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Fill-osophy: Proper Fill Goes Well Beyond Just Adding Loudspeakers
Looking at the possibilities and necessities in a wide range of SR situations...
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Under & Over
Almost all point source and line array systems used in performance venues and churches are trimmed at a height that facilitates even coverage to all exposed seats, and in as compact a manner as possible.

In venues with balconies, there will be seats that are shadowed by the balcony overhang. and in many venues the ceiling, or the acoustic reflectors suspended over the audience, obstruct sound from reaching the rear-most and highest seating.

The devices used for under balcony fill are likely to vary from small (i.e., dual-5 or dual-6, 2-way) to medium small (single-8 or -10, 2-way) and installed as close to the ceiling as possible. Although multipurpose loudspeakers are often deployed for this, there are purpose-built fill devices available from a wide range of manufacturers.

Over balcony devices vary from medium-small (single-8 to single-10, 2-way)  up to mid-size 2- and 3-way horn-loaded designs. Most often, we use multipurpose products adapted to this application (Figure 5).

For portable sound applications such as Broadway show bus and truck tours, under and over balcony loudspeakers are likely to be hung from lighting pipes and/or box trusses that are already installed or brought in for lighting.

Rock n’ roll shows in road houses seldom carry their own fill loudspeakers and will tie into the installed fill systems. When these are aligned and equalized to the primary system, they can work very well. However, not taking the time to measure and correct the alignment, etc. can result in severely compromised sound for those who are seated in the “wrong” seats.

Figure 5: Under balcony and over balcony fill deployment.

With installed systems, we have the opportunity (and often the need) to position under and over balcony devices in a more streamlined manner. Yoked fill loudspeakers are most often used, provided there are structural elements behind the ceiling surfaces to anchor them to. In some cases we can work with the architect/client to embed the loudspeakers into the ceiling and color-match them.

Placement & Coverage
In general, it’s good practice to position overhead fill loudspeakers forward of the target seats so that, along with delay, the acoustic energy from these is localized toward the stage.

More often than not, under balcony ceilings do not work well with recessed ceiling loudspeakers due to the direction that the sound is projected as well as the resulting limited area that these will cover.  However, acceptable results can be achieved with such loudspeakers when the ceiling is curved or angled upwards, from front-to-back.

Where we place these devices and where their coverage begins are determined primarily by intuition and experience. It’s been my experience that sighting where the balcony occlusion begins to obstruct where one sees (while seated) the HF elements in the primary loudspeaker(s) simply doesn’t work and locating the fill devices 2-3 rows ahead of this point is necessary.

From this point to several feet above standing height at the rear wall determines the required vertical coverage. We should avoid reflections from the ceiling, especially when it is flat and low. Ceilings that are curved up, from front-to-back, are less of a concern. Reflections off untreated rear walls are seldom an issue because we typically angle the fill loudspeakers down and therefore the reflections are “grounded” (absorbed) by the audience.

Figure 6: Polar graphs showing coverage, in both axes, of a typical small-format 90-degree (h) by 40-degree (v) loudspeaker.

The depth of the under balcony seating determines whether one or two delay “rings” are required as well as the coverage required from these devices. Unless complex computer models are constructed (and you trust them), when determining the best-suited fill loudspeaker and how many are needed, one should (at the very least) utilize the manufacturer’s polar response graphs or beamwidth chart and pay particular attention to the coverage pattern over the 2 kHz -12.5 kHz range.

This frequency range significantly affects clarity/intelligibility as well as timing cues (localization). Note that in most cases the specified coverage is less in both axes at these higher frequencies (Figure 6).

Tom Young is the principal consultant at Electroacoustic Design Services (EDS) with both worship and performance space projects in and around New York City and throughout New England. EDS specializes in sound reinforcement system design, loudspeaker system measurement and optimization, acoustic design and noise reduction. He’s also the moderator of the Church Sound Forum here on PSW.


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