Acoustic Diffusion in Open-Plan Offices

1) Project overview: what, where, who, and why

In early 2025, SonusGearFlow was brought into a retrofit project for a 9,600 sq ft (about 892 m²) open-plan office on the 6th floor of a refurbished warehouse building in Austin, Texas. The tenant was a 120-person product and engineering company that had outgrown a quieter suite and moved into a visually striking, mostly hard-surfaced floorplate: polished concrete slab, exposed brick perimeter walls, glass-fronted meeting rooms, and an open ceiling with painted steel deck at 13 ft (4 m).

The stakeholders included the facilities project manager (client-side), the architect of record, the MEP consultant, and our team: an acoustical consultant, a systems tech for measurement logistics, and a project manager focused on installation coordination. The “why” was straightforward: the office looked great but performed poorly. Staff complaints centered on speech privacy, distraction in heads-down zones, and fatigue from “constant chatter.” HR had a measurable retention concern, and leadership wanted an acoustic solution that preserved the open, collaborative feel without turning the space into a grid of cubicles.

The initial request from the client was specifically to “add diffusion.” They had read about diffusion in studios and assumed it was the missing ingredient. Part of our job was to validate where diffusion would help, where it would not, and what combination of absorption, scattering, zoning, and masking would deliver the outcome they actually needed.

2) Challenges and requirements at the outset

The baseline conditions were typical of open-plan offices with modern finishes: high reflectivity in the speech band (500 Hz–4 kHz), long decay times for a non-audio space, and line-of-sight propagation across work zones. We were asked to improve perceived comfort without making the office “dead,” and without obstructing daylight or sprinklers. The client also had strict constraints:

Operational constraint: Work could only occur evenings and weekends; no more than two consecutive weekends of disruptive work.
Budget constraint: Hard cap of $85,000 for materials and installation (excluding design/consulting).
Aesthetic constraint: Exposed ceiling must remain visible; no full ceiling grid.
Code/MEP constraint: Maintain sprinkler coverage, avoid HVAC throw interference, and meet fire rating requirements (ASTM E84/Class A where required).
Performance goals: Reduce perceived speech distraction in heads-down zones, improve speech privacy at focus booths, and reduce overall reverberant character.

During kickoff, we clarified measurable targets that could be checked post-install:

Reverberation: Reduce RT60 (midband average) from ~0.95 s to ~0.55–0.65 s in open areas.
Speech clarity vs. privacy balance: Reduce long-range intelligibility without compromising local conversation. Practically, we targeted improved spatial decay and reduced “reach” of speech across zones.
Noise control: Keep mechanical background consistent (NC 35–40) and introduce controlled sound masking to stabilize the sound field once reflections were addressed.

3) Approach and methodology chosen

We treated the project as an acoustics retrofit, not a studio build. Diffusion was included, but only as one tool. The methodology combined:

Baseline measurements to quantify decay and identify dominant reflection paths.
Hybrid treatment strategy: broadband absorption for decay control; diffusion/scattering to reduce harsh flutter and “specular” slap between glass and brick; and zoning elements to break up propagation.
Sound masking tuned to speech privacy goals once the room acoustics were stabilized.

Measurement and documentation used practical tools appropriate for an occupied office:

Room EQ Wizard (REW) for impulse response capture and RT estimates.
A calibrated USB measurement mic (miniDSP UMIK-1) for speed and repeatability.
A handheld SPL meter (Class 2) for spot checks and masking verification.
Balloon pops and starter pistol as simple impulse sources for quick comparative checks (we used balloon pops after-hours due to building rules).

We also reviewed the architectural plan for sightlines, collaboration hotspots (stand-up tables, kitchenette), and focus zones (engineering rows, phone booths). Instead of distributing diffusion randomly, we placed it where it would intercept strong lateral reflections and help maintain a natural sound field after absorption reduced the overall decay.

4) Step-by-step execution narrative

Week 1: Baseline survey and measurements

We performed measurements on a Tuesday night from 7:30 pm to 11:00 pm when the office was empty but HVAC was running at typical nighttime settings. The open floor was divided into five measurement zones: heads-down work area (north), collaboration area (center), kitchenette (southwest), corridor spine, and the glass meeting-room frontage.

