How SOWND Certification Works

SOWND Certification is a performance-based standard for inclusive, conversational acoustic comfort. It exists because the built environment is overwhelmingly designed for the acoustically typical - one in three people can't reliably hold a conversation in the spaces we design, build, and operate, not because the acoustics haven't been considered, but because there has been no consistent way to prove they have.

Certification translates existing acoustic metrics - reverberation time and background noise - into clear, client-facing evidence that a space meets a baseline of conversational comfort for noise-sensitive occupants, including people with hearing loss, ADHD, autism, and other sensory sensitivities.

Certification is issued at three tiers:

Bronze - Acoustic Foundations. The acoustic environment has been verified at completion against human-centred thresholds. This is the starting point.
Silver - No-Drift Operations. Operational practices are in place to maintain that acoustic performance day-to-day, not just at handover.
Gold - Distinctive Experience. The full end-to-end experience - acoustic, visual, service, communication - is optimised for comfort, choice, and reliable participation.

Bronze certifies one thing specifically: that the space meets a baseline of reverberation control and background-noise control in the speech frequency range (500–2000 Hz) appropriate to its declared use type. It does not define statutory occupancy limits, replace building-regulation requirements, or guarantee comfort under all operating conditions.

The current framework version is Bronze V1.0 (2026).

Who Verifies a Certification

Every SOWND certification is reviewed by an independent acoustic consultant against the framework's threshold criteria. Verification is not self-declared.

The SOWND Certification Framework is maintained in partnership with the Institute of Sound and Vibration Research (ISVR) at the University of Southampton. Current certifications are reviewed by:

Dr Daniel Lurcock - CEng, MIOA

Principal Consulting Engineer, ISVR Consulting, University of Southampton

Acoustic reports submitted for certification are reviewed against the thresholds and methodology described below. The assessor confirms whether the evidence supplied - typically post-installation measurements or validated predictive data - meets the Bronze pass criteria for each space and its declared use type.

Scope & Sampling - What Gets Certified

A SOWND certification applies to a defined set of spaces within a venue. It does not, by default, apply to the entire building.

Each certification lists:

Total spaces at the venue - how many spaces exist in the scope the client asked to be considered.
Spaces assessed - how many of those spaces were measured or modelled and submitted for review.
Space-level outcomes - each assessed space is marked individually as Verified Pass, Verified Fail, Not Applicable, or Pending.

A venue's tier (Bronze, Silver, Gold) reflects the outcome for the assessed spaces. Where only a sample of spaces has been assessed, that is stated plainly on the certification so that visitors, clients, and specifiers can see exactly what has and has not been verified.

Bronze is intended for unamplified conversational environments and informal gathering zones. It is not applied to - and is not a substitute for - sound insulation/privacy assessment (DnT,w / Rw), façade/environmental noise compliance, or amplified-sound management.

Methodology

Bronze is performance-based. A space is awarded Bronze when it meets both the reverberation and background-noise thresholds for its declared use type, confirmed by evidence that has been reviewed by the independent assessor.

There are two routes to that evidence.

Performance-measured route

Post-installation acoustic measurements taken by the project acoustic consultant and submitted in the standard Stage 3 / Stage 4 acoustic report. Bronze is confirmed by cross-referencing the reported Tmf and NR / LAeq values against the threshold table.

Pre-validated Design Route

Where an approved design-and-installation procedure has been applied in accordance with its design intent, the treated space may be awarded Bronze without additional post-install acoustic assessment. Approval of a design route is based on the robustness of the design and installation process - including the prediction approach, the inherent acoustic performance of the system, installation reliability, and quality control.

The first approved design route is SonaSpray acoustic finishes (Oscar Acoustics) specified by the project acoustic consultant. Responsibility for confirming product type, thickness, coverage, and detailing remains with the project acoustic consultant. Additional approved routes are being added.

Bronze remains performance-based under either route: approved design routes do not preclude alternative acoustic solutions capable of meeting the same thresholds.

What's Measured

Bronze draws on two primary acoustic quantities:

Reverberation time (Tmf)

The arithmetic mean of reverberation time across the 500 Hz, 1000 Hz, and 2000 Hz octave bands. This is the speech frequency range, and controlling reverberation here is the single biggest lever on conversational clarity.

Background noise (NR / LAeq)

Expressed as an NR rating (preferred) or LAeq, for steady-state internal noise. This typically covers building services and ambient noise, not amplified sound or transient events.

