This is particularly important in arenas, where flying the subwoofers puts the upper, more distant audience sections in the middle of the array’s beam.
The benefit is particularly noticeable at the sides of the stage.
Flown left and right stacks of directional subwoofers. A few directional designs are now on the market, with these boxes using phase cancellation to produce microphone-like directional patterns - cardioid and hypercardioid, mainly.
Using directional subwoofers can help reduce the wave interference problems of the flown left-right array described just above.
If the woofers are directional AND if they’re aimed correctly, then there won’t be as many places in the audience that can hear both stacks at the same time, and interference will be less.
To get the desired effect, however, they must be pointed significantly off stage.
If not, both sides will still be almost equally loud everywhere, and there will still be just as much interference as with conventional subwoofers.
Figure 4 shows what happens with two flown stacks of cardioid woofers pointing straight ahead. There’s less coming off the back, but lobing is bad.
Figure 4: Flown cardioid woofers, no toe-out.
In contrast, Figure 5 demonstrates the outcome of flying those same cardioid subwoofers, with each stack pointed 30 degrees offstage.
Figure 5: Flown cardioid woofers, 30 degree toe-out.
Lobing is reduced, although still significant. Unfortunately, front-to-back rejection is almost non-existent.
Still, it’s a lot better than conventional subwoofers flown left-right. I haven’t explored many different aiming scenarios for rigs like this, but I’m fairly certain there’s room for improvement.
For example, hypercardioid subwoofers would probably work better than the cardioid ones modeled here.
Flown single stack. This configuration positions a single stack of subwoofers somewhere above center stage, usually near the downstage edge. It’s my favorite bass configuration.
Figure 6 tells a lot of the story. Coverage is very uniform and there’s no lobing at all.
Figure 6: Flown single stack.
A great feature of this approach is that for typical array sizes (12 feet to 16 feet high), there is a null 90 degrees off axis at about 55 Hz.
This means that the stage doesn’t get blasted with sub-bass energy. Artists usually like this, and television producers love it.
Unfortunately, many productions can’t accommodate a line of subwoofers hanging in the middle, which is space often reserved for lighting or video.
Sometimes it’s possible to hang the subwoofers higher up, above the other stuff.
If the stack is wide (two subwoofers wide instead of one), the pattern will narrow, especially at the upper end of the sub-bass range.
To fly or to stack? Yes, that is the question!
Often it depends on the act, your taste, the production budget and other factors.
Sonically, stacked bass has a solid, heavy quality with lots of punch, especially at the house mixing position. Flown bass has an airier, more melodic quality.
One potential issue with flown bass is floor bounce. This is a problem that mainly occurs in arenas.
When bass bounces off a floor, reflections arrive at the seats (especially the upper seats) much later than the direct waves from the subwoofers, which causes time smear.
The effect is quite noticeable in empty rooms, less apparent when the floor is covered with people.
With bass flown in two stacks, time smear between stacks is a constant problem, unless directional subwoofers are used properly, as I’ve illustrated here.
Vertical coverage, especially at the sides of the stage, is definitely less of a problem with flown bass.
Jeff Berryman served as the director of Jasonaudio, a touring sound company based in Canada, and is a senior scientist with Electro-Voice.