acoustics with factors.ppt

7/29/2019 acoustics with factors.ppt

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Room and Auditorium Acoustics

1. Criteria in Acoustical Design

2. Problems in Acoustical Design

3. Control of Reverberation Time

4. Design of Auditoriums

5. Home Listening Rooms


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Paths of sound in room


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Intensity vs. time for pulse


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Average Intensity vs. Time

for a constant tone


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Ideal Reverberation Times


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Acoustical Characteristics

1. Liveness2. Intimacy

3. Fullness

4. Clarity

5. Warmth

6. Brilliance7. Texture

8. Blend

9. Ensemble


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Liveness

Measure of reverberation time

Good or bad?


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Intimacy

Room said to be intimate when the

first reverberation arrives within

20 ms of the direct sound.

Good or bad?


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Fullness vs. Clarity

Refers to the amount of

reflected sound relative to

the amount of direct sound

Good or bad?


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Warmth vs. Brilliance

Warmth increases with

increasing TR

for low frequencies


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Texture

Good texture when at least

five reflections arrive within

60ms of direct sound


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Blend and Ensemble

Ability to hear the

entire performing groupon the stage (ensemble) and

in the audience (blend)


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Acoustical Design Problems

1. Focusing of sound

2. Echoes3. Shadows

4. Resonances

5. External noise6. Double-valued T

R


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Focusing of Sound

Occurs with use of

parabolic surfaceseither behind performers

or at rear of auditorium


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Echoes

Highly reflective flat or

parabolic wall shapes

Flutter echos from

parallel walls

Standing waves

between parallel walls


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Resonances

Rectangular practice rooms

Parallel walls

Singing in the shower


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External noise

Box within a box construction

Practice rooms and concert halls

in adjacent areas


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Double-valued TR

Playback room with reverberation

Concert halls with side areas


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AuditoriumDesign


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General Design Considerations

1. Visual

2. Ventilation3. Acoustical

a. seating

b. stagec. room shape

d. room walls


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Control of TR

TR

= 0.050 V / A

Where:

TR

= reverberation time in second

V = room volume in cubic feet

A = total room absorption in sabins


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TRCalculation

A = a1A1 + a2A2 + a3A3 + a4A4+

An is one section of absorbent areaan is absorption coefficient

TR

= 0.050 V/A


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Some Absorption Coefficients

Frequency (Hz)

Material 125 250 500 1000 2000 4000

Concrete/brick 0.01 0.01 0.02 0.02 0.02 0.03

Glass 0.19 0.08 0.06 0.04 0.03 0.02

Plasterboard 0.20 0.15 0.10 0.08 0.04 0.02

Plywood 0.45 0.25 0.13 0.11 0.10 0.09

Carpet 0.10 0.20 0.30 0.35 0.50 0.60

Curtains 0.05 0.12 0.25 0.35 0.40 0.45Acoustical board 0.25 0.45 0.80 0.90 0.90 0.90


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Absorptions (in sabins)Frequency (Hz)

Material 125 250 500 1000 2000

Unupholstered seat 0.15 0.22 0.25 0.28 0.50

Upholstered seat 3.0 3.1 3.1 3.2 3.4

Adult person 2.5 3.5 4.2 4.6 5.0

Adult/upholstered seat 3.0 3.8 4.5 5.0 5.2


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Dekelbaum

Concert Hall

at the

U MDSmith Center


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Dekelbaum Concert Hall (front)


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Dekelbaum Concert Hall (rear)


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Dekelbaum Concert Hall (top)


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U MD Tawes Recital Hall


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Microphone

configurationin

concert hall


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Loudspeaker

configurationin home

listening rooms


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The End

acoustics with factors.ppt

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