Room acoustic modelling techniques: A comparison of a ... · Room acoustic modelling techniques: A...

Room acoustic modelling techniques: A comparison of a scale model and a computer model for a new opera theatre

ISRA 2010, Melbourne, Australia

Jens Holger Rindel

Odeon A/S

Outline

• The project• Computer model • Results from computer simulations• Scale model and measurement technique

ISRA Melbourne 2010 2

• Scale model and measurement technique• Materials and adjustment of absorption• Results from scale model measurements• Comparison of results and methods• Conclusion

The project

Ankara Congress and Cultural Centre

Opera theatre with approx 1400 seats

Architect: Özgür Ecevit, Turkey

Acoustic consultant: Jordan Akustik and J.H. Rindel


Design goals

ISO 3382 parameters (with full audience)


Computer model – room modelModel in the final phase 3. Design and materials were adjusted according to results from the previous phases.


2 source positions stagepit

7 receiver positionsmain floorbalconies

Materials

Air absorption 80 80% abso 900 Orchestr 500 Wooden f 30 30% abso 908 Occup. c 50 50% abso 705 Panel, p

Absorption area distributed on materials

m²

Sab

ine

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000 Absorption coeff icients


Frequency (Hz)63 125 250 500 1000 2000 4000 8000

1,000

500

0

Odeon©1985-2010 Licensed to: Odeon A/S Restricted version - research and teaching only!

80 80% absorbentgfedcb 900 Orchestra w itgfedcb 500 Wooden f loor gfedcb 30 30% absorbentgfedcb 908 Occup. chairsgfedcb 50 50% absorbentgfedcb 705 Panel, plastegfedcb

Absorption coeff icients

Frequency (Hz)63 125 250 500 1000 2000 4000 8000

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

Odeon©1985-2010 Licensed to: Odeon A/S Restricted version - research and teaching only!

Scattering coefficients (500 1000 Hz):0.6 – Audience, orchestra, back walls, balcony bottoms0.1 – All other surfaces

Calculation results


Average of 7 receiver positions

Calculation results



EDT – Grid response

1 kHz octaveSource on stage


Strength G – Grid response



Clarity C80 – Grid response



LF – Grid response



Scale model 1:20


Equipment

• Sound source: Electric spark source (designed at DTU)

• Useful frequency range: 1,6 – 110 kHz, corresponding to 80 – 5500 Hz, i.e.


corresponding to 80 – 5500 Hz, i.e.

125 – 4000 Hz octave bands in scale 1:20

• Microphone: BK4136 ¼”-microphone, a BK2636 measuring amplifier and a Rockland 852 dual high/low-pass filter

• MIDAS software for measurements and analysis

Measurement setup


Spectrum of spark source (Frequency / 20)


Air conditions

• Temperature and humidity was kept very stable. RH around 60%

• The MIDAS measurement system adjusted the impulse response to compensate for the excessive air attenuation at the high frequencies


attenuation at the high frequencies

Audience

• Wooden fibre plate glued to a styrofoam back, in which the shapes of the “heads” of


the “heads” of the audience are cut out.

Some of the surfaces of the front and back were covered with a layer of tape, in order to adjust the absorption.

Absorption of model audienceAudience on occupied chairs, medium upholstered

0,8

1

1,2

1,4

Abs

orpt

ion

B. & H.

Model 1


0

0,2

0,4

0,6

125 250 500 1000 2000 4000

Frequency, Hz

Abs

orpt

ion

Model 1

Model 2

Ref: Beranek & Hidaka, J. Acoust. Soc. Am., Vol. 104, No. 6. 1998

Adjustment of absorption

ANKARA OPERA HOUSE, PHASE IIIClosed stage opening - Source in pit

2

2,5

Rev

erbe

ratio

n tim

e, T

30 (

s)

Final


0

0,5

1

1,5

125 250 500 1000 2000 4000

Frequency, Hz

Rev

erbe

ratio

n tim

e, T

30 (

s)

Final

Simulated

Model 1

Model 2

Adjustment of absorption

Ceiling in the auditorium with

Low frequency absorption added


• Principle: To obtain the correct reverberation time in the relevant frequency range, although the contribution from air attenuation is higher in the model than in the real hall

auditorium with additional absorption

Adjustment of scattering

Wrinkled foil attached to the walls to


to the walls to represent a diffusing treatment

RT – Source on stage

ANKARA OPERA HOUSE, PHASE IIISource on stage

11,21,41,61,8

2

Rev

erbe

ratio

n tim

e, T

30 (

s)

Measured


00,20,40,60,8

1

125 250 500 1000 2000 4000

Frequency, Hz

Rev

erbe

ratio

n tim

e, T

30 (

s)

