ASA/NOISE-CON 2005 Meeting, Minneapolis, MN

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Historic Recording Gives Choir "Alien" Feeling:
In Anechoic Space, No One Can Hear You Sing

Experiment Benefits Acoustical Research and Design

Ron Freiheit -
Wenger Corp., 555 Park Dr.
Owatonna, MN 55050

Popular version of paper 4pMU3
Presented Thursday Afternoon, Oct. 20, 2005
ASA/NOISE-CON 2005 Meeting, Minneapolis, MN

An eighty-voice college choir is closed inside an anechoic research chamber, a space designed and built to eliminate all echoes and sound reflections. For singers, the environment is eerily quiet – a quiet softer than anything they experience in everyday life. Several choir members, feeling claustrophobic, have to leave. In a normal rehearsal or concert space, each singer can hear the group’s unified sound reflected back from the walls and ceiling. However, all interior surfaces in this chamber are covered with sound-absorptive fiberglass wedges, intended to prevent any reflections. For optimal sound isolation, the chamber was constructed as a concrete “building within a building.”

This choral performance by a St. Olaf College choir, which took place in October 2003, at a 3M research facility in St. Paul, Minn., was an unqualified success. The result was an anechoic choral recording – “pure” sound – meant for use in a type of acoustical research called auralization.

Auralization software helps acoustical consultants predict – and perfect -- how a proposed performance space, like a concert hall, will sound while still in the design stages. The software considers the room size and shape, along with the acoustical properties of all surfaces, and applies these combined parameters to an anechoic recording such as the “pure” sound of this choral recording. The result is the auralization or acoustical ‘signature’ of the new space.

A Tool Growing in Popularity

“Auralization is becoming a more popular tool in acoustical design and its importance will increase in the future,” explains Dr. Rendell Torres, a professor at the Architectural Acoustics Program at Rensselaer Polytechnic Institute in Troy, N.Y.

“It’s also a valuable tool for communication,” comments Torres. “Acoustical consultants can demonstrate the differences in possible design choices to architects and clients. It’s visualization for the ears.”

Collaborating on this choral-recording project were 3M Corporation, St. Olaf College of Northfield, Minn., and the Wenger Corporation, based in Owatonna, Minn., a manufacturer of music education and performance equipment.

Ron Freiheit, manager of acoustics research at Wenger, proposed this recording to help advance research in the field of architectural acoustics. During new construction and renovation projects, Wenger works closely with architects, acoustical consultants and other design professionals to help create superior acoustical environments, ranging from school rehearsal facilities to professional performing arts centers.

“This choral recording complements existing anechoic recordings,” says Torres. “It’s a great project.” Torres is aware of some anechoic choral recordings made for a small research project in Germany; he said these recordings were not intended for wide distribution, only for research.

Overall, Torres says the worldwide library of anechoic music is rather small, with only a handful of CDs available and some out of print. These recordings are known in the industry by the companies that produced them, including Bang & Olufsen, Yamaha and Denon. Most anechoic recordings feature large instrumental groups, such as symphony orchestras, or a solo musician with accompanying instruments.

“With anechoically recorded choral music, this popular music form can now be included in the auralization of concert halls, theaters and even churches,” explains Freiheit. “And as the software becomes more sophisticated and widespread in the future, this recording will help acoustical consultants and other design professional create facilities that accommodate a broader range of the performing arts.”

Demonstrating Benefits

Wenger has already used this anechoic choral recording in its own research and marketing activities, to demonstrate the acoustical benefits of an acoustical shell.

In a typical auditorium, the proscenium arch and curtain separating the stage and audience area pose several acoustic challenges for music performance. The fly-loft space above the stage – designed to accommodate theatrical curtains, lighting and scenery – traps much of the group’s sound, compromising acoustics for both the performers and the audience.

In this environment, an acoustical shell (consisting of sound-reflective overhead panels and shell towers) is critical to achieving proper performance acoustics. Together, these two elements create a “blending chamber” for sound produced on stage, enabling musicians to hear themselves and each other, and allowing the director to hear all parts distinctly. The shell greatly improves sound projection to the audience, uniting the stage and audience areas into one acoustical space.

Using this anechoic choral recording and auralization software, Freiheit created an interactive PowerPoint presentation (see link below) that demonstrates the “before/after” impact of acoustical treatment in an average high school auditorium – treatment that includes acoustical shell towers, ceiling panels and acoustical clouds above the audience area.

In the Wenger demo, users select a seat location inside the “virtual” auditorium and hear the same choral music selection as it would sound – with and without acoustical treatment. The selection is 33 seconds of ‘Almighty and Everlasting God’ by Renaissance composer Orlando Gibbons, which was performed a cappella by the St. Olaf choir in the anechoic chamber.

The volume and dynamics of the recorded selection are exactly the same each time. In the demo, any audible differences are due entirely to the changes in acoustical treatment and listening location inside the auditorium. For each location, the visual representation of the auditorium on the screen will correspond with the sound you are hearing, showing both your location within the auditorium and the presence – or absence – of acoustical treatment.

The demo starts “before” (no acoustical treatment) and then switches to “after” (with acoustical treatment). This cycle is repeated twice during the 33-second sound clip: before/after/before/after.

Most listeners notice an increase in the volume of the music, along with an increase in its clarity or brightness.

Download Freiheit's PowerPoint presentation

Download free Powerpoint Viewer from Microsoft

Comment from Acoustical Consultant About this Anechoic Recording:

Dennis Paoletti, principal of the firm Shen Milsom & Wilke / Paoletti in San Francisco, is an acoustical consultant with more than 35 years of experience on hundreds of performing arts facilities. He says this anechoic choral recording will serve as a valuable resource to consultants, including the Concert Hall Research Group (CHRG). Paoletti is a member of the CHRG, an international consortium of acoustical consultants, researchers and design professionals. Members share research and experience to improve architectural acoustics in the design of concert halls and related performing arts spaces.

Paoletti says acoustical consultants can already use computer analysis to create maps and graphics that visualize sound energy as arrows, waves and colors. He describes auralization as the “fourth dimension” of architectural renderings and says it will become more common as costs come down, ease-of-use improves and computing speed increases.

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