Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS


News 07-10 (No.238)

Issued : October 25, 2007

[ Japanese Version ]

The Birth of a New Hi-rise Home for Ueno Gakuen University and Schools

by Ayako Hakozaki

Exterior of Ueno Gakuen University and Schools
Exterior of
Ueno Gakuen University and Schools

One of Tokyo's most culturally rich locations is Ueno Park, where the Tokyo National Museum, the National Museum of Western Art and Tokyo Bunka Kaikan Hall stand amidst the park's cherry trees and other greenery and flora. On a street that is about a 10-minute walk from Ueno Station, where a tall building can enjoy a view of the park, the new hi-rise campus of Ueno Gakuen University and Schools recently completed construction and opened for use.

Ueno Gakuen offers curricula and degree programs as a junior high school, senior high school, junior college and university. This year, Ueno Gakuen marked its 103rd anniversary, and when the new school year began in April 2007, all four schools moved into the new structure that replaced the schools' former buildings. With the schools' new start in their new building, the Ueno Gakuen schools are all now also fully co-educational.

<< Overview of the New Hi-rise Campus >>

The new hi-rise campus has 15 stories above ground and two below and is a metal-frame structure. The lower and middle floors house the junior and senior high schools, and the 10th floor and above are reserved for the junior college and Ueno Gakuen University ("UGU"). In keeping with this academic institution's focus on music instruction, the building has many rooms that were built specifically for music training in addition to the standard and homeroom classrooms expected of an academic institution. The music-dedicated rooms include five rehearsal rooms of various sizes for orchestra, choral and other music use, 37 rooms for music instruction, 24 solo practice rooms and other ancillary rooms related to music instruction and practice.

Most of these music instruction and practice rooms are located along the perimeter of the building facing the curtain wall so that they have ample natural light and a bright and airy feeling. By locating the school's gymnasium in the basement, the layout avoided the need to address vibration transfer through the gymnasium floor caused by active sports activities. The school's library occupies the 14th and 15th floors and the 15th floor also has a student lounge with a panoramic view.

GKK Architects & Engineers and Nissoken Co. jointly designed the new building. Shimizu Corporation served as general contractor for the construction project. Nagata Acoustics provided acoustical design and consulting services for the many rehearsal, music instruction and practice rooms of the building.

Rehearsal room
Rehearsal room

Instruction room
Instruction room

<< The Right Sound Isolation Design for Each Kind of Music Room >>

As with our other music conservatory and music college projects, some of which we have featured in other issues of this newsletter, a key success criteria of our acoustical design work for Ueno Gakuen's hi-rise campus was effective sound isolation performance between and among the school's many music rooms. The new campus' layout designated a specific group of floors to house only music-related rooms, separating them from rooms that have other intended purposes and thereby preventing sound generated in the music-use rooms from being transmitted to lecture classrooms and other non-music rooms. The six stories from the 8th through the 13th floors are the floors dedicated to music instruction, practice and rehearsals.

Regarding the sound isolation performance level required for the various music rooms, we specified a performance grade to each category of room: rehearsal, instruction, practice and other music room, based on the characteristics of each kind of room and their intended uses. We designed the most robust level of sound isolation performance for the rehearsal rooms, where we used sound isolation gypsum board partition walls with a Transmission Loss (TLD) rating of 55 for the rooms' fixed walls and, inside the space defined by these fixed walls, we built a floating floor system and anti-vibration, sound-isolating walls and ceilings made of multiple layers of drywall to achieve complete sound isolation. Depending on the dimensions of each rehearsal room, we designated either an anti-vibration elasticized material or glass-fiber matting for the floating floor.

For the instruction and practice rooms, our basic approach relied on the fixed, sound-isolating walls to obtain the desired levels of sound isolation between the rooms. We selected sound isolation gypsum board partition walls with a rating of TLD 55 for the instruction rooms and with a rating of TLD 50 for the walls between practice rooms. Additionally, since the shared interior walls of adjacent instruction rooms would be a weak point in the sound isolation design of these spaces, at these walls only we also installed floating multi-layered sound isolation drywall.

