How to Design an Acoustic Meeting Room That Passes WELL v2 First Time

68% of meeting rooms in modern office buildings fail at least one acoustic criterion when tested against WELL v2 Feature 74 — not because the standards are unreasonably strict, but because acoustic design is treated as an afterthought rather than a design discipline. The typical failure pattern: an architect specifies a visually appealing exposed concrete ceiling, the HVAC engineer sizes ductwork for thermal performance without considering acoustic noise, and nobody calculates RT60 until a WELL assessor requests the data at commissioning. By that point, remediation costs three to ten times what design-stage treatment would have cost.

This guide presents a complete acoustic design process for meeting rooms, from the earliest concept decisions through post-construction verification. It follows the sequence that professional acoustic consultants use, with a worked example based on a 20-person meeting room that must pass WELL v2 Feature 74.

Start With Room Proportions, Not Materials

Acoustic performance begins with room geometry. Before selecting a single acoustic product, establish three geometric parameters that constrain every subsequent decision.

Volume

Room volume determines the total absorption required to achieve a given RT60. Per the Sabine equation (ISO 3382-2:2008 §A.1):

A_required = 0.161V / T60_target

A larger room needs proportionally more absorption. A 20-person meeting room at 90 m³ (V = 7.5 m × 4.0 m × 3.0 m) needs A = 0.161 × 90 / 0.6 = 24.2 m² Sabine to achieve RT60 ≤ 0.6 s. The same room at 120 m³ (2.7 m ceiling height in a deeper floor plate: 8.0 m × 5.5 m × 2.7 m) needs A = 0.161 × 120 / 0.6 = 32.2 m² — 33% more absorption from a room with only 20% larger ceiling area.

Room Proportions

Rooms with ratios close to 1:1:1 (cubic) produce strong modal resonances at specific frequencies, creating uneven bass response. The optimal proportions for speech rooms are approximately 1.0 : 1.4 : 1.9 (height : width : length), based on Bolt's room ratio recommendations. These ratios distribute room modes more evenly across the frequency spectrum, reducing the severity of individual resonances.

For a 3.0 m ceiling height, the recommended width and length ranges are:

• Width: 3.0 × 1.4 = 4.2 m (minimum practical width for a 20-person meeting room)
• Length: 3.0 × 1.9 = 5.7 m (minimum practical length)

Ceiling Height

A higher ceiling increases room volume (requiring more absorption) but also increases the distance from the acoustic ceiling to seated ear height (1.2 m), reducing the first-reflection energy from the ceiling. For speech intelligibility, early reflections from the ceiling are beneficial — they reinforce the direct sound path. A ceiling at 2.7 m gives a path length from source mouth (1.5 m standing) to ceiling to receiver ear (1.2 m seated) of approximately 4.0 m. At 3.5 m ceiling height, this path increases to approximately 5.8 m, arriving later and contributing less to clarity.

The practical range for meeting room ceiling heights is 2.7–3.2 m. Above 3.2 m, the ceiling absorption has diminishing returns for speech clarity, and below 2.7 m the room feels oppressive and HVAC distribution becomes constrained.

The Ceiling: Your Primary Absorber

In a typical meeting room, the ceiling provides 60–75% of the total acoustic absorption. The ceiling is the largest unobstructed horizontal surface, it faces the primary speech direction (upward from seated talkers), and it can accept thick, high-performance absorbers without sacrificing usable floor or wall space.

Ceiling Selection Criteria

Cavity depth is critical for low-frequency performance. The same ceiling tile tested at 200 mm cavity will show α₁₂₅ ≈ 0.30, while at 400 mm cavity it may reach α₁₂₅ ≈ 0.55. At 50 mm cavity (common in refurbishment projects with limited ceiling void), α₁₂₅ may drop to 0.10. This is a 5.5× difference at the frequency most responsible for "boomy" meeting rooms.

The Exposed Ceiling Problem

Exposed concrete soffits are architecturally fashionable but acoustically catastrophic for meeting rooms. A bare concrete ceiling has α ≈ 0.02 across all frequencies — it absorbs almost nothing. A meeting room with an exposed concrete ceiling, carpet floor, and plasterboard walls will have RT60 of 1.5–2.5 seconds, making speech unintelligible beyond 3 metres and rendering video calls unusable.

If the architect insists on an exposed ceiling, the acoustic budget must shift entirely to walls and suspended elements (rafts, baffles, or clouds). This costs two to three times more than a suspended ceiling solution for the same RT60 outcome, and the low-frequency performance is almost always worse because wall-mounted panels lack the cavity depth available in a ceiling void.

Wall Treatment: Targeted, Not Total

Most meeting rooms do not need full wall treatment. The ceiling and carpet floor provide sufficient broadband absorption for RT60 compliance. Wall treatment serves two specific purposes:

1. Flutter echo control: Parallel reflective walls less than 8 m apart can produce flutter echoes — a rapid series of reflections that creates a metallic "buzz" on hand claps. Treating one wall of each parallel pair with a panel having α ≥ 0.50 at 500–4000 Hz eliminates flutter. Treatment area: 25–40% of one wall per pair.

1. Bass absorption supplement: If the ceiling cavity is shallow (< 150 mm) and bass RT60 exceeds the target, wall-mounted mineral wool panels with a 100 mm air gap provide resonant absorption at 100–300 Hz. Treatment area: 3–6 m² per room.

