THE DAYS OF SUMMER
Apr 1, 2000 12:00 PM, Clare Climaco
Wolf Trap's Filene Center amphitheater unveils a new, versatile sound reinforcement system for the 2000 season.
If the Kennedy Center is America's White House for the performing arts, then Wolf Trap is its summer home. Tucked away on 130 acres (52 hectares) of rolling Virginia farmland, Wolf Trap's pristine surroundings make it an idyllic stage for summer entertainment. The 7,000-seat Filene Center, a partially enclosed wooden amphitheater, is the centerpiece of Wolf Trap Farm Park. There, audiences can enjoy performances ranging from the National Symphony Orchestra, the Wolf Trap Opera Company or a host of pop, country, folkand blues acts.
The Filene Center, a wooden pavilion designed to aesthetically complement the surrounding park, attracted thousands of park visitors every year, but the structure burned down in 1982. A temporary structure was used until the new Filene Center was finished in 1984, the same time the house sound system was installed. Although the system was less than perfect, the nonprofit Wolf Trap Foundation, lacked the money to replace it. Funding came in 1998, and the production crew's hope for a new, cutting-edge sound system was within reach.
Project scope
The amphitheater is designed to blend in with its surroundings. A roof tops the structure built of fire-resistant Douglas fir and southern yellow pine, 102 feet (31 m) tall at its highest point. The roof protects a 45 foot (13.7 m) tall proscenium opening, and sidewalls surround the 116 foot (35 m) wide by 64 foot (19.5 m) deep stage. A rear wall behind the stage contains a 30 foot (9 m) high by 40 foot (12 m) wide doorway, which is typically closed during performances.
The Filene Center is divided into two main sound systems - the house system, which covers about 3,800 seats under the roof, and a separate lawn system for 3,200 lawn seats. Although the long-term goal is to upgrade both systems, noted Wolf Trap production manager John Gray, installing a new sound system for the covered seating area took first priority.
Dave Heffelefinger, who has served as house engineer for more than 13 years, had his eye on the L-ACOUSTICS V-DOSC system since hearing it and mixing on the system.
"I found that instead of equalizing for feedback and room anomalies," Heffele-finger said, "I could actually EQ for the music. It took the reverberant room out of the equation. As an engineer, I could now hear things more precisely."
Soon after, the production team set out to seriously explore V-DOSC for the venue. They contacted Jeffrey Cox, founder of Cox Audio Engineering, Oxnard, CA, which manufactures the French-designed V-DOSC arrays for North America. Cox, brought in veteran system designer Patrick Baltzell. The team discussed the system's goals.
Cox said, "I wanted to provide nothing less than the best possible system for the wide variety of world-class artists and entertainment presented there."
"Our old system wasn't focused tightly enough," Gray said. "We wanted to reduce the splash on the internal surfaces of the venue and provide even coverage for every seat in the house, which is difficult because of the width of the seating area. We also wanted to eliminate the lobes and nulls associated with a multi-source system by using as close to a single-source system as possible.
"It's a performing arts house. The events there, operas, dance performances, symphonies and some pop acts, don't require high SPLs. What we did need was high articulation, clarity and coverage for the gamut of events."
Heffelefinger described his vision for an all-encompassing, three-channel left-center-right system that would bring the venue an unprecedented level of sound coverage and clarity. The plan was presented to the production team, but when costs were a bit over budget, they decided to explore a two-channel stereo system that could allow future expansion. Baltzell then designed a system that provided complete coverage from the two main clusters.
"The design would have worked better if it had been three channels; the coverage would have been perfect everywhere," Baltzell said. "But the problem was that it also increased the cost by a third. So from that, I had to massage everything a bit, add fill speakers on the sides, and that worked."
Design challenges
Baltzell completed the system design on paper, and in March 1999, he visited the venue to start planning where the arrays would actually hang. According to him, that is where the fun started.
"There's always a struggle when you're putting up boxes. Some people want them up and away, out of sight," he said, "but sound-wise, that's not the best way to go. The system just sounds better when they're down and closer to the audience. It's aconstant battle."
