Links between concert hall geometry, objective parameters, and sound quality
Robert Essert
Arup Acoustics, Boston House, 36-38 Fitzroy Square, London W1P 5LL, UK
Now at Sound Space Design, 2 St. George's Court, 131 Putney Bridge Road, London, SW15 2PA, UK
[email protected]
Invited paper presented at the joint meeting of the Acoustical Society of America/ DAGA/ Forum
Acusticum, Berlin, March 1999. J. Acoust Soc Am. 105(2) p. 986 (1999).
For decades, the design of concert halls was driven by considerations of time history alone (T60, C80, ITDG), and as
a result, little importance was attached to room geometry. The subjective importance of binaural dissimilarity has
been a strong, though often simplistic, influence on recent designs. While listening experience has shown which
fundamental room forms sound better than others, computer modeling and statistical analysis have enabled
systematic investigation of the degree to which the geometry affects the sound. Using simple parametric models, this
study will investigate effects of surface parallelism, concavity, and convexity on spatial and monaural objective
acoustical parameters and on essential subjective attributes.
Links between concert hall geometry,
objective parameters and sound quality
Robert Essert
Arup Acoustics, London
Now at Sound Space Design, London
[email protected]
ASA/DAGA/Forum Acusticum 1999 Berlin,
Invited paper 2aAAa5, 16 March 1999
Essert/ASA-DAGA Berlin99
1
Aims
• To investigate some basic geometric
parameters that we encounter in hall design
and the objective and subjective differences as
they are varied.
• To use trends among shapes as a means for
greater understanding.
Essert/ASA-DAGA Berlin99
2
Architectural Scales
Large
Scale
Size, Dimension
Audience capacity
Medium
Scale
Gross Geometry
Surface Shaping
Small
Scale
Detail, Textures, Finishes
Essert/ASA-DAGA Berlin99
3
Gross Scale: Some Simple Rules of Thumb
Quantitative
• SPL and subjective loudness decrease with
greater audience area
• Duration of reverberant decay increases with
increased ceiling height
Qualitative
• C80 and subjective clarity can be increased in
a tall space with the addition of suspended
surfaces
Essert/ASA-DAGA Berlin99
4
Room Shape has great influence on….
Spatial
Qualities
Envelopment, Spaciousness
IACC, LF
Mono
Qualities
Subjective Clarity, Reverberance,
Loudness
EDT, T60, C80, G
Essert/ASA-DAGA Berlin99
5
Quantifying Effects of Geometry on Sound
We know many of the general principles, but
• How much does the sound depend on
geometry?
– Subjectively?
– Objectively?
• What are the additional / unexpected effects?
--> Modelling and auralisation
Essert/ASA-DAGA Berlin99
6
Computer Model Case Studies:
Simple variations on a shoebox
•
•
•
•
plan shape
ceiling pitch
seating slope
hall width
Essert/ASA-DAGA Berlin99
7
Procedure
• Modelling software: CATT 7.0 - beam tracing
with frequency-dependent surface diffusion
• Compared results produced by CATT
• Listened to results enough to give a qualitative
indication of the degree of audibility
Essert/ASA-DAGA Berlin99
8
Plan Variation: Fan, Shoebox, Reverse Fan
Audience:600m²
Volume:6326m³
Audience:600m²
Audience:600m²
Volume:6258m³
Volume:6326m³
L = 30 m, W = 20 m H = 10 m
Walls of fans pivoted to achieve the same
floor area as shoebox.
Audience absorption on floor.
Plaster walls with moderate diffusion.
Essert/ASA-DAGA Berlin99
9
G-10 Three Plans: Fan, Shoebox, Reverse Fan
G-10
Three Plans
9
8
7
G-10 (dB)
6
Fan
5
Shoebox
4
Rev Fan
3
2
1
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
10
2k
4k
T30 Three Plans: Fan, Shoebox, Reverse Fan
T30
Three Plans
3.5
3
T30 (sec)
2.5
Fan
2
Shoebox
1.5
Rev Fan
1
0.5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
11
2k
4k
LEF2 Three Plans: Fan, Shoebox, Reverse Fan
LEF2
Three Plans
25
LEF2 (%)
20
15
Fan
Shoebox
Rev Fan
10
5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
12
2k
4k
C80 Three Plans: Fan, Shoebox, Reverse Fan
C80
Three Plans
7
6
5
C80 (dB)
4
Fan
3
Shoebox
Rev Fan
2
1
0
125
250
500
1k
-1
Frequency (Hz)
Essert/ASA-DAGA Berlin99
13
2k
4k
EDT Three plans: Fan, Shoebox, Reverse Fan
EDT
Three Plans
3
2.5
EDT (sec)
2
Fan
1.5
Shoebox
Rev Fan
1
0.5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
14
2k
4k
RT Comparisions: Fan Plan
Reverb Time Calculations
Fan Plan
3
2.5
2
RT (sec)
Sabine
Eyring
1.5
Ray Trace T30
Ray Trace T15
1
0.5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
15
2k
4k
Reverb Time Comparisons: Shoebox Plan
Reverb Time Calculations
Shoebox Plan
4
3.5
3
Sabine
RT (sec)
2.5
Eyring
Ray Trace T30
2
Ray Trace T15
1.5
1
0.5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
16
2k
4k
Reverb Time Comparison: Reverse Fan Plan
Reverb Time Calculatoins
Reverse Fan Plan
3.5
3
RT (sec)
2.5
Sabine
2
Eyring
Ray Trace T30
1.5
Ray Trace T15
1
0.5
0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
17
2k
4k
Shoebox: Spatial Distribution
Essert/ASA-DAGA Berlin99
18
Fan Plan: Spatial Distribution
Essert/ASA-DAGA Berlin99
19
Reverse Fan: Spatial Distribution
Essert/ASA-DAGA Berlin99
20
Wall Plan Subjective vs Shoebox
Wall Plan
Subjective Change vs Shoebox
Spaciousness
Envelopment
Fan
Clarity
Rev Fan
1
Reverberance
Loudness
-1.5
-1
-0.5
0
subjective scale
Essert/ASA-DAGA Berlin99
21
0.5
1
1.5
Floor Rake (Slope) Geometries
Audience:612m²
Volume:6799m³
Z
Y
Y
5m
Room
Rake0
Rake3
Rake5
L = 30 m, W = 20 m H = 10 m +
Floor slope increased in 2 steps.
