Clear Messages
Nov 1, 1998 12:00 PM, Gregory A. DeTogne
A traditional Roman Catholic church, St. Mary of the Angels is nearly 100 years old. Situated in Chicago's Bucktown, the house of worship was temporarily shut down when the surrounding neighborhood felt the pressures of urban decay. Today, with the area undergoing revitalization, the church is open again. Having endured a rebirth of its own, it caters to a large, ethnically diverse congregation. On Sundays, masses can be heard in English, Spanish and Polish. Sound reinforcement needs within the main sanctuary largely involve speech intelligibility, although the liturgy relies upon a choir and pipe organ as well.
Jim Brown knows the church well. As owner and principal consultant of The Audio Systems Group, a firm based not far away from St. Mary's in Chicago's Ravenswood neighborhood, Brown first met with parish leaders almost three years ago to assess the sound system problems that had been plaguing the sanctuary. The congregation was having serious difficulty understanding the spoken word during services.
Brown listened for himself and examined the environment. He found that the existing system-installed only a few years before-lacked directional control. Brown also discovered that the church, in seeking to minimize the system's presence, had requested that all audio components be inconspicuous. The previous designer responded by selecting loudspeaker devices too small to control the low end.
"For the most part, the existing system was composed of direct radiators," Brown recalled. "There was also a pair of small horns with approximately 18 inch (457 mm) mouths. The pattern control of these devices fell apart at about 2 kHz. The delay loudspeakers, which were single-cone direct radiators, lacked any directivity."
Unfocused, omnidirectional low-frequency energy spilling into the reverberant field kills intelligibility. Acoustical analysis conducted in the sanctuary disclosed reverberation times of 6.5 seconds at 500 Hz, 6 seconds at 1 kHz, and 4.7 seconds at 2 kHz. Brown estimated that the system had to reduce reverberant energy to at least 250 Hz for optimum performance.
Following his initial acoustical analysis, he modeled the room in EASE then penned a design he was confident would solve the problem. Because of the room's long reverberation times within the low- and mid-frequency bandwidths, his solution depended largely upon the use of large-format horns, which could help maintain the desired pattern control down to 250 Hz, thereby bringing focus to the low- and mid-bands similarly to the high.
Once presented to the church, the administrators voted in favor of testing the plan prior to tackling the permanent installation. Brown called upon RC Communications, a division of Rent Com. Located near O'Hare International airport in Schiller Park, the firm pulled the necessary components from its inventory of rental gear.
Brown's vision was turned into temporary reality using large-format, fiberglass horns coupled with 7 inch (178 mm) exit compression drivers. Coaxially mounted within the mouths of the large-format horns were small-format, high-frequency horns that carried signals from 2 kHz on up. Genie lifts moved these assemblies into position and held them in place for the duration of the trial period.
Using a Pole Grabber designed by RC Communications president Rob Stein-berg, columnar enclosures were temporarily rigged and installed in pairs mounted end-to-end along pillars running down the center of the church. Housing six 4 inch (102 mm) drivers each, the columns created 12-element line arrays for delay.
With processing and power coming from a portable rack, the demo was up and running. Originally intended to prove its worth over a week-long period, the system stayed in place for about a month. Once the demo had ended, the church returned to the old system and considered the options.
Having carefully considered the situation, the church ultimately decided to go with Brown's proposed system rehabilitation. Funding for the project arrived more than a year after the demo. With the emergence of this problem-solving upgrade, audio sins of the past were atoned for by a main sanctuary system supported by a separate cantor system located in an antiphonal balcony at the end of the building opposite the altar. Armed with a budget of approximately $50,000, the church gave Brown approval to implement his final design. Already established as the contractor of choice in everyone's mind, RC Communications applied half of the rental bill to the purchase of the new system, and construction began in June 1997.
