Acoustic Design for Meeting Rooms, Offices and Classrooms: RT60 Targets by Room Type
Every room where an audience listens has a reverberation time it should hit — and the world's most famous concert hall spent fifty years proving what happens when it doesn't.
Acoustic design for meeting rooms starts with one number: the RT60 target, matched to what the room's occupants are actually there to listen to. A conference room built for speech wants roughly 0.6–1.3 seconds. An orchestral hall wants 1.6–3.0. Get that single value wrong and no amount of finish quality rescues the room — which is why the discipline is not confined to concert halls, and why offices, classrooms, restaurants and airport terminals all have an RT60 range whether anyone specified one or not.
This article sets out the recommended ranges by room function, works through two contrasting cases, and looks at what the Sydney Opera House Concert Hall's fifty-year acoustic history actually demonstrates.
Recommended RT60 Ranges by Room Type
| Room type | Primary listening activity | Recommended RT60 (seconds) |
|---|---|---|
| Conference hall | Dialogue | 0.6 – 1.3 |
| Cinema | Dialogue, effects and music | 0.6 – 1.2 |
| Theatre | Dialogue and music | 1.0 – 1.8 |
| Pop / rock concert room | Amplified music | 1.4 – 2.0 |
| Orchestral concert room | Unamplified acoustic music | 1.6 – 3.0 |
| Worship room | Dialogue and music | 1.8 – 3.2 |
| Restaurant | Dialogue with background music | up to 1.8 |
| Night club | Music at high sound pressure level | 0.6 – 1.6 |
These are commonly used industry design ranges, not code values. For a standards-backed target set by room type and volume, the reference is DIN 18041:2016-03 — note the edition, as the 2004 version it replaced is still widely cited.
Why Beautifully Designed Rooms Still Fail Acoustically
Everyone has sat through one: a conference panel that is hard to follow, a rock concert that arrives as mud, a restaurant where you cannot speak quietly at your own table, an airport announcement that is simply unintelligible. None of these is a decoration problem. Each is a room whose RT60 does not match what it is being asked to do.
They happen for a structural reason rather than a technical one: acoustic consultants are brought in after space planning, not during it. By then the volume, proportions and primary surface materials are fixed, and the acoustician's role has quietly changed from shaping the room to compensating for it. The result is a space that looks right in the renders and becomes functionally redundant the moment people try to use it for its stated purpose.
What RT60 Measures and Why It Comes First
RT60 — reverberation time — is how long sound energy in a room takes to decay by 60 decibels after the source stops. It is the first value to calculate for any room with an audience, because it constrains almost everything downstream: whether speech stays intelligible, whether unamplified music carries to the back row, how much absorptive area the interior budget has to accommodate, and where that area has to go.
Our companion article on reverberation time and echo control covers the Sabine equation and the measurement standards in more depth. The short version for design purposes: RT60 rises with room volume and falls with total absorption, so a target is met by trading one against the other — and volume is usually fixed long before absorption is discussed.
Conference Room vs Concert Hall: Two Opposite Targets
Take a conference room for a maximum audience of 800, where roughly 80% of what the audience does is listen to dialogue. That room needs an RT60 short enough that consecutive words do not overlap — long decay smears one syllable into the next, and intelligibility collapses well before the room sounds obviously "echoey" to a casual visitor.
Now take an orchestral hall seating around 2,000, where roughly 90% of the activity is listening to acoustic music. An orchestra typically uses no amplification at all: a violin, a soprano, a solo tenor has to reach the back row purely through the reflection and diffusion the room provides. Cut that room's RT60 in pursuit of clarity and the performance no longer reaches the audience at all. The two requirements are not on a spectrum of "more or less acoustic treatment" — they are opposite design problems that happen to share a unit of measurement.
Case Study: What the Sydney Opera House Concert Hall Actually Proves
The Sydney Opera House is the example everyone reaches for, and it is usually cited backwards. The Concert Hall — around 2,600 seats, 45 metres long, opened 1973 — was criticised for its acoustics from almost the moment it opened. The problem was geometric and largely locked in: the hall is very tall, and by the assessment of the renewal team at least a third longer than an ideal concert hall should be, so acoustic energy from the orchestra dissipated instead of reaching the audience. The room's outer form was determined by Utzon's shells; the acoustics had to fit inside whatever that left.