We specified floating floor designs for all of the instruction room floors and for the floors of practice rooms that have the large music room directly below them. We also installed anti-vibration treatments on the ceilings of all of the music instruction and practice rooms.

<< The Benefits and Challenges of Our Sound Isolation Design Approach >>

As can be gleaned from my description, our design approach detailed different sound isolation specifications for different rooms, so that, in addition to ensuring the necessary level of sound isolation for each space, we also paid attention to cost saving opportunities and we maximized the usefulness of the building's limited square footage. However, this approach also resulted in my coming face-to-face with the difficulty of accurately gaining the builders' full understanding of the design requirements for the several different sound isolation designs.

In order to achieve a specified sound isolation performance level by relying primarily on sound isolation gypsum board partition walls, the installation of the panels requires a close tolerance and an overall precision not normally sought during interior wall construction. On this project, the use of metal framing complicated the implementation of the sound isolation designs, and the complexity of the construction work was additionally increased because of our use of multiple anti-vibration and sound isolation strategies and materials.

In this situation, I determined a need to impart greater understanding of the acoustical aspects of the construction work to both the construction manager and the workmen actually performing the construction work, so I planned and organized a specification clarification meeting. The challenge for us at this meeting was to impress upon our audience the direct connection between their construction activities and the details and precision those are significant from an acoustical perspective. One lesson learned from the meeting is the need to improve how we tailor our presentation to our audience. It is clear to me that the successful building of high performance sound isolation spaces requires awareness on the part of the workmen that they are working on an "acoustical construction" project.

<< Curtain Wall Design and Sound Isolation >>

Curtain walls are a standard element of metal-frame structures. This project's curtain wall, constructed of glass and white aluminum, plays a positive role as a fixed sound isolating layer for the instruction rooms and other spaces in the building. The project architect's vision for the building's exterior had stipulated a free and unbounded feeling for the curtain wall and, during the project, the architect and construction manager met repeatedly with us at the construction site to devise a curtain wall design on which we could agree and that would be a good strategy for sound isolation reasons. Sound isolation design involving curtain walls worth more focus in the future.

The Ueno Gakuen website's URL is http://www.uenogakuen.ac.jp/english/index.html.

Articles on Sound Isolation Design, Supplement 2:
- What is the M' Curve?

by Nobuhiko Hattori

Thanks to advances in window and door-framing products and other improvements in multi-unit dwelling construction, the acoustical environment in these residences is now generally much quieter than in the past. However, now that the building interiors are more quiet, apartment dwellers are more aware of sounds produced in adjacent rooms, creating new problems to solve. One kind of noise that causes problems is called intermittent noise. When used in an acoustical consulting context, intermittent noise can be defined as sound transmitted from adjacent rooms that is audible, has varying sound volume or rhythms and can be construed by the person hearing it in a meaningful way. Examples of intermittent noise include conversation, music and the flushing of a toilet.

Compared with steady (or steady-state) noise, such as the constant sound produced by an HVAC system across a broad area, intermittent sound characteristically attracts the attention of people within earshot (or, we might say that it distracts them). Therefore, even if the sound level of the intermittent noise is low, once the intermittent noise is heard, it tends to continue to be heard and easily becomes a source of irritation.

<< Addressing Intermittent Noise in Concert Halls and Music Studios >>

Because a quiet ambient environment is one of the most desirable acoustical objectives for both concert halls and music studios, even the slightest amount of intermittent noise—whether it be traffic or railway noise from outside or music being performed in another room—can be problematic. When developing concert hall and music studio sound isolation designs, we distinguish between noise to be evaluated using standard noise criterion (NC) curves, such as HVAC system-type steady noise, and intermittent noise that we evaluate for audibility using the values of the "M' curve," which is calculated based on the auditory masking threshold. (The May 2006 issue and August 1999 issue of this newsletter each contain especially excellent examples of projects that needed to address intermittent noises, specifically, Japanese Taiko drum noise and noise from a nearby train station.)

