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

Nagata Acoustics News 05-10 (No.214)
Issued : October 25, 2005

Marlboro Music Festival Auditorium Gets an Acoustical Renovation

by Yasuhisa Toyota

This year, as every year for more than half a century, for 7 weeks from the end of June through the middle of August, Marlboro Music Festival gathered gifted young professional musicians, veteran master professionals and concert patrons to the woodsy, rural campus of Marlboro College.

Marlboro College is located, in Marlboro, Vermont, about a 4-hour drive north from New York and 2.5 hours northwest from Boston. Begun in 1951 by the great pianist Rudolf Serkin with the help of Adolf Busch, his father-in-law, the festival held its 55th season this year. After Mr. Serkin's passing in 1991, the music festival board asked the eminent pianists, Mitsuko Uchida and Richard Goode, to be Artistic Advisors with Andras Schiff. Mitsuko Uchida and Richard Goode have been Artistic Directors since year 2000.

<< Marlboro Music Festival >>

The music festival auditions young professional musicians, selecting some 50 participants each year to join about 20 established musicians, known as the "seniors," to work on chamber music repertoire. The young musicians and seniors rehearse and perform side-by-side as colleagues, in an intensive learning environment through which the young musicians polish their skills and gain musical insights first-hand from the seniors.

The young musicians may return to the festival for a maximum of 3 years, so about 1/3 of the musicians are new to the festival each year. During the intensive 7-week program, both the young musicians and the seniors share the same environment with the dining facilities as "one large musical family." On the weekdays, the young musicians and seniors engage in all-day rehearsals, and on the weekends they display the fruits of these efforts in concerts open to the public.

Given the rural location of Marlboro College, the uninitiated visitor might well wonder how the festival can repeatedly draw concertgoers to its performances, but the festival ensembles consistently perform to full, or near-full, audiences in the college auditorium, which holds 500 seats. The festival performances enjoy this popularity despite minimal formal publicity and the fact that each concert's program is published only one week in advance. Most concert patrons purchase their tickets without knowing what works will be performed. The large and steady turnout of patrons at Marlboro Music Festival is a testimony to the festival's long history and the accomplished playing that characterizes the concerts.

<< Acoustical Renovation of the Festival's Auditorium >>

The music festival's administrative office requested Nagata Acoustics to do an acoustical renovation of the flat-floored, 500-seat auditorium at Marlboro College where the festival holds its concerts. Our U.S. office took the lead in planning and executing the renovation project, which aimed to correct two problems identified by the client:

After studying the possible approaches and options for this project, we decided to concentrate the renovation work on the area around the auditorium's stage. Because the auditorium is only used as a concert hall in the summer months of the Marlboro Music Festival, while during the rest of the year it serves as the Marlboro College gym, renovating the entire hall was not a practical option. Of course, the renovation budget also played a role in determining the project's scope and approach.

The specific changes we implemented in the renovation can be summarized in two main points. (1) We removed a very large, overhead acoustical reflections canopy in order to make better acoustical use of the entire auditorium's space. (2) At the rear of the stage, we installed an acoustical reflection shell with a shallow overhang to direct sound reflections back to the musicians on stage.The accompanying before-and-after photos show the renovation's two major changes.

Acoustic Renovation around Stage
(left:Before, right:After)

After the renovation, comments by the seniors were collected. Many of them were quite positive about the acoustical renovation, saying gThe balance of each instrument has really improved. Before, for example, there were times when only the piano could be heard loudly, and the strings, especially the viola, couldn't be heard at all. Now, each instrument can be heard well with good balance among them.h

Sound Isolation Design - Part 1 of a Series:
Ask about Sound Isolation Considerations in Your Initial Design Plans!

by Chiaki Ishiwata

Sound Isolation Matters in Our Everyday Situations
Japan has a long reputation as a very crowded country, and it is not surprising that since the 1970s, multiple-dwelling houses have filled the urban and suburban landscapes of Japan's major population centers. My childhood coincided with Japan's apartment complex boom and I will never forget one of the tragic consequences that occurred during the 1970s decade. This was a period when many Japanese families bought pianos and considered piano lessons a necessary part of a well-rounded education. Unfortunately, the noise from one household's piano practice led to this family's murder by a downstairs neighbor whose unit was separated from the piano practice by only a concrete slab. The "piano murder incident" shocked Japan when it occurred and surely this was an extreme and sad response to unwanted sound.