Baseline findings:

RT60 (500 Hz–2 kHz): 0.90–1.05 s in open zones; highest near glass frontage.
Flutter echo: Strong between the 54 ft glass run and opposing painted drywall at 14–18 ft spacing.
Speech propagation: Conversations at the kitchenette were intelligible 60–70 ft away in the heads-down area, especially along the corridor spine.
Background noise: NC 32–34 at night; daytime rose to NC 38–40 with more HVAC load and occupancy.

Week 2: Design development and mock-up

We presented a treatment plan with three layers:

Ceiling-hung absorption baffles over the most reflective open zones to reduce mid/high decay.
Diffusion/scattering elements on select wall segments to reduce harsh reflections and keep the room from feeling acoustically “flat.”
Sound masking to provide consistent ambient sound level and reduce speech intelligibility at distance.

The client was wary of heavy visual changes. To de-risk aesthetics and performance, we built a small mock-up over a 20-desk section using four ceiling baffles and two wall-mounted diffusers. The mock-up ran for one workweek. Feedback from that zone was immediate: fewer “zingy” reflections and less distraction from passing conversations. That feedback unlocked approval for the broader install.

Weeks 3–4: Procurement and coordination

Lead times drove the schedule. PET felt baffles were available in 2–3 weeks; custom wood diffusers were 4–5 weeks. To meet the two-weekend disruption window, we chose stock-finish diffusers and standard baffle sizes.

Coordination tasks included:

Sprinkler contractor sign-off for hanging locations and clearances.
MEP check for supply diffusers (air) to avoid short-circuiting throws.
IT coordination for sound masking controller placement and network access (the client wanted monitoring on the facilities VLAN).

Weekend 1: Overhead absorption installation

Friday night, a two-person lift crew and one lead installer laid out ceiling baffles with laser lines to maintain consistent spacing and avoid the “random art” look. We installed 72 PET felt baffles, each 48 in x 12 in x 1 in (1220 x 305 x 25 mm), suspended at 10.5 ft above finished floor to preserve sightlines and lighting distribution. Spacing averaged 24 in on center in the densest zone and 36 in on center elsewhere.

We concentrated baffles above:

The heads-down work rows (largest area, most complaints).
The corridor spine (to reduce long-path reflections).
The collaboration hub (to reduce overall “loudness buildup” without killing energy).

Weekend 2: Diffusion, partial wall treatment, and masking rough-in

Diffusion went primarily on the glass-frontage sidewalls and on a brick segment opposite the kitchenette. We installed 18 two-dimensional QRD-style diffusers, each 24 in x 24 in x 4 in (610 x 610 x 100 mm) in a prefinished birch veneer. These units were selected for broad scattering in the upper midrange (roughly 800 Hz and up), where speech reflections were most objectionable. We avoided deep one-dimensional diffusers because they protruded too far into circulation paths.

In addition, we added 10 fabric-wrapped broadband absorber panels (48 in x 24 in x 2 in, mineral wool core) in targeted locations where diffusion alone would have been counterproductive—namely, the direct reflection points opposite the most active talk zones. The goal was to prevent “ping-pong” reflections across the glass and the corridor.

For masking, we used a networked sound masking system with 32 plenum-rated emitters hung above open zones, grouped into four zones. We ran power and control cabling during Weekend 2 but delayed final tuning until post-install measurements confirmed the revised acoustic baseline.

Week 5: Commissioning, tuning, and post measurements

After installation, we repeated measurements in the same five zones at similar times. We also performed a walking speech test: one talker at normal voice (about 60–62 dBA at 1 m) at the kitchenette, while an evaluator noted intelligibility at set distances along the corridor and into heads-down zones.

5) Technical decisions and trade-offs made

The biggest trade-off was correcting the initial misconception that “diffusion fixes open offices.” Diffusion can reduce specular reflections and flutter, but it does not reduce overall sound energy the way absorption does, and it does not stop direct-path speech. In an open-plan office, intelligibility at distance is the enemy; diffusion alone can sometimes make the space feel subjectively louder by spreading energy more evenly.

