## Why Low Frequencies Are Omnidirectional — and Why That Changes Everything
At frequencies below roughly 100 Hz, the wavelength of sound in air exceeds three metres. A subwoofer cabinet is physically small relative to that wavelength, which means it cannot direct low-frequency energy the way a high-frequency horn controls treble. The low end radiates in all directions simultaneously. This is not a flaw in design — it is physics.
The practical consequence is significant: wherever you place a subwoofer, you are also placing energy behind it, beside it, and above it. In a venue with hard reflective surfaces — concrete floors, brick walls, low ceilings — those omnidirectional reflections return to the audience as reverberant energy that muddies the low end, reduces punch, and makes it harder to perceive clarity in the bass register.
Placement, therefore, is not about where the sound goes. It is about where it does not go.
## The Four Primary Placement Strategies
**Ground stacking** is the most common approach in touring and rental contexts. Subwoofers are placed directly on the floor at the front of the stage. The floor acts as a reflective boundary, increasing bass output by up to 6 dB relative to free-field through acoustic coupling. This is efficient but offers no directional control — low frequencies radiate rearward toward the stage and into the side fills just as readily as they radiate toward the audience.
**Flown subwoofers** eliminate floor coupling entirely. Energy that would otherwise reinforce low frequencies from the ground reflection is lost, but the system becomes more consistent across the vertical listening plane. Flown subwoofers are common in permanent installs where even coverage is prioritised over raw output efficiency. The structural load requirements are considerable.
**FOH cluster** configurations position subwoofers at or near the front-of-house mix position, often in a central groundstack. The long throw distance means the low end arrives at the front of house in phase with the main system, but the rear of the venue — directly behind the subs — receives significant energy. This can be problematic for broadcast positions or open-air events where rear radiation is undesirable.
**Cardioid subwoofer arrays** represent the most technically demanding strategy, and the most effective for directional low-frequency control.
## How Cardioid Arrays Work
A cardioid sub array uses destructive interference to cancel rear-directed low-frequency energy. The principle is straightforward: if two equal-amplitude sound waves meet 180 degrees out of phase, they cancel. The challenge is manufacturing that phase relationship at the rear of the array without disrupting the front.
The most common cardioid configuration uses three subwoofers: two facing forward and one reversed (physically rotated 180 degrees, facing rearward). The reversed cabinet is delayed by an amount equal to the time it takes sound to travel the distance between it and the forward-facing cabinets — typically in the range of 2 to 6 milliseconds depending on cabinet depth — and its polarity is inverted.
The result: at the front of the array, all three cabinets contribute constructively. At the rear, the reversed cabinet's direct output is in phase with the forward cabinets' rear radiation, but the delayed and inverted signal creates the destructive interference required for cancellation. A well-executed cardioid array achieves 12 to 18 dB of attenuation at the rear compared to the front — a substantial reduction that directly translates to reduced stage wash, reduced spill into broadcast areas, and a cleaner mix environment.
Timing precision is not optional in this configuration. The delay figure must be matched to the actual physical offset of the reversed cabinet to within a fraction of a millisecond. Even small errors in delay time erode cancellation dramatically. Use a measurement system — not guesswork — to verify rear attenuation once the array is configured.
## Room Modes and Why You Must Measure Them
In any enclosed space, standing waves — room modes — build up at frequencies whose wavelength is a simple integer fraction of a room dimension. In a room 15 metres long, a strong mode will appear around 11 Hz and its harmonics. These modes create peaks and nulls across the room that no amount of EQ will fully resolve, because EQ applies globally while modes are spatially specific.
Measuring room modes before system tuning requires a calibrated measurement microphone, a measurement platform, and multiple measurement positions across the listening area. The goal is to identify which frequencies are building up, where the peaks and nulls are worst, and — critically — whether repositioning the subwoofers can shift the modal pattern to a more even distribution.
Minor repositioning of subwoofers — even by half a metre — can meaningfully alter where modal reinforcement occurs. This should always be explored before reaching for a graphic EQ.
## The Correct Order of Operations
This is the most frequently violated principle in subwoofer deployment:
1. **Placement** — get the cabinets in the right position and orientation first
2. **Time alignment** — align the subwoofers to each other, then to the full-range system
3. **Crossover** — set the crossover frequency and filter order
4. **EQ** — correct measurable deviations from flat, not perceived tonal preferences
5. **Limiting** — protect the transducers
Attempting to EQ out a problem that placement would have solved is a waste of DSP headroom and frequently makes the system harder to control at high drive levels. Every boost applied at the subwoofer crossover frequency is a request for more amplifier power and more excursion from the driver — headroom you will want when the show is at full level.
SSOUNDS designs its subwoofer systems with cardioid-capable configurations in mind: the cabinet depth, sensitivity, and DSP integration parameters are documented to give system engineers the precise delay values, polarity assignments, and level trims needed to execute cardioid deployment without approximation. When the physics are this demanding, your engineering partner should make the numbers available before the doors open.