Clear Messages
Nov 1, 1998 12:00 PM,
Gregory A. DeTogne
A traditional Roman Catholic church, St. Mary of the Angels is nearly 100years old. Situated in Chicago’s Bucktown, the house of worship wastemporarily shut down when the surrounding neighborhood felt the pressuresof urban decay. Today, with the area undergoing revitalization, the churchis open again. Having endured a rebirth of its own, it caters to a large,ethnically diverse congregation. On Sundays, masses can be heard inEnglish, Spanish and Polish. Sound reinforcement needs within the mainsanctuary largely involve speech intelligibility, although the liturgyrelies upon a choir and pipe organ as well.
Jim Brown knows the church well. As owner and principal consultant of TheAudio Systems Group, a firm based not far away from St. Mary’s in Chicago’sRavenswood neighborhood, Brown first met with parish leaders almost threeyears ago to assess the sound system problems that had been plaguing thesanctuary. The congregation was having serious difficulty understanding thespoken word during services.
Brown listened for himself and examined the environment. He found that theexisting system-installed only a few years before-lacked directionalcontrol. Brown also discovered that the church, in seeking to minimize thesystem’s presence, had requested that all audio components beinconspicuous. The previous designer responded by selecting loudspeakerdevices 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 18inch (457 mm) mouths. The pattern control of these devices fell apart atabout 2 kHz. The delay loudspeakers, which were single-cone directradiators, lacked any directivity.”
Unfocused, omnidirectional low-frequency energy spilling into thereverberant field kills intelligibility. Acoustical analysis conducted inthe sanctuary disclosed reverberation times of 6.5 seconds at 500 Hz, 6seconds at 1 kHz, and 4.7 seconds at 2 kHz. Brown estimated that the systemhad to reduce reverberant energy to at least 250 Hz for optimum performance.
Following his initial acoustical analysis, he modeled the room in EASE thenpenned a design he was confident would solve the problem. Because of theroom’s long reverberation times within the low- and mid-frequencybandwidths, his solution depended largely upon the use of large-formathorns, which could help maintain the desired pattern control down to 250Hz, thereby bringing focus to the low- and mid-bands similarly to the high.
Once presented to the church, the administrators voted in favor of testingthe plan prior to tackling the permanent installation. Brown called upon RCCommunications, a division of Rent Com. Located near O’Hare Internationalairport in Schiller Park, the firm pulled the necessary components from itsinventory 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 weresmall-format, high-frequency horns that carried signals from 2 kHz on up.Genie lifts moved these assemblies into position and held them in place forthe duration of the trial period.
Using a Pole Grabber designed by RC Communications president RobStein-berg, columnar enclosures were temporarily rigged and installed inpairs mounted end-to-end along pillars running down the center of thechurch. Housing six 4 inch (102 mm) drivers each, the columns created12-element line arrays for delay.
With processing and power coming from a portable rack, the demo was up andrunning. 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, thechurch returned to the old system and considered the options.
Having carefully considered the situation, the church ultimately decided togo with Brown’s proposed system rehabilitation. Funding for the projectarrived more than a year after the demo. With the emergence of thisproblem-solving upgrade, audio sins of the past were atoned for by a mainsanctuary system supported by a separate cantor system located in anantiphonal balcony at the end of the building opposite the altar. Armedwith a budget of approximately $50,000, the church gave Brown approval toimplement his final design. Already established as the contractor of choicein everyone’s mind, RC Communications applied half of the rental bill tothe purchase of the new system, and construction began in June 1997.
Unlike the demo system, Brown’s permanent plans called for reusing as muchof the church’s existing electronics as possible to keep within the budget.As luck would have it, new constant-beamwidth, horn/loudspeaker technologyfrom Renkus-Heinz became available just as the project began, which helpedto 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-1CoEntrant drivers and their own passive crossovers. Slated for installationin high-flying aeries located above the altar to the left and right of thecongregation, the loudspeakers represented effective replacements for thecostlier large-format, horn/compression driver combinations used in therental system.
“The rental horns worked fine, but we really didn’t need something thatlarge in this space,” Brown said. “The Renkus-Heinz two-way horns aredesigned to supply constant directivity from 400 Hz up to 20 kHz. TheirCoEntrant drivers have been optimized as well-they are sweet and smoothsounding. These drivers max out at about 6 dB lower than the rentalsystem’s, but if you don’t need those kinds of levels-and we didn’t-theRenkus-Heinz components sound better. What we’ve created is musical,natural and intelligible.”
Renkus-Heinz’s engineering department channeled the smooth response andhigh sensitivity of a proprietary 8 inch (203 mm) midrange driver and a 1inch (25 mm) compression driver through a single, 2 inch (51 mm) exit tocreate the CDT-1. Employing a variation of the company’s compound manifoldfound in its modular CE3T touring cabinets, the CDT-1 is based upon thesame patent ideas that cover their CoEntrant Waveguide designs. Availablefor use with a variety of Renkus-Heinz’s own horns, as a retrofit forexisting 2 inch (51 mm) horns, or as a prepackaged mid/high device (modelsCDT350 and CDT500), the CDT-1 provides a working tool offering tightpattern control.
“Listen to the CDT-1 in an application like St. Mary’s, and you’ll hear asignificant improvement in sound quality over a traditional 2 inch (51 mm)driver,” Renkus-Heinz’s Ralph Heinz said. “As a Catholic church with aconservative liturgy, St. Mary’s didn’t have an issue with SPLs. Theirmajor concern was natural voice reproduction. The CDT-1 coupled to ourlarge-format horns provided sound quality at a price they could afford.”
