In the early days of sound reinforcement for houses of worship, the typical modus operandi was to stack a bunch of speakers on the platform and point them toward the congregation. We turned it up loud enough so it was at a reasonable level in the back of the sanctuary, which meant that we ended up punching the front-row worshippers in the face with a ton of SPL. (Evidently some younger members actually liked it this way). Eventually we got a bit more sophisticated and started hanging stacks of speakers from the ceiling. These “line arrays” enabled us to point some of the speakers toward the seats in the back and some of them downward toward the seats in the front. The speakers facing the rear of the room are turned up louder than the ones facing the front, which made the SPL heard by each section of people roughly equal — nice and consistent. This worked so well that we continue doing it — now and in the foreseeable future.
This solution is effective, but not perfect. Sometimes, particularly in really large churches, front row seats are so close to the platform that they end up being pretty much behind the line array speakers. As we all know from personal experience, when we get behind a typical speaker, the highs and mid-highs virtually disappear, the mids are substantially reduced in level and we’re left with low-mids and lows — lots of thump and bump, but not much else. This is because higher frequencies are comparatively directional, and they are dispersed in the direction in which we point them. Lower frequencies are more omnidirectional — they are dispersed pretty much in a sphere emanating from our speaker boxes.
The Mush Mix
The net result? Folks in the up-front seats hear (and feel) that thump and bump, but not much of the clarity and intelligibility we get from the higher frequencies. The FOH engineer works hard to carefully craft a great-sounding blend, but for the people in the front rows, it’s all for naught — not only do close-in listeners miss a substantial chunk of the frequency spectrum, but the mix they hear tends to feature a disproportionately large amount of any element that produces a lot of stage volume — loud guitar amps, drums and so on. Unfortunately, what they’re hearing is not under the control of the FOH engineer, is unbalanced, and sounds awful. Balconies can create a similar issue, which is somewhat common in older houses of worship. The balcony interferes with the dispersion of sound energy, and the result is that the folks under the balcony are not getting the full SPL or frequency range heard by those who are not under it.
So how can we solve this problem? We strategically add some additional speakers in places that ensure that the folks up front and under the balcony are getting the full auditory picture. These are known as “fill speakers,” and we’re talking about a couple of different kinds of them here; front fills and under-balcony fills. Here’s the fundamental thinking on fills in general. If you have a section of the congregation that can’t hear some of the main FOH mix, you can “fill” it in with these additional speakers, fed with whatever the FOH engineer wants to send to them. Front fills are just that — right up front, and directed specifically to cover the gap that the regular FOH rig does not. Under-balcony fills are indeed hung under the balcony to provide whatever ends up missing from the FOH mix as a result of interference from the balcony. Front fills are usually smaller speakers at the front lip of the platform, directed toward the front rows.
Not So Easy…
It might seem we could just copy and paste the FOH mix and pipe it to our fills, but it’s not quite that simple. Here’s an example to explain why that is the case. Let’s say we have an uncaged drum kit and a couple of live guitar amps on the platform. They are going to contribute to the overall FOH mix heard by most of the congregation throughout the room. But right up front, where parishioners may not be hearing the full bandwidth and SPL of the main mix, the stage volume of the drums and amps will be substantial due to sheer proximity to those sources, and that will result in an improperly balanced mix in which drums and guitars will be over-represented. Vocals, keys, and other things that are comparatively quiet (or completely unheard) on the platform will be under-represented in what the front row hears. For this reason, the FOH engineer has to sort out what needs to be fed to the front-fill speakers to fill in the mix and keep it consistent with the main FOH rig. Hence, it makes sense to feed the fill speakers from auxiliaries so they present the right components of the mix at the right levels to cover the gaps.
Another issue that figures in here is phase coherence. It’s a safe bet that in a properly tuned FOH line array, phase alignment has been sorted out and we have a nice coherent signal arriving at the ears of the congregation. In the same way, we would time align the low end between our line arrays and any subs tucked into under-platform bunkers, it’s important to align any under-balcony fills so as to avoid having audio from the fills arriving substantially before the sound from the main array. This is the exact same principle as with delay towers. The delay times should be determined scientifically with precision measurement and built into the speaker processing DSP, so our FOH engineer doesn’t even have to think about that aspect of operation. Fig. 1 shows a simplified signal flow diagram for handling this process. The FOH console feeds its main output bus to our speaker DSP, which in turn feeds the main arrays, and also a delayed signal to our under-balcony fills. A matrix/submix output feeds the front fill speakers, and enables our mix engineer to present a different blend to the fills as to the main arrays. Although the diagram does not show it, it’s a good idea to ensure that whatever’s coming from the front fills is time-aligned with the main arrays as well.
It is important that the fills are fed by an auxiliary that lets our engineer send a blend that’s different from the main array mix. Returning to our previous example, the worshippers in the front row would be getting more direct SPL from the uncaged drums and guitar amps, so adding to them by simply routing the main mix into the fills would result in a poorly balanced mix with drums and guitars over-represented. Our engineer will want to decrease these elements in the fills mix. Similarly, the engineer would want to emphasize any element with little or no stage volume. Vocals would be comparatively quiet, so they’d be bumped up a bit, and anything appearing in the FOH mix exclusively via DI (keyboards and tracks, for instance) will need to be substantially boosted in the fills mix.
One obvious way to increase intelligibility during the pastor’s message is to feed a bit of it into the fills mix. This really is a necessity, particularly in large rooms where the highly directional intelligibility frequencies of speech are passing right over the heads of those in the very front row.
What goes into the fills mix should be determined in a subjective way. The FOH engineer should take a tablet, walk up to the front row, and literally develop the blend by listening and mixing the same way they mix the main arrays. And under-balcony fills should be blended subjectively in the same way.
Delivering a consistent aural experience to everyone in the sanctuary should be a high priority for all houses of worship, and in particular, churches with flown speakers of any kind that leave a coverage gap in the front rows or under a balcony should go out of their way to fill in those gaps.
John McJunkin is the chief engineer and staff producer in the studio at Grand Canyon University.