The Over-Treatment Trap

Rooms with RT60 below 0.25 s feel uncomfortable for speech. Conversations sound effortful because the lack of reflections reduces the natural reinforcement that speakers rely on for vocal feedback. Meeting participants unconsciously raise their voices, increasing fatigue and reducing meeting effectiveness. A meeting room is not a recording studio — some reverberation is desirable.

Target RT60 for a meeting room is 0.3–0.6 s at 500–2000 Hz. Below 0.3 s is over-treated. Above 0.6 s risks WELL F74 failure and degraded video call quality.

Worked Example: 20-Person Meeting Room

Room Specification

• Dimensions: 8.0 m × 5.0 m × 3.0 m
• Volume: 120.0 m³
• Total surface area: 2(40) + 2(24) + 2(15) = 158.0 m²
• Occupancy: 20 people (boardroom table arrangement)
• Target: WELL v2 Feature 74 Part 1 — RT60 ≤ 0.6 s (500–2000 Hz average)
• HVAC target: Background noise ≤ 35 dBA (NC-30)

Surface Schedule and Absorption

Total Absorption and RT60 Calculation

WELL F74 Check (500–2000 Hz average): (0.419 + 0.318 + 0.281) / 3 = 0.339 s — Pass (≤ 0.6 s)

The room passes with margin. The acoustic ceiling alone, combined with carpet, delivers compliance without any wall treatment. The RT60 at 125 Hz is 0.790 s, which exceeds the mid-frequency values by a factor of 2.3× — this room will have noticeable bass reverberation. If subjective quality matters (it does for video calls), consider adding 4–6 m² of wall-mounted mineral wool panels with 100 mm air gap to bring the 125 Hz RT60 below 0.6 s.

Adding Occupants

Twenty seated adults contribute approximately 10 m² Sabine of additional absorption at 500–2000 Hz (approximately 0.5 m² Sabine per person). This reduces the occupied RT60 at 1000 Hz from 0.318 s to approximately 0.276 s. The WELL measurement standard specifies "furnished, occupied conditions" — meaning the occupied RT60 is the compliance value, not the empty-room measurement.

HVAC Noise Specification

The NC-30 Target

For enclosed meeting rooms, WELL Feature 74 Part 2 requires background noise ≤ 35 dBA. Achieving this requires specifying the HVAC system to NC-30 or lower at the diffuser outlet.

Specify the following in the MEP brief:

• Fan coil units: NC-25 at rated duty (manufacturer data per AHRI 885)
• Diffuser face velocity: ≤ 2.0 m/s for supply, ≤ 1.5 m/s for return
• Flexible duct connections: Minimum 600 mm between rigid ductwork and terminal units to isolate vibration
• Silencers: On supply and return branches serving meeting rooms, rated for IL ≥ 15 dB at 250–2000 Hz
• Duct cross-talk: Verify that ductwork connecting adjacent rooms does not provide a flanking path with TL < 35 dB

The "Last Tuesday" Test

HVAC noise varies with load. A system designed for NC-30 at peak cooling may be NC-20 at part load and NC-35 during the building's overnight conditioning cycle when dampers open for free cooling. WELL measurements should be taken during typical occupied conditions — not the quietest or loudest operating point. Specify that the building management system log operating mode during acoustic testing.

Video Call Acoustics: Beyond the Standard

WELL v2 Feature 74 does not explicitly address video call quality, but meeting rooms where video calls produce complaints consistently have the same acoustic signature: RT60 above 0.5 s combined with early reflections from the table surface arriving at microphone height (typically 0.8–1.0 m on a conference phone or laptop).

For rooms where video calls are the primary use:

• RT60 target: ≤ 0.4 s (500–2000 Hz average), which is stricter than WELL's 0.6 s
• Table surface: Felt or fabric desk pad to reduce table reflections (α ≈ 0.30 vs α ≈ 0.02 for bare MDF)
• Microphone position: Ceiling-mounted beamforming microphones reject reflected sound more effectively than table-mounted units, but they require the ceiling to be reflective in the microphone's pickup zone — creating a design conflict with the acoustic ceiling

Design Checklist

The Cost of Getting Room Design Right

Designing acoustic performance into a meeting room at schematic design adds approximately £800–£2,000 per room to the acoustic consultant's fee. The treatment cost (acoustic ceiling, carpet, limited wall panels) is £2,000–£5,000 per room for a standard meeting room.

Retrofitting a meeting room that fails WELL F74 costs £8,000–£25,000 per room: ceiling replacement (£3,000–£8,000), wall panel installation with finishing (£2,000–£6,000), HVAC noise remediation (£3,000–£10,000), re-measurement (£1,500–£3,000), and WELL reassessment fee (£3,000–£5,000). The retrofit path costs four to eight times more and delivers a worse result, because retrofit solutions are constrained by existing services, finishes, and floor-to-ceiling heights.

Design it once. Design it right.

Related Reading

• How to Pass WELL v2 Feature 74 First Time — the complete 8-step process from concept to WELL Online submission
• WELL v2 Feature 74 Decoded — every clause, every threshold, every calculation
• The 8-Step Acoustic Design Process — the general workflow from brief to handover