Sharing airborne installation space high above the sanctuary floor with thetwo-way horn/CDT-1 driver combinations were a pair of custom 4 Vdirectional bass arrays, also from Renkus-Heinz. Designed by Jim Brown, thelow-frequency cabinets were built using spaced woofer principlespopularized by Craig Janssen. In defining the concept, Janssen found thatwhen mounting a pair of drivers one above the other a half wavelength apartat a given frequency, one could take advantage of the resultingcancellation to maintain low-end pattern control.
Each of the custom low-frequency Renkus-Heinz boxes are outfitted with fourhigh-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 300Hz to provide the desired cancellation effects, each woofer operates to 200Hz without breaking out of specified coverage areas. An additional octaveof pattern control is given to both the horizontal and vertical planes as aresult, minimizing spill into the reverberant space (and to the micsdirectly below on the altar) while providing speech with more body.
Outfitted with 12 loudspeakers apiece wired in series/parallel to present a12 V load at their terminals, three pairs of custom column-mounted,transformerless delayed arrays wend their way through the nave seating areafrom front to back. Designed by Brown with help from acoustic consultantDavid Prince (who built the first model), the cabinets were assembled by RCCommunications using enclosures built expressly for the task by R&R Cases,another local firm. Each measuring 6.16 inches (156.5 mm) wide, thecabinets stand almost 44 inches (1.1 m) tall while maintaining a depth of 6inches (152 mm). Four identical copies of these arrays were mounted in theantiphonal balcony. One pair provides reinforcement for the separate cantorsystem; the other brings audio to the choir.
Electro-Voice’s RE11 mics got the call for choir duty in the antiphonalbalcony, as did a Mackie 1202 12-channel mixer for the separate system usedto reinforce the cantor and other soloists in the balcony. This smallersystem aims its share of the delay columns back toward the congregation.Given their tight, vertical bandwidth, the custom line arrays extend to thealtar, allowing the celebrant to hear the cantor clearly.
While most house mixing functions are managed automatically by a pair ofSCM810 mixers from Shure Brothers, a Mackie 1604VLZ 16-channel mixerresides behind a locking hinged panel at the rear of the antiphonalbalcony. This console is used on the few occasions when a manual mix may berequired throughout the house.
Personnel from RC Communications on the job, including project managerKevin Tucker, Les Stlarczyk and John Von Helms, initially thought theprocess of running cable from the control room to the balcony at the otherend of the building could spell trouble. As things turned out, the jobproved to be no problem once Von Helms discovered an easy path across thesanctuary via a narrow parapet 8 feet (2.4 m) below the ceiling. With Brownand others looking on, he simply walked along the ledge some 70 feet (21.3m) above the floor. The cables followed on subsequent trips and are nowneatly concealed.
As planned, the system upgrade was brought to completion without purchasingnew power amps, EQs or delays. All of the loudspeaker wiring was reused aswell. The reapplied units maintained their former roles for the most part.An assortment of Altec power amps (four model 9444Bs and a pair of model9442s) fueled the system. Equalization arrived via Ashly GQX3101 1/3-octaveunits and Rane 2/3-octave stereo GE215s, while Yamaha D1030 processing wasused for delay and crossover. Williams hearing assistance can be found atthe top of the east equipment rack.
Within the realm of system upgrades, however, not everything can berecycled. The old automixer was replaced with the Shure SCM810s, which,according to Brown, “have excellent gating logic and matrix operation, plusindividual EQ on each of their eight channels, which is really importantgiven all the different mics in use.”
While Brown was doing a bit of housekeeping, he also replaced miniaturepodium mics in the altar area with Electro-Voice RE11s. “These micsvirtually eliminate proximity effect. With reverb times in excess of 7seconds at 250 Hz, any excess low-frequency energy caused by proximityeffect can spell disaster.”
Cutting through Chicago’s RF jungle are three Comtek M72C wirelesstransmitters and MR182 receivers, two of which receive Rane GE215 EQ beforereaching the first Shure SCM810.
With new audio commissioned for use just in time for Christmas masses in1997, Brown and members of the RC Communications crew returned in June 1998to retune and adjust the system to compensate for architectural enclosuresthe church had built to conceal the large-format Renkus-Heinz horns. Sincethe Christmas past, work on restoration of the interior’s plaster surfaceshad meant that nearly half of the nave had been rebuilt and repainted.
When Brown and Steinberg walked into the church, they were struck by afeeling that the sanctuary sounded more reverberant than before.Measurements confirmed their intuitions, revealing increased reverberationtimes of 7.5 seconds at 500 Hz, 7.2 seconds at 1 kHz, and 6.25 seconds at 2kHz. The new plaster had created harder, more reflective surfaces that hadto be considered when retuning.
Something else was also different; when the system was tuned in December of1997, the heat was on, and the humidity was below 10%. In June, humidityhovered at approximately 70%. Being a 100-year-old church, air conditioningwas not economically feasible, so the resulting increase in the air’smoisture 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 theincreased reverberation and higher humidity. Although the acousticalenvironment 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 andnodding happily, Brown recalled that this was a job where there were noleftovers, saying, “When you’re dealing with tough design problems wherereverb times are truly distressing, everything has to come out right. Thereis no margin for error; you can’t give away even the smallest amount ofcontrol. EQ has to be within an inch of its life. You have to ring thesystem out, and it takes just the right mics, horns and so forth. Wesweated over the details because it was the only way, and I’m glad it paidoff.”