There are many sound isolation matters in our everyday situations. For example, the sound of noisy street traffic outside can interrupt our sleep, the sounds from a noisy classroom can prevent the teacher and students in an adjacent room from hearing each other and rock music band rehearsals in community centers may interrupt meetings and conferences taking place in adjacent or nearby rooms. When we encounter these or similar situations, we naturally make a judgment about the environment being acceptable or noisy and unpleasant. Since most of us can recall encountering this kind of situation, it is clear that sound isolation affects our daily lives in a very immediate way.

<< The Difficulty of Improving Sound Isolation during a Hall's Renovation >>

Recently, in Japan, we are experiencing an increase in hall renovation projects, a phenomenon perhaps related to Japan's economic situation. Often, the renovation objectives include improving the sound isolation performance characteristics between a large and small hall or between a hall and rehearsal room.

Some halls being renovated were constructed before the proliferation of electrically amplified instruments in rock bands and other ensembles. Some halls that did not plan for simultaneous use of a large and small hall find that the demand for their facilities now requires simultaneous use of adjacent halls. Over time, the way people use these halls has changed and the halls' desires to improve sound isolation mostly represent their recognition of these changes.

However, in considering what sound isolation improvements can be made during hall renovation projects, we must recognize that the sound isolation strategies we most frequently adopt for new construction are no longer available options. For example, we cannot change the layout of the building to create greater distance between a hall and a rehearsal room, nor can we divide large and small halls built as a single structure into two structurally separate buildings. The articles in this newsletter that mention our success in achieving high levels of sound isolation performance often also mention that we implemented an anti-vibration, sound isolating structure. If we add this kind of room structure to an existing room, the room will both become smaller and the floor of the room will become higher than the corridor to which its door connects, creating exit and entry problems. In addition, a building's load conditions can make it unfeasible to add a floating concrete foundation into an existing structure.

<< The Old Adage Still Applies: Get it Right the First Time! >>

While this advice may come too late for halls doing renovations, for any new construction project, the best strategy continues to be to include sound isolation considerations in the original design plans. The sound isolation materials and structure behind a hall's interior walls are not visible to the eye the way the interior finishings are, but they may nevertheless represent a significant expense in a hall's budget, so it is wise to include this cost in the project's initial estimate.

Sound isolation costs may decrease or grow, depending on the site location selected for a hall and the layout of rooms in the architectural design. In addition, if the project defines the sound isolation limitations and required performance expectations during the planning stage, then later "surprise" operational difficulties and unanticipated plans for the building can be averted.

The basic approach to sound isolation design begins with the use of walls and horizontal slabs with large mass. Even structural design decisions such as whether to build with a reinforced concrete or steel structure should include a total evaluation of this decision's impacts on the project, including the impact on the building's sound isolation performance requirements and objectives. The earlier in a project that the acoustical design team can be included in decision-making, the greater the added value that they can provide to ensure the best sound isolation design solution.

This article begins the new series: Sound Isolation Design, with the aim of providing the reader insights into various technical, yet fundamental aspects of sound isolation design. In this Part 1 of the series, I will focus on three topics that frequently arise when we talk about sound isolation design.

<< Sound Isolation and Sound Absorption >>

When a project includes improved sound isolation as one of its requirements, achieving an appropriate balance between the room's sound isolation performance and sound absorption characteristic is an essential consideration. Sound isolation and sound absorption are not the same thing, and it is important not to confuse these two characteristics of a room's acoustics. Fundamentally, sound isolation refers to the phenomena of repelling or bouncing back sound so that the energy generated by sound waves does not escape outside the location where it is being isolated. Conversely, sound absorption refers to the conversion of sound wave energy into heat energy or otherwise dissipating sound energy so that the sound energy in a room becomes reduced.