Key decisions:

Absorption first, diffusion second: We used ceiling baffles as the primary RT control. Without that, diffusion would have been treating symptoms while leaving long decay intact.
Diffusion placement: We placed diffusers where we had confirmed flutter or strong lateral reflections. We did not place diffusers behind talkers in the kitchenette; scattering there would have increased spread into adjacent zones.
Shallow diffusers: 4 in depth balanced performance with corridor safety and aesthetics.
Masking after acoustic treatment: Masking is easier to tune when the room is not excessively live. We targeted a masking level around 44–46 dBA in open areas, adjusted by zone based on user feedback and measured background.
Material choices for compliance: PET felt and mineral wool panels met the required flame spread ratings, and hanging hardware was selected to satisfy the building engineer’s requirements for seismic restraint (even though Austin is low seismic, the landlord required safety cabling).

6) Results and outcomes with specific details

Post-install measurements showed consistent improvement:

RT60 (500 Hz–2 kHz): Reduced from ~0.95 s average to ~0.60 s average across open zones. The glass frontage zone dropped from 1.05 s to 0.65 s.
Flutter echo: Previously audible claps and balloon pops produced a distinct flutter between glass and drywall; after diffusion plus targeted absorption, the flutter was no longer perceptible in the same locations.
Spatial decay / speech reach: In the walking speech test, intelligibility of kitchenette speech dropped from “clearly understandable” at ~60 ft to “intermittently understandable” at ~45–50 ft, with masking engaged bringing it further down to “mostly unintelligible” beyond ~40–45 ft along the corridor line.
Perceived comfort: The heads-down area reported fewer distraction events, especially during peak lunchtime. The collaboration area remained usable without a “muted” feeling; people still described it as lively, but not sharp.

Timeline and budget performance were also tracked:

Design + measurement: 2 weeks (including mock-up).
Procurement: 3–4 weeks lead time (overlapped with design sign-off).
Installation: Two weekends, plus one weekday night for commissioning.
Installed cost: $82,400 (materials + labor). Rough breakdown: baffles $31k, diffusers $21k, wall absorbers $9k, masking system $18k, misc hardware/lifts $3.4k.

7) Lessons learned and what could be done differently

Several practical lessons emerged:

Mock-ups prevent aesthetic-driven rework: The one-week pilot zone avoided a late-stage debate about visual impact and reassured leadership that the space would not look like a recording studio.
Diffusion needs a reason: The most effective diffusers were those aimed at known flutter paths. In zones where the main issue was direct speech transmission, diffusion offered little value compared to absorption and masking.
HVAC and masking interact: On one particularly warm day, higher airflow raised background noise to NC 42 in the collaboration hub; the masking level that felt right at NC 38 felt too strong. If we were doing it again, we would log HVAC noise over a full week before final masking targets.
Zoning could be stronger: We improved comfort without changing furniture layout. If the client allowed minor layout shifts, adding two 6 ft-high (1.8 m) partial-height bookshelf partitions perpendicular to the corridor would have reduced line-of-sight propagation further, likely allowing a lower masking level.

8) Takeaways applicable to other projects

Start with measurement, not assumptions: Even simple impulse response captures and consistent zone measurements can prevent misapplied treatments.
In open offices, absorption does the heavy lifting: Use ceiling baffles/clouds to reduce RT in the speech band; it’s the fastest path to perceptible improvement.
Use diffusion tactically: Apply it to eliminate flutter and harsh specular reflections, especially between glass and parallel hard surfaces. Avoid scattering energy out of loud zones into quiet zones.
Masking works best after the room is controlled: Treat reflections first, then add masking for privacy and consistency. Tune by zone and validate with real walk tests.
Plan for operations: Two-weekend installs are achievable if procurement choices align with schedule and if sprinkler/HVAC coordination is handled early.
Define “success” in plain terms: Pair numbers (RT60, background level) with operational outcomes (how far speech carries, where focus work is feasible).

The end result wasn’t a silent office—nor should it be. It was an open-plan environment where conversations stayed local, sharp reflections were tamed, and the acoustic character supported both collaboration and focus. For project managers, the most replicable insight was sequencing: quantify the problem, reduce decay with overhead absorption, apply diffusion where it solves a specific reflection issue, and only then tune masking to meet privacy goals without overcorrecting.