Originally published in Interiors & Sources

09/27/2004

Fine Tuning: Hill Auditorium

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What is Digital Signal Processing (DSP)?

By Frans Swarte, Kirkegaard Associates

 

DSP describes the audio processing equipment used for setting relationships among loudspeakers – the main loudspeaker system (a center cluster, a left and right cluster, or a complete left-center-right system) and any other speakers in a room such as a front-fill stagelip, underbalcony fills, upper balcony fills, subwoofers, etc. Located between the mixing console and the amplifiers in the audio signal chain, DSP provides the functions of routing (mixing/splitting), equalization, time delay, and dynamics control of the loudspeaker system.

The signals from the mixing console are routed to the loudspeakers, with settings of frequency range, level and timing, equalization, and dynamic control for each. Before the advent of DSP “boxes”, these parameters were set with several pieces of equipment, such as matrix mixers, crossovers, delays, equalizers, and compressor/limiters. This could take the audio signal mostly through several stages of analog to digital conversions and back, which degrades and delays the audio signal. “More boxes” also means more real estate in equipment racks, cable terminations, and manuals to read – in other words, more cost.

The DSP box combines all these functions in one piece of equipment accessed by the engineer in an object-oriented programming environment. This is similar to working with spreadsheets: the DSP provides a blank sheet, onto which blocks can be dragged, and software for setting the audio parameters within each block. The blocks are connected by “dragging” wires between the inputs and outputs of each block. In this manner, the order of processing modules is established for each signal path through the DSP.

Typically, double-clicking the dragged-in blocks will reveal buttons, sliders, and meters that allow the user to set the parameters as desired, in real time. Most manufacturers market a basic box with eight inputs and eight outputs. Depending on the complexity of the loudspeaker layout and the amount of computing power required, multiple boxes can be coupled together.

Tactile interfaces that provide direct access to specific parameters have become the new frontier for the manufacturers. Such interfaces are still very much behind in time compared to, say, theatrical lighting systems, but the development is nevertheless exciting and promising.

In the summer of 1913, the new Hill Auditorium at the University of Michigan in Ann Arbor premiered as a stellar example of acoustic amplification in a large space via architecture. Designed by renowned Detroit architect Albert Kahn, the 4,578-seat hall was to become a favorite of international artists including Caruso, Rachmaninoff, Horowitz, and Yo Yo Ma, and a host to world-class orchestras. It earned a place on the National Registry of Historic Places for its unique acoustic signature and interior parabolic shape, designed by acoustician Hugh Tallant.

As the primary performance auditorium for the University of Michigan School of Music, Hill Auditorium has been operating by and large as originally constructed for nearly a century. Recently, the legacy firm of Albert Kahn Associates returned to the building as architectural firm-of-record to undertake a thorough restoration and upgrade. The $40-million mission was intended to restore Hill to its former glory — enhancing its legendary acoustics while bringing its antiquated amenities and infrastructure into the 21st century.

After an initial feasibility study in 1990, the project suffered a near ten-year delay due to unfavorable economic conditions. Eventually the renovation was expanded to include major technological improvements such as new electrical, plumbing, HVAC, lighting, and catwalk systems, together with critical acoustical and audio modifications such as sound and light locks, acoustic treatments, and an in-house sound reinforcement system.

Starting his firm in 1895, Albert Kahn was the first architect to integrate architects and engineers under the same roof. It was this team concept that allowed him to bring speed to his design and construction of buildings. By 1938 Kahn was responsible for 20 percent of all architect-designed factories in the U.S. His designs in this area pioneered the functionalism at the root of European Modernism.

“When the war broke out, Kahn was in the best position to be able to respond quickly in terms of building these huge manufacturing facilities in record time in order to meet the demands of the war effort,” explains Susan R. Arneson, marketing manager for Albert Kahn Associates. “His innovations with then-new materials like reinforced concrete and modern support trussing allowed him to open up expansive spaces to house massive manufacturing equipment.”

Although Kahn’s impact on industrial design worldwide is well known, few are aware of the diversity of his practice. His relationship with the University of Michigan reached 100 years with the renovation of a classroom facility in 2003 that was Kahn’s very first UM commission. “The core of the central campus has more than thirty Albert Kahn buildings designed between 1903 and his death in 1942,” notes Arneson.

For the renovation of Hill Auditorium, Albert Kahn Associates would once again rely on a design team structure. The firm worked closely with QUINN EVANS | ARCHITECTS as theater and historic preservation architect, Fisher Dachs as theater consultant, Gary Steffy Lighting Design, and Kirkegaard Associates, which handled both acoustics and audio/video design on the project.