Measured

Simulated


RT – Source in pitANKARA OPERA HOUSE, PHASE III

Source in pit

11,21,41,61,8

2R

ever

bera

tion

time,

T30

(s)

Measured


00,20,40,60,8

1

125 250 500 1000 2000 4000

Frequency, Hz

Rev

erbe

ratio

n tim

e, T

30 (

s)

Simulated


EDT – Source on stageANKARA OPERA HOUSE, PHASE III

Source on stage

11,21,41,61,8

2E

DT

(s)

Measured

Simulated


00,20,40,60,8

125 250 500 1000 2000 4000

Frequency (Hz)

ED

T (

s)

Simulated


EDT – Source in pitANKARA OPERA HOUSE, PHASE III

Source in pit

11,21,41,61,8

2E

DT

(s)

Measured

Simulated


00,20,40,60,8

1

125 250 500 1000 2000 4000

Frequency (Hz)

ED

T (

s)

Simulated


G – Source on stage

ANKARA OPERA HOUSE, PHASE IIISource on stage

02468

10S

tren

gth,

G (

dB)

Measured

Simulated


-10-8-6-4-20

125 250 500 1000 2000 4000

Frequency (Hz)

Str

engt

h, G

(dB

)

Simulated


G – Source in pit

ANKARA OPERA HOUSE, PHASE IIISource in pit

-202468

10S

tren

gth,

G (

dB)

Measured

Simulated


-10-8-6-4-2

125 250 500 1000 2000 4000

Frequency (Hz)

Str

engt

h, G

(dB

)

Simulated


C80 – Source on stageANKARA OPERA HOUSE, PHASE III

Source on stage

02468

10C

larit

y, C

80 (

dB)

Measured

Simulated


-10-8-6-4-20

125 250 500 1000 2000 4000

Frequency, Hz

Cla

rity,

C80

(dB

)

Simulated


C80 – Source in pitANKARA OPERA HOUSE, PHASE III

Source in pit

02468

10C

larit

y, C

80 (

dB)

Measured

Simulated


-10-8-6-4-20

125 250 500 1000 2000 4000

Frequency, Hz

Cla

rity,

C80

(dB

)

Simulated


Comparison of methods

Source on stage


P1

3

P1

Receiver 3: Sound propagation elevated over audience surface, no attenuation of direct soundReflection from audience surface

Comparison of methods

Source in pit


P2

3

P1

Receiver 3: Sound propagation close to audience surface (attenuation missing in simulation)No direct sound; Diffraction across pit wall (Odeon ver. 10)

C80 – comparison of methods

Stage to main floor


Pit to main floor

Discussion - 1Scale model Computer model

Room model detailing High degree of detail possible (butexpensive)

Simplified geometry preferredHigh degree of detail possible

Materials Absorptionapproximated

Absorption data accurate (if available)


approximated accurate (if available)

Scattering Included with detailed modelling

Scattering coefficients assigned to surfaces with simplified details

Diffraction Included Approximated or missing in some cases

Attenuation of sound propagating across audience area

Included with detailed modelling of audience

Not included (yet)


Air attenuation Compensation needed (less abs. in materials or impulse response boosted)

Accurate (calc. from temperature and RH)

Frequency range Limited at low and high frequencies

Full audio range


high frequencies

Reverberation time Used for calibration. Absorption of materials adjusted to meet expected RT

Predicted by simulation

EDT, G, C80 … From measured impulse response

From calculated impulse response

LF, IACC Special miniature transducers needed

From calculated impulse response (3D)


Auralisation Quality limited by transducers

High quality possible. Any HRTF may be applied

Reproduction throughloudspeakers

Not possible Ambisonics or n-channel surround

Sources with special Possible, but difficult Possible. Application


Sources with special directivity (musical instruments)

Possible, but difficult Possible. Application of directivity data or multi-channel auralisation

3D analysis of early reflections

Possible with laser beam and light-reflecting surfaces

Easy, coupled to reflectogram


Echo and flutterechodetection

Inspection of impulse response

Inspection of impulse response.Auralisation of impulsive sound

Colouration Not possible Possible with high quality auralisation


quality auralisation

Detection of weak spots in the audience area

Not realistic to cover all seats by measurements

Possible through grid mapping of all parameters

Grid mapping of results

Not possible High resolution grids possible (long calculation time)

Conclusion

• Both methods have weaknesses and advantages

• Results: No big difference between measured and simulated room acoustic parameters

• Main problems in scale models:– Transducers (directive sources, dummy head)– Transducers (directive sources, dummy head)

– Auralisation with sufficient quality

• Main problems in computer models– Data for scattering surfaces; can be measured in scale model

reverberation chamber (ISO 17497-1)

– Simulation of the attenuation of sound propagation across the audience area


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