Project Memo: Ongoing Acoustical Challenges
Using a diverse strategy to transform a venue’s signature

By E. Victor Brown

A perspective of the room.

Turning a 107-year-old neo-gothic Catholic Church into a concert venue takes time, patience and great care. Case in point: the Sacred Heart Music Center in Duluth, Minnesota, so named after its former incarnation as Sacred Heart Catholic Church, which is in the midst of an ongoing transition process, with final acoustical and system solutions yet to be finalized.

At the same time, the project serves as a very interesting study of the myriad of factors and elements that go into devising solutions for a diverse number of needs and parties involved. Specifically, serious measurement, modeling, analysis and the resulting data, as well as experience, are being married with evaluation of actual live performances to provide sufficient information to guide a final outcome.

The building’s primary elements include a one-of-a-kind historical organ almost as old as the church, a six-second-reverberation time, and national historic registry credentials for both. The unique challenge posed is expansion of live concert programming beyond choral and organ concerts, particularly when very little in the room can change ­ both acoustically and aesthetically. Therefore, the goal for the sound team becomes finding ways to work with the space, rather than against it.

An EASE map showing the entire space.

The pews have long been removed, but other than that, the original 1895 structure essentially remains the same, including a soaring 45-foot ceiling height interrupted by numerous concave domes. When the non-profit board overseeing Sacred Heart decided to expand program offerings, they turned to Kent Peterson, an acoustical consultant with the architectural firm of Short Elliot Hendrickson.

In a fitting bit of symmetry, Peterson has a family connection to Sacred Heart’s past ­ his grandmother attended and was eulogized in the church. Short Elliot Hendrickson, with numerous offices scattered over eight states in the U.S., specializes in architectural design as well as industrial, environmental and municipal work, has Peterson dividing his professional time between standard noise issues/acoustical guidelines with acoustical measurement, system design and installation.

“I work with equipment for noise handling that has to be calibrated and certified every year in order to comply with state and federal noise guidelines, along with more familiar tools such as (SIA) SMAART and (ADA) EASE in conjunction with sound pressure level (SPL) meters to determine the noise floor of a building. The goal is to account for all HVAC and other noise as a basis before any design work can commence,” he explains.

UNCHANGED FOOTPRINT

Specifically, the charge at Sacred Heart is to attempt to optimize the space for more contemporary types of musical styles such as folk and those with slightly more percussive elements. While nothing is essentially “wrong” with the space from an acoustical standpoint, Peterson is seeking to minimize reverberation times through use of removable acoustic elements that leave the original décor elements and aesthetic footprint unchanged.

“What we’re after is making the space a little more of a ‘core’ venue for the city, not detracting from what it does best while expanding the reach to accommodate more contemporary, ‘artful’ types of music,” he notes, adding that all design changes have to first be approved by the board as well as the National Historic Registry and the Organ Historical Society.

What EASE says about the reverberation situation in the former worship sanctuary.

Measurements taken during initial site visits revealed that a hot-water-based heating system helps keep the ambient noise floor down, and further, the venue is far from heavily trafficked highways and airport flight paths, further enhancing the noise situation. In fact, a number of recordings featuring the organ and symphonic groups have been done in the room over the years. Further, mainstream acts such as Low and Crash Test Dummies have used the space for recording projects as well. Simultaneous to the early noise verification process, a search was undertaken to locate whatever architectural plans of the building might still be available, a quest which proved fruitful. This treasure trove of hard information, combined with ongoing laser-based dimensional measurements, were compiled in EASE to create an accurate acoustical model of the space.

Subsequent reverberation numbers derived from the model correlated nicely with the impulse testing done on sight. According to Peterson, the EASE reverberation numbers are slightly elevated due to the exclusion of the more nebulous characteristics of the space.

Together, the modeling and measurements have provided a solid base for evaluating the possible incorporation of treatments like acoustical curtains and/or other elements such as a removable wooden band shell. Noting that final decisions have yet to be made, Peterson says, “The direction will have to be split between what is aesthetically and economically feasible in terms of both acoustic treatment and an electro-acoustic or sound reinforcement scenario.”

Predicted levels (at 2 kHz) from a Cobra array in the coverage zone.

TIGHT CONTROL When looking at the project’s limited budget, Peterson considers both acoustic treatment as well as an amplified system to fulfill the long- and short-term needs. With loudspeaker enclosures, high directivity without increased reflection is critical. He envisions the need for restrictive low-frequency control down to about 500 Hz. During the evaluation process, Peterson has also attended several concerts to get a “real-world” assessment of the venue. Choral performances, of course, have proven well suited to the space, but more instrumental, amplified applications have been plagued by a wash of reflections. Vocal intelligibility has also suffered to a good degree. Sound reinforcement had been limited to small, rather lightly powered trapezoidal loudspeakers on stands located front left and right.

