As open-plan offices have become the norm, one question keeps coming up from facility managers: "The office is fairly quiet — so why can't employees concentrate?"
The issue is not 'noise level' but 'Speech Intelligibility'. The quieter the environment, the more clearly a neighbour's phone call or conversation cuts through — raising cognitive load and destroying focus. This is known as a Speech Privacy problem.
Sound masking is often presented as the universal fix. Without a proper acoustic diagnosis first, however, installing it alone can make things worse.
The ABM Framework: Absorb + Block + Mask
The internationally recognised approach to solving office acoustic problems is the ABM (Absorb-Block-Mask) framework. Each element plays a distinct role, and leaving any one out prevents a complete solution.
ABSORB — Reduce reflection on walls and ceilings to lower reverberation (RT60). Materials: PET absorbers, melamine foam, wood-wool boards.
BLOCK — Physically stop sound transmission to adjacent spaces. Materials: carpet tile, partitions, desk screens.
MASK — Cover residual speech intelligibility with engineered background noise. System: Soft dB Sound Masking.
Warning: Sound Masking Alone Can Backfire
There is a common misconception that sound masking (SM) is a cure-all. In reality, installing SM without diagnosing the room's acoustic condition can make the problem worse.
SM works by injecting a uniform background noise (pink-noise spectrum) into the space to reduce the STI (Speech Transmission Index). For this mechanism to operate correctly, two preconditions must be met:
- The masking sound must be uniformly distributed throughout the space
- The masking sound itself must not be affected by reverberation
In spaces with high reverberation time (RT60) — reverberant, untreated rooms where RT60 > 0.8 s — three problems arise:
1. Energy Build-up
The acoustic energy from SM speakers reflects repeatedly off walls, ceilings, and floors. Direct sound plus reflected sound stack up, producing a perceived noise level 5–10 dB above the intended target (40–48 dBA).
2. Spectral Distortion
When the SM masking curve (200 Hz–5 kHz) overlaps with the room's resonant frequencies (room modes), certain bands are amplified and the result degrades into an unpleasant 'hum'.
3. Loss of Spatial Uniformity
The core requirement of SM is to maintain a uniform background noise within ±2 dB across the entire space. High reverberation causes large position-to-position SPL variations — some seats become too loud, others receive no masking benefit at all.
The Correct Sequence: Absorption First, Masking as the Final Layer
Within the ABM framework, A (Absorb) is a prerequisite for M (Mask). This is not merely a matter of 'better results' — it is a technical necessity: without absorption, M simply does not work properly.
Absorption only · SM only · Absorption + SM — same room, different outcome
Outcomes in a reverberant open-plan office (4 metrics). ◆ = recommended state.
| 기준 | 흡음만 (Absorb only) | SM 만 (Mask only) | 흡음 + SM (ABM) |
|---|---|---|---|
| RT60 (reverberation) | 0.5–0.7 swithin target | 1.0 s+unchanged | 0.5–0.7 sWELL v2 met |
| STI (intelligibility) | 0.55–0.65fair, no privacy | unpredictabledistortion | 0.35–0.45privacy met |
| Perceived noise | neutralflat | +5–10 dBenergy build-up | comfortable (40–45 dBA)WELL v2 met |
| Speech Privacy | partialclearer, not private | can backfireunpredictable STI | fully metASTM E1130 pass |
Absorptive treatment creates the acoustic environment in which SM can operate precisely — by reducing the proportion of reflected sound, SM only needs to mask the direct sound, allowing it to run at a lower level (40–45 dBA) with accurate zone-by-zone control.
Why Expert Consulting Is Essential: The Tornex Approach
Installing speakers is not the end of the job. A sequential process of Diagnosis → Absorption → SM Design is mandatory, and Tornex guarantees correct installation through the following five-step workflow:
① On-site Measurement
We obtain RT60, background noise level, and floor plan data — conducting professional measurements as a registered acoustic measurement firm.
