Overview
The sound lock is the acoustic buffer that protects VO Live (B304, NC-12 target). Entry to VO Live is through the buffer spine corridor (Wall W5, STC 55) and Door D3 (STC 45). The buffer volume decouples the VO booth from the adjacent Control Room (B311, NC-18 target), so the talent microphone is shielded from equipment noise during recording sessions.
D2 deleted (Rev2) — Control uses external D5. The former Control-side buffer door (D2) is removed; the Control Room is now entered by its own dedicated external door (D5, south wall). The sound lock is therefore a single acoustic door (D3) working with the decoupling buffer volume: sound must cross the buffer and pass through D3 before reaching VO Live, and the buffer’s W5 walls (STC 55) plus the D3 door leaf together carry the isolation.
Sound Lock Diagram
CONTROL ROOM (B311) BUFFER SPINE VO LIVE (B304)
NC-18 target Corridor NC-12 target
entered via external D5 (D2 deleted Rev2)
┌─────────────────┐ ┌──────────────────┐ ┌─────────────────────┐
│ │ │ │ │ │
│ Equipment │ │ 15 cm wide │ │ Talent mic │
│ noise sources │ │ acoustic buffer │◄──►│ position │
│ (monitors, │ │ │ D3 │ │
│ computer, │ │ W5 walls both │ │ NC-12 requires │
│ Apollo x4) │ │ sides (STC 55) │ │ maximum isolation │
│ │ │ │ │ │
└─────────────────┘ └──────────────────┘ └─────────────────────┘
◄────── W5: STC 55 ──────► ◄── D3: STC 45 ──►
VO LIVE ISOLATION PATH: buffer decoupling volume (W5, STC 55) + D3 (STC 45)
Control is entered by its own external door D5 (STC 50), south wall.
Components
Sound Lock Elements
Door & Wall Schedule
| Element | Type | STC Rating | Dimensions | Notes |
|---|---|---|---|---|
| D3 | Acoustic door | 45 | 80 × 220 cm | VO/Control partition → swings north into VO Live [AC] |
| W5 | Buffer spine wall | 55 | 15 cm width | Both sides of buffer corridor |
D2 deleted (Rev2) — Control uses external D5. The former Control-side buffer door is removed; only D3 serves the VO Live sound lock.
Isolation Chain
Isolation Path
How the Sound Lock Protects VO Live
Sound traveling toward VO Live must cross the decoupling buffer volume and then pass through Door D3:
| Barrier | STC | Role |
|---|---|---|
| Buffer spine walls (W5, both sides) | 55 | Buffer boundary: carries the isolation around the decoupling volume |
| Buffer air gap (15 cm corridor) | — | Decoupling volume: breaks the direct vibration path |
| D3 — acoustic door (VO/Control partition) | 45 | Final barrier: attenuation before VO Live |
Real-world performance depends on flanking paths, seal quality, and the buffer volume. With D3 properly sealed and no flanking leaks, the buffer volume plus the STC 55 W5 walls and the STC 45 D3 leaf hold the VO Live noise floor at its NC-12 target.
Key principle: The buffer air gap decouples D3 from the surrounding structure. The door frame shares no common stud or structural member with the adjacent partitions. This prevents vibration short-circuiting the isolation.
Clearances & Geometry
Buffer Spine Dimensions
Critical Measurements
| Parameter | Value | Source |
|---|---|---|
| Buffer spine width | 15 cm | x = 213.6 to x = 228.6 (DXF) |
| Buffer spine X start | 213.6 cm | DXF verified |
| Buffer spine X end | 228.6 cm | DXF verified |
| D3 location | VO/Control partition (Wall W6) | North of buffer |
| D3 clear width | 80 cm | Door schedule |
| Door height | 220 cm | Door schedule |
| Ceiling height | 275 cm AFF | SSOT |
Swing clearance: D3 swings north (away from the buffer) into VO Live — it must not swing INTO the buffer corridor. The former Control-side door D2 is deleted (Rev2); Control is entered by external D5.