Mechanical/Electrical

A key element in the renovation involved removing the building’s huge squirrel-cage air-handling units and heating plant housed beneath the lobby and auditorium. A new mechanical/electrical addition was constructed below-grade just north of the auditorium, connected by two tunnels for routing utilities into the facility. “Bringing all the mechanical systems from the basement to the new construction around the building kept the noise of the systems completely out of the historic structure,” said Scott Pfeiffer of Kirkegaard Acoustics.

“We designed a separate lower-level mechanical/electrical space to hold all the air conditioning and handling units plus new electrical services to accommodate possible future backstage expansion,” explained Albert Kahn Associates project manager Vitas Bagdonas. “In addition to relocating those new systems, we had the challenge of very little space for major duct work throughout the existing facility.”

The design team determined that a basement area under the auditorium could be converted to a pressurized plenum after removal of old mechanical air handlers. “By creating small floor diffuser openings in the slab, the air slowly filters up and doesn’t need the massive cooling and pressure of a down-flow system, thus reducing cost and noise,” noted Kirkegaard consultant Frans Swarte.

Main floor and balcony seating issues were simultaneously addressed with the ventilation design, facilitating better integration of patron flow and safety such as new cross aisles and side exits. Reclaimed and reconstructed space under and directly behind the stage provided storage, production support, cable pass, conduit runs, and access points for a new 200-amp breakout service for visiting audio productions.

The addition of the new utility tunnel required separating the auditorium’s basement and plenum space from the tunnel due to fire code regulations. This fire-rated passage in effect became a walk-through audio and video cable pass system, surrounded by the under-stage pressurized plenum area. The plenum runs from under-stage support areas to a new primary visiting audio/lighting mix position near the back of the hall. Strategically placed access points allow convenient cable snake runs from the stage to the in-house mix position.

Sound/Light Locks

The auditorium originally had a reverb time (RT) of 1.7 seconds when full, but hard surfaces such as wooden seats and a wood parquet floor over concrete made the RT climb to as much as four seconds when empty, according to a 1913 article by acoustician Tallant in Brickbuilder Magazine. A 1949 renovation brought the RT to a relatively constant 1.6 seconds, where it has remained for the last fifty years. Those modifications included padded velour seating and a seating rake change, which reduced the number of seats in the hall by more than four hundred to 4,169.

The current renovation further reduced seating to 3,710, with the goal of enhancing the RT of 1.6 with slight differences between frequency bands. “We intended to keep it the same or increase the RT by a little bit in the low frequencies for acoustic performances,” explained Pfeiffer. “While it wasn’t considered a bass-deficient room, they had a desire for a little more.”

Kirkegaard Associates worked closely with QUINN EVANS | ARCHITECTS to design and document sound and light locks at all levels and entrances to the auditorium proper. By fully extending a half-wall separating the back row from a pre-existing rear cross aisle, the team created the main floor sound and light locks. Sound and light locks were also incorporated at the side egress portions of the hall. The mezzanine level has two vestibules outside of the hall itself between the grand monumental stairs and the hall. At the balcony, the entire lobby functions like a sound and light lock with the addition of aesthetic and acoustic treatments as well as double leather-clad doors.

“We weren’t able to create separate vestibules there due to lack of space, but there are double doors now at every point coming into the auditorium, helping to accomplish one of Kirkegaard’s primary goals of unaltered acoustics and greater isolation from lobby and entrance vestibule sound,” explained QUINN EVANS project manager Kenneth Clein.

Kirkegaard also reintroduced acoustical panels from Tallant’s original specifications to the auditorium’s long curving back wall and reconfigured both the under-balcony ceiling and its intersection with the back wall, adding raised box seating in the last few rows. This provides an intimate acoustical environment while reducing unwanted reflections to the front.

The redesign included a new wooden stage surround to replace the plaster that originally defined the stage space from the auditorium. New support spaces, loading dock, and infrastructure for sophisticated concert-level sound systems and lighting trusses were also provided, including a new audio/video room in the basement.

In-House Sound

A focal point of the auditorium has always been its large pipe organ, which was part of the original design. The first organ, acquired from the 1893 Columbian World Exposition in Chicago, had been moved to Hill from another campus building during construction. A new custom organ replaced it in 1928, yet the massive organ chamber has always been a defining physical element of the stage. The auditorium’s organ console can be hydraulically lowered into a storage area in the basement. Unfortunately, the organ’s massive pipes occupy the majority of space of the rear reflector of the stage/auditorium parabola, creating a challenge for placement of a house loudspeaker system.

A former unsightly and inadequate center loudspeaker cluster had eventually failed and was never repaired. “We knew that they would like to use the house system for small-scale live music reinforcement as well, so it had to have significantly higher fidelity than a speech-only system, but not the output level of a concert system as most acts requiring that bring their own,” explained Swarte.