A concert by Texas-based blues artist Marcia Ball offered the first opportunity to evaluate “harder-edged” programming amplified with a larger sound reinforcement system. With a vocal and piano style mixture of both blues and “swamp” rock, Ball’s performance upped the ante. “I couldn’t see ‘speakers on sticks’ for an artist like Marcia Ball and a grand piano, so I started evaluating options,” Peterson notes.

Predicted results of one of the Cobra stacks (at 1 kHz).

He talked with Jeff Taylor of Dynacord about the desire for a highly directive sound system with a compact footprint and easy set-up parameters. Taylor recommended Cobra compact line array loudspeakers, specifically, two Cobra full-range modules and one Cobra subwoofer, stacked discretely at the far stage wings. The stacks would be driven by a Cobra CSR 12 system rack including two Dynacord L2400 amplifiers and a Dynacord DSP 244 processor.

“I had prior experience with the Dynacord line array, and with the EASE modeling that had been framed out, I could actually take a look at this system’s directivity in general, and further, to make sure energy was focused on the audience area and away from the side and back walls, as much as possible,” Peterson says.

While Peterson looked at more on the acoustic side, Taylor focused on meeting the equipment rider for the Ball concert, and also specified additional elements to further assist the process. Using a Klark Teknik DN9340 Helix digital equalizer and K-T DN6000 real-time analyzer, and running pink noise through the system, optimization was more finely tuned, with final adjustments made in the good old analog realm ­ in other words, by ear ­ using familiar source material on CD.

Marcia Ball at Sacred Heart in mid-concert form.

Ball’s engineer John Medina opted for an Electro-Voice 510 dynamic microphone for her vocals, feeling that this particular unit suited the unique dynamics of her voice given the unusual acoustical situation. Specifically, the goal was eliminating a bit of the higher end “sibilance” found with the condenser mic she normally uses. For the piano, a pair of EV RE 200 condenser instrument mics was spaced above the hammers, with an additional EV N/D 468 dynamic mic positioned toward the far end.

According to Taylor, mic placement was pretty straightforward, with loudspeaker placement proving far more critical in this venue.

ATTAINING HEIGHTS

Without need to be overly concerned with excessive low frequencies in the performance, most attention went to proper array height and positioning to direct energy on the 350-plus-member audience. The stepped front stage area resided an additional four feet above the main floor, so ground stacking the arrays there supplied the necessary height.

Cobra arrays are supplied with an adjustable board/platform that allows tilting of an entire stack or just select boxes. In this case, the boards were used to give each entire array a 2.5-degree downward tilt, focusing the peak of each stack toward the back half of the audience area, which helped more evenly distribute coverage, according to Taylor.

The microphone setup for Ball and her piano.

When full, the room’s reverb time drops to half, or about three seconds. But, further help with the reverb situation was defined in the form of delaying the output of the main system, via DSP, to present a more coherent acoustical energy source from the center of the stage. The idea is to have energy/output from the stage and system sum naturally, thus requiring less overall amplification, and therefore not “exciting” the room unnecessarily. “Specifically, 14 milliseconds of delay was applied to align the output of the speakers with the energy of the grand piano. By keeping the number and length of arrival times added by the system to a minimum, intelligibility and dynamic headroom increased,” says Taylor.

The sound team has also found potential for a significant amount of low frequency (near and below 500 Hz) build-up in the rear of the room. But with just a single voice and piano, this wasn’t a huge concern for this particular show. Further, the piano low-end was also digitally delayed in relation to the system’s overall output. In the final analysis, the live concert proved an excellent source of further data that will help drive the final solutions in the room.

One of the Cobra stacks in position for the concert, two mid-high modules over one sub.

TREADING LIGHTLY Currently, Peterson is working with several acoustical curtain manufacturers about the possibility of easily removable and rolling curtain structures that could be operated with small chain motors (likely hidden). He’s also working with sources on development of some type of acoustical band shell that can be quickly setup and struck. “In my next presentation to the board, I’ll have some specific recommendations using these elements that will help cut the reverb time as much as 1.5 seconds in some critical vocal frequencies,” he adds. The lessons learned from the data acquisition and analysis, as well as the Ball performance and its highly positive reviews, make Peterson optimistic about the future direction of the project.

“With my grandmother having attended the church, I feel like she’s looking over my shoulder to not detract from this space, and at the same time, my father, who’s still an organist, is constantly cautioning me about doing anything that will ruin that organ. So I’m treading very lightly,” he concludes.

E. Victor Brown is a veteran pro audio journalist whose work is published in several industry publications. Reach him at evictb@sbcglobal.net

January 2004 Live Sound International