Baltzell's original design called for the clusters to hang about 32 feet (9.8 m) from the bottom of the array to the stage, but two obstacles surfaced that had been unknown to Baltzell during the design phase.
"I went from old drawings where the clusters were hanging about 32 feet from the stage, so I assumed that's where I could hang the VDOSC," he said, "but at some point, the clusters were moved farther apart and higher to solve certain problems."
Those problems involved a fixed lighting booth, hanging wooden acoustical panels and a display screen, which is mounted over the stage to show opera translations. Baltzell had to adjust the left-right position of the clusters to avoid blocking a spotlight that is used to guide performers on and off stage. Two 10 foot (3 m) wide circular wooden acoustical panels, which hang above the stage, were quickly removed to make way for the clusters. The display screen proved to be another obstacle.
"The opera scenery is tall and grand, and the screen has to be above the scenery," Baltzell said. "So you're now imposing an impossible trim and severely limiting how low the clusters could be hung. So we ended up having to raise the speakers substantially, like 5 feet (1.5 m) or 6 feet (1.8 m) more than what we had originally designed them for."
Moving the clusters up and farther apart, Baltzell said, introduced some wrinkles into the original design.
"Originally when I had just the mains all in a line, I didn't need speakers anywhere else except for sidefills to hit the areas that I couldn't hit with two clusters. I didn't need under-balcony speakers, but when we moved the clusters up, the balcony shadowed the back orchestra level rows."
Each main array is made up of 10 rectangular V-DOSC boxes or elements stacked in a line array. Each element contains two 15 inch (381 mm) direct radiating cones, four 7 inch (178 mm) kevlar cones arranged in a V-shaped flare, and two 2 inch (51 mm) compression drivers mounted onto the proprietary DOSC waveguide. When properly arrayed, the configuration creates a cylindrical wavefront with a 90 degree horizontal dispersion, resulting in seamless sound emanating from a single source.
The two arrays cover five zones in the venue. The top four elements in each array cover the seats in the balcony. By minimizing the angle between the upper array boxes, the coupling of the high frequencies, the length of the throw and the single point source effect are maximized. The six additional elements in the arrays can be seen as two sets of three elements. Elements five through seven (counting from the top element as number one) are aimed at orchestra-level rows 19 through 29, while the lowest three V-DOSC boxes (eight through 10) are angled to cover orchestra level rows 11 through 18. The L- ACOUSTICS ARCS loudspeakers (a two-way loudspeaker that, using the DOSC waveguide, arrays horizontally) are presently located just below the cluster to provide near-range coverage for rows three through 10. Two additional ARCS per side are hung from trusses for side-fill. Two L-ACOUSTICS MTD108s, single 8 inch (203 mm) loudspeakers with 1 inch (25.4 mm) drivers, are mounted on the front lip of the stage for front-fill. The under-balcony seats (orchestra-level rows 29 through 35) are presently covered by previously existing loudspeakers, but they will be replaced before the 2000 season begins. Also, 21 QSC PowerLight 6.0 superscript PFCs provide up to 63,000 W for the main clusters.
Four L-ACOUSTICS SB218 subwoofers (two 18 inch or 457 mm loudspeakers each) per side were built into two wooden enclosures and flown 8 feet (2.4 m) from the stage on each side of the proscenium wall. The subs are driven by a pair of PowerLight 9.0 superscript PFCs with two subs running off one amp channel. Each amp channel offers 4,500 W into 2 V.
Wolf Trap sound department head William Valentine said, "The Power-Lights are quiet and clean. They have a transparent sound with an airy low-end. The PowerLights also proved to be practical. Installation was a breeze. Now, we have half as many amps with six times more power."
Results
The new system has solved the uneven coverage, room reverberation, and lobes and nulls that had plagued the previous, 15-year-old system.
"Previously, we had the problem of multiple zones hitting each person in the audience," Valentine said. "The best seats in the house were being hit by five different sound point-sources, with the result being that coherence was sacrificed for volume and frequency distribution. Now, the coverage is more even than it's ever been. It is very coherent."
The L-ACOUSTICS wavefront concept also helped minimize reverberation and optimize room acoustics. The venue was originally designed to be reverberant to complement piano, guitar and vocal acts, and the team considered covering all the hard surfaces with acoustical treatments.
