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

Nagata Acoustics News 01-7 (No.163)
Issued : July 25, 2001

Acoustical Design of Indoor Swimming Pools

by Hideo Nakamura

In Japan, as elsewhere, there is strong interest in participatory sports as a means to maintain and improve personal health. Swimming ranks high in popularity because it can be pursued at a variety of intensities from the most leisurely laps to hard training workouts, and it can be enjoyed both individually and as a family or group activity. Local Japanese governments operate heated indoor pools that rely on heat produced from garbage incineration facilities as their energy source, providing inexpensive, year-round public swimming facilities that draw crowds of swimmers in every community where they are built.

<< Acoustics Can Have a Big Impact in Small Indoor Pools >>

One may ask if acoustical design is necessary in planning an indoor swimming pool. One example of where it would have avoided costly major reconstruction was a small scale, 25-meter indoor pool used by a swimming school. The sound reverberations in this facility were so obtrusive that it was impossible for students to understand directions called out to them by their swimming coaches. We were not contacted to provide solutions until after the pool's users complained. In this example, whether the lack of an acoustician's participation during the planning and design stages was due to ignorance of the potential impact of acoustical considerations or whether it was due to budget constraints, the result was that the pool owner ultimately incurred huge remedial expenses.

<< Quality Acoustics Are Essential in Large Indoor Pool Facilities >>

Recently, the trend in Japan is toward the construction of large-scale public swimming facilities that have a 50-meter indoor pool plus a smaller pool, a diving pool and spectator seating. These facilities host competitions and award ceremonies at which the event promoters, participants and spectators expect amplified speech to have a high degree of clarity. If an appropriate acoustical design is not part of the planning and design processes for this kind of project, the danger that the outcome will hinder the facility's successful operation is even larger than the risks for a small indoor pool facility.

Certainly, the appropriate acoustical design work for an indoor swimming pool does not require the intense consideration of music-affecting details and refinements that are part of the work of concert hall acoustical design. But the interior room design, HVAC (heating, ventilation and air-conditioning) noise control and the sound system are all as relevant to an indoor swimming pool project as to a classical music concert hall. Unless these acoustical design aspects of the project are given adequate attention, each has the potential to become the source of user complaints.

<< Case Study: The Acoustical Design of a Large Indoor Pool >>

Ibaraki Prefecture
Indoor Swimming Pool Pavilion
Below are highlights from my recent participation as the acoustical consultant on a large indoor swimming pool facility construction project.

* Project Summary
Our acoustical design was implemented on the publicly funded Ibaraki Prefecture Indoor Swimming Pool Pavilion. This project was built in Ibaraki Prefecture's Oyama City. The pavilion's construction was completed in June 2000. The pavilion houses one 50-meter and one 25-meter pool, as well as a 1,000-seat arena for sports competitions.

* Interior Room Design
Our fundamental approach to the pavilion's interior room design followed the same approach that we use for large sports arenas in general, which is to focus on the prevention of long path echoes. In addition to making the entire ceiling a sound-absorbing surface, wherever possible we made the surfaces of the side walls sound-absorbing surfaces as well, in order to obtain the maximum overall square-footage of sound absorbing surface. However, selecting the sound-absorbing materials to implement our design presented a challenge because the interior furnishings of indoor swimming pools are exposed to high levels of humidity and are likely to be splashed with water, conditions that limited our choice of sound-absorbing materials.

For this project, we selected 25mm-thick ceramic wood-fiber cement boards for the sound-absorbing surface of the center portion of the ceiling, and we installed 1.6mm-thick aluminum-fiber sound-absorbing material on the remainder of the ceiling and on approximately half of the surface area of the indoor side walls. In order to ensure that amplified speech would be heard clearly, we aimed to achieve a reverberation time below 3.0 seconds (at 500 Hz).

* HVAC Noise Attenuation Design
Indoor swimming pools use powerful ceiling exhaust systems to prevent buildup of water droplets, creating a challenging environment from the perspective of noise attenuation. For this project, we set a goal of below NC-40. To achieve this goal, we selected exhaust equipment and circulation fans that produce low levels of noise. We also installed sound isolation enclosures around a portion of this equipment.

* Sound System Design
Microphone on the boat
to receive the amplified sound
over the water
It is well understood that in an enclosed, large-volume space that has a long reverberation time, the two critical factors in achieving clear amplified sound are speaker selection and speaker placement. For this indoor pool, we chose directionally controlled speakers with anti-humidity protective treatment and we designed a dispersed placement layout. The objectives of this design were:

(1) to place the speakers as close as possible to the locations that the amplified sound is intended to reach; and;
(2) to localize the coverage area of each speaker in such a way that sound from the speaker does not go beyond the delineated coverage area for that speaker.

