Soundvision: Subwoofer Design Guide 4 of 8

Reference: SV-SUBS-01. Placement, cardioid configuration, arc spacing, and the physics that actually governs sub pattern control — the part of a design most people either over-trust or under-think.

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Placing & Visualizing Coverage

Add the sub source and reposition it in real time while watching the coverage pattern update — this is faster than guessing a position and recalculating repeatedly. When judging the visual coverage pattern, look at it near your actual operating range (e.g. around 60Hz) rather than at whatever frequency the software defaults to — a near-omni-looking pattern at a much lower reference frequency can hide real decisions you still need to make. Check the realistic mount height against the stage edge — subs modeled floating above where they'd actually sit will show coverage that doesn't match what gets built. Some current Soundvision versions can calculate tops and subs together rather than switching views back and forth — use that if it's available to you; otherwise just be deliberate about checking both.

Cardioid: Custom vs. Preset

The L-Acoustics cardioid preset is a fixed, closed configuration — reliable, but you can't adjust how much rear reduction vs. front output you're trading off. A custom cardioid (split into a forward-facing group and a separate reversed-polarity, delayed rear-facing group) gives manual control over the pattern — you can dial toward more supercardioid (tighter rear null, less front gain) or more standard cardioid depending on what the room needs. Trade-off to expect: the preset tends to have a flatter reduction curve across frequency; a well-tuned custom setup can gain a couple of dB more front output and a bit more rear reduction, at the cost of needing to actually tune the delay/polarity split yourself (by ear or measurement) rather than trusting a fixed recipe.

The Common Mistake: Aiming Subs Like They're Directional

Don't physically toe subs inward "at" the stage hoping to clear low end off it. Subs are non-directional at this scale — angling them that way, then mirroring with symmetry, more often ends up concentrating low end onto center stage instead of clearing it. Straight, un-toed subs with a correctly configured cardioid pattern generally clear the stage more effectively than physical aim does — check a probe at the stage position itself, not just out in the audience, to confirm which approach actually reduces stage-level low end.

Arc Spacing & Delay-Steering

Don't chase an exact "frequency" for a sub arc's radius — in practice a sub arc is delay-steering applied across a curved layout, not a tuned resonant shape. Rule of thumb on spacing: keep the spacing between adjacent sub elements inside roughly what a half-wavelength at your upper operating frequency allows — L-Acoustics' own guidance is not to exceed about that spacing. Practically: for an 80Hz upper limit, keep element spacing under about 2m (~6ms); for a 60Hz limit, under about 2.8m. Go wider and you risk a side-lobe/null appearing inside your actual passband, not just above it. A tighter, closer-radius arc gives a more even result with less steering per element; a wider spread gives more steering control but a higher chance of holes. Use the model to pick a starting layout, then confirm/adjust the actual delay values by ear or measurement on site — this is not a fully calculable step.

Element Count & the LF Pattern (Physics)

More sub elements narrow the array's low-frequency pattern, but not in a clean, uniform way — as you add elements, expect the pattern to alternate between control and momentary loss of control at specific frequencies as you cross phase-cancellation nulls, not a smooth continuous narrowing. Check several discrete frequencies across your actual sub operating band individually, not just one representative frequency — a layout that looks great at one frequency can show a standing null a third of an octave away. "Longer array = more low-frequency control" is a half-truth — array length helps, but you have to know the actual phase relationships between elements at each frequency to know whether a given length is helping or has pushed you past a null into the next lobe.

Back Lobe & Corner Check

Even a well-configured cardioid array isn't a hard zero behind it — check what's actually happening at the ceiling and in rear corners specifically, not just the general rear coverage. Corners multiply. A rear lobe that lands directly in a hard corner can gain roughly 9dB from the corner's boundary reinforcement alone — in the worst case, louder there than the main PA is at the audience. Always check corners explicitly if the room has one near the array.

Ground + Flown Sub Time-Alignment

If you're running both flown and ground subs, they need their own explicit delay relationship — don't assume they're aligned just because both are time-aligned to the tops individually. Expect the correct split to be somewhere in a working range (on the order of 10–15ms difference between ground and flown is a realistic starting neighborhood, not a rule) rather than one exact number — find it by comparing the combined coverage map with the delay swept through that range, and confirm on site by ear/measurement.

Source: adapted from a purchased L-Acoustics Soundvision video tutorial series. Rewritten and condensed into a quick-reference workflow in Ryan's own words from the source material.