Soundvision: Fills, Delay Lines & Time-Alignment Guide 5 of 8

Reference: SV-FILLS-01. Once the main hang and subs are solid, fills and delay lines are what actually even out the room — and every one of them needs its own delay set against the system it's filling in for, not just a position.

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Placing a Fill (Front Fill / Outfill)

Mute the main PA, then initialize/optimize the fill on its own — you want to solve its coverage in isolation before worrying about how it blends with the main system. Check against real rigging constraints, not just the theoretical optimum — a position the software likes but that's physically impossible to hang isn't a usable answer. Review the SPL hit points. If coverage is uneven, consider breaking the fill into more individual amp channels (the same logic as amp assignment on the main hang) rather than accepting a flatter but less-controlled result.

Delay-Align a Fill to the Main PA

Switch to delay mode and place a probe at the crossover zone between the main PA and the fill. Read the time offset directly off the probe, then apply that delay to the fill group so it arrives after (not before or exactly with) the main system at that position. Verify with polarity, not just delay. Unmute both sources together and confirm the combined level goes up relative to either alone. If it drops instead, something's out of polarity — fix that before trusting the delay value.

Sub-Center vs. Sub-Left/Right — A/B It Directly

Build both layouts in the same session (copy/paste the sub group, reposition one copy as split left/right) so you can mute between them and compare rather than judging from memory. Name every probe by exact position (e.g. "S center 3", "K1 left") as you place them — with several sub configurations open at once it gets easy to lose track of which reading is which. Sub-center tends to be the more even, "democratic" option across the full width of the audience. Sub-left/right is usually heavier for people standing closer to either side, and needs the same polarity/delay checks as any split system. Factor in practicality, not just the SPL map — a center-flown sub cluster isn't always something the venue or rigging plan can actually support, in which case the "better" option on paper isn't the real option.

Ground Front Fills & Flown Subs Behind the PA

Space ground front fills at a regular interval across the stage width (e.g. roughly every 2m for a typical stage) rather than eyeballing gaps — then adjust the end positions since the stage usually isn't perfectly centered on the PA's aim line. If flown subs behind the PA are a real option (rigging permitting), position and mirror them with the symmetry tool the same way you would a main hang — set X/Y/Z position once on one side and mirror rather than re-placing by hand. Compare with/without every fill and delay group toggled to confirm each one is actually contributing (adding coverage or level) rather than just adding complexity to the session.

Documenting the Result

For a clean summary view, average the SPL map across a representative frequency range (roughly 125Hz–10kHz is a reasonable broadband summary) rather than presenting a single narrow-band snapshot. Take walkthrough screenshots at this stage for client/production documentation — it's much faster to capture these once the design is settled than to reconstruct the view later.

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.