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

Nagata Acoustics News 98-7iNo.127j
Issued : July 25, 1998

Building Layouts and Sound Isolation Planning

by Toshiko Fukuchi

Many Japanese cultural centers recently completed, or now in the planning or construction phases, house multiple auditoriums and/or rehearsal and practice rooms in close proximity under a single roof. In designing the floor plans of these projects, the proximity of the facilities to each other is virtually pre-determined by the sponsors' decision on the total number of rooms and the limitations of the site's available land and adjacent roads and railroad lines. In addition, these cultural centers increasingly include a large number of rehearsal and practice rooms near the center's hall(s) in order to promote daily use of the facilities by the local community. When a center's practice rooms and hall(s) must be located in close proximity, the degree to which the various facilities can be used simultaneously will, of course, greatly affect the overall usage of the cultural center and its ability to maximize the number of people who benefit from the center's very existence.

Other examples of facilities that require special attention to sound isolation are projects in which a hall is built as part of a multi-purpose building designed primarily, or at least in part, as office and retail space. This kind of structure is also more and more prevalent in Japan. Here, the objective of creating as quiet a hall as possible impacts significantly on the acoustical characteristics and sound quality that can reasonably expected of the hall.

In both of the above kinds of projects, the most frequently raised complaint that any hall may receive is that sound from the adjoining space is audible inside the hall during its musical or theatrical performances. It does not take a well-trained ear to experience displeasure when outside sounds mix with an ensemble's otherwise pleasurable music or distract the audience from an actor's lines. Moreover, once a hall becomes saddled with a reputation for poor sound isolation, improving that reputation can be even more difficult than fixing the actual problem.

Post-construction strategies to improve a room or structure's sound isolation involve major structural changes that require considerable investments of both time and money. Therefore, the earlier that sound isolation is taken into consideration in planning a hall the better, and the best time to plan for adequate sound isolation is when deciding the floor plan layout. It is no exaggeration to say that whether the floor plan is good or bad can be enough to make or break the reputation of the completed hall.

<< Measurements and Calculations Relevant to Sound Isolation >>

Before discussing the sound isolation in specific halls, I will review the measurements and calculations I use in evaluating a hall's sound isolation. The volume of sound that we expect to be generated (in the middle frequencies) in a hall or rehearsal room is as follows: Large orchestras produce approximately 110dB SPL (Sound Pressure Level); medium-size orchestras produce approximately 100dB SPL; solo piano produces approximately 90dB SPL; and music that uses electric instruments (such as rock music) can be expected to produce in excess of 120dB SPL.

While the general trend may be towards performances and music genres that produce louder sound, the ambient noise in halls is yearly becoming less and less, making halls quieter and quieter. The norm for classical music concert halls is now under NC-15. ("NC" is the value used to measure how quiet the inside of a hall is, with the smaller the NC value the more quiet the hall. In a hall with a value of NC-15, the space is sufficiently quiet that one can hear the sound of another person breathing.) Since at NC-15, the intensity of 500Hz of sound is 22dB, to determine the level of sound isolation required to isolate a space from 100dB of sound so that the space maintains its NC-15 quietness, we simply subtract 22dB (or approximately 20dB) from 100dB and thereby know that approximately 80dB of sound isolation is required. Likewise, to prevent orchestral music from leaking to other adjacent rooms, 90dB (for the middle registers) of sound isolation would be necessary.

The concrete walls of reinforced concrete structures being built are approximately 150mm thick. When such a concrete wall has no doors or windows to decrease the sound isolation, it provides TL (Transmission Loss) for between 50dB and 60dB (at 500 Hz). As doubling the thickness of the concrete wall would only improve the TL by 5dB or 6dB, the immensity of the challenge involved in achieving sound isolation for 90dB of sound is obvious.

At Nagata Acoustics Inc., we have achieved the desired sound isolation in several projects by using rubber resilient system and a steel frame-work to virtually encapsulate the hall within a separate (known as a "box-within-a-box configuration). The negative aspects of this solution are that it takes space away from the size of the hall and increases the costs of the project.

