By space
How conference room acoustics work
Rooms built for speech, increasingly heard through a microphone by someone who isn’t there — and why glass, ceilings and air-conditioning decide how they sound.
7 min read4 sourcesChapter 23 of 24
Schematic
A conference room in plan. Ceiling absorption over the table, absorption on the wall facing the display, the glass wall left as the reflective surface it is, and the microphone hearing the whole room.
Animated illustration of the principle. Not measured data.
A conference room has one acoustic job: every word, from every seat, intelligible — in the room and on the call. Most fail it, and they fail it in the same three ways: too much glass, a hard ceiling, and a noise floor from the air-conditioning that a microphone picks up long before an ear does.
Why speech rooms are different
Speech intelligibility depends on consonants, which are short, quiet and high-pitched. Reverberation and background noise mask exactly those sounds first. A room can feel fine to talk in across a table and still be unintelligible to the person at the far end, or on the call, because the reverberation that seems harmless at two metres has buried the consonants by six.
Published guidance puts meeting rooms around 0.4–0.6 s, and the lower end of that is better for rooms used on calls, because the far-end microphone hears more reverberation than a person in the room does.
The glass problem
Glazed walls are near-total reflectors across the range, and rooms with two glazed walls facing each other flutter. The options are limited: the glass usually has to stay. So the other surfaces have to do more — a fully absorbent ceiling, and absorption on whichever solid walls remain, sized to reach the target on their own. Where a glass wall faces the display, a short-pile floor and an absorbent ceiling above the table break up the path between them.
The ceiling is the largest surface you can treat without anyone noticing, and in most conference rooms it is the whole solution.
Noise
Air-conditioning noise is the most common reason a room sounds bad on a call. A fan-coil unit above the ceiling, a diffuser directly over the table, or a duct with high velocity produces a broadband hiss and a low rumble; the microphone’s automatic gain then raises the noise floor as people pause. Targets are set as a noise criterion curve, and reached through unit location, duct velocity and grille selection — decisions made with the mechanical engineer, not after the room is furnished.
Privacy runs the other way: what is said in the room should stay in it, which is a matter of the partition’s isolation, the door seals, and any shared ceiling plenum.
The microphone
A ceiling array microphone hears the room’s reverberation from above the table; a table microphone hears it from close by. Both work better in a treated room and neither fixes an untreated one. Loudspeaker placement for the far-end voice follows the same first-reflection logic as any room, and the echo cancellation in the system has an easier job when the room’s reverberation is short.
For integrators and architectsThe numbers, the standards, and what to specify
- Targets
- RT60 around 0.4–0.6 s mid-band (DIN 18041 gives about 0.47 s for a 100 m³ meeting room), lower for video-first rooms; STI or a related speech metric where it is contractually important; background noise as an NC / NR curve appropriate to the room’s use.
- Ceiling
- High-absorption ceiling tiles or a suspended absorbent raft over the table; note that a lay-in ceiling with a shared plenum is a privacy flanking path to the next room.
- Glass
- Where glazing dominates, treat the ceiling and the remaining solid surfaces to reach the target on their own; micro-perforated or fabric-covered treatment on the display wall.
- Mechanical
- Coordinate unit placement and duct velocities with the HVAC designer; noise from services is set in that design and is expensive to retrofit.
- AV integration
- Microphone type and loudspeaker positions chosen with the treatment scheme; run the room’s reverberation and noise figures past the conferencing system’s stated operating ranges.
What to write into the brief
- RT60 target and a background-noise criterion in the brief; ceiling treatment and HVAC noise coordinated at design stage; partition isolation and door seals specified for privacy.
Sources
- 01DIN 18041:2016 target formulas, as quoted in Germany’s federal BNB rating system (criterion 3.1.4)RT targets by room volume and use, and the tolerance band across frequency.
- 02Acoustics Today (Acoustical Society of America), 2020 — ANSI/ASA S12.60 classroom limits0.6 s for rooms under 283 m³, 0.7 s up to 566 m³.
- 03UK Department for Education — BB93: Acoustic design of schools, performance standards (2015)Mid-frequency RT limits for lecture rooms, drama studios and halls (Table 6).
- 04IEC 60268-16:2020 — Objective rating of speech intelligibility by speech transmission index
External links open in a new tab. Figures quoted in this chapter are taken from these sources; a Science of Sound measurement is only ever presented as one, with its file, date and instrument.
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