Measurements are taken in unoccupied conditions in line with standard acoustic reporting practice, so that the verified performance reflects the space's inherent design rather than one specific day's activity.

Where provided, octave-band data (125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz) is included in the full report for transparency. STI (Speech Transmission Index) and acoustic capacity are not required for Bronze V1.0; they will be introduced progressively in V2.0 as the modelling roadmap matures.

Pass / Fail Thresholds

A space passes Bronze when it meets both the reverberation threshold and the background-noise threshold for its declared use type. If one metric is absent (for example, at an early reporting stage), Bronze may be stated as provisional pending confirmation.

Space type (Bronze scope)	Tmf (500–2000 Hz)	NR	LAeq
Restaurant / Café	≤ 0.80 s	≤ 35	≤ 40 dB
Bar / Informal gathering	≤ 0.70 s	≤ 40	≤ 45 dB
Open-plan office / Co-working	≤ 0.60 s	≤ 35	≤ 40 dB
Meeting room / Cellular office	≤ 0.50 s	≤ 30	≤ 35 dB
Training / Seminar room	≤ 0.60 s	≤ 30	≤ 35 dB
Healthcare waiting area	≤ 0.60 s	30–35	35–40 dB
Atrium / Circulation (used for gathering)	≤ 0.80 s	≤ 40	≤ 45 dB
Auditorium / Lecture (informal gathering zones)	≤ 0.70 s	30–35	35–40 dB

Where Bronze sits against established guidance

Thresholds are drawn from established acoustic standards for education, healthcare, and office spaces, then selectively extended to a wider range of conversational and gathering spaces that are typically left uncontrolled.

Restaurant / Café - aligned with best-practice reverberation guidance (~0.7–0.9 s).
Meeting rooms, training rooms, healthcare waiting areas - aligned with BS 8233, BB93, and HTM 08-01 guidance.
Open-plan offices - more demanding than typical BCO guidance (NR 35 vs. NR 38–40).
Atria, circulation, and gathering zones - a novel application. These spaces are rarely governed by statutory limits; Bronze introduces a consistent conversational-performance expectation where none previously existed.

The thresholds are intentionally conservative. They are designed to identify spaces that meet a baseline of inclusive conversational usability - not to define acoustic excellence.

Review & Recertification

A SOWND certification is not a one-time stamp. It is kept live through an annual review cycle.

Annual desktop review

Each year, the acoustic measurement evidence for the certified space(s) is reviewed to confirm no material changes have occurred. Where no valid measurement data is available, an in-person measurement is commissioned.

Triggered physical re-assessment

Certification is re-assessed in person if there are significant alterations to room layout, acoustic treatment, or building use that could affect the certified performance.

Bronze in-person inspection

Bronze also includes an in-person inspection prior to certification issuance, to confirm that the acoustic treatment has been installed as designed and that the physical plaque and QR-code placement are in order.

Every certification carries a clear Valid Until date and an Annual Review Due date, both visible on the venue's cert page.

Standards Context & Governance

Bronze thresholds are aligned with, and derived from, established acoustic and inclusion standards:

BS 8233:2014 - Guidance on sound insulation and noise reduction for buildings.
BB93 (2015) - Acoustic design of schools: performance standards.
BCO Guide to Specification (2019) - British Council for Offices.
HTM 08-01 (2013) - Acoustics, Health Technical Memorandum series.
PAS 6463:2022 - Design for the mind: neurodiversity and the built environment.
ISO 3382-1:2009 - Measurement of room acoustic parameters.

Bronze is differentiated not by inventing new acoustic limits, but by applying consistent conversational-performance expectations across sectors and to space types that are typically unregulated.

Framework governance

The SOWND Certification Framework is maintained by Sownd Affects in partnership with ISVR Consulting, University of Southampton. Current framework version: Bronze V1.0 (2026).

Each certification page records the framework version, the measurement standard applied, the assessment route used, and the assessor's name and credentials, so that the basis of every certificate is fully traceable.

What Bronze certification is not

It is not a statutory occupancy limit.
It is not a replacement for fire, building-regulation, or licensing requirements.
It is not a guarantee of comfort under all operating conditions - particularly where amplified sound is introduced or occupancy exceeds design assumptions.
It is not coverage of sound insulation, privacy (DnT,w / Rw), façade noise, or environmental noise compliance.