<< Three Case Studies >>

Hall Arrangement Examples
The attached illustrations show some examples of hall arrangement. In floor plan (a), two halls are located on the same level, with small rooms intended as office space and practice rooms sandwiched between them. In (b), three halls are situated next to each other; and, in (c), four halls are also in close proximity, but they are also stacked one on top of the other. Among the three floor plans, the facility in illustration (a) is the best floor plan from the perspective of sound isolation planning.

Floor plan (a): In this layout, the two halls are approximately 30 meters apart, so there is no need for advanced sound isolation techniques as the physical separation of the halls is sufficient to isolate the sound of each from the other. However, if the rehearsal room in the corridor between the halls will be used simultaneously with either of the two halls, rubber resilient system is necessary to provide sufficient sound isolation.

Floor plan (b): In this layout, without the use of expansion joints, the sound isolation characteristics (level difference) between the halls is at best 70dB (at 500Hz). As a result, such performances as Japanese taiko drums or the lower frequencies sound of wind instruments can be heard beyond the hall in which they are produced, and the halls cannot, therefore, be used simultaneously. However, if expansion joints are used in the construction of each of the halls, the sound isolation characteristics (level difference) of each hall improves to between 80dB and 90dB (at 500Hz).

I wish to add a note of caution with regard to the use of expansion joints in this kind of example. From a construction perspective, the space created between the expansion joints and the frame may be filled-in on both sides with styrofoam or separator walls. However, for acoustical reasons, it may be important for the expansion joints not to be connected in any way; in this case, it is essential to remove the styrofoam and/or separator walls and have plain airspace instead.

Floor plan (c): In this floor plan, obviously, expansion joints cannot be used between the halls to improve the sound isolation. The only way to enable simultaneous use of the halls would be to employ rubber resilient system. However, using the box-within-a-box a resilient configuration is ill-advised when a hall is large scale and the stage has complex systems and apparatus. At best, the floors, walls, and ceilings can separately be supported by rubber resilient system, producing sound isolation for up to about 70dB to 80dB. When a facility has this kind of stacked floor plan, the halls cannot be used simultaneously without incurring the displeasure of at least one, if not both, audiences.

<< In Conclusion >>

The space and monetary expense consumed by rubber resilient system, as well as the additional construction work required, militates against its implementation except in special circumstances. Given the high cost of land, stacked facilities such as the one shown in floor plan (c) may be inevitable. Nevertheless, whenever possible, a single level floor plan along the lines of illustration (a) should unequivocally be encouraged, with floor plan (b) as a possible alternative, provided that expansion joints are used. If hall sponsors can be persuaded on the importance of floor plans to their hall(s)' sound isolation and the overall success of their facility, they will surely continue to understand the value of a well-designed floor plan as they manage their facility's operational success long after the construction is completed.

A New Start for the Disney Concert Hall Project (Los Angeles)

by Yasuhisa Toyota

Interior Model of Disney Concert Hall
Nagata Acoustics Inc. is the acoustical consultant for Disney Concert Hall, Los Angeles. We are, of course, especially glad that the project is now moving forward again this year. Previously, the project was plagued with fiscal woes that drew all activity to a screeching halt. Some outside observers even questioned whether the hall would ever be completed.

<< History of the Project >>

A full decade ago, in 1988, the Disney Concert Hall project committee invited a number of architects and acousticians to present their ideas for a new home for the Los Angeles Philharmonic Orchestra. As a result of that competition, the U.S. architect Frank O. Gehry, a local Santa Monica resident, was selected as the hall's architect. Nagata Acoustics was chosen as the acoustical consultant. But, as the design planning for the hall progressed, it became clear that the cost of the hall would well exceed the scale of the project's original budget. In the autumn of 1994, midway through the architect's preparation of the hall's Construction Documents, a "freeze" order was put on the entire project. At that point in time, the on-site construction of a six-level underground parking garage (with a 2,500 vehicle capacity) had not only been completed, but was already fully operational.

