Reverberation Time: Why a Room Sounds Harsh or Comfortable

Why it matters on a project

Acoustic complaints are the most common post-occupancy complaint in offices, and the most expensive to fix afterwards, because the remedy means adding surfaces to a finished, occupied space.

The frustrating part is that reverberation is entirely predictable at design stage. It is arithmetic — volume and absorption — not a matter of taste.

What you can change

Element	Absorbent?	Notes
Suspended mineral fibre ceiling	Yes	Usually the biggest single contribution
Exposed concrete soffit	No	Fashionable, and acoustically the worst choice
Carpet	Yes	Also reduces footfall noise
Hard flooring	No	Reflects speech and footfall
Glazed partitions	No	Reflective on both sides
Solid walls, painted	No	Unless treated
Acoustic wall panels	Yes	Effective where surfaces face each other
Soft furnishing and people	Yes	Real, but not something to design around

The pattern behind most bad offices

Three decisions taken separately, each defensible, and together the problem:

1. Exposed soffit for height and an industrial look — removes the ceiling.
2. Glazed partitions for daylight — replaces absorbent walls with glass.
3. Hard flooring for durability and appearance — removes the floor.

Every absorbent surface in the room has now been specified away. The space looks excellent in photographs and is tiring to occupy.

If those choices are wanted, the absorption has to be reintroduced deliberately — acoustic rafts or baffles under the soffit, absorbent wall panels, or carpet in the working zones.

Measurement and prediction

Reverberation time is measured in finished rooms under ISO 3382-2, and the absorption data for materials comes from tests under ISO 354. For open-plan offices, ISO 3382-3 addresses the measures that describe that condition better — how far speech remains intelligible across the floor.

Because it can be calculated from volume and surface absorption, the check belongs at design stage, when the fix is a specification change.

Common mistakes

• Specifying an exposed soffit with no compensating absorption. The single most common cause.
• Treating acoustics as something to assess after occupation. By then the remedy is disruptive and visible.
• Assuming glazed partitions solve meeting room acoustics. They control transmission between rooms, not reverberation within them.
• Adding panels to the wrong surfaces. Absorption works where reflections actually occur, usually the ceiling first.
• Ignoring the floor. In an open plan it is often the largest available absorbent area.

Standards referenced

Reverberation time measurement to ISO 3382-2; sound absorption measurement to ISO 354; open-plan office acoustics in ISO 3382-3. Target values and acoustic design for a specific space must be established by the project's acoustic consultant.