Solving A Conundrum Deployment of a new subwoofer configuration. by Todd Hartmann I’ve spent the past several years experimenting with various types of subwoofer arrays and have arrived at the same conclusion each time: with each method, something is gained while something else is lost. Left-right placement enhances coverage on the sides at the expense of drastic power alleys and cancellation zones. Horizontal arrays produce even coverage in front of the array at the expense of a major drop-off on the sides. With delayed arcing, side coverage is improved, at the expense of tightness. With cardioid “front-back-front” setups, tightness is enhanced at the expense of output SPL. I could go on, but you get the idea. Sub deployment is especially tricky in arenas, where the large open area and hard (usually concrete) surfaces make for the addition of low-end “mud” in the diffused field, along with the need to cover a wide area in the horizontal plain – usually 180 degrees or more. One of the more common practices I see in the field is flown leftright sub arrays, where hangs of usually eight or more boxes are flown either just outside of or behind the main PA hangs. While the throw is fantastic, cancellation from left to right is a mathematical certainty. My choice has been a horizontal array, where boxes are placed along the front of the deck and spaced evenly at a quarter-wavelength of the target frequency. The coverage on the floor is extremely solid and even, but it’s virtually non-existent elsewhere. I wrestled with this problem last year with a system provided for an Easter Sunday worship service presented by Austin Stone Community Church at the Frank Erwin Center on the campus of the University of Texas in Austin. While the primary function of the Erwin Center is hosting college basketball games, it’s also booked solid most of the year with A-list tours that draw 15,000-17,000 in attendance. The floor is elongated, stretching 110 feet from the deck to front of house, while the upper levels begin to widen, until the arena becomes almost perfectly 18
Live Sound International June 2012
The scene on Easter Sunday at the Erwin Center.
round at the top of the mezzanine. My typical horizontal array was less than ideal for this venue. While the floor sounded (and felt) fantastic, you only had to climb a few rows off to the sides before the low-end began to drop off quickly. While some of this can be corrected by delayed arcing (delaying the outside boxes to create a virtual arc), the added difference in arrival times causes the entire array to lose much of its tightness due to smearing in the time domain. I left that gig determined to find a solution. There had to be a better way to get even coverage, both in front and on the sides, without power alleys or cancellation zones. In an ideal situation, the low-end should come from a single source, equidistant from the main left-right hangs. But where would it be located? NEW DIRECTION This past Easter Sunday, when the church returned to the arena, I had the unique opportunity to try a different approach. Working with local audio providers Big House Sound, we designed and deployed a large-scale, flown, end-fire subwoofer array. This had yet to be tested, but once the rig was in the air, jaws began to drop.
The Adamson subs making up the end-firing arrays, being raised into place by the author. www.ProSoundWeb.com
:: Spotlight ::
The main hangs consisted of 12 the subs harder to get that tight “feel” Part of the idea came from fellow Adamson Y18s per side, with four Y10 I’m looking for. On the flip side, I tend engineer/tech Sarah Butt, who had for down fill and 12 Y10s for out hangs. to use less low-end in my mixes with worked under Kenny Chesney system The rig was powered by 30 Lab.Grupcardioid subs, attaining a clean, tight engineer John Mills for one of the pen PLM 10000Q amplifiers, with all feel at lower levels when I’m not deal“Goin’ Coastal” tour dates at Cowboys system DSP done inside the amps. ing with a lot of late reflections from all Stadium in Arlington. Mills’ design for Determining the exact end-fire spacof that backfiring energy. a large Electro-Voice X-Line rig incoring to optimize gain and delay porated two monstrous hangs time was a joint effort involvof subs (20 per hang) flown ing Adamson and it’s distribudead center of down stage, tor in France, DV2. The result between the mains. The theory was a textbook cardioid pattern made sense – two hangs acting from 40 Hz to 80 Hz, where as a single source, dead center the subs were crossed over. The of the rig, with no cancella“EF66” preset, as Adamson tions or drop-offs anywhere in called it, spaced the two hangs the venue. This got my brain 66 inches apart around a center spinning. frequency of 51 Hz. There were four primary To prevent the rig from issues to address in order for swinging (and hence changing my approach to be a success. the precise spacing), a piece of First, it had to be cost-effecsteel pipe was linked between tive. This is already an expenA look at the centrally located end-fire array, as well as some of the rear pick point of the sive gig, and I couldn’t afford the mains. downstage hang and the front to add a lot more boxes. Secpoint of the upstage hang. CheeseborPLAYING IT OUT ond, we needed to take advantage of the ough clamps allowed us to adjust spacI decided on two arrays, each comprised 90-degree off-axis null directly beneath ing once the rig was floating. Finally, a of six Adamson Systems T21 subwoofa vertically flown sub array to reduce the cable bridge constructed of minibeam ers, one behind the other in an end-fire back-pressure on stage. Third, the arrays spanned from the sub hang downstage formation. With significantly more outneeded to be short, since longer arrays center to the stage left cable pick, in order put power than most dual-18-in subs on reduce vertical coverage by making the to reduce added tow on the hang. the market, it required less of them to get hang more directional. They needed to the desired SPL, and also kept the hangs behave as a point source. MISSION ACCOMPLISHED short. Four additional T21s were spread Finally, we needed it to be cardioid. Any reservations were quickly forgotten across the floor to help fill in some of the I’ve found that the boomy low-end in once we heard the rig. I was afraid that gap before the flown subs took over. arenas typically results in me pushing
At left, a screen shot of the system modeling; above, polar data of the “EF66” end-fire array, based on a ground stack two cabinets high. 20
Live Sound International June 2012
We’re fortunate to benefit from some pretty great minds, using their ideas to take things to a new level. I have tremendous respect for people like Dave Rat, who consistently puts new concepts out there simply because they’re passionate about live audio, and want to make us all better as a whole. We are, in a sense, standing on the shoulders of giants. I truly look forward
to what future discoveries will be made and how they will continue to improve one of the coolest fields a person could find themselves employed in. n
Todd Hartmann is the audio engineering coordinator for the Austin Stone Community Church as well as A1 systems engineer for Big House Sound in Austin, TX.
the flown subs might lose some of their “punch” without the ground coupling, but that certainly wasn’t the case here. The low-end was extremely tight, even and clean. There was no more than 7 dB of drop-off from the first row to the top of the mezzanine, and more importantly, the ratio of subs-to-mains remained constant, leaving the mix to sound full and clear, no matter where you were located. Behind the rig, the cardioid pattern performed beautifully. The sections behind the stage were so quiet it almost felt eerie. In the past four years working with Big House, I’ve heard this rig deployed dozens of times, and became used to the large amounts of backpressure these subs typically produce – but not this time. It was practically silent, except for the late 500-millisecond reflections coming back from behind front of house.
The Easter Sunday sound crew at the Erwin Center, left to right: Mark May (system tech), Sarah Butt (A2), Todd Hartmann (front of house, designer), Fiona Cheung, (patch), Mateo Rodriguez (monitor engineer), and Cody Hester (A3).
When all was said and done, we couldn’t have been more pleased with the outcome. It was hands-down the smoothest, tightest and most even lowend I’ve ever gotten out of an arena system. The comments about the superb low-end coverage haven’t stopped coming in, and one production manager told us that it sounded better than the rig a major tour brought in just a few weeks prior. Whether or not that statement is true, I don’t know, but we’ll take the compliment nonetheless! I fully believe in giving credit where credit is due, especially in this industry. www.ProSoundWeb.com
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Live Sound International
Published on Dec 7, 2012