Image courtesy of Bayside Church, Roseville, CA.
Though it doesn’t benefit the back of the venue as much as the front, the efficiency bump from floor-mounted subs is a proven fact.
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When it comes to live sound, subwoofers are peculiar members of the loudspeaker family. Though tasked with reproducing a relatively narrow range of frequencies, subwoofers usually take up the most physical space and amplifier power. Their output represents the longest audio wavelengths (more than 40 feet), which are notoriously hard to control as they careen around a venue.
Thanks to those long wavelengths, sub placement has a pronounced effect on the sound of the entire system. It has been a topic of heated debate for decades. In front of the stage, under the stage, flown with left/right arrays, flown in the middle—you’ll see variations of these placements in churches and concert venues worldwide. As with most things in live sound, there are advantages and disadvantages to both floor-mounted and flown subwoofers.
In front of the stage, under the stage, flown with left/right arrays, flown in the middle—you’ll see variations of these placements in churches and concert venues worldwide.
Before we can discuss what constitutes effective subwoofer placement, let’s define the goal: consistency of sound pressure level (SPL). As with higher frequencies, optimal bass coverage is consistent in volume from one side of the room to the other (no hot spots, no dead zones). It’s also consistent from front to back, with minimal fall-off in volume between those eager worshippers in the third row and those napping in the back seats.
Traditional loudspeaker wisdom states that subwoofers on the ground are twice as efficient as flown subs (6 dB louder in technical terms). A hanging subwoofer spreads its energy out above and below it, whereas a floor-mounted sub has the floor to reflect half of the bass energy back into the room. The latter speaker is filling half as much space with the same sound energy (“half space”).
Image courtesy of Bayside Church, Roseville, CA.
Sometimes traditional wisdom withers under the bright light of science. French speaker manufacturer L-Acoustics put the “floor-mounted subs are better” theory to the test in 2018 and made several interesting discoveries. First, the real-world difference in efficiency between flown and floor-mounted subs is less than typically thought (closer to 3 dB). Second, flown subs can provide more consistent volume from front seats to back (around 10 dB fall-off as compared to 20 dB in some floor-mounted configurations). Third, flown subs can provide more even coverage from side to side (avoiding the predictable pattern of hot spots and voids from floor-mounted subs). L-Acoustics found that a vertical column of flown subs, centrally placed, offered the most consistent coverage.
DAVID ROEDIGER, PRODUCTION MANAGER, BAYSIDE CHURCH, ROSEVILLE, CA—“At Bayside, we desire to achieve the most even frequency and SPL coverage for our worship spaces. Our teams have decided that the best way to achieve those outcomes is to get low frequency energy in the air and on the ground.”
With that, the great flown-subs debate is surely settled for your church and every other. Not quite—there are many other factors to consider. To explore these, we spoke with two church sound experts about sub placement in houses of worship. David Roediger is production manager for Bayside Church, which has nine campuses in the Roseville, California, area. Neil Brown is technical director for Hope Community Church, a multisite church in Raleigh, North Carolina.
NEIL BROWN, TECHNICAL DIRECTOR, HOPE COMMUNITY CHURCH, RALEIGH, NC—“Most ceilings are less solid than floors, which means you’ll probably be dealing with more resonant frequencies. This is especially true in larger buildings that favor metal ceilings.”
Most of the remaining factors in sub placement have little to do with sound, and instead involve logistical and practical concerns.
Sightlines
Subs mounted on the floor will never block anyone’s view of stage or screen, and will be easier to hide in most churches. Flown subs, on the other hand, can be hard to position so they don’t block sightlines. “It might be that a center flown sub array is scientifically the most efficient solution for your space,” Roediger says, “but maybe the diminished returns of negatively impacted sightlines and function is enough to warrant a compromise.”
Ceiling Loading
Speakers are heavy, and flying subs adds to the load on your church’s roof. Consulting an engineer is a must before flying speakers, and some structures may need to be reinforced (at considerable cost). Ceilings can also experience mechanical resonances that floors will not, from certain building materials or ducting. “Most ceilings are less solid than floors,” Neil says, “which means you’ll probably be dealing with more resonant frequencies. This is especially true in larger buildings that favor metal ceilings.”
Access: Configuration, Repair, Replacement
Unless your flown subs are rigged with a winch system, access can be inconvenient and even expensive (if you have to rent a lift). Remote control systems will allow you to adjust phase and other parameters with the click of a mouse, but they won’t repair or replace drivers from the ground. When it comes to access, floor-mounted subs can’t be beat. “It is much more difficult to hang a sub from the ceiling than to place it on the floor,” Neil concurs. “It also adds difficulty when servicing the subs.”
Stage Coupling, Low-Frequency Feedback
Because floor-mounted subwoofers are usually positioned close to (or even under) the stage, they can cause low-frequency feedback problems even with judicious use of high-pass filters. “This is one drawback of floor-mounted subs,” Neil says, “if you have a hollow stage or something that is going to excessively rattle with resonant frequencies.” Flown subs are far less likely to couple with the stage and cause feedback.
Ease of Installation, Positioning
Floor-mounted subs have the advantage of being easy to move to test different configurations. Spaced, clustered, straight line, arc—all are fairly easy to accomplish. Not so with flown subs. Due to the complexities of installation and fewer placement options, flown subs are likely to be raised into their designated position and remain there permanently.
Efficiency
Although it doesn’t benefit the back of the venue as much as the front, the efficiency bump from floor-mounted subs is a proven fact. Where budgets or physical space are tight, getting more output from fewer speakers can be an advantage.
Available Space
Where space near the stage is at a premium, flown subwoofers offer an obvious advantage. Moving your subs from the ground to a flown position could free up room for a stage expansion or an extra row of seats.
Flown, Floored—or Both
When asked what advice he would offer churches facing the decision of where to place their subs, Roediger says, “More often than not, the end result is going to be a compromise between the ‘best’ scientific solution and all the other variables involved: weight, rigging points, cost/budgets, sightlines, trim height, time, SPL requirements, coverage, facility use.”
Roediger continues, “At Bayside, we desire to achieve the most even frequency and SPL coverage for our worship spaces. Our teams have decided that the best way to achieve those outcomes is to get low frequency energy in the air and on the ground. We still have low-end energy coming from our ground-deployed subs, but the subs are not responsible for reproducing all our low-end energy. Rather, they are adding to and complementing the coverage of low frequencies being reproduced by the main PA. I have yet to attend or mix a live musical event with only a flown sub configuration that had both the coverage AND the impact I’ve come to expect from a concert-quality audio system.”
Asked the same question, Brown cuts straight to the point. “Flying your subs will cost you more in time and money,” he says, “and you’ll get less out of your speakers. Don’t fly your subs.”
To read the L-Acoustics AES Convention paper on flown subs, go to: https://www.aes.org/e-lib/browse.cfm?elib=19777.
