Basilica of the National Shrine

In Uncategorized by tfwm

Since 1979, I have helped the Basilica of the National Shrine of the Immaculate Conception, the nation’s premier cathedral, with its audio systems, including operating their sound, doing maintenance on the system and completing ongoing installations of new equipment. My longtime association with the Basilica began with RCI Systems, a systems design/installation company in Germantown, MD, and was enhanced by the support of DMX MUSIC when RCI was acquired by DMX MUSIC in 2000. RCI was one of several systems designers and contractors that DMX MUSIC combined with their own offices to build a comprehensive, national network capable of providing the highest level of design, engineering, installation, project management and service to clients like the Basilica, as well as music, visual imaging and message marketing services.

In 2003, I worked with Chris Koawl, project manager for DMX MUSIC, and Robin Jones, principal in the U.K.-based consulting firm RG Jones Ltd. I supervised the design and installation of a major upgrade to the Basilica’s sound system to improve speech intelligibility. The project took place over the better part of three years, with a budget estimated at $175,000. The cathedral now has an audio capability that matches its place in history. When its cornerstone was laid in 1920, the church was intended to represent the achievements of American Catholics and be the foundation of the Archdiocese of Washington, D.C., the nation’s third largest. Completed in 1950 and dubbed “America’s Patronal Church,” the National Shrine has over 60 chapels and oratories within its huge main section. The cathedral includes the Great Upper Church, which seats 3,500 and has been known to hold close to 6,000 worshipers. Based upon this esteemed heritage, DMX MUSIC set about bringing a 21st century audio system into the world’s eighth-largest cathedral structure.

Part of History
Obviously, I have a feel for the National Shrine, having done so much work there over the last quarter of a century. This church has been in a continuous state of upgrade all that time. But about three years ago we embarked on a major upgrade, primarily to rectify one thing: speech intelligibility. We had done a speech transmission index (STI) scan of the sound and found the intelligibility rating came in somewhere around 50, marginal is around 55 to 60. We wanted to get it between 70 and 80, which is analogous to what you’d hear with two people talking to each other across a mid- to large-sized living room.

The main obstacle to achieving this rating is the size of the church, which is massive. The length of the Great Upper Church area is about 600 feet and 175 feet from the floor to the top of the tallest dome. As a result, its RT-60 reverberation time is over six seconds, which is not conducive to intelligible speech at all. By the time the direct sound arrives at the listener, it’s obscured by a whole maze of indirect reflections that envelop it like a cloud and distort its intelligibility. The church is the primary structural interface, equivalent of an embassy between the U.S. Catholic Church and the Vatican, as well as the seat of one of the largest diocese in the U.S. It is also the focal point for many visiting dignitaries and special events, many of which are broadcast by the church’s EWTN network and by national media. We knew we had to improve the audio capabilities of the Shrine.

Given its size and the intrinsic beauty of the architecture, there was nothing we could do in terms of addressing the problem from an acoustical standpoint. The solution would have to be in the distribution of the sound. We shot the space with a TEF-20 analyzer and located the critical points at which to place speaker systems. We chose a combination of EAW LS-832 and LS-432 speaker enclosures based on a combination of their size and their output, which matched the large area we had to cover. These are column speakers. We put a combination of 832 and 432 speakers on either side of the opening to the main altar area, which forms the middle of the T-bar of the cross shape of the interior. Across the T, we placed two more on either side further away, ultimately using just the LS-432 boxes on the outermost areas.

We then mounted LS-432’s to the walls along the side of the building. The speakers are powered by 20 Crown K-2 amplifiers, with delays by an Ashley Protea processor. They are set to create a series of delays in the four main zones of the church building going lengthwise. Delaying the direct sound is a standard technique used in large-volume enclosed spaces. The first set of stacks is delayed by 15 milliseconds (ms.) to match it with the choir and the immediate floor area in front of the altar. Since electrical signals travel at close to the speed of light, depending upon impedance, and sound travels at a tiny fraction of that, we want to slow down the time of arrival of sound through the speaker system so that it arrives more synchronously with the live sound. The next two sets of speakers are set at 80 ms. and 150 ms. respectively. At the bottom of the church is the Narthex, a large entry nave. There, we put additional EAW 432 speakers with a 200 ms. delay on them. We also put in a Soundcraft 24-input Spirit console as the FOH position.

What this speaker placement did was allow us to distribute the sound very evenly; the stacks have wide horizontal dispersion and tight vertical dispersion characteristics, so the sound is very focused on specific parts of the seating area. That, in turn, allowed us to lower the overall volume of the system, which results in much more direct sound than reflected sound. That’s the gist of how we solved the intelligibility problem.

There are also several sub-zones of the four main zones. These include speakers set into the chapels and oratories along the sides of the building, as well as in the apse in the north end of the church, the top of the cross, so to speak. During special events, the church will have worshipers spilling over into these areas. They get the same sound delayed according to the zone of the main area that they’re adjacent to. There are also four LS-432 speakers used as monitors for the altar area. That also feeds into the idea of highly focusing the sound directionally and allowing us to keep the volume down overall.

Downstairs is the church crypt, which is not nearly as large as the Great Upper Church but which hosts many of its own services, often in other languages and often simultaneously with services upstairs. In this area, which seats up to 900, we use the same speaker systems but instead of a manned front-of-house (FOH) mixing position, we used a pair of Shure SCM-810 mixers that automatically find the microphones with signal and duck or mute the others. All of the microphones are AKG of various models.

Video
There are also provisions for a series of 27-inch to 35-inch video monitors, which are rented as needed for large events and placed around the interior of the main building. The wiring for those and for the upgraded audio system required us to cut into the marble floor of the Shrine in places, then re-grout over it. In some parts, we had to actually take out sizable chunks of the marble and replace them. Part of the strategy was to get the entire system onto the same power grid and use the same ground. This would help us condition the power and have it consistent throughout the system. Until this last upgrade, there were still a few outlets in the church that didn’t have grounds. Everything is now tied to the building ground.

Other aspects that we added were a multi-box so that outside media can plug into the building for broadcasting special events, and there are plugs into which external speakers can port into if the need arises to get sound out to crowds gathered around the church.

We were able to achieve the goal of dramatically improved speech intelligibility, including achieving an intelligibility rating between 70 and 80, without having to treat walls and use other acoustical solutions. I’ve done a number of so-called ‘mega-churches’ in recent years, and doing the audio for a huge structure when it’s a ground-up proposition is much easier than dealing with a nearly century-old building with so much marble and other reflective surfaces. But that’s part of the beauty of working on glorious old churches like this: you get to make what makes them beautiful come alive even more.