Unlike the demo system, Brown's permanent plans called for reusing as much of the church's existing electronics as possible to keep within the budget. As luck would have it, new constant-beamwidth, horn/loudspeaker technology from Renkus-Heinz became available just as the project began, which helped to meet both performance and monetary criteria.
Central among the Renkus-Heinz components were a pair of new two-way, CBH400-9 large-format 90 degrees x 40 degrees horns coupled with CDT-1 CoEntrant drivers and their own passive crossovers. Slated for installation in high-flying aeries located above the altar to the left and right of the congregation, the loudspeakers represented effective replacements for the costlier large-format, horn/compression driver combinations used in the rental system.
"The rental horns worked fine, but we really didn't need something that large in this space," Brown said. "The Renkus-Heinz two-way horns are designed to supply constant directivity from 400 Hz up to 20 kHz. Their CoEntrant drivers have been optimized as well-they are sweet and smooth sounding. These drivers max out at about 6 dB lower than the rental system's, but if you don't need those kinds of levels-and we didn't-the Renkus-Heinz components sound better. What we've created is musical, natural and intelligible."
Renkus-Heinz's engineering department channeled the smooth response and high sensitivity of a proprietary 8 inch (203 mm) midrange driver and a 1 inch (25 mm) compression driver through a single, 2 inch (51 mm) exit to create the CDT-1. Employing a variation of the company's compound manifold found in its modular CE3T touring cabinets, the CDT-1 is based upon the same patent ideas that cover their CoEntrant Waveguide designs. Available for use with a variety of Renkus-Heinz's own horns, as a retrofit for existing 2 inch (51 mm) horns, or as a prepackaged mid/high device (models CDT350 and CDT500), the CDT-1 provides a working tool offering tight pattern control.
"Listen to the CDT-1 in an application like St. Mary's, and you'll hear a significant improvement in sound quality over a traditional 2 inch (51 mm) driver," Renkus-Heinz's Ralph Heinz said. "As a Catholic church with a conservative liturgy, St. Mary's didn't have an issue with SPLs. Their major concern was natural voice reproduction. The CDT-1 coupled to our large-format horns provided sound quality at a price they could afford."
Sharing airborne installation space high above the sanctuary floor with the two-way horn/CDT-1 driver combinations were a pair of custom 4 V directional bass arrays, also from Renkus-Heinz. Designed by Jim Brown, the low-frequency cabinets were built using spaced woofer principles popularized by Craig Janssen. In defining the concept, Janssen found that when mounting a pair of drivers one above the other a half wavelength apart at a given frequency, one could take advantage of the resulting cancellation to maintain low-end pattern control.
Each of the custom low-frequency Renkus-Heinz boxes are outfitted with four high-powered, 6.5 inch (165 mm) woofers that receive signals at 400 Hz. Spaced in their cabinets to be one half of a wavelength apart at about 300 Hz to provide the desired cancellation effects, each woofer operates to 200 Hz without breaking out of specified coverage areas. An additional octave of pattern control is given to both the horizontal and vertical planes as a result, minimizing spill into the reverberant space (and to the mics directly below on the altar) while providing speech with more body.
Outfitted with 12 loudspeakers apiece wired in series/parallel to present a 12 V load at their terminals, three pairs of custom column-mounted, transformerless delayed arrays wend their way through the nave seating area from front to back. Designed by Brown with help from acoustic consultant David Prince (who built the first model), the cabinets were assembled by RC Communications using enclosures built expressly for the task by R&R Cases, another local firm. Each measuring 6.16 inches (156.5 mm) wide, the cabinets stand almost 44 inches (1.1 m) tall while maintaining a depth of 6 inches (152 mm). Four identical copies of these arrays were mounted in the antiphonal balcony. One pair provides reinforcement for the separate cantor system; the other brings audio to the choir.