<< Disney Concert Hall's Raison d'Etre >>

The Disney Concert Hall project is the brain-child of the late Lillian Disney, Walt Disney's widow and a dedicated patron of the arts during her long lifetime of 98 years. Mrs. Disney initially donated $50 million for the construction of the 2,400-seat concert hall, which, upon completion, would become part of the Music Center of the Los Angeles County in downtown Los Angeles. A primary function of the new hall is to be the home hall of the Los Angeles Philharmonic. The site of Disney Concert hall is located directly across from Dorothy Chandler Pavilion, where the Los Angeles Philharmonic currently holds its regular season performances.

<< Disney Corporation, Others, and a Revived Economy Add Support >>

Since autumn 1994, when the freeze was put in place, the project's supporters persistently worked to raise the necessary funds to resume development of Disney Concert Hall. As the U.S. economy strengthened, donations grew. Then, in December 1997, Disney Corporation decided to infuse $25 million into the project. (Prior to this corporate donation, all contributions bearing the Disney name had come been from the Disney family.) Suddenly, all lights were green again and the Disney Hall project is now happily moving forward at a rapid pace.

Presently, every effort is being concentrated on completion of the Construction Documents. Groundbreaking is scheduled for March 1999. Construction of the hall is expected to last approximately three years. If all goes as planned, therefore, Disney Concert Hall's completion and opening will take place in 2002.

<< A Perspective from Outside the United States >>

Four years ago, when Nagata Acoustics was told that the project had been frozen, we were quite literally dumfounded. This turn of events would have been totally beyond the realm of possibility in Japan. Here, when a project is begun, the budget is set, and then it becomes the responsibility of the architect and general contractor to complete the project within the allotted budget and time schedule. In Japan, the assumptions that the budget and timeline will be met pass for plain common sense.

By contrast, in the United States, at a point when the budget is still somewhere between a rough estimate of the available funds and a final figure, the design of the project moves forward and, a give-and-take process unfolds in which the budget becomes finalized as the design also reaches its final form. Depending on the project, if there is consensus on surpassing an initial budget, the founders and supporters of a U.S. project will work very hard to raise the extra money needed to realize the architectural design they want built. Consequently, in the United States, and in Europe as well, we frequently hear of projects being temporarily put on hold because of a lack of funds to implement the project's design. In recent memory, concert halls in Philadelphia and Bremen (in Germany), as well as the Cardiff Opera House in the U.K., come to mind as projects that were put on hold because of funding problems. The construction of the Sydney Opera House is also known to have surpassed its original budget in terms of both the time and money required for its completion.

With so many examples of projects in the United States, Europe, and elsewhere, in which costs overran budgets and completion dates went beyond schedules, perhaps Japan's typically on-budget, on-schedule project completions are the ones that should cause surprise! When the budget and completion deadline for a Japanese project are reasonable, everything flows smoothly. But we also encounter situations where the sponsor, often a governmental body, makes seemingly impossible demands to restrain costs or set an early completion date. There are also too many situations in which the budget and timeline are set without sufficient study and input from experts, and then the architect, acoustician, and contractor all must somehow meet the unreasonable expectations.

In Japan, where a firm budget and schedule rule, halls are completed and opened for use according to their original plans. In the United States and elsewhere, priority is given to deciding exactly what will be built, even if the result is that a project may not be completed until many years after it was originally needed or desired. Is one of these methods better than the other? Perhaps it all depends on those ubiquitous factors of who, what, when, where, and why.

16th International Congress on Acoustics Meets in Seattle

by Keiji Oguchi

The 16th International Congress on Acoustics ("ICA") was held from June 20 through June 26, 1998, in Seattle, Washington. The meeting was held jointly with the 135th meeting of the Acoustical Society of America, and was the largest gathering of acoustical professionals ever held. Four acousticians from Nagata Acoustics Inc. participated in the Congress: Yasuhisa Toyota delivered a lecture on Sapporo Concert Hall; and, Keiji Oguchi, Toshiko Fukuchi, and Akira Ono contributed poster presentations on, respectively, the Queensland Conservatorium of Music, Sumida Triphony Hall, and Fukui Concert Hall.