To achieve the latter objective, it was beneficial to use the strategy of "aiming from the top down" in defining the area to be serviced by each speaker.

One undesirable effect of dispersed speaker layouts is that they can give the amplified sound an unnatural sense of directionality. This problem can be successfully remedied by channelizing each speaker's output into fine gradations and precisely setting the delay and other specifications of each channel. Unlike the priorities that we would set for the sound system of a theater or a concert hall with a stage, in facilities such as this indoor pool project, it is fair to consider unnatural directionality a secondary priority and clarity of sound as the primary concern.

* Measured Acoustical Characteristics
We measured the reverberation time of the indoor pool facility both before and after the pool was filled with water and the results are shown in the accompanying chart. At 500 Hz, we measured a reverberation time of 2.7 before the pool was filled and 2.4 seconds after it was filled with water. Our measurements also obtained a }0.1 value for the absorptive coefficient of the water surface at mid-range octaves.

The results of our measurement of noise from the HVAC systems showed that we obtained NC-39`44. We measured the clarity of amplified sound at STI of 0.51`0.69 (fair). Overall, each of these areas of measurement confirmed that the work achieved the parameters we established at the outset of the project.

Reverberation characteristics

<< Post Completion Project Evaluation >>

Since the Ibaraki Indoor Swimming Pool Pavilion opened in October 2000, it has been used for many competitions and similar events, and it has earned a favorable reputation for the clarity of its amplified sound. Our ability to develop an acoustical design and implement it at each stage of the project, thereby successfully achieving the objectives we established at the outset, owes much to the understanding of the client, who recognized acoustics as an important consideration throughout the project. The client's stance also ensured that we received cooperation from the other engineering and construction organizations that participated in the project.

Much technical research and advancement remains to be done on topics that affect achieving amplified speech clarity in the large volume enclosed space of an athletic facility. Among these topics, I would especially mention the current limitations on the choice of sound-absorbing materials and sound system equipment that can be used in the high-humidity environments of indoor swimming pools. In addition to technological limitations, these kinds of facilities typically face budgetary limitations as well. When appropriate concern is given to acoustical considerations before and during the building of this type of facility, it prevents the huge costs of large-scale remedies for acoustical problems discovered after a facility is completed. To this end, I hope that all of the persons who have a say in these kinds of facilities projects will deepen their understanding of the need for acoustical consulting expertise and ensure the inclusion of an acoustical consultant among their professional resources.

ASA's "Another 20 Years of Music Hall Experience Poster Session"

by Yasuhisa Toyota

On June 4 - 8, 2001, the Acoustical Society of America (ASA) convened its 141st Meeting, held in Chicago. I attended the meeting with four other Nagata Acoustics colleagues (Satoru Ikeda, Toshiko Fukuchi, Keiji Oguchi and Akira Ono). The ASA holds regular meetings semi-annually at various U.S. locations. In the past, Nagata Acoustics did not often send representatives to these meetings and, even when there was a presentation on a topic of particular interest to our acoustical consulting focus, we typically sent at most one or two attendees.

<< Comparisons with the "20 Years ..." Poster Session of 1982 >>

There were special circumstances that led Nagata Acoustics to send five of our acousticians to the 141st ASA Meeting. At this meeting, the ASA's Architectural Acoustics Committee hosted a poster session entitled "Another 20 Years of Music Hall Experience." The word "another" in this poster session title points to the special significance of the session, because it hints at the first "Music Performance Halls, Two Decades of Experience (1962-1982)" poster session, held 19 years ago at the 103rd Meeting of the ASA, which, coincidentally, was also held in Chicago. The poster session at the 103rd Meeting, in 1982, chronicled music performance hall construction over the previous 20 years and was preserved in the ASA's publication of a printed volume containing all of the poster session's submissions.

The posters submitted to the first "Music Performance Halls" poster session contained detailed information on the characteristics of each hall presented, as well as diagrams and other visual representations of the halls and acoustical statistics. As such, it provides an excellent source of knowledge on the state of the art for music performance hall acoustics during the 20-year period of time it covers. The poster submissions totaled 81, mostly U.S., halls.

<< Nagata Acoustics' Participation in 1982 >>

Nagata Acoustics participated in the first "Music Performance Halls, Two Decades of Experience (1962-1982)" poster session, submitting poster presentations on six of our halls, each with their distinguishing characteristics. These six halls are shown as follow, together with the year they opened, their seat count, and a note on a distinguishing characteristic.

