In video calls, a voice that sounds perfectly fine when heard directly in the same room often comes across as a boomy, muddled blur on the far side of the screen.
The cause is usually the acoustics of the meeting room itself. The human ear filters out reverberation to a degree, but a microphone captures the direct sound and the reverberation bouncing back off walls and ceilings together, without distinguishing between them.
Why sound gets noticeably worse on video calls
When you talk face to face, the direct sound from the speaker’s mouth arrives first and loudest. The reverberation that follows is relatively quiet, and the brain corrects for it naturally.
A meeting-room microphone, however, sits on a desk or ceiling 1–3 m from the speaker. The greater the distance, the weaker the direct sound and the larger the share of reverberation — so remote participants hear sound of low clarity.
A microphone cannot filter out reverberation the way the human ear does.
Three metrics for meeting-room acoustics
Meeting-room acoustics come down to three metrics: reverberation time (RT60), speech clarity (STI), and sound insulation (STC). Each measures a different thing.
Reverberation time, RT60, is how long it takes for sound to fall by 60 dB after it stops. The difference between the long ring of a clap in a tiled bathroom and its quick fade in a carpeted living room is exactly RT60.
| 기준 | RT60 · Reverberation time | STI · Speech clarity | STC · Insulation |
|---|---|---|---|
| What it measures | Length of the room’s ring | How well speech is understood | Blocking to the adjacent space |
| Unit · range | seconds (s) | 0–1 index | integer in dB terms |
| Key standards | ISO 3382-2 · DIN 18041 | IEC 60268-16 | ASTM E413 · ISO 717-1 |
| Meeting-room target | about 0.5 s | 0.60 or higher | 45–50 or higher |
| When it’s poor | Booming ring | Speech smears | Next-room talk leaks |
RT60 — when reverberation is long, the mic captures the ring
Because a meeting room is a space where speech clarity is paramount, DIN 18041 classifies it as Group A. The recommended reverberation time is set by the room’s volume; a typical small-to-mid meeting room targets around 0.5 seconds.
The method for lowering reverberation time to target and the procedure for sizing the absorption area are set out in five steps in “Guidelines for Applying Absorbent Materials”.
STI — how clearly speech is conveyed
The Speech Transmission Index (STI) expresses how losslessly speech is conveyed as a number between 0 and 1. The closer to 1, the clearer.
It is graded in bands, like a test score: 0.75 and above is excellent, 0.60–0.75 good, 0.45–0.60 fair, and below 0.45 is hard to follow.
An approach that deliberately lowers STI in open offices to secure speech privacy is covered in “The Open-Office Paradox”.
STC — sound leaking to or from the next room
If RT60 and STI concern clarity inside the room, sound insulation (STC, Sound Transmission Class) deals with sound leaking past the walls. It matters most in rooms where confidentiality counts, such as executive meetings and HR interviews.
Why insulation and absorption are different tasks, and what order to build them in, is covered from the basics in “Sound Insulation vs. Absorption”.
Acoustic targets by meeting-room type
Priorities shift with the character of the space. We have organized them into four representative types.
Acoustic targets by space type
Small video-call room (2–6 people)
“We’re on video calls often, and the other side keeps saying it ‘echoes.’”
Large conference room · seminar room
“It’s large with a high ceiling, and speech doesn’t carry to the back.”
Executive room · interview room
“The conversation must not leak outside.”
Multipurpose · town hall
“We run presentations, meetings, and events all in one space.”
From diagnosis to installation — the order
Approaching meeting-room acoustics in the following order reduces trial and error.
Step 1 — Diagnose. Clap once in an empty meeting room. If the ring drags on, it’s a reverberation (RT60) problem; if a normal conversation in the next room comes through clearly, it’s an insulation (STC) problem.
Step 2 — Absorb. Add an absorptive finish of NRC 0.75 or higher to the ceiling and upper walls to bring reverberation down to target. If the area is insufficient, reverberation won’t fall enough.
Step 3 — Insulate. For rooms that need confidentiality, secure STC with door gaskets, wall mass, and plenum barriers. Because reinforcing insulation after construction is costly, decide it first.
Step 4 — Lay out. Place microphones close to the speaker and away from noise sources such as HVAC diffusers and projector fans. Even in the same room, layout alone changes clarity.
Differences between absorptive materials (PET, melamine foam, wood wool) are covered in “Acoustic Materials Compared”, set against NRC, fire performance, and design.
The measurement principle of NRC, the basis for these figures, can be found in “What Is NRC?”.
Frequently asked questions
Frequently asked questions
Q1Will video-call sound improve just by adding absorptive panels?
Q2What reverberation time is right for a meeting room?
Q3How do you check STI?
Q4Are glass-walled meeting rooms acoustically bad?
Q5Will switching to better microphones and speakers solve it?
Glossary
RT60 (reverberation time) — the time for sound pressure to fall by 60 dB after sound stops.
STI (Speech Transmission Index) — an index from 0 to 1 for how losslessly speech is conveyed.
STC (Sound Transmission Class) — an integer, in dB terms, for how much walls, doors, and the like block sound.
NRC (Noise Reduction Coefficient) — a value from 0 to 1 for the proportion of sound a material absorbs.
αw (weighted sound absorption coefficient) — a single absorption rating (Class A–E) weighted per ISO 11654.
DIN 18041 — a standard for interior acoustic quality; a meeting room is Group A (speech clarity first).
Reference standards
ISO 3382-2:2008 — method for measuring indoor reverberation time (RT60).
IEC 60268-16:2020 — measurement and evaluation of speech intelligibility (STI).
DIN 18041:2016 — interior acoustic quality (meeting room = Group A).
ASTM E413 / ISO 717-1 — rating of sound insulation (STC / Rw).
ISO 11654:1997 — classification of sound absorption (αw).
KS F 2805 — reverberation-room measurement of sound absorption.