Meeting Room Echo on Video Calls — The £800 Fix That Takes One Weekend

85% of corporate meeting rooms have an RT60 above 0.6 seconds — the maximum recommended by WELL v2 Feature 74 for rooms used for speech communication. The consequence is audible on every video call: the far-end participants hear your voice wrapped in a reverberant haze that makes you sound like you are speaking from the bottom of a stairwell. The echo canceller in your conferencing system cannot fix this. It was never designed to. And the £2,000 ceiling microphone array you installed to "improve audio quality" is picking up the room reflections with even greater fidelity, making the problem worse.

The fix is acoustic treatment — specifically, adding enough sound-absorbing surface area to bring the RT60 below 0.5 seconds. For a typical 4-person meeting room, this costs approximately £800 in materials and takes one weekend to install. Here is the exact specification.

Why Meeting Rooms Sound Terrible on Video Calls

Meeting rooms are small, hard-surfaced boxes. A typical 4-person room measures 4m × 3m × 2.7m — a volume of 32.4 m³ enclosed by approximately 68 m² of surface area. These surfaces are almost universally reflective:

• Ceiling: Plasterboard or suspended mineral tile (the cheaper, non-acoustic variety with α ≈ 0.10)
• Walls: Painted plasterboard (α = 0.02–0.05)
• One glass wall: Most meeting rooms in modern offices have at least one glass partition or window wall (α = 0.04–0.06)
• Floor: Carpet tile on concrete (α = 0.15–0.30 at 500 Hz — the one saving grace)
• Table: Hard laminate or veneer (α ≈ 0.05)
• Monitor/TV: Hard plastic/glass (α ≈ 0.02)

Why Echo Cancellers Cannot Fix This

This is a critical distinction that most IT departments do not understand. Video conferencing echo cancellers solve acoustic echo — the phenomenon where the far-end audio plays from the room's speakers, bounces off the walls, re-enters the microphone, and is transmitted back to the far end as an echo of their own voice.

What echo cancellers do NOT solve is room reverberation — the reflections of the near-end speaker's own voice. When you speak in a reverberant meeting room, your voice hits the walls, ceiling, and glass, and the reflected energy returns to the microphone along with your direct voice. The echo canceller has no way to separate the direct speech from its reflections because both originate from the same source (you). The far end hears everything: your voice plus the room.

This is why investing in better microphones, better speakers, or more expensive conferencing hardware does not solve the problem. A £3,000 ceiling microphone array in a reverberant room captures reverberant audio with more microphones. The quality of the capture is higher. The quality of the room is unchanged.

Worked Example: A 4m × 3m Meeting Room

Room Specification

• Length: 4.0 m
• Width: 3.0 m
• Height: 2.7 m
• Volume: 4.0 × 3.0 × 2.7 = 32.4 m³
• One long wall: floor-to-ceiling glass partition (4.0 × 2.7 = 10.8 m²)
• Three remaining walls: painted plasterboard
• Ceiling: standard plasterboard
• Floor: carpet tile on concrete
• Furniture: 1 meeting table (2.4m × 1.2m), 6 mesh-back task chairs

Surface Areas and Absorption at 500 Hz

Current RT60

Using the Sabine equation per ISO 3382-2:2008 §A.1:

RT60 = 0.161 × 32.4 / 6.04 = 0.86 seconds

This is 43% above the WELL v2 Feature 74 maximum of 0.6 seconds and 72% above the 0.5 seconds recommended by video conferencing manufacturers. On a Zoom or Teams call, the far end hears a distinct reverberant tail on every word, and the STI (Speech Transmission Index) per IEC 60268-16:2020 §4 drops from approximately 0.75 (good) in a well-treated room to approximately 0.55 (fair) — the threshold where word intelligibility begins to suffer.

With 6 occupants present (each contributing approximately 0.5 sabins), the absorption increases to 9.04 sabins and RT60 drops to 0.58 seconds — marginal compliance when the room is full, but above target when only 1–2 people use the room for a video call (the most common scenario).