The acoustical materials we use for sound absorption differ from the materials we select to achieve good sound isolation. Glass wool appears often in designs for sound absorption because of its excellent sound absorbing properties, but its very porous nature and its light weight make its sound isolating effectiveness extremely low. Concrete and gypsum board, by contrast, are materials that reflect sound, so they cannot be expected to absorb sound, but they are often used as sound isolation materials.

Basically, where sound isolation is required, materials that isolate sound must be used to achieve the desired performance characteristic. However, in addition to building a sound-isolating wall, an effective design also diminishes the sound energy by adding sound absorbing treatments to the room in which the sound is transmitted. In the case of HVAC rooms and other mechanical rooms known to be noise sources, incorporating sound absorbing measures in these rooms' designs will lower the sound pressure level in these rooms. The lower sound pressure in these kinds of rooms results in decreased sound pressure levels being transmitted to the sound isolating wall or structure, and is therefore an important strategy from the perspective of achieving a project's sound isolation goals.

<< The Larger Value is the Better the Sound Isolation Performance>>

When Nagata Acoustics News & Opinions articles discuss sound isolation performance, for example, we may write: "The sound isolation performance between the rehearsal room and the concert hall is 70 dB." This measure equates to the difference between the sound pressure level (dB:decibels) in the room where the sound originates and the sound pressure level in the room to which the sound may be transmitted. The sound isolation performance discussed here is not a performance of the wall or the materials used for sound isolation. Rather, it is a comprehensive sound isolation performance between rooms, including any sound or vibration transmission through the ceilings and floors and the effects of sound absorption measures, in addition to the direct contribution to sound isolation performance of walls and other sound-isolation structural elements.

The larger the sound isolation performance value, the better the sound isolation performance. The sound isolation performance is a relative value. For example, if the sound isolation performance between a rehearsal room and a hall is 70 dB and the sound produced in the rehearsal room equals 100 dB, the decibel strength of the sound that transmits to the hall is 100-70 = 30 dB. If the sound produced in the rehearsal room equals 120 dB, then a larger sound equal to 50 dB will be transmitted into the hall. The amount of the transmitted sound in the receiving room changes relative to the volume of the sound generated in the room of the sound source.

<< Double a Wall's Thickness to Increase Sound Isolation by 5dB >>

Surface density is the fundamental factor that determines a material's sound isolation properties. The greater (heavier) the surface density of a material, the more effective will be its sound isolation performance. In physics, this rule is known as the mass law. When designing sound isolation elements, the challenge is to determine the heaviest isolating material that can be used. When the surface density is doubled, sound isolation performance increases by about 5 dB.

For example, in general, a slab of concrete measuring 150 mm. (6 in.) has a sound isolation performance value of 50 dB (for mid-range frequencies). If the concrete's thickness is doubled to 300 mm. (12 in.), then the sound isolation performance value increases by about 5 dB. However, if one begins with concrete that is 300 mm. (12 in.) and the aim is to increase sound isolation performance by 5 dB, the thickness of the concrete must again be doubled to 600 mm. (24 in.). Clearly, increasing surface density alone quickly becomes a most impractical approach to improving sound isolation performance. Instead, this is where the acoustical engineer adopts special sound isolation strategies, such as creating 2 walls with a corridor between them, or implementing a floating "box-in-a-box" structure.

Before the discussion becomes more complex and technical, I will pause until the next article in the Sound Isolation Design series. I hope that this and the following articles shed light on sound isolation considerations and help our readers make decisions that lead to the sound environments you desire to achieve.

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Nagata Acoustics News 05-10 (No.214)
Issued : October 25, 2005

Nagata Acoustics Inc.
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