Chapter-8 Room and Auditorium Acoustics

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Chapter-8Room and Auditorium Acoustics

• Criteria in Acoustical Design
• The acoustical quality of a room is determined
  largely by its Reverberation time.
• Acoustical Characteristics
• Liveness
• Intimacy
• Fullness
• ClarityWarmthBrillianceTextureBlend
• Ensemble
• 3. Problems in Acoustical Design
• 4. Calculation of Reverberation Time

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Reverberation Time
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Reverberation Time
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.
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Ideal Reverberation Times
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Liveness and Intimacy
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.
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Fullness and Clarity
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Warmth
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Brilliance
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Texture
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Blend and Ensemble
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.
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Problems in Acoustical Design

• The following acoustical problems must be
  avoided
• Focusing of sound
• Echoes
• Shadows
• Resonances
• External noise

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Calculation of Reverberation Time
An approximate formula for the reverberation
time, TR is given below
V Volume of the room in cubic feet, S speed
of sound in ft/s, A absorption in sabin.
A1, A2,are the areas of the various types of
absorbing surfaces, and a1, a2, are the
absorption coefficients of the respective
surfaces.
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Absorption Coefficients
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Examples of Reverberation Times
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.
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Acoustical Ceiling Panels
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.
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Review