CONCERT HALLS
A long, enveloping tail
For symphonic music, a reverberation time of about 1.8 to 2.2 seconds helps reflections blend the whole orchestra into one enveloping sound.
Match a hallClap in a hall and listen to it fade.
That fading tail is reverberation: sound bouncing off walls, ceiling and seats until it dies away. How long it lasts decides whether a hall is good for talking, for an orchestra or for an organ, and acousticians measure it in seconds.
- Short tail for speech
- Long tail for orchestras
- People soak up sound
- What the seconds mean
THE SHORT ANSWER
The right echo
depends on the job.
Reverberation time is how long sound takes to fade.
Different uses need different amounts.
SCHOOL HALLS
Built to a standard
England's school acoustics standard, BB93, sets 0.8 to 1.2 seconds for a new assembly or multi-purpose hall, and 0.6 seconds or less for a new primary classroom.
See the numbers
STONE AND SONG
The longest tails
Organ music and plainchant can carry a very long reverberation of about 3 seconds without losing clarity, because the notes and words are long.
What shapes it
WHAT SHAPES THE SOUND
Size, surfaces
and people.
A formula first proposed in 1898 links reverberation time to just two things: the volume of the room and how much sound its surfaces absorb.
Bigger rooms ring longer
Larger volumes make reflected sound travel further between bounces, which lengthens reverberation.
Soft surfaces soak it up
Drapes, rugs and porous panels absorb sound; they need to be large enough that sound waves do not simply pass round them.
The audience is part of it
Walls, furnishings and the audience all absorb sound, so a full hall sounds different from an empty one.
Shape guides the reflections
Research on shoebox-shaped halls points to strong early reflections arriving from the sides as a key to their admired sound.
TWO NUMBERS WORTH KNOWING
Measured in seconds,
built into the rules.
One figure for the great concert hall,
one for the hall at the local school.
1.8–2.2 s
Suggested reverberation time
Based on the views of a wide sample of experts, symphonic music suits a long reverberation time, longer than opera or chamber music at 1 to 1.6 seconds.
SYMPHONIC MUSIC · UNIMORE
0.8–1.2 s
New assembly or multi-purpose hall
England's BB93 standard sets this range for new school halls. A new sports hall over 530 m² may have up to 2 seconds.
SCHOOL HALLS · BB93
Reverberation time is defined as the time it takes sound to fall by 60 decibels, about one million times weaker, after the source stops.
A QUICK HALL MATCH
What is the hall
for?
Pick a use to see the reverberation time acoustics guidance suggests. The bar shows how long the sound tail should be, from short to very long.
Based on a university acoustics course and England's BB93 school standard. Real halls vary with size, seats and audience.
TASTE STILL MATTERS
Not everyone loves
the same hall.
In a listening study at Aalto University in Finland, 28 assessors compared recordings of six concert halls from three seats with two pieces of music. The acoustics varied from seat to seat and with the music played.
The listeners split into two groups: some preferred clarity over reverberance, while others loved strong, reverberant and wide sound. Even the most admired halls did not please everyone in blind listening.
In conversation
Questions people ask
What is reverberation time?
It is the time sound takes to fade by 60 decibels, about a millionfold, after the source stops. It is the main measure acousticians use for how live or dry a room sounds.
What is the best reverberation time for a concert hall?
For symphonic music, an acoustics course based on expert opinion gives about 1.8 to 2.2 seconds. Opera and chamber music suit 1 to 1.6 seconds, and speech about 1 second.
Why do school halls sound echoey?
Hard floors, walls and high ceilings reflect sound. England's BB93 standard limits a new assembly or multi-purpose hall to a reverberation time of 0.8 to 1.2 seconds.
Does an audience change the sound?
Yes. Reverberation depends on how much sound the walls, furnishings and audience absorb, so a full hall can sound different from an empty one.
Why are shoebox concert halls so admired?
Researchers measuring shoebox halls found they deliver strong reflections from the side walls very early, which acousticians link to their full, enveloping sound.
Sources
Each figure on this page comes from the sources below.
- University of Modena and Reggio Emilia, Physics, Waves, Music: Architectural acoustics
- GOV.UK: BB93 Acoustic design of schools, performance standards
- Department for Education: BB93 Acoustic design of schools (PDF, 2015)
- Journal of the Acoustical Society of America (2016): Concert hall acoustics, repertoire, listening position and individual taste (Aalto University PDF)
- Proceedings of the Institute of Acoustics (2015): The secret of the Musikverein and other shoebox concert halls (Aalto University PDF)