Transcript Document 7695519
Technology in Architecture
Lecture 13 Sound in Enclosed Spaces Reverberation Auditorium Design
Sound In Enclosed Spaces
Sound Absorption
Amount of sound energy not reflected S: p. 761, , F.18.2
Sound Absorption
Absorption coefficient α=I α /I i α=absorption coefficient I α =sound power intensity absorbed (w/cm 2 ) I i =sound power impinging on material (w/cm 2 ) 1.0 is total absorption
Sound Absorption
Absorption coefficient S: p. 759, T.18.1
Sound Absorption
Absorption A=Sα A=total absorption (sabins) S=surface area (ft 2 or m 2 ) α=absorption coefficient sabins (m 2 )= 10.76 sabins (sf)
Sound Absorption
Total Absorption Σα=S 1 α 1
+ S
2 α 2
+ S
3 α 3
+…+S
n α n or ΣA=A 1
+ A
2
+ A
3
+…+A
n
Sound Absorption
Average Absorption α avg =ΣA/S α avg <0.2 “live” α avg >0.4 “dead” S: p. 764, F.18.6
Reflection in enclosed spaces
Acoustical phenomena S: p. 777, F.18.20
S: p. 777, F.18.21
Ray diagrams
Trace the reflection paths to and from adjoining surfaces angle of incidence = angle of reflection I R
Ray 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 in enclosed spaces
Auditorium sound reinforcement S: p. 779, F.27.23
Reverberation
Reverberation
Persistence of sound after source has ceased S: p. 761, F.18.2
Reverberation Time
Period of time required for a 60 db drop after sound source stops T R
= K x V/ΣA
T R : reverberation time (seconds) K: 0.05 (English) (0.049 in SR-6) or 0.16 (metric) V: volume (ft 3 or m 3 ) ΣA: total room absorption, sabins (ft 2 or m 2 )
Reverberation Time
Application Volume 3.5
ft 3 x1000 35.0 350 S: p. 772, F.18.13
Reverberation Time
Calculated for “center band frequencies” 125 250 500 1000 2000 4000 Pay specific attention to 125 hz and 500 hz
Reverberation Example
Compile data
Material Absorption Coefficient Material Surface Area SR-6: p.121
Reverberation Example
Compare to requirements and adjust 3.5
ft 3 x1000 35.0 350 S: p. 772, F.27.13
Auditorium Design
Auditorium Design
Room Acoustics Noise Control Sound System
Auditorium Design Factors
Audience Size Range of Performance Activities Audience Sophistication
Auditorium Design Parameters
1. Audience Size (floor area): 6-8sf/seat 2. Reverberation (volume): Motion Picture Theatre Lecture Hall 100 cf/seat 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 Parameters
3. Ceiling Height= Volume/Floor Area generally…20 x T R
Auditorium Design Parameters
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 Parameters
5. Stage opening: 40-50’ wide x 25’ high
Auditorium Design Parameters
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’
Auditorium Design Parameters
7. Check Echoes
Auditorium Design Example
Given data RR-7: p.119
Reverberation Time
Symphonic 492,480 ft 3 3.5
ft 3 x1000 35.0 350 T R =1.5 seconds S: p. 772, F.18.13
Auditorium Design Example
Given data SR-6 : p.115, F.5-11
Auditorium Design Example
Given data SR-6 : p.116, F.5-12
Auditorium Design Example
Area takeoffs SR-6 : p.120
Auditorium Design Example
Locate coefficients S: p. 759, T.18.1
Auditorium Design Example
Absorption Coefficients SR-6 : p.121
Auditorium Design Example
Compute absorption Compute reverberation SR-6 : p.121
Auditorium Design Example
Compute T R 500 for given data: T R =0.049 x V/ ΣA =0.049 x 492,480/12,538 =1.92 seconds
Auditorium Design Example
Compute absorption needed for volume: T R =1.5 seconds ΣA=0.049 x V/T R =0.049 x 492,480/1.5
=16,088 sabins
Auditorium Design Example
Adjust to meet absorption Add acoustical tile on walls
Auditorium Design Example
Determine acoustical tile area
Auditorium Design Example
Determine acoustical tile area Sabins design - Sabins given Sabins short 16,088 12,538 3,550 Translate to area of acoustical tile Sabins/Δα=3,550/0.67= 5,299 sf
Auditorium Design Example
Add 5,299 sf of acoustical tile on walls Recompute T R500
Auditorium Design Example
Recompute T R-500 for revised data: T R-500 =0.049 x V/ ΣA =0.049 x 492,480/16,088 =1.5 seconds Compute T R-125 for revised data: T R-125 =0.049 x V/ ΣA =0.049 x 492,480/9,593 =2.52 seconds
Auditorium Design Example
Compare T R-500 with T R-125 : T R 125 /T R 500 =2.52/1.5= 1.68
Ratio should be 1.6-1.85
to offset hearing deficiency