Ceiling height adjusted for equal volume.
Audience absorption on floor.
Plaster walls with moderate diffusion.
Floor slope
0
5.7 deg
9.5 deg
Essert/ASA-DAGA Berlin99
22
G-10: Three rakes
G-10
Three Rakes
8.0
7.0
6.0
G-10 (dB)
5.0
Rake0
4.0
Rake3
Rake5
3.0
2.0
1.0
0.0
71.5
73.2
75.9
78.9
Frequency (Hz)
Essert/ASA-DAGA Berlin99
23
81.2
83.1
T30: Three Rakes
T30
Three Rakes
4.0
3.5
3.0
T30 (sec)
2.5
Rake0
Rake3
2.0
Rake5
1.5
1.0
0.5
0.0
71.5
73.2
75.9
78.9
Frequency (Hz)
Essert/ASA-DAGA Berlin99
24
81.2
83.1
LEF2: Three Rakes
LEF2
Three Rakes
30.0
25.0
LEF2(%)
20.0
Rake0
15.0
Rake3
Rake5
10.0
5.0
0.0
71.5
73.2
75.9
78.9
Frequency (Hz)
Essert/ASA-DAGA Berlin99
25
81.2
83.1
C80: Three Rakes
C80
Three rakes
4.5
4.0
3.5
3.0
C80 (dB)
2.5
Rake0
2.0
Rake3
1.5
Rake5
1.0
0.5
0.0
125
-0.5
250
500
1k
-1.0
Frequency (Hz)
Essert/ASA-DAGA Berlin99
26
2k
4k
EDT: Three Rakes
EDT
Three Rakes
4.0
3.5
3.0
EDT (sec)
2.5
Rake0
Rake3
2.0
Rake5
1.5
1.0
0.5
0.0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
27
2k
4k
Floor Rakes: Subjective vs Shoebox
Floor Rakes
Subjective Change vs Shoebox
Spaciousness
Envelopment
Rake3
Clarity
Rake5
Reverberance
Loudness
-1
-0.8
-0.6
-0.4
subjective scale
Essert/ASA-DAGA Berlin99
28
-0.2
0
Ceiling Pitch Variation
Shoebox plus 2 celing pitches
All with equal volume and floor area
H1= 20 m
H2= 30 m
H3= 40 m
3
1
2
Source just inside
one end
Essert/ASA-DAGA Berlin99
29
Flat Floor
20m x 30m
G-10: Ceiling Pitch
G-10
Ceiling Pitch
10.0
9.0
8.0
G-10 (dB)
7.0
6.0
Hall1
5.0
Hall2
4.0
Hall3
3.0
2.0
1.0
0.0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
30
2k
4k
T30: Ceiling Pitch
T30
Ceiling Pitch
4.5
4.0
3.5
T30 (sec)
3.0
Hall1
2.5
Hall2
2.0
Hall3
1.5
1.0
0.5
0.0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
31
2k
4k
LEF2: Ceiling Pitch
LEF2
Ceiling Pitch
30.0
25.0
LEF2(%)
20.0
Hall1
Hall2
15.0
Hall3
10.0
5.0
0.0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
32
2k
4k
C80: Ceiling Pitch
C80
Ceiling Pitch
5.0
4.0
3.0
C80 (dB)
2.0
1.0
0.0
125
-1.0
Hall1
Hall2
250
500
1k
-2.0
-3.0
-4.0
-5.0
Frequency (Hz)
Essert/ASA-DAGA Berlin99
33
2k
4k
Hall3
EDT: Ceiling Pitch
EDT
Ceiling Pitch
6.0
5.0
EDT (sec)
4.0
Hall1
3.0
Hall2
Hall3
2.0
1.0
0.0
125
250
500
1k
Frequency (Hz)
Essert/ASA-DAGA Berlin99
34
2k
4k
Ceilng Pitch: Subjective Relationships
Ceiling Pitch
Subjective Change vs Shoebox
Spaciousness
Envelopment
Hall2
Clarity
Hall3
Reverberance
Loudness
-1.5
-1
-0.5
0
subjective scale
Essert/ASA-DAGA Berlin99
35
0.5
1
Shoebox comparisons
Length = constant 30 m
Height = constant 10m
Varied width (10, 20, 30, 40m), surface diffusion
Audience:250m²
Volume:2501m³
Audience:900m²
10 m wide
30 m wide
10% Diffusion (freq indep)
50% Diffusion
Essert/ASA-DAGA Berlin99
Volume:9003m³
10% D
50% D
36
Conclusions
• Reverberation efficiency (reverberance for a
given volume) for rectangular rooms is greater
than these other shapes
• For these simple shapes we can demonstrate
trends with models that correspond to
experience in real world
Essert/ASA-DAGA Berlin99
37