"But the cost got prohibitive and the options weren't aesthetically pleasing," Valentine said. "After we installed V-DOSC, we found that the baffling became unnecessary. We got the V-DOSC to focus the sound off the walls. This system reduces reverb time for all frequency bands, especially the mid- and high-frequency ranges. Measuring with an empty room, our previous RT subscript 60 was 1.8 seconds. V-DOSC reduced that to 1.3 seconds, and that reduces by half again when the house is full."
The Filene Center itself is located on a border and just beyond the park's edge are private homes. A tighter-sounding system has meant that shows more consistently meet the 95 dB house limit, reducing complaints from neighbors.
"We put a lot of time and effort into selecting a new system for this venue, and the result is worth it. We enjoy even coverage throughout the house and far fewer complaints from the audience and neighborhood," said Gray.
FOH and monitors
The house mix position, located midway and slightly to the right of the orchestra area's center section, is equipped with a Yamaha PM4000-48C, which offers 48 available input channels, eight VCA masters, eight group masters, eight auxiliary busses, and an 11 8 mix matrix. An Allen & Heath SC-416XA 16-in/4-out matrix is also available as an auxiliary desk. New outboard components installed last summer also include XTA DP 226 processors and remote-controllable BSS Varicurve system EQs. The XTA processors each have two ins and six outs that provide system-wide DSP functions in a 1 RU box. Each input has gain, delay and eight bands of parametric control, while each output consists of a high- and low-pass filter, five bands of parametric EQ, and limiter, delay, gain and polarity controls.
"When they did the original installation more than 15 years ago, they didn't have the all-in-one boxes, so we had the EQ, the crossovers, and all Urei LA-4 compressors at the end of the chain before the signal hits the amplifier. Prior to the new XTA processors, we were using BSS Omnidrives, which did away with all of the individual components in the signal chain. Now, we have about 30 or so Urei LA-4s lying around, so I now have several at the house mix position. I love using them, and many visiting engineers are pleased to see them."
System equalization is handled by Klark-Teknik DN 405 parametric EQs in every zone. In addition to the Klark-Tekniks, remote-controllable BSS Varicurve FCS-926 dual EQs are also used, allowing freedom and convenience of correcting EQ from anywhere in the facility. Other house outboard gear includes 18 Valley People compressor/limiters and expander/noise gates, a TC Electronics M5000 for effects processing, Yamaha SPX digital processors and a Lexicon PCM-70.
Audio patching remained unchanged since the original installation. With more than 4,000 audio patch points available, the system remains flexible. Mic inputs, tie lines and loudspeaker lines are available throughout the theatre. All mics are routed to 1-in/4-out active mic splitters. Splitter outputs are routed to the house, lawn and onstage mixing consoles. A spare splitter is available for touring acts or for recording and television uses a,s are tie lines between the stage and all mixing consoles.
The Filene Center stage monitor system primarily consists of Meyer UM-1 and ElectroVoice Delta Max DML215 wedges driven by a slew of QSC Series Three amps. The monitor mix position uses a RAMSA S-840F console equipped with 40 mic inputs and 18 discrete outputs. Processing gear - 15 Digitech MEQ Mono-28 EQs, three Urei LA4 compressors and a Yamaha SPX 90 digital processor - are mounted in a rack that contains a TRS patchbay, providing access to all 69 mic splitters, along with stage, house and lawn lines. It also provides access to all inputs, outputs, break points and any outboard equipment.
This new system will be fine-tuned over the 2000 season. Six new L-ACOUSTICS dV-DOSC loudspeaker elements, a compact, full-range, two-way enclosure that also uses the DOSC wave-guide, will replace the existing ARCS as downfill below the mains. Additional pairs of dV-DOSC will also replace the delay loudspeakers under the balcony as specified in the original plan.
"In the past, visiting engineers would try to compensate for the fact that they had to use the house system by cranking up the SPL, but that would muddy the sound and boost the SPL beyond the 95 dB house limit," Gray said. "Now, they are quite interested in mixing on our system, and the engineers get a tighter, more focused sound without cranking it up."
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