Target

RT60 ≤ 0.5 seconds (all occupancy levels, including single-occupant video calls)

A_required = 0.161 × 32.4 / 0.5 = 10.43 sabins

Current absorption (empty room, worst case): 6.04 sabins. Absorption deficit: 4.39 sabins.

Treatment Specification

50mm polyester felt panels (recycled PET, fabric-faced) with NRC ≥ 0.80 and α = 0.85 at 500 Hz.

Panels required: 4.39 / 0.85 = 5.16 m² — specify 6 m² to provide a 15% design margin.

Panel Placement (Priority Order)

1. Ceiling cloud — 3 m² (1 panel, 1.5m × 2.0m)

A single rectangular panel suspended 100–150mm below the plasterboard ceiling, centred directly above the meeting table. This addresses the strongest first reflection path (voice → ceiling → table → microphone) and is the single most impactful treatment in the room.

Mounting: 4 stainless steel eye bolts into ceiling joists, steel wire or aircraft cable, with 100mm stand-offs. The air gap behind the panel improves low-frequency absorption by moving the panel away from the pressure antinode at the rigid ceiling boundary.

Absorption added: 3.0 × 0.85 = 2.55 sabins

2. Rear wall panel — 2 m² (2 panels, each 1.0m × 1.0m)

The wall directly opposite the display screen/camera. This surface receives and reflects speech energy from all participants facing the screen. Two 1.0m × 1.0m panels mounted at seated head height (centre at 1.2m above floor) with 25mm air gap behind.

Absorption added: 2.0 × 0.85 = 1.70 sabins

3. Glass wall treatment — 1 m² (acoustic curtain or film)

The glass partition is the most problematic surface because it cannot accept panel mounting. Two options:

• Option A: Acoustic curtain (heavy, multi-layered fabric, α ≈ 0.55 at 500 Hz) across the lower half of the glass wall (1.0m × 1.0m section). Cost: £60–£100.
• Option B: Micro-perforated acoustic film applied to the glass (α ≈ 0.30–0.50 at 500 Hz depending on product). Less effective but invisible. Cost: £80–£150.

Absorption added: 1.0 × 0.55 = 0.55 sabins

After Treatment: Verification

RT60 = 0.161 × 32.4 / 10.53 = 0.50 seconds

Target achieved. With occupants present (adding 0.5–3.0 sabins depending on count), RT60 drops further to 0.39–0.47 seconds — comfortably within the target range regardless of how many people are in the room.

Cost Breakdown

The Weekend Installation Plan

This treatment can be installed by one person with basic DIY skills in approximately 4–5 hours. Two people can complete it in 3 hours.

Tools Required

• Cordless drill with 6mm masonry and 3mm pilot bits
• Spirit level (or phone app)
• Tape measure
• Pencil
• Step ladder (for ceiling work)
• Screwdriver (Phillips #2)

Day 1 (Saturday morning, 3 hours)

Hour 1: Ceiling cloud

1. Mark the ceiling for 4 eye bolt positions, evenly spaced to support the 1.5m × 2.0m panel
2. Drill into ceiling joists (use a stud finder) and install eye bolts
3. Attach aircraft cable to panel frame corners using crimps
4. Hang panel, adjust cable lengths until panel is level at 100–150mm below ceiling

1. Mark wall at 1.2m centre height for each panel
2. Install Z-clip upper halves on wall (4 fixings per panel into plasterboard — use toggle anchors if no studs)
3. Attach Z-clip lower halves to panel backs
4. Hang panels

1. Install curtain track on the ceiling or wall above the glass partition
2. Hang acoustic curtain panel
3. Adjust to cover the designated 1.0m section

Day 2 (Sunday morning, 1 hour): Verification

Perform a clap test in the treated room with the door closed. The reverberant tail should be noticeably shorter — a crisp "clap-stop" rather than the "clap-ringggg" of the untreated room.

For precise measurement, use AcousPlan's mobile measurement tool or a free app like REW to capture the impulse response and compare the before and after RT60 values across octave bands.

Make a test video call. Ask the far-end participant to assess the audio quality. The most common feedback after treatment is: "You sound much closer" or "It sounds like you are in a studio." The reverberant haze is eliminated and the direct-to-reverberant ratio improves dramatically.

