Step By Step 1: Design

This post is the first in a series that follows an example step-by-step through a representative design and tuning process for a mid-sized arena. On the macro level, I follow pretty much the same steps and workflow as I would always follow on a similar job. However, along the way, we will see how the specifics of the day demand adjustments and changes where necessary.

We start with an empty venue. (Figure 1) The stage is in place and we have our laser in hand. (Note: don’t ever assume the stage is square-on to the venue, or centered on the venue’s center line. I check my measurements against the floor geometry and ceiling steel to make sure I’m truly centered.)

Figure 1 - Empty venue

Making the Model

Two quick measurements for the floor dimensions (175 ft length x 88 ft width). The venue seating profile is symmetrical enough (sides and back) that we can shoot a single profile for the On-Axis app from OK-Sound. (Sometimes the side elevation of the upper tiers can be significantly higher than the rear profile, in which case we need to take two sets of measurements.) Stand on the center line and shoot to the front and rear of each seating tier (we have three rakes counting the VIP boxes between 100 and 200 level, so that’s six data points, each of which having a distance and a vertical angle). The app has a convenient setting that allows some of the profile shot points to be to seat-back height rather than floor height which simplifies the task considerably. It can also connect via Bluetooth to my laser disto and pull the measurement data directly into the model. Then I add in the stage and set the project origin to assign (0,0) to the downstage edge of the stage. There is a scoreboard but it’s retracted fully and not low enough to need to consider it in the model.

Figure 2 - Left: Elevation Profile measurement view in On-Axis. Right: Export preview.

The app can export geometry directly into most common prediction software platforms. In this case I have a “base” ArrayCalc file that contains the full system we’re carrying for this tour, with all the proper amplifier assignments and parameters, with starting geometry for Mains / Flown Subs / Sides / 270 / Front Fill / Ground sub that I can quickly adapt for each venue. By setting the downstage center as the (0.0) point in the imported geometry, the entire PA lands right in place to start (Figure 3).

FIGURE 3 - the PA start file (left) and the imported geometry (right)

Designing the System

Now we can refine source placement. Mains and subs are at +/- 32 feet off center in the base model (the stage is 60 feet wide) but we have up-down steel to dead hang at +/- 35.5 ft so we’ll shift outwards a few feet. Likewise the raked seating protrudes far enough into the floor area that we’d have to fly our side hangs from the seats on house left unless we move the points, so we’ll move the points. The furthest we can go without hitting seats is +/-42.5 ft which puts our side hangs about 3 feet closer to the mains and subs than I typically prefer. We may need to get a bit mechanically creative with our trims to avoid collisions, but let’s start by seeing how splays affect the curvature and go from there.

Mains

I increased the height of the rear wall of the 200 level to allow for my preferred 2 boxes of overshoot and then evenly spaced center line impacts (as well as we can manage) down to the barricade at 8 ft. Due to the steel configuration the points won’t be perfectly in line, so given the choice I’ll take a slight toe-in on the mains to help with the center gap, knowing I can still land the 180 line without concern. The bottom 4 elements are wide elements. (Figure 4 & 5)

FIGURE 4 - Mains splays, section view

FIGURE 5 - Mains @ 250 Hz (left) and 2500 Hz (right)

Subwoofers

We will continue with the same flown 7-element array that’s been working very well for even front to back energy distribution in arena-size venues, with the same 5-degree incline that cleans up the stage a bit and further aids uniformity (see Dimensional Focus: Vertical Plane for more). We need to increase the trim just a tad to avoid collision with the curvature of the mains. This gives us approximately a 3 dB rise from mix position forward, and a 3 dB drop from mix position to the last row of 200 level. (Figure 6)

FIGURE 6 - Subwoofer iso geometry (left) and 50 Hz prediction plan view (right)

As previously noted, the slight thinning out of the sub coverage right against the barricade will be rectified by our “front fill” subs in the pit. Also, this is a situation where toeing the subwoofers outwards doesn’t make sense - we already have plenty of energy on the sides. In a typical full-size arena, I don’t end up toeing outwards with a flown line length of 7 - 9 subwoofers. When the room is shallower - as in this design - it sometimes makes sense.

Sides

Taking a look at the mains prediction (Figure 5) gives us a clear idea of where our Side hang needs to pick up the coverage: we need the edges of the top horns to stretch basically all the way down the side of the arena at the 200 level, while having much less work to do at the bottom. So let’s put the wide boxes on top (6 over 6). In a typical arena design this toe out is somewhere between 50 and 55 degrees. Figure 7 shows plan view of Sides (left) and Mains + Sides (right) at 2500 Hz. We can see that we’ll need to turn down the gain on the side hang a few dB (approximately 1 color contour) and we are making it comfortably to the 180 line - notice the importance of the overshoot here at making sure the coverage is sufficient in the 200 level at 180 line. Putting the top box into the last row onaxis means leaving some undercoverage closer to the array. This is an example of where a landing strip 2D prediction fails.

Figure 7 - Sides (left), Mains + Sides (right) @ 2.5 khz

From there, the only remaining bits are the front fills and pit subs, which don’t change at all from day to day unless the venue architecture forces our hand. So we’re ready to deploy. In the next installment, we’ll look at the tuning process.