March 11, 2013, by Todd Hartmann
Designing an audio system isn’t always as simple as picking your favorite boxes, throwing some amps in racks, and “firing it up.” While favored loudspeakers might indeed be a starting place, there are vital factors that must be addressed, including the coverage needs of the room, characteristics or obstacles in the room that could be problematic, weight limits with respect to flying components, and so on.
Another issue can be the musical “feel” the client is going for. Different loudspeaker designs can have different voicings, some of them better suited for a given genre than others. Specifying the proper tools for the job is no small task, but it doesn’t have to be an overwhelming endeavor.
Over the past year, I’ve worked with these factors, and much more, while designing a mobile system for the Austin Stone Community Church in Austin, TX. Once the homework was done, the results have proven to pay off.
The Austin Stone is among a growing demographic of churches that are entirely portable, choosing to utilize a third-party venue instead of incurring the cost of it’s own purpose-built facility. Services are held in the gymnasium of Austin High School, which seats roughly 1,800, with one of the four weekly services broadcast via stream to three satellite campuses.
Located in the heart of Austin, it should be no surprise that the “feel” of the services is rock ‘n’ roll, with big drums and guitars occupying most of the space in the mix. For the last 10 years, the church has rented full audio production – and yes, that means trucking everything in and flying PA on a weekly basis.
EASE plots displaying direct SPL at 400 Hz for one of the other line arrays evaluated (left) and the d&b Q1. (click to enlarge)
As one can imagine, this ends up costing a lot, not to mention other joys associated with rentals such as the occasional miswired rack, forgotten cables or RF antennas, and jamming hardware. In the summer of 2011, the idea was introduced to church leadership about finally purchasing a rig of their own.
The rental system included flown line arrays, subwoofers on the ground, and front fill loudspeakers across the down-stage edge. The main arrays were flown with half-ton motors dead-hung from the steel support beams spanning the gymnasium.
Acoustically, it’s a hostile environment; the large cinder block room spans 140 by 110 feet, and the enormous parallel surfaces lend themselves to a large buildup of energy in the reverberant field. As a result, definition is difficult to achieve across the spectrum.
The need became evident for a road-ready system with superb pattern control, both in the mid/high range as well as the low-end. To achieve our 105 dB (A-weighted) requirement across the entire listening plane, the cabinets had to be capable of producing 138- 139 dBA at 1 meter.
In addition, the arrays had to fit within the working 1,000-pound weight limit. Because of the already high cost of the project, we couldn’t afford to add larger motors to accommodate heavier loudspeakers.
Another complication was the load-in. The gymnasium is on the second floor of the building, which means in addition to a long push down multiple hallways, the gear must be sent up (and down) via a 5-person elevator. This required the cabinets to not only be light, but small enough for four stacks to fit in a single elevator load.
Finally, the rigging had to be simple enough for a small (sometimes just two) volunteer crew to fly the arrays without needing a large amount of time or extra manpower.
We determined that the needs of the application could be met with “midsize” line array elements, and there are a lot of great choices in this genre.
An isobar plot showing horizontal directivity of the Q1. Red lines delineate the 75-degree horn pattern. (click to enlarge)
The contenders were first evaluated on the basis of the required box count versus cost. Two of the models, with 5- and 6-degree vertical splay, required an array of seven to eight cabinets per side in order to meet the required 40 degrees of vertical coverage and target SPL.
Conversely, another model under consideration – the d&b audiotechnik Q1 with a 14-degree vertical splay – required one less cabinet per side to achieve the same results. In addition, a single Q10 (40 degrees vertical x 110 degrees horizontal) could be substituted as the bottom cabinet in the array for even greater coverage in the near field.
All options were then examined more closely, using isobar plots to determine their horizontal directivity (one manufacturer was unable to offer any data in this area) and how they would “behave” in the room.
In addition to the manufacturers’ prediction software, a model of the room – including all acoustic obstructions – was created in AFMG EASE for the purpose of more extensive mapping. This helped determine what the primary and secondary reflections in the diffused field would look like, as well as intelligibility. It also helped us to calculate maximum trim heights in order to fire under obstacles such as vinyl banners and retracted basketball goals.
