Office acoustics fails in three different ways: the meeting room is not private, the open desk is too loud, or the café echoes. Each one has a different metric and a different fix. Treating "acoustics" as one problem is the most common reason a fit-out reads beautiful and works badly.
Three numbers worth knowing
- STC (Sound Transmission Class) — how well a wall stops sound passing through. Higher is better. Aim for STC 35–40 in standard meeting rooms, 45+ in client rooms, 50+ in board rooms or HR rooms.
- NRC (Noise Reduction Coefficient) — how much sound a surface absorbs. Aim for ≥ 0.85 NRC on collaboration ceilings; ≥ 0.95 in cafés and lobbies.
- RT60 (Reverberation Time) — how long a sound persists in a room. Cafés should sit at 0.6–0.8 seconds; open-plan office floors at 0.5–0.7 seconds.
Where the spec usually slips
Glass partitions on meeting rooms are the most common slip. A standard 10mm glass partition runs STC 30–32; that is not private. To get STC 38+, you need double-glazing with a 12mm air gap, or laminated acoustic glass, plus a rubber-gasketed door with a drop-seal at the bottom. Without the door treatment, the wall does not matter.
Open-plan acoustics is a pattern, not a product
No single product will fix open-plan noise. The fix is a layered set: high-NRC ceiling, carpet floor, freestanding acoustic baffles every 20–30 m², soft furniture in social zones, and a deliberate "quiet zone" of focus desks separated from the collaboration spine. Skipping any layer cancels the others. We have walked into too many offices where someone bought £40,000 of acoustic baffles and forgot the carpet.
Quick test: walk the office
Two practical tests for an existing office. Stand in a meeting room with the door closed; have a colleague speak normally outside. If you can hear what they are saying, the STC is failing the brief. Stand in the open-plan zone at 11 a.m.; clap once. If the clap takes longer than 0.7 seconds to die, your reverberation is failing.
A working spec for a 10,000 sq ft office
- Open desk ceiling: NRC ≥ 0.85, mineral fibre with deep grid suspension.
- Meeting room walls: STC 38, double-glazed where glazed, with rubber-gasketed doors.
- Café: NRC ≥ 0.95 ceiling, fabric-wrapped acoustic panels on at least one wall.
- Quiet rooms / focus pods: STC ≥ 45 envelope, white noise system tuned to mask residual leakage.