Electro-Voice's RE11 mics got the call for choir duty in the antiphonal balcony, as did a Mackie 1202 12-channel mixer for the separate system used to reinforce the cantor and other soloists in the balcony. This smaller system aims its share of the delay columns back toward the congregation. Given their tight, vertical bandwidth, the custom line arrays extend to the altar, allowing the celebrant to hear the cantor clearly.
While most house mixing functions are managed automatically by a pair of SCM810 mixers from Shure Brothers, a Mackie 1604VLZ 16-channel mixer resides behind a locking hinged panel at the rear of the antiphonal balcony. This console is used on the few occasions when a manual mix may be required throughout the house.
Personnel from RC Communications on the job, including project manager Kevin Tucker, Les Stlarczyk and John Von Helms, initially thought the process of running cable from the control room to the balcony at the other end of the building could spell trouble. As things turned out, the job proved to be no problem once Von Helms discovered an easy path across the sanctuary via a narrow parapet 8 feet (2.4 m) below the ceiling. With Brown and others looking on, he simply walked along the ledge some 70 feet (21.3 m) above the floor. The cables followed on subsequent trips and are now neatly concealed.
As planned, the system upgrade was brought to completion without purchasing new power amps, EQs or delays. All of the loudspeaker wiring was reused as well. The reapplied units maintained their former roles for the most part. An assortment of Altec power amps (four model 9444Bs and a pair of model 9442s) fueled the system. Equalization arrived via Ashly GQX3101 1/3-octave units and Rane 2/3-octave stereo GE215s, while Yamaha D1030 processing was used for delay and crossover. Williams hearing assistance can be found at the top of the east equipment rack.
Within the realm of system upgrades, however, not everything can be recycled. The old automixer was replaced with the Shure SCM810s, which, according to Brown, "have excellent gating logic and matrix operation, plus individual EQ on each of their eight channels, which is really important given all the different mics in use."
While Brown was doing a bit of housekeeping, he also replaced miniature podium mics in the altar area with Electro-Voice RE11s. "These mics virtually eliminate proximity effect. With reverb times in excess of 7 seconds at 250 Hz, any excess low-frequency energy caused by proximity effect can spell disaster."
Cutting through Chicago's RF jungle are three Comtek M72C wireless transmitters and MR182 receivers, two of which receive Rane GE215 EQ before reaching the first Shure SCM810.
With new audio commissioned for use just in time for Christmas masses in 1997, Brown and members of the RC Communications crew returned in June 1998 to retune and adjust the system to compensate for architectural enclosures the church had built to conceal the large-format Renkus-Heinz horns. Since the Christmas past, work on restoration of the interior's plaster surfaces had meant that nearly half of the nave had been rebuilt and repainted.
When Brown and Steinberg walked into the church, they were struck by a feeling that the sanctuary sounded more reverberant than before. Measurements confirmed their intuitions, revealing increased reverberation times of 7.5 seconds at 500 Hz, 7.2 seconds at 1 kHz, and 6.25 seconds at 2 kHz. The new plaster had created harder, more reflective surfaces that had to be considered when retuning.
Something else was also different; when the system was tuned in December of 1997, the heat was on, and the humidity was below 10%. In June, humidity hovered at approximately 70%. Being a 100-year-old church, air conditioning was not economically feasible, so the resulting increase in the air's moisture content made a significant difference in high-frequency response. What sounded good at Christmas was now too bright above 6 kHz.
Undaunted, Brown and company re-equalized the system to deal with the increased reverberation and higher humidity. Although the acoustical environment had become more difficult, the system performed as required, even when the sanctuary was nearly empty.
Now that all is said and done, and the system has left everyone smiling and nodding happily, Brown recalled that this was a job where there were no leftovers, saying, "When you're dealing with tough design problems where reverb times are truly distressing, everything has to come out right. There is no margin for error; you can't give away even the smallest amount of control. EQ has to be within an inch of its life. You have to ring the system out, and it takes just the right mics, horns and so forth. We sweated over the details because it was the only way, and I'm glad it paid off."
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