC-20-level of quietness. Other frequent causes of interior noise are the deterioration of anti-vibration elastic, friction where ends of construction materials meet, and joists that have lost their resilience. The whistling sound of outdoor winds is caused by either a lack of noise abatement measures around exhaust ducts or by deteriorating sealants around lids and other closures.

Some of these noise examples are often masked by the louder noise of an HVAC system. When the HVAC system is renovated and made quieter, then people become aware of these other noises. In recent times, there is an increase in complaints received by halls that have adjacent restrooms. The hall's audience patrons point out that they can hear the noise of toilets flushing and being refilled.

As clients come to expect an exceedingly low level of HVAC noise, their inquiries about renovations to reduce the noise of other aspects of hall functionality is simultaneously on the rise. Audience claims extend well beyond equipment noise to include complaints about being able to hear the "click-clack" of footsteps in-and-around a hall and about the sound of dishes being washed at a hall's cocktail bar. Halls even receive complaints about being able to hear the sound of musical instruments being tuned in backstage dressing rooms. For all of these kinds of concerns, the key point to remember about renovations is that they are always fraught with existing constraints. The potential renovation solutions for these kinds of recent complaints require large-scale projects and large-scale remedial renovations are rarely implemented. I would like to see each hall renovation idea approached from the perspective of how to make the most effective use of each facility's existing strengths as well as contemplating its post-renovation potential.

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Nagata Acoustics News 02-6(No.174)
Issued : June 25, 2002

Nagata Acoustics Inc.
Hongo Segawa Bldg. 3F, 2-35-10
Hongo, Bunkyo-ku, Tokyo 113-0033 Japan
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