Between 2016 and 2022 the NSW Government funded a major acoustic renewal, with ARM Architecture and Arup leading the design. The work added 18 purpose-designed acoustic reflectors above the stage in place of the original acrylic "donuts", acoustic diffusion panels on the timber box fronts, an automated draping system that dampens reverberation for amplified programming, and automated stage risers so players can hear each other. The hall reopened in July 2022.
The lesson for a project team is not that the Opera House is a model to copy. It is that a fifty-year-old geometric decision cost roughly a hundred million dollars to partially correct, and that the correction consisted almost entirely of measures — reflectors, diffusion, adjustable absorption — that could have been designed in at a fraction of the cost had the acoustician been in the room when the volume and proportions were set.
Matching the Target to What the Audience Is Listening To
The common thread is that acoustic design follows the audience's primary listening activity and the type of source involved. Broadly, an audience is listening to dialogue, to music, to a mix of the two, or to a mix that also includes deliberate noise and effects. Architects and acoustic engineers classify rooms accordingly — conference rooms for dialogue; cinemas for dialogue, effects and music; theatres for dialogue and music; pop and rock rooms for amplified music; orchestral rooms for unamplified music; worship spaces for dialogue and music; restaurants for dialogue over background music; and night clubs for music at high sound pressure levels — each with its own RT60 range from the table above.
From Target to Built Room: Panels, Surfaces and Interior Design
Setting the RT60 range is the easy half. Hitting it means a specific combination of absorptive and reflective surface area, distributed deliberately rather than evenly, and coordinated with the interior designer and architect rather than added afterwards. Absorption concentrated on one wall behaves differently from the same total area spread across four, and an interior scheme finalised before the acoustic layout usually leaves the acoustician competing with the design for the same surfaces.
Done in the right order, a room can be both beautiful and functional — which is the whole point, and the way ALTA Integra runs acoustic engineering and design for meeting rooms, offices, classrooms and performance spaces alike.
FAQ
What is RT60 in acoustic design?
RT60, or reverberation time, is how long sound energy in a room takes to decay by 60 decibels after the source stops. It is the first value calculated when designing any room with an audience, because it determines whether speech stays intelligible and whether unamplified music carries to the back of the room.
Do offices and classrooms need acoustic design, or just concert halls?
Any room where people need to hear dialogue clearly has an RT60 range it should meet — offices, classrooms, meeting rooms, worship spaces and restaurants included. The target differs from a concert hall's, but the consequence of missing it is the same: a room that cannot do the job it was built for.
What RT60 range suits a conference room?
Roughly 0.6 to 1.3 seconds. The main activity is listening to dialogue, which needs clarity rather than a long musical decay — beyond that range, consecutive words begin to overlap and intelligibility falls away before the room sounds obviously reverberant to a casual visitor.
Why does an orchestral hall need a much longer RT60 than a conference room?
Acoustic music performed without amplification relies on the room's own reflections and diffusion to carry and blend sound to the audience. Orchestral halls are therefore designed at roughly 1.6 to 3.0 seconds. Shortening that in pursuit of clarity removes the mechanism by which the performance reaches the back rows at all.
Were the Sydney Opera House Concert Hall's acoustics always good?
No. The hall drew acoustic criticism from its 1973 opening, largely because its height and length were dictated by the building's outer shells. A major acoustic renewal ran from 2016 to 2022, adding 18 stage reflectors, diffusion panels on the box fronts and an automated draping system. It reopened in July 2022.
When should an acoustic consultant join a project?
As early as possible — ideally during initial space planning, before volume, proportions and finishes are fixed. ALTA Integra works with architects and developers in Indonesia and Southeast Asia from concept stage, so the RT60 target shapes the design rather than having to compensate for it afterwards.
Sources
1. DIN 18041:2016-03, Acoustic quality in rooms (replaces DIN 18041:2004-05).
2. Sydney Opera House, "Renewing an icon" — Concert Hall upgrade completed July 2022.
3. Dezeen, "Sydney Opera House concert hall reopens after extensive renovation," September 2022 (ARM Architecture and Arup).
4. ISO 3382-2:2008, Measurement of room acoustic parameters — Part 2: Reverberation time in ordinary rooms.
