Reverberation Time (RT60): The Number That Matters
Ask ten people what "good acoustics" means and you'll get ten vague answers. Ask an acoustic engineer, and the conversation almost always starts with one number: RT60, reverberation time. It's the closest thing our industry has to a single, comparable figure for how a room behaves, and it's worth understanding properly rather than just quoting the number a supplier gives you.
What RT60 actually measures
RT60 is the time it takes for a sound to decay by 60 decibels after the source stops, roughly the difference between a sound at its loudest and it being inaudible against typical background noise. A room with a long RT60, a stone-floored hall, an empty warehouse, still has speech and music bouncing around it a full second or more after someone stops talking. A room with a short RT60 kills that decay quickly, sound stops when the source stops.
The Sabine equation: the formula behind the number
The standard way to calculate reverberation time is the Sabine equation, developed by physicist Wallace Sabine in the 1890s and still the working formula acoustic consultants use today: T60 = 0.161 × V / A, where V is the room's volume in cubic metres and A is the total absorption in the room, measured in metric sabins (square metres of fully absorptive surface). The equation tells you something practical: bigger rooms need proportionally more absorption to hit the same reverberation time as a smaller one, and every hard, reflective surface, glass, concrete, plasterboard, adds to the volume side of the equation without adding anything to the absorption side.
What counts as a good number, and why it changes by room type
There's no single "correct" RT60. A general UK classroom under BB93 targets 0.6 to 0.8 seconds; a SEN or hearing-impaired teaching space is held to a much stricter 0.4 seconds. A domestic living room typically sits comfortably around 0.4 to 0.6 seconds without any special treatment. An untreated open-plan office or empty industrial unit can easily run to 1.5 to 2 seconds or more. A concert hall designed for orchestral music deliberately targets a longer reverberation, often 1.8 to 2.2 seconds, because that's what makes orchestral music sound rich rather than dry. Getting this backwards, treating a speech-focused space like a concert hall or vice versa, is one of the most common specification mistakes we see.
Why the same treatment plan performs differently room to room
Because RT60 is driven by the ratio of absorption to volume, identical treatment, the same number and type of panels, produces a different result in a small meeting room than in a large open-plan floor. This is why a generic "how many panels do I need" answer is close to useless without knowing the room's actual volume and its existing surface finishes. It's also why a consultant calculates the required absorption area before specifying panels, rather than treating panel selection as the first step.
Common questions
Can RT60 be too short? Yes. A room that's over-absorbed can feel acoustically dead and unnatural, particularly for music or performance spaces where some reflection is part of the intended sound.
Does furniture count as absorption? Soft furnishings, carpets and upholstered seating all contribute meaningfully to the total absorption figure, which is why an empty room measures very differently to the same room furnished and occupied.
Working out what your room needs
See our guide to NRC ratings to understand how individual products are tested, or book a free survey to have your room assessed properly rather than estimated.
Related product guides: acoustic ceilings: tiles, baffles or rafts, acoustic wall panels.
From first survey to final finish
One team handles all seven stages, the same way on every project, so you always know what happens next.
A surveyor visits the site, or works from your drawings and photos when a visit isn't practical. Either way, the room, its surfaces and how it is used are recorded before any advice is given.
Reverberation, ambient noise and noise transfer are read against what the space is used for. The findings arrive as a written report with recommendations, yours to keep with no obligation to proceed.
Treatment is modelled against a reverberation target, then drawn up with panel positions, fixings and finishes. Nothing moves forward until you have approved the design.
Every quotation comes with the specification behind it, listing products by type, quantity and finish with costs set out line by line. What is quoted is what the design calls for.
Panels, baffles, ceilings and screens come from our Acoustic Solutions range and are supplied to the approved specification. What arrives on site matches what was designed.
Our own engineers fit to the approved drawings, checking positions and fixings as they go. One team supplies and installs, so nothing is handed between contractors.
Optional: after fit-out the space can be measured again and compared with the original survey, so the improvement is measured rather than assumed. Results are reported against the relevant standards and the written record goes into your building file.
Stay connected with insights
Get the latest updates from our acoustic design experts