The Congress covered a diverse range of acoustical specialties, including engineering acoustics, physical acoustics, underwater acoustics, bio-acoustics, and psychological acoustics, to name some but not all, as well as the field of architectural acoustics that most interested the Nagata Acoustics Inc. attendees. In the field of architectural acoustics alone there were plenty of breakout sessions to keep us busy, including a two-day workshop on opera house acoustics and two case study sessions on projects built in Tokyo, Japan. The extensive programming drew an unprecedented 135 presentations which we also avidly reviewed.

<< Opera House Workshop >>

The opera house workshop was the sequel to two separate sessions held in 1995. MCHA held a symposium in Kirishima, Japan followed shortly thereafter by a separate symposium by the Italian organization CIARM at Ferrara University. This time, MCHA and CIARM joined together to plan the Congress' two-day workshop. At this workshop, I was especially intrigued by the discussion of how diffracted sound waves from the tier box seating of traditional horse-shoe-shaped opera houses help produce the rich sound quality heard in these opera houses' orchestra seating. In addition, the portion of the workshop on orchestra pit acoustics and the acoustical data from Venice's Gran Teatro la Fenice, which had unfortunately been the victim of fire just two weeks earlier, were among the more memorable parts of the workshop for me.

<< Case Study Sessions on Tokyo Projects >>

The fourth day of the meeting included case study sessions on two new Tokyo structures: the New National Performing Arts Center, including Tokyo Opera City; and, Tokyo International Forum. U.S. acousticians had a hand in the acoustical consulting for both of these projects, and this seems to have influenced their selection for inclusion as stand-alone case study sessions at the meeting. Dr. Beranek is Acoustical Director of the New National Performing Arts Center, and Jaffe Holden Scarbrough Associates, Inc. are the acoustical consultants for Tokyo International Forum.

<< Acoustical Measurements and a Presentation on Discrepancies >>

Unlike some previous meetings, at this Congress, reports on the physical measuring of acoustical characteristics were primarily focused on C80, G, and IACC, rather than on the measurement of reverberation time. Perhaps the relative silence on reverberation time reflects general acceptance of the ISO 3382 standard for measuring room reverberation time. (Please see my article in our January, 1998 news for further comments on standardizing the measurement of room reverberation times.) My poster presentation happened to be next to the presentation of New Zealand's Dr. Marshall. In Dr. Marshall's poster presentation, he focused on the discrepancies in reverberation time measurements that result from minor adjustments to the location or direction of the sound source, as well as from minor differences in the placement of microphones. Other parameters also show discrepancies depending on details of measuring methods. Reviewing Dr. Marshall's presentation strengthened my opinion that until the conditions of measurement for acoustical parameters are defined and stipulated in sufficient detail to substantially limit measuring discrepancies, it is almost futile to compare the results of different professionals' acoustical measurements.

<< Seattle's New Benaroya Hall >>

With Seattle's new 2,500 seat symphony concert hall, Benaroya Hall, nearing completion, the ICA meeting provided an excellent opportunity to visit this new concert venue. The site of this hall is in very close proximity to a railroad tunnel, and therefore provide a good case study on sound isolation and anti-vibration strategies. The hall's acousticians implemented a box-within-a-box configuration and floated the entire frame on rubber pads. The room acoustical consulting for the new Seattle hall is one of the field's most esteemed professionals, Dr. Harris. The new hall has a rectangular main floor surrounded by three balcony tiers, and looks very much the same as New York's Avery Fisher Hall and Salt Lake City's Abravanel Symphony Hall. However, the dispersion-enhancing shape of the new Benaroya Hall represents a marked departure from Dr. Harris' former halls.

Nagata Acoustics News 98-7iNo.127j
Issued : July 25, 1998

Nagata Acoustics Inc.

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