Kirkegaard determined that only highly directional sound could blend with the natural acoustics and overcome the reverberation of the hall. They chose a DSA (Digitally Steerable line Array) loudspeaker system with a radiation pattern matched to the shape of the room so as to avoid sound aimed at highly reflective surfaces. The system includes a unit with internal amplification and digital signal processing (DSP) that doubles the line length of the low frequency section, providing directivity control down to 150 Hz. “At Hill it works great because we need opening angles of twelve and fifteen degrees for each audience segment that is covered (main, mezzanine, and balcony floor levels), and the DSA retains punch at those relatively wide vertical angles,” explained Swarte.

A DSP processor in the basement rack room combines the main mix with that of the utility mixer and also provides equalization and delay parameters for the stage-lip array, which adds subtle in-fill for the first few rows of seats. Control is routed to the stage manager’s position and house mix position. The stage-lip array also improves the listener’s sense of directional (vertical) realism in the main audience area when used in combination with touring third-party flown loudspeakers. Extensive system tuning was necessary in order to achieve these goals.

Hill’s new power system for all audio and video consists of a K13-rated central transformer connected to a star network of power and grounding distribution with isolated ground. All signal types differing in bandwidth, voltage, or power are run in separate conduit to avoid EMI (electromagnetic interference). Systems integrator Phillips Pro Audio installed a separate network of UTP (unshielded twisted pair) cabling to be used with Ethernet or proprietary protocols for transmission of audio and video.

A total of 24 microphone lines for the speech system come to the A/V room in the basement near production support areas. Here, they route to a microphone splitter with two splits and a direct output. The two splits can be brought to a newly refurbished recording room, stage feeds, or to a new loading dock breakout panel. A wireless microphone package was included with receivers mounted semi-permanently in the new stage manager’s rack located backstage-right by client request.

Stage Management

Microphone, tie lines, video and data lines, as well as production intercom, are accessed through input panels around the stage and the catwalks. Three primary panels are located in the stage surround behind architecturally matching wood-finished doors. In addition, dedicated recording microphone lines are located around the stage and in the attic above, with low capacitance microphone cabling that routes to the new recording room.

A new, attic-level catwalk system for the hall was overseen by Albert Kahn Associates, giving audio, video, and lighting techs needed access to fixtures, inputs, and rigging. A ladder from the mezzanine level is concealed in the former projection booth, which also housed the hall’s lighting controls. The booth was replaced by a modern production booth at balcony level.

Relocating the booth also added 45 prime seats in the center of the mezzanine level in exchange for roughly the same number at the top of the balcony. “From the owner’s perspective, it was a real positive because some of the best seats in the house were being taken up by a poorly located and small projection booth,” said QUINN EVANS’ Clein.

In terms of house lighting, care was taken to maintain historical accuracy while not impacting acoustics. Kirkegaard Associates worked closely with architectural lighting consultant Gary Steffy Lighting Design and theater consultant Fisher Dachs to minimize noise from the lighting system in the hall. Refurbishing the distinctive bands of lights that adorn the parabolic shell was a big part of maintaining the aesthetic and acoustic signature of the auditorium.

Interior design consultant Mariuca Brancovenau of New York was responsible for developing the overall interior decorative scheme, based on a a comprehensive historic paint analysis conducted by QUINN EVANS. The original paint evaluation was accomplished using microscopic and spectrographic analysis, then mapped and documented as Munsell colors. “We found the same element in various parts of the room painted four or five different shades of a similar color, so it wasn’t clear what was going on in certain areas,” explained Clein. “That’s where Mariuca’s judgment was central to the auditorium’s design outcome.”

“We had a good understanding of the building from extensive surveying and documentation of its historic elements,” Clein continued, “and we spent significant time in the field during construction and during any demolition. Still, each week of construction brought the discovery of some unexpected condition that impacted the project. Ultimately, the real success of Hill’s renovation came from the responsiveness of the contractors, designers, consultants, and building owner working together as a team.”

THE AUTHOR IS A FREELANCE MARKETING AND PUBLIC RELATIONS PROFESSIONAL WITH CLEAR IMAGES MEDIA CONCEPTS, BASED IN KALAMAZOO, MICH., AND CHICAGO, ILL., WHICH PROVIDES CONSULTING AND AUDIO/VIDEO PRODUCTION SERVICES FOR PUBLIC AND PRIVATE CLIENTS. HE CAN BE CONTACTED BY E-MAIL (EVICTB@GLOBAL.NET) OR PHONE (269) 342-4162.

 


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com

 
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