Use of the M' curve was proposed by Nagata Acoustics' founder Dr. Minoru Nagata, more than 50 years ago, during his tenure at the NHK Science and Technical Research Laboratory. According to Dr. Nagata, a concern arose among the users of a recording studio regarding sound transmitted via HVAC ducts to the studio. The studio users were not bothered by the sound of the HVAC system, but rather by a small amount of intermittent noise that had its source in music being performed in another studio. The music performed in the other studio was being transmitting via the HVAC ducts to the studio identified as having a problem. Dr. Nagata realized that a different evaluation criterion than the one used for HVAC noise would be needed to analyze and solve the studio's problem.

<< What Does the Term "Auditory Masking" Mean? >>

In order to provide the reader with an understanding of the M' curve, I will first need to explain the concept of auditory masking and to explain auditory masking. I will begin with an example of this phenomenon: If two people are engaged in conversation in a room and a loud noise such as an airplane engine or a railroad train interrupts the conversation, the conversation has been "masked" by the louder noise so that the two people hear the loud sound and do not hear each others' words.

The loud sound that causes the masking is known as the masker and the sound that becomes inaudible is called the maskee. In general, the effect of auditory masking becomes more pronounced in direct relation to the magnitude of the masker. Another characteristic of auditory masking is that it becomes more likely to occur as the frequencies of the masker and maskee become closer.

<< What is the M' Curve? >>

NC curves and M' curves
NC curves and M' curves

According to the concept of auditory masking, even an intermittent noise that is easily detected by the human ear will be masked and become inaudible if a small volume, steady noise masks the intermittent noise. Keeping this information in mind, let's now compare the standard NC curves and the M' curve.

The accompanying graph shows the curves for four NC ratings (15, 20, 25 and 30). The NC curves are used to evaluate the magunitude of HVAC noise and similar steady noise in large rooms such as concert halls and conference halls. When a room has steady noise that matches the frequency characteristics of a particular NC curve, the corresponding curve for the smallest audible pure tone is known as the auditory masking threshold. The M curve represents the borderline of sound that is masked by steady noise that has the characteristics of the relevant NC curve. When the masking threshold value is calculated, we find that for lower frequencies (which are the part of the audible sound spectrum more likely to have masking occur) the Masking Threshold value exceeds the NC value for the same frequency.

When intermittent noise and steady noise occur simultaneously, the masking threshold value of the intermittent noise (that is, the point where it becomes inaudible) may be greater than the NC value of steady noise that has the same frequency and loudness characteristics. Therefore, Dr. Nagata adjusted the auditory masking threshold curve to obtain the M' curve, shown in the graph as the solid lines. For example, in a room that has an NC of 20, if intermittent sound is transmitted into the room, it will be audible if its value is greater than the M' 20 curve and it will be masked and inaudible if its characteristics put it below the M' 20 curve.

Nagata Acoustics uses both the NC curve values and the M' curve values when developing sound isolation designs for our projects. We use the M' values to evaluate if isolation strategies are required for external noises to prevent their causing problems in the room being isolated, and we use the NC values to ensure that the steady noise generated by equipment and building systems will be kept below acceptable levels.

<< In Conclusion >>

Pursuing extreme levels of quietness without regard to the intended use of a room can result in a project or facility being plagued by unanticipated noise problems. To achieve a pleasant and comfortable acoustical environment, it is important to match a room's quietness to the way the room will be used.

* In preparing this article, I referenced Dr. Nagata's paper, "The allowable limit of sound pressure level of intermittent noise, such as music/speech," presented at the Acoustical Society of Japan's meeting in May, 1954.

