Whether designing a sound system for a tour, festival or installation, the audio mixer and system engineer have many options when it comes to main and sub array design and implementation.
When considering sub bass loudspeakers, should they be flown or ground stacked? If flown, should they be located right next to the mains, behind the mains, or somewhere between the main and side arrays? Should a cardioid configuration be implemented?
As much as we try to put together the “perfect” PA system, these decisions are often made without the audio team having much to say about it. Set design, weight and sight lines (and oh yes… budget) can be contributing factors in what can be flown, and what must be ground-stacked.
Assuming none of these factors constrict the mixer and system engineer’s decision making, there are still many things to consider in designing the most powerful, coherent sound system suited to the engineer and artist’s desires. Let’s dive in!
Flown Or Ground Sub Arrays?
In other words, where do you want the boom? One benefit of flown sub bass loudspeakers is that the entire flown system covers the full spectrum of frequencies while emanating from the same point in space. With ground-stacked subs, there can be problems with varying arrival times of overlapping low frequencies depending on where you’re sitting in the audience in relation to the flown and ground speakers. With the subs flown next to the mains, varying arrival times are less likely or at least minimized.
For example, people sitting in the 10th row directly in front of one side of the ground subs will probably experience their energy arriving earlier than the flown main arrays. Conversely, people in the second tier of an arena are more than likely physically closer to the flown main arrays, so that energy will arrive at their ears first.
So, it leads to this question: At what location in the room do we choose as the spot to time-align the main loudspeakers to the subs when the subs are on the ground? The funny thing is that there’s really no “right” spot. It’s going to be slightly “off” everywhere except for the position where you timed it, so don’t sweat it. For the record, often my choice of location is the aisle just off center at front of house because it’s the most central part of the coverage when in an arena, but it’s not dead center.
Another thing to consider is how much signal should be sent to the sub bass loudspeakers, as well as whether it’s an artist and audience that appreciates being pummeled throughout the performance. For Metallica fans, this probably isn’t a problem, but a Sarah McLachlan audience may feel differently about it.
Flown subs reduce the distance differential from loudspeakers to audience so that everyone in the venue experiences a more even sub bass level. Ground-stacked subs have the advantage of coupling with the floor for some added horsepower, but the added “thump” will be strongest on the venue floor and not make it higher up in an arena. This may be what the mix engineer wants and insists on, however, even though it may not be the best thing for the overall audience experience.