Operational Sequencing
Recording Protocol
The Cardinal Rule: Keep D3 Closed During Recording [AC]
The sound lock only provides its full isolation when D3 is closed. Holding D3 open during a take creates a direct acoustic path from the buffer/Control zone into VO Live, defeating the isolation and exposing the talent microphone to equipment noise.
Entry Procedure (Control/buffer → VO Live)
- Confirm recording is paused or talent is aware of entry
- Step through the buffer corridor to D3
- Open D3 (step into VO Live) — move through promptly
- Close D3 fully behind you — verify seal engagement
Exit Procedure (VO Live → Control/buffer)
- Open D3 (step into the buffer corridor)
- Close D3 fully behind you — verify seal engagement
- Return through the buffer to the Control zone
Do NOT: Hold D3 open during recording sessions. Do NOT prop the door open with wedges or stops. Do NOT remove the door closer — it ensures automatic seal engagement.
Recommendation: Install a visual indicator (e.g., “RECORDING” light) at the buffer entry to remind operators to keep D3 closed during takes. [HP]
Seal Requirements
Door Sealing System
D3 Requires
| Seal Type | Location | Purpose |
|---|---|---|
| Perimeter compression seals | All four edges of door frame | Block airborne sound at jamb, head, and threshold edges |
| Automatic drop seal (mortise) | Bottom of door leaf | Seals the gap between door bottom and threshold when door closes [AC] |
| Acoustic threshold | Floor at door position | Provides a flat, smooth surface for drop seal to press against |
| Magnetic or cam-lift gaskets | Frame perimeter (optional upgrade) | Increases seal compression force for higher STC performance |
Critical: A 1 mm gap around an acoustic door can reduce its effective STC by 10–15 dB. Seal integrity is the single most important factor in door performance.
Seal Maintenance
- Inspect compression seals monthly for wear, cracking, or compression set
- Test drop seals by sliding paper under closed door — paper should not pass
- Replace seals immediately if any degradation is found
- Lubricate drop seal mechanism annually
Installation Notes
Construction Sequence
Sound Lock Installation Order
- Complete buffer spine wall framing (W5 both sides) and insulation [AC]
- Install the door frame for D3 — frame must be mechanically isolated from the surrounding partitions (no shared studs)
- Seal frame-to-wall junction with acoustic sealant (continuous bead, no gaps)
- Hang the door leaf — verify swing clearances
- Install perimeter compression seals on all frame edges
- Install the automatic drop seal on the door leaf
- Install the acoustic threshold — must be level and smooth
- Adjust the door closer for reliable, complete closure
- Test: close the door and inspect all edges for light leaks (light = sound leak)
Hold Point: After installation, perform a light-leak test on D3. Shine a torch from one side while the room is dark on the other side. Any visible light indicates a seal failure that must be corrected before proceeding. [HP]
Do NOT: Share frame members between D3 and adjacent partitions — this creates a structural flanking path. Do NOT use standard (non-acoustic) door hardware. Do NOT omit the drop seal — the floor gap is the most common failure point.
QC Checklist
Verification
Sound Lock Acceptance Criteria
- D3 frame isolated from adjacent partitions — no shared structural members [AC]
- D3 closes fully and latches without assistance
- Perimeter seals compress visibly when the door closes
- Drop seal deploys and retracts smoothly
- Light-leak test: no visible light around any closed door edge [HP]
- Paper test: paper cannot slide under the closed door
- Door swing verified: D3 north (into VO Live), clear of the buffer corridor
- D2 deleted (Rev2) — confirm Control is served by external D5
- Buffer spine walls (W5) continuous and sealed top to slab
- Frame-to-wall acoustic sealant continuous on D3
Acceptance: Sound lock is accepted when all items pass and the light-leak test shows zero leaks on D3.