A closer look at one of the 6-element Q1 main arrays in place. (click to enlarge)
Following this process, it was a relatively easy decision as to which model would provide the optimum solution for this specific application. In addition to the vertical splay advantage noted earlier, the d&b Q1 also weighed in at less than half of the other boxes, and exhibited far better pattern control.
It incorporates a dipolar LF driver arrangement that maintains horizontal directivity down to 400 Hz, which means dramatic reduction in the diffused field since wall reflections are primarily contained to the 75-degree horizontal pattern of the array.
All of this resulted in main left and right arrays, flown in the optimal locations according to modeling, each comprised of five Q1 elements and one Q10 element at the bottom.
In addition, much of d&b’s subwoofer line, when properly deployed, can yield the same tighter pattern control in the low frequency ranges. As a result, we decided to pair the arrays with four d&b J-Sub subwoofers, evenly spaced along 18 feet of the floor in a tight-formation horizontal array.
The J-Sub is a cardioid, triple-18-in subbass cabinet, housing two forward-firing drivers and one rear firing, with a switchable cardioid and hypercardioid pattern. When paired together, the pattern of the sub array complements that of the main arrays almost perfectly.
The D12 amplifiers were divided into two 16-space racks, with four amps for each side of the PA.
In each rack, a pair of D12s powers the main hang of five Q1s and a single Q10 down fill, while another pair of D12s powers two of the J-Subs. A single D6 amplifier drives an additional pair of Q10 front fill loudspeakers on the stage.
To keep things simple for the volunteer setup crew, each rack contains mono-gender input/through multi-pin connectors, mated to the panel of the stage I/O rack for the console.
An added benefit to choosing the d&b components is that the new system instantly became very rider-friendly. In my mind, it would be a waste to keep a rig of this caliber locked up in a warehouse during the five days a week it isn’t in use.
By providing a system that not only meets the church’s needs but the rider requirements of touring acts as well, it could become a revenue-generating investment, and in fact has already gathered considerable interest among regional audio rental houses.
The four J-Subs evenly spaced in a horizontal array. (click to enlarge)
Further, due to the nature of the dipole configuration, the excessive wall reflections and long decay times were dramatically reduced. As a result, system tuning was unnecessary for the most part, compared to other rigs I’ve brought in where extensive EQ was required to clean up the room. At front of house, it feels like you’re mixing on studio monitors. Every detail, every nuance is there, without the “rock ‘n’ roll smear” or sounding like a large hall reverb is assigned to the left-right bus.
In the low-end, the J-Subs have far surpassed our expectations with not only their output, but also the tightness with which each transient is delivered. I’ve started using a good deal less low-end in my mixes any time I work with cardioid subs, simply because tightness and clarity reduce the need for higher SPL.
Finally, it should be noted that the importance of the “little things” cannot be overemphasized. Simply put, don’t skimp on the small additions that will make both your life and your crew’s lives easier on a daily basis. High-quality multi-pin connectors such as those from LK, though more expensive, can last the lifetime of the system (because who has time to replace pins when you’ve got a gig to run?).
An amp rack from design (top) to completion. (click to enlarge)
Another huge time-saver is racks with “slam-latch” doors. For this project, I used Olympic Cases Fast-Pack racks, and the convenience alone of not having to hunt down rack lids at the end of the night has been worth the cost. Lastly, LED strips can be easily mounted behind the rack frame to create an illuminated, shadow-free area to quickly patch, and it looks a lot cleaner than using rope lights.
With any project, it takes a team of dedicated, passionate individuals who are all striving for the same degree of excellence. Zach Richards of Big House Sound and Joe DiFalco of d&b were instrumental in providing not only the data, but also insightful recommendations with optimizing DSP capabilities and array placement. Big House was gracious enough to let us take over the back corner of their warehouse for three weeks, and even set aside a few of their techs for soldering duty.
Last but not least, my good friend and assistant James Muturi spent many a late night by my side unboxing gear, wiring racks, and stenciling cases. We can look back on all of the hard work knowing that we helped transform a high school gymnasium into one of the best-sounding rooms in Austin.
Todd Hartmann is the audio engineering coordinator for the Austin Stone Community Church as well as a freelance audio engineer.