A permanent sound system,
built into the hall.

Section 2

Why engineering is audible in this room.

A hall this big, with a hard ceiling and a wood floor, is loud when empty. Sound bounces back and forth long after the source has stopped — the technical name is reverberation time. In an empty Oakland Expo hall it measures around 5.83 seconds. That's long enough that the start of one word overlaps with the end of the previous one. Words run together. Speech becomes mush.

Bodies absorb sound. A typical banquet (~800 seated) brings the reverb tail down to ~4.3 seconds. A full Eid prayer crowd (~2,000 people) brings it to ~3.45 seconds. Even occupied, this is a long-reverb room — well past the threshold where intelligibility breaks down with a poorly-distributed system.

The delay-and-echo problem at this scale

The other failure mode is delay between speakers. Sound travels about 1.13 feet per millisecond. If a speaker 80 feet farther away fires at the same moment as a near one, you hear the same word twice, ~70 ms apart. Past ~30–40 ms, the brain perceives an echo and intelligibility collapses. The fix is per-row delay zoning — each row of speakers is held back so its output arrives in sync with the natural wavefront from the stage. Without it, distributed systems in long rooms sound like a slap-back echo chamber.

Section 4

The recommended approach.

Distributed audio on the venue's existing structural columns. Two speakers per column, mounted at 14 ft above finished floor, aimed down at the audience plane. A small equipment rack at the head-end holds the amplifiers (for the passive option) or just the DSP and Dante switch (for the powered option). One DSP, configured for four stage orientations (north-end, south-end, long-wall-east, in-the-round), handles all delay zoning. Operators select the stage orientation on a touchscreen — the system reconfigures every speaker in one tap.

Section 8

Mounting & downtilt — a deliberate decision.

Speakers mount at 14 ft above finished floor (AFF), two per column, oriented back-to-back to cover both halves of the bay. At 14 ft, with audience ear-height at 5 ft and the worst-case half-bay of 23 ft, the geometric downtilt is ~11° below horizontal.

The choice of 14 ft is deliberate: low enough for short throws into the audience (better direct-field, less reverberant pickup), high enough to clear typical event sightlines (12-ft stage backdrops, head-tables). A lower mount (10-12 ft) would give better intelligibility but risks blocked views; a higher mount (16-20 ft) would lengthen the throw and shallow the downtilt, increasing reverberant contribution.

Section 12 · Pricing engine

The numbers — full breakdown.

Prices are Sweetwater list as of the most recent fetch. Live re-verification will run at order time (Sweetwater's bot-protection currently blocks automated price checks; final invoice prices may shift by ≤2%). The Sugar IT commission line is shown explicitly at $0 — normally 5%, waived for this client.

Option B (Passive 70V) — headline

Sweetwater fetch status: automated price fetching is currently blocked (HTTP 403 — vendor bot protection). Obai will re-verify each line item against his Sweetwater account before the purchase order is cut. Any line that has moved by more than ±2% will be re-quoted before commitment.

Section 14

The canopy — portable kit, separate scope.

The attached 148'×124' canopy is semi-outdoor with very few columns to mount on. It's also used less frequently than the main hall. For Eid 2026 and ongoing day-to-day, the recommendation is a small portable kit on stands — a pair of QSC K12.2 full-range speakers + a subwoofer + tripod stands + a 4-channel mixer. Total ~$3,200 (included in the bill of materials above).

A permanent canopy install — weatherized speakers, dedicated zones, structural mounts — is flagged as a separate future engagement, contingent on a site survey of canopy structure and conduit pathways. We don't price it here because we don't know the answers yet.

Section 18 · Appendices

Full worked math.

Appendix A · Reverberation time (Sabine)

RT60 = 0.049 × V / A. Volume V = 260.5 × 239.1 × 20 = 1,245,300 ft³.

RT60 empty = 0.049 × 1,245,300 / 10,836 = 5.83 s.

Add 800 seated × ~3.5 sabins = 2,800 sabins → 13,636 sabins → RT60 banquet = 4.34 s.

Add 2,000 Eid × ~3.5 sabins = 7,000 sabins → 17,836 sabins → RT60 Eid = 3.45 s.

Appendix B · Critical distance

Dc = 0.141 × √(Q × R). For Q=6, occupied hall: Dc ≈ 43 ft.

Beyond 43 ft from a centralized speaker, reverberant field dominates; adding SPL doesn't improve intelligibility. Only distribution does. Math behind "distributed beats centralized."

Appendix C · SPL at the far corner

Worst-case half-bay diagonal: 23 ft horizontal × 9 ft vertical = 24.7 ft slant.

Direct-field falloff: −20 × log₁₀(d/1m) = −17.5 dB at 24.7 ft.

Option A (DZR12-D 133 dB SPL cont @ 1m): 133 − 17.5 = 115.5 dB single-speaker.

Option B (CBT 70J-1 121 dB SPL @ 1m): 121 − 17.5 = 103.5 dB single. Back-to-back pair +3 dB → ~106 dB. Reverberant tail +3 dB occupied.

Appendix D · Delay per zone

Speed of sound 1.13 ft/ms. Bay 39.5 ft → per-bay delay 35.0 ms. Haas bias 12 ms.

DSP holds four such delay maps (one per stage orientation). Preset recall retunes every zone.

Appendix E · Output bus count

7 zones × 4 orientations = 28 + 1 sub + 1 canopy + 4 aux = 34 buses.

Q-SYS Core 110f: 128 channels with sub-ms per-output delay — comfortably exceeds requirement.

Appendix F · Coverage geometry

Each column: 2 speakers back-to-back, 90° each = 180° per pair around the column. Vertical 60° at 11° downtilt aims on-axis peak at half-bay listener (5 ft ear, 23 ft horizontal). Adjacent columns share bay edges with ≈3 dB overlap — headroom ensuring no listener falls outside an on-axis cone.

Section 20

About Obai.

Six marquee credits — not a resume.

Email obai@obaisukar.com · Sugar IT