② 3D Simulation
We use the treble.tech 3D acoustic simulator to map current STI. Pre/post absorption and pre/post SM results are compared visually.
③ Absorption Design
Optimised placement of PET acoustic panels, melamine foam, and wood-wool board. Target RT60 ≤ 0.6 s.
④ SM Design
Zone layout, speaker spacing, and masking curve configuration for the Soft dB system.
⑤ Post-installation Verification
We confirm RT60 change, STI, and SM uniformity with measured data, then fine-tune as required.
This process has been validated repeatedly through Tornex's consulting experience. Ad-hoc installation backfires — only a diagnosis-driven, sequential approach produces the right outcome.
Global Deployments
The Soft dB sound masking system — developed on over 30 years of acoustic expertise based in Canada — is installed and operating in thousands of facilities worldwide.
What does my space need — ABM priority decision
Reverberant meeting / hall / reception
RT60 > 0.8s, low clarity
Speech bleeds through walls
Low STC, neighbor speech audible
Open office — too clear + privacy needed
Quiet but conversations heard
Symptom clear, cause unclear
Complaints high, no data
Legal / HIPAA / financial counsel
Privacy Index ≥ 95% required
ABM application by space type
Soft dB sound masking — 30 years of Canadian acoustic engineering, deployed in thousands of facilities worldwide.
| 기준 | 공간 유형 | 주요 과제 | ABM 적용 | 기대 효과 |
|---|---|---|---|---|
| Open-plan office | Open-plan | Speech noise → focus loss | Ceiling PET + carpet + SM | STI < 0.4 → privacy |
| Near meeting room | Adjacent meeting | Confidential leak | Wall abs + partition + directional SM | Confidential speech protected |
| Medical facility | Medical | Patient privacy | Exam-room absorption + SM | HIPAA-level privacy |
| Financial institution | Financial | Counsel confidentiality | Counter absorption + directional SM | Transaction info protected |
FAQ — Sound Masking and Acoustic Design
Q1Why can sound masking alone cause the opposite effect if installed without absorption treatment first?
Q2What is the ABM framework in office acoustic design?
Q3How do I know if my office needs sound masking?
Q4What is Speech Privacy and how is it measured?
Q5Can sound masking replace absorption panels?
Glossary
- SM (Sound Masking) — A system that injects an engineered uniform background noise (pink-noise spectrum) via ceiling speakers to reduce speech intelligibility (STI).
- ABM Framework — Absorb → Block → Mask. The internationally recognised framework for acoustic design in open-plan offices.
- RT60 (Reverberation Time) — The time (in seconds) for sound pressure to decay 60 dB after a source stops. Recommended ≤ 0.5 s for open workspaces (WELL v2).
- STI (Speech Transmission Index) — Speech intelligibility on a 0–1 scale. ≥ 0.6 = clear for meetings; < 0.45 = reduced intelligibility; < 0.20 = Confidential.
- AI (Articulation Index) — Syllable recognition rate on a 0–1 scale; adopted by ASTM E1130. AI < 0.2 = Confidential, AI < 0.05 = Inaudible.
- PI (Privacy Index) — PI = (1 − AI) × 100%. PI ≥ 95% = Confidential. The standard metric for office speech privacy.
- dBA / NC — dBA = A-weighted sound pressure level (corrected for human hearing sensitivity). NC = Noise Criteria curve rating. SM recommendation: NC 40 (≈ 44 dBA).
- STC (Sound Transmission Class) — Sound isolation rating for walls, doors, and glazing. General office partition: STC 40–45; confidential meeting room: STC 50+.
- ISO 3382-3:2022 — Standard for acoustic measurement in open-plan offices. Octave bands 125 Hz–8 kHz, spatial decay of speech, STI, and comfort distance.
- ASTM E1130-16 — Standard for objective measurement of speech privacy in open offices. Based on AI (Articulation Index).
References
The standards, figures, and recommended values in this article can be verified in the following primary sources.