Shapes and Sounds

SOURCE: https://www.constructionspecifier.com/shapes-and-sounds-designing-concert-halls-with-curves/

by Chuck Mears, FAIA

IMG_1070The marriage of shape and sound are used to create world-class acoustical experiences inside the New World Center, designed by Frank Gehry, and the Kauffman Center for the Performing Arts, designed by Moshe Safdie.

Billowing clouds, curved ceilings, and swooping lines all have dramatic impact on the way concertgoers experience sound. Both architects relied on the use of curved surfaces to diffuse sound and to create the distinctive appearances, each with dramatically different visual results.

Gehry chose to expose the curved elements, enclosing them in a glazed box that allows passersby to glimpse the flowing interiors. Safdie used giant curves to define the shape of his building, composed of two symmetrical half shells of vertical concentric arches, which perch on a magnificent site overlooking the city. However, in both cases, the ability to interpret the acoustician’s nuanced instructions to exacting perfection was the key to creating an acoustical masterpiece in two of the United States’ most important symphonic institutions.

This article deconstructs the delicate balance between shaped walls, curved ceilings, and sound—principles that can apply in any performance space.

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Technology has changed how spaces are designed. This image is a 3D framing model for an acoustic ceiling.

A look back in time
Concert halls have historically been designed with the architectural trends of the day. The science of architectural acoustics is just over a century old, but before it was hit or miss. Many of the early European halls, which were heavily ornamented on the walls and surfaces, were fortunate accidents, as the ornamentation served to diffuse sound.

It was not until Wallace Clement Sabine, an assistant professor at Harvard, was called on to correct an acoustically disastrous lecture hall on campus that modern acoustical science was launched. Sabine was able to determine, through experimentation, there is a definitive relationship between the quality of the acoustics, the size of the chamber, and the amount of absorption surface present. In 1898, he formally defined ‘reverberation time’—still the most important characteristic currently in use for gauging a room’s acoustical quality—as the number of seconds required for sound intensity to drop from the starting level by an amount of 60 dB.

In the 20th century, with growing popularity of ticketed concerts, many cities decided to build large-capacity venues, basing them on the parallelepipic form employed in some churches. The first reference model, called the ‘shoebox,’ places the orchestra directly in front of the audience; with musicians and spectators face-to-face. When designing for this type of architecture, acousticians must consider the shape and volume of the auditorium, and the materials used to achieve the ideal acoustic experience. What volume is required? How should the room be shaped?

Most auditoriums built since the 1950s have reproduced or adapted the shoebox model, which has the advantage of being well referenced, and therefore mastered by acousticians. However, contemporary architects like Safdie and Gehry are redefining the old models, and acousticians are learning new ways to incorporate complex design trends with the current knowledge base of acoustical engineering.

Designed by Moshe Safdie,
the Kauffman Center for the
Performing Arts’ prosceniumstyle
Muriel Kauffmann Theater
brings world-class cultural
events to Kansas City, Missouri.
Shown here are both early
framing and completed work.

The sound (and reverberation) of music
On a clear summer night, an outdoor concert can be entrancing. However, entering a well-designed concert hall can be even more magical, as the audience is enveloped in the music. This is because sound in a concert hall is related to vibrational energy.

Sound results from pressure fluctuations that travel through the medium of air. Various sources, such as an opera singer, a viola, or a horn, generate the air vibrations. The vibrations occur at varying rates, resulting in different frequencies of sound, which are perceived by humans as different pitches.

Low-pitched sounds (like that produced from a bass drum) vibrate at low frequencies, such as 20 to 250 cycles per second, or hertz (Hz). High-pitched sounds (like that of a piccolo) vibrate at high frequencies, such as 5000 to 20,000 Hz. Generally, humans can hear sounds from 20 to 20,000 Hz. These vibrations emanate in sound waves, which travel around the room, becoming reflected, absorbed, or transmitted at the walls or boundaries of the room. This is why the shape and size of the space, background noise, reverberation, as well as its material properties, are important.

In an enclosed environment, sound reflects—or reverberates—for a period after a source has stopped emitting sound. A space with a long reverberation time is known as a ‘live’ environment. Conversely, when sound dies out quickly, it is called a ‘dead’ environment. Speech is best understood in the latter, but music can be enhanced in the former, as the notes blend together.

Adding to an acoustician’s checklist are the different types of music that will be played in a space, as many venues today accommodate various styles. Reverberation time is affected by size and amount of reflective or absorptive surfaces in a space, making it one of the key considerations in a concert hall’s overall design and architecture.

For the Kauffman Center, form meets function—curves are both expressive aesthetic and carefully considered acoustic component.

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Kauffman Center for the Performing Arts
Kansas City, Missouri’s Kauffman Center landed the Midwestern city among the ranks of world-class theaters like the Berlin State Opera in Germany and Disney Concert Hall in Los Angeles. The approximately 26,500-m2(285,000-sf) facility has two technically sophisticated performance spaces: the proscenium-style Muriel Kauffman Theatre and Helzberg Hall.

With a seating plan similar to the traditional horseshoe of opera theaters in Europe, the Muriel Kauffman Theatre houses an acoustic infrastructure disguised within the aesthetics of the space, and showcases the integration of the architectural imagination with acoustical engineering.

Architect Moshe Safdie wanted the audience to experience a sense of warmth and intimacy with the performers. Referencing the fanning element of the facility’s north façade, the Muriel Kauffman Theatre curves around the seating pit and balcony; it naturally focuses sound waves to each of the 1800 seats.

The seats were built with materials that narrow down the range between sound reflectance and absorption when occupied and when vacant—a difference of only 0.2 seconds. At the same time, semi-cylindrical bumps were installed behind the louver wall to balance out the acoustical focusing caused by the round shape of the theatre. Further, shallow balcony overhang design helped deliver direct sound to the audience from the stage. In this balancing act of absorption and reflection, shapes and textures have everything to do with the sound quality.

 

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