technology in architecture lecture 17 sound in enclosed spaces reverberation auditorium design...
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Technology in ArchitectureTechnology in ArchitectureTechnology in ArchitectureTechnology in Architecture
Lecture 17Sound in Enclosed Spaces
ReverberationAuditorium Design
Lecture 17Sound in Enclosed Spaces
ReverberationAuditorium Design
Sound AbsorptionSound AbsorptionAbsorption coefficient
α=Iα/Ii
α=absorption coefficient Iα=sound power intensity absorbed (w/cm2)Ii=sound power impinging on material (w/cm2)
1.0 is total absorption
Sound AbsorptionSound Absorption
Absorption
A=Sα
A=total absorption (sabins)
S=surface area (ft2 or m2)α=absorption coefficient
sabins (m2)= 10.76 sabins (sf)
Sound AbsorptionSound Absorption
Total Absorption
Σα=S1α1 + S2α2 + S3α3 +…+Snαn
or
ΣA=A1 + A2 + A3 +…+An
Sound AbsorptionSound Absorption
Average Absorption
αavg=ΣA/S
αavg <0.2 “live”
αavg >0.4 “dead”
S: p. 774, F.18.6
Reflection in enclosed Reflection in enclosed spacesspaces
Acoustical phenomena
S: p. 787, F.18.20
S: p. 788, F.18.21
Ray diagramsRay diagrams
Trace the reflection paths to and from adjoining surfaces
angle of incidence = angle of reflection
I R
Ray diagramsRay diagrams
Trace the reflection paths to receiver
Reflected sound path ≤ Direct sound path+55
Note: check rear wall and vertical paths
Note: SR-6=RR-7 SR-6: p.116, F.5-12
Reflection inReflection inenclosed spacesenclosed spaces
Auditorium sound reinforcement
S: p. 789, F.18.23
Reverberation TimeReverberation Time
Period of time required for a 60 db drop after sound source stops
TR= K x V/ΣA
TR: reverberation time (seconds)
K: 0.05 (English) (0.049 in SR-6) or 0.16 (metric)
V: volume (ft3 or m3)ΣA: total room absorption, sabins (ft2 or m2)
Reverberation TimeReverberation Time
Calculated for “center band frequencies”
125 250 500 1000 2000 4000
Pay specific attention to 125 hz and 500 hz
Reverberation ExampleReverberation Example
Compile data Material Absorption
Coefficient Material Surface Area
SR-6: p.121
Reverberation ExampleReverberation Example
Compare to requirements and adjust
S: p. 782, F.27.13
ft3x1000 3.5 35.0 350
Auditorium Design FactorsAuditorium Design Factors
Audience SizeRange of Performance ActivitiesAudience Sophistication
Auditorium Design Auditorium Design ParametersParameters
1. Audience Size (floor area): 6-8sf/seat
2. Reverberation (volume): Motion Picture Theatre 100 cf/seat Lecture Hall 100 cf/seat Music Room/Auditorium 200-250 cf/seat Symphony Hall 200-300 cf/seat Choral Rehearsal 350 cf/seat Band Rehearsal 500 cf/seat
Auditorium Design Auditorium Design ParametersParameters
3. Ceiling Height= Volume/Floor Area
generally…20 x TR
Auditorium Design Auditorium Design ParametersParameters
4. Typical Dimensions
L:W:H = 2H:1.5H:H
Determine acceptable width (80-120’)
Determine length (L = SF/Width)If Length ≥120’, use balcony
Auditorium Design Auditorium Design ParametersParameters
6. Shape Walls and Ceilings
a) source is 5’ from stage front, 5’ above stage floor
b) trace reflectances from back wall, side walls, and ceiling @ 40-60’ from stage
40’ 60’
Reverberation TimeReverberation Time
Symphonic492,480 ft3
TR=1.5 seconds
S: p. 782, F.18.13
ft3x1000 3.5 35.0 350
Auditorium Design ExampleAuditorium Design Example
Compute absorptionCompute reverberation
SR-6: p.121
Auditorium Design ExampleAuditorium Design Example
Compute TR 500 for given data:
TR=0.049 x V/ ΣA
=0.049 x 492,480/12,538 =1.92 seconds
Auditorium Design ExampleAuditorium Design Example
Compute absorption needed for volume:
TR=1.5 seconds ΣA=0.049 x V/TR
=0.049 x 492,480/1.5 =16,088 sabins
Auditorium Auditorium Design Design ExampleExample
Adjust to meet absorption
Add acoustical tile on walls
Auditorium Design ExampleAuditorium Design ExampleDetermine acoustical tile area
Sabins design 16,088- Sabins given 12,538 Sabins short 3,550
Translate to area of acoustical tile
Sabins/Δα=3,550/0.67= 5,299 sf
Auditorium Auditorium Design Design ExampleExample
Add 5,299 sfof acoustical tile on walls
RecomputeTR500
Auditorium Design ExampleAuditorium Design ExampleRecompute TR-500 for revised data:
TR-500=0.049 x V/ ΣA =0.049 x 492,480/16,088 =1.5 seconds
Compute TR-125 for revised data:
TR-125=0.049 x V/ ΣA =0.049 x 492,480/9,593 =2.52 seconds
Auditorium Design ExampleAuditorium Design Example
Compare TR-500 with TR-125 :
TR-125/TR-500=2.52/1.5= 1.68
Ratio should be 1.6-1.85to offset hearingdeficiency