Hall Name
Special Characteristic
Ueno Gakuen College
Ishibashi Memorial Hall
622Classical music concert hall
Hachinohe City Kokaido
1,060Convertible space
Niigata Music and Culture Hall
525Arrangement with multiple practice rooms
Musashino Music College
Bach Saal
1,202Classical music concert hall
Sapporo City Education and
Culture Hall
1,100Variable reverberation time
Aichi Koseinenkin Hall
1,666Anti-vibration strategy near subway line

<< Our Participation Quadrupled in the "Another 20 Years ..." Session >>

The "Another 20 Years of Music Hall Experience (1982-2002)" Poster Session was open to submissions on music performance halls built or scheduled to open during this 20-year period. Prior to the June Meeting, the ASA announced that it would again publish a volume of all of the poster submissions after the close of the session.

The two decades of work included in this poster session coincide almost exactly with the era of intense music performance hall building activity throughout Japan. Nagata Acoustics served as the acoustical consultant on a large number of these projects. We realized that the poster session presented an excellent opportunity to make a collection of posters documenting our hall design activities, especially since our poster collection would later also be preserved in book form. Our first idea was to submit posters for as many of our halls as possible. While refining our plan to conform to our time and expense limitations, we eventually restrained our initial exuberance and decided to submit posters detailing 24 concert halls from among our more numerous total list of projects worked during those 20 years. The following lists the 24 concert halls we presented.

Hall Name
1Kumamoto Prefectural Theatre Concert Hall
2Fukushima Concert Hall
3Matsumoto, The Harmony Hall
4Suntory Hall
5Casals Hall
6Tsuda Hall
7Tokyo Metropolitan Art Space Concert Hall
8Concert Hall ATM in Art Tower Mito
9Okayama Symphony Hall
10Katsushika Symphony Hills, Mozart Hall
11Philia Hall
12Asahikawa city, Taisetsu Crystal Hall
13Kioi Hall
14Kyoto Concert Hall
15Queensland Conservatorium of Music
16Nagaoka Lyric Hall Concert Hall
17Sapporo Concert Hall "Kitara"
18Harmony Hall Fukui
19Sumida Triphony Hall
20Sogakudo Concert Hall of
The Tokyo National University of Fine Arts and Music
21Akiyoshidai International Art Village Concert Hall
22Nara Centennial Hall Concert Hall
23Toppan Hall
24Ishikawa Concert Hall

<< The Small Number of "Players" in Concert Hall Acoustical Design >>

The ASA logged 103 registrations for poster submissions to "Another 20 Years of Music Hall Experience (1982-2002)," of which 90 posters were actually submitted and displayed on the day of the poster session. Given the scholarly nature of the ASA, we had felt some hesitation about the propriety of submitting many posters from our one company, but it was readily apparent at the session that the participating American acoustical consulting firms had similarly submitted numerous posters per firm. Four firms submitted 74 of the total of 90 posters displayed. The firms that submitted the largest number of posters, together with the number of posters each submitted, is shown in the accompanying list. One conclusion we may draw is that in the field of concert hall acoustical design, most of the projects are worked by a limited number of consulting firms.

Consulting Firm
1 Kirkegaard & AssociatesChicago, USA
2 Nagata Acoustics, Inc.Tokyo, Japan
3 Jaffee Holden Acoustics, Inc. Norwalk, USA
4 Artec Consultants, Inc.New York, USA

<< Summary of the Poster Session Day's Activities >>

The poster session lasted an entire day, from 9:00 a.m. to 5:00 p.m. During the three morning hours, presenters were expected to stay in the area where their posters were displayed so that they would be available to answer questions from session attendees. Since we had five acousticians from Nagata Acoustics, we each took responsibility for four or five of the halls displayed on our posters, and the other firms that presented multiple posters staffed their display areas in similar fashion. All of the participating consulting firms also took interest in other firms' poster displays and shared information in a collegial atmosphere.

The poster specifications followed those established for the first 20-year compendium session. The format is one hall per poster, and each poster contains summary data of the hall owner, architect, acoustician and cost, technical specifications, plan-view and elevation drawings, reverberation time and photographs.

Because all of the posters followed the same format, it was easy to compare the various characteristics of the different halls displayed. This consistency will also add to the value of the printed volume that the ASA plans to publish, in which the posters will be reduced to an appropriate size for printing, distribution and reference. This session's participants were also required to provide electronic files of their posters as the ASA intends to make a CD-ROM version available as well. Specifics on ordering the printed and/or electronic versions of the poster session should be available soon, directly from the Acoustical Society of America (http://asa.aip.org).

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Nagata Acoustics News 01-7(No.163)
Issued : July 25, 2001

Nagata Acoustics Inc.
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