The Frequency Dimension: Why 50mm Panels Are Sufficient for Meeting Rooms

Speech occupies the frequency range of approximately 125–8000 Hz, with the critical information concentrated between 250 and 4000 Hz. The modulation frequencies that determine speech intelligibility (and therefore STI) are in the 0.63–12.5 Hz range, modulating carrier frequencies from 125 to 8000 Hz.

A 50mm mineral wool or PET felt panel with a 25–100mm air gap behind it provides the following absorption:

At 500 Hz and above, the panel provides α ≥ 0.85 — excellent absorption. At 250 Hz, the panel is moderately effective (α = 0.55 without gap, 0.80 with gap). At 125 Hz, the panel has limited effect without an air gap (α = 0.15).

For meeting rooms, this frequency profile is acceptable because:

1. The room is small (32.4 m³), and small rooms do not support strong resonant modes below 150 Hz. The lowest axial mode is f = c / (2L) = 343 / (2 × 4.0) = 42.9 Hz — well below the speech range.
2. The primary complaint (reverberant speech on video calls) is driven by mid-frequency energy (250–2000 Hz), which the panels control effectively.
3. Low-frequency reverberation in a room this size decays faster naturally because the surface-to-volume ratio is high — there are more absorption events per second.

What About Acoustic Foam Tiles?

Acoustic foam (open-cell polyurethane) is widely marketed for meeting rooms, often as self-adhesive tiles in pyramid or wedge profiles. While foam does absorb sound, it has significant disadvantages compared to mineral wool or PET felt:

The fire rating difference is critical. Many commercial buildings require wall and ceiling treatments to meet Class B or better per EN 13501-1. Standard acoustic foam fails this test. Installing flammable foam in a commercial meeting room may violate building regulations and void insurance coverage.

The absorption performance difference means you need approximately 40–60% more foam area to achieve the same RT60 reduction as mineral wool panels. The apparent cost advantage disappears when the larger treatment area is accounted for.

Signs Your Meeting Room Needs Treatment

Not sure if your meeting room has an acoustic problem? Here are five diagnostic indicators:

1. Far-end complaint: Remote participants on video calls say "you sound echoey" or "it sounds like a bathroom." This is the most reliable indicator because the far end hears the room's reverberation without the visual context that helps in-room participants ignore it.

1. The laptop test: Open a voice recorder on your laptop, place it at the meeting table position, clap once, and play back the recording. If you hear a reverberant tail lasting more than half a second, the room needs treatment.

1. The glass wall dominance: If one or more walls are floor-to-ceiling glass, the room almost certainly exceeds 0.6 seconds RT60 unless the ceiling has high-performance acoustic tiles (α ≥ 0.70).

1. Hard ceiling: If the ceiling is plasterboard, concrete, or decorative metal panel (not acoustic tile), the room is under-absorbed. Even "acoustic" suspended ceilings vary enormously: a cheap mineral tile might have α = 0.10, while a high-performance tile has α = 0.90. Check the product data sheet for the installed tile.

1. Raised voices: If participants in the meeting room find themselves raising their voices to be heard clearly, the room's reverberation is reducing speech clarity (lowering STI) and forcing speakers to increase vocal effort to compensate.

Acoustic Performance Standards for Meeting Rooms

Several standards specify RT60 limits for meeting rooms. Your treatment design should target the most stringent applicable standard:

For video conferencing, the practical recommendation from all major conferencing equipment manufacturers is RT60 ≤ 0.5 seconds. This is more stringent than most standards because the microphone is less forgiving than the human ear — it captures and transmits reverberant energy that an in-room listener's auditory system would partially suppress through precedence effect processing.

Related Reading

• WELL v2 Feature 74 Acoustic Requirements Decoded — complete guide to WELL acoustic compliance
• Your RT60 Calculation Is Probably Wrong — And Sabine's Formula Is Why — when Eyring gives more accurate results than Sabine
• How Much Does Acoustic Treatment Cost? — cost breakdowns for seven room types including meeting rooms