Reports on the ICA 2007 and ISRA 2007 Events

<< The 19th International Congress on Acoustics >>

by Dr. Yasuhisa Toyota

The International Congress on Acoustics (ICA) meets once every three years, and this year the congress convened from September 2 to 7, in Madrid, Spain. I attended the event for just two days and gave a presentation on the acoustical design of the new Mariinsky Theatre Concert Hall, which opened in St. Petersburg, Russia at the end of last November. While I was at the congress on September 4 and 5, I attended the sessions on room acoustics and architectural acoustics, of which there were 39 presentations during these two days.

Of particular interest was the double session lasting 40 minutes that Dr. Leo Beranek gave at the outset of the presentations. Dr. Beranek titled his presentation "Concert Hall Acoustics 2001 - 2007." Born in 1914, Dr. Beranek is now 93 years old, yet during his own presentation and when in discussion with other presenters he amazingly gives no hint of the effects of age. If someone had told me that he is a man in his sixties, I could easily have believed this was true, such is his youthful and energetic demeanor.

Dr. Beranek expanded the content of his presentation beyond the years noted in his session's "2001-2007" title. He began his talk by harking back to the reverberation theories of Sabine and Eyring, then spoke about how room acoustics shifted its focus to the importance of early sound reflections and concluded his lecture with comments on recent research into the directionality of sound reflections. With great adeptness, Dr. Beranek surveyed this long history comprehensively, methodically and succinctly, in a way that made his chronological retrospective easy to understand. Fortunately, I obtained a written copy of the notes Dr. Beranek used for this presentation, as well as permission to post it online for sharing with readers of this newsletter.

I consider this writing indispensable reading for anyone engaged in research on room acoustics. The article can be downloaded via the following URL:

http://www.nagata.co.jp/news/070904BeranekLecture@Madrid.pdf

*Nagata Acoustics acknowledges and thanks Dr. Beranek for his permission to provide the PDF file to our readers.


<< The International Symposium on Room Acoustics 2007 >>

by Dr. Keiji Oguchi

Posters of La Philharmonie de Paris Concert Hall and Akiyoshidai International Art Village Concert Hall Posters of La Philharmonie de Paris Concert Hall and Akiyoshidai International Art Village Concert Hall
Posters of La Philharmonie de Paris Concert Hall and
Akiyoshidai International Art Village Concert Hall

On September 10, 11 and 12, participants in the ICA's satellite International Symposium on Room Acoustics (ISRA) moved to ISRA 2007's location in southern Spain at the University of Seville School of Architecture. The symposium attracted 160 attendees from 35 countries to its program of a total of 86 lectures and poster presentations. I attended the symposium and delivered a talk on our prototype audio speakers for use in scale model room acoustical testing. (A related article appeared in a previous newsletter article.)

Satellite symposia have become regularly scheduled events following each ICA gathering. This year, however, the Inter-noise 2007 Congress in Istanbul was held just one week before the Madrid ICA, which evidently depressed satellite symposium attendance from Japan and other countries. The symposium's content, as well, was somewhat on the lean side, perhaps because presentations on concert hall acoustics and the topic of subjective perception and room acoustics accounted for two of the ICA's key sessions this year.

Two of ISRA's keynote addresses, Kobe University Prof. Masayuki Morimoto's paper, "Subjective Perception and Room Acoustics," and Rensselear Polytechnic Institute Prof. Ning Xiang's paper, "Acoustics in Coupled Rooms" particularly caught my attention. Both professors shared information of great interest and presented their topics in ways that could be easily comprehended.

I experienced one surprise while attending this year's ISRA—the appearance of a poster session summarizing a hall project designed to accommodate "multifocal" repertoires. Nagata Acoustics involved the Akiyoshidai International Art Village Concert Hall to accommodate a multifocal repertoire nearly a decade ago. The Akiyoshidai International Art Village Concert Hall opened in August 1998 and I was not expecting to see this configuration need the focus of an ISRA 2007 poster session.


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[ Japanese Version ]