1. The acoustical quality of a room is determined by its reverberation time, which is the time it takes for sound to decay 60 decibels after the source stops. 2. Reverberation time depends on the volume of the room and absorption of surfaces. Larger rooms and rooms with more reflective surfaces have longer reverberation times, while smaller rooms and rooms with more absorptive surfaces have shorter reverberation times. 3. Ideal reverberation times for concert halls range from 1.7 to 2.05 seconds, though the frequency response is also important for acoustical quality.

2. 1.
1.
Criteria in Acoustical Design
The acoustical quality of a room is determined largely
by its Reverberation time.
Acoustical Characteristics:
Liveness
Intimacy
Fullness
Clarity
Warmth
Brilliance
Texture
Blend
Ensemble
3.
Problems in Acoustical Design
4.
Calculation of Reverberation Time

4. The reverberant sound in an auditorium dies away with time as the sound
energy is absorbed by multiple interactions with the surfaces of the room.
In a more reflective room, it will take longer for the sound to die away and the
room is said to be 'live'. In a very absorbent room, the sound will die away
quickly and the room will be described as acoustically 'dead'.
But the time for reverberation to completely die away will depend upon how
loud the sound was to begin with, and will also depend upon the acuity of the
hearing of the observer.
Reverberation time is defined as the time for the sound to die away to a level 60
decibels or (1/1,000,000) below its original level.

6. Liveness: A room is said to be “live” when the reverberation time is longer
than the average for similar rooms.
Intimacy: Refers to how close the performing group sounds to the listener.
Intimacy is achieved whenever the first reflected sound reaches the listener
less than about 20 ms after the direct sound.

11. Blend:
Blend refers to the mixing of the sound from all the instruments of the orchestra or
ensemble throughout the audience.
Proper blend is achieved by mixing the sound from various instruments and voices
on the stage before distributing to the audience.
Ensemble:
Ensemble refers to the ability of the members of the performing group to hear each
other during performance, enhancing the ability of the players to play together
effectively.

12. The following acoustical problems must be avoided:
Focusing of sound
Echoes
Shadows
Resonances
External noise

13. An approximate formula for the reverberation time, TR is given below:
V
TR = 55.2
SA
V = Volume of the room in cubic feet, S = speed of sound in ft/s, A = absorption in sabin.
V
TR = 0.050
A
A = a1 A1 + a 2 A2 + a3 A3 + a 4 A4 + .......
0.050V
TR =
.
a1 A1 + a 2 A2 + a3 A3 + a 4 A4 + ......
A1, A2,…are the areas of the various types of absorbing surfaces, and
a1, a2, … are the absorption coefficients of the respective surfaces.

14. TR =
0.050V
.
a1 A1 + a 2 A2 + a3 A3 + a 4 A4 + ......

15. One way to respond to the question "What is a good range of reverberation
times for concert halls?" is to give examples of some of the most famous halls
in the world.
For the overall average reverberation times:
Vienna, Musikvereinsaal : 2.05 seconds
Boston, Symphony Hall: 1.8 seconds
New York, Carnegie Hall: 1.7 seconds
But the overall average reverberation time does not tell the whole story. The
variation of reverberation time with frequency is also important.

16. Over the audience and over the stage, ceiling clouds and
panels produce balanced and blended sounds for a variety
of venues, resulting in a rich, directed sound that the
discriminating audiences have come to expect.