Advanced techniques for the determination of sound spatialization

in Italian Opera Theatres

ENRICO REATTI, LAMBERTO TRONCHIN & VALERIO TARABUSI

AMTA 08 - 24-26 June 2008 Bucharest

Acoustic and spatialization

- Acoustic map of a typical “Italian style” opera theater

- Impulse responses and acoustical parameters

- Simulate the same space and conditions by a numeric model and obtain again IRs and acoustical parameters

- auralization of an anechoic excerpt like a way to compare the experimental study and the numerical one

Plan

It was built in the second half of the 18th century by the architect Antonio Galli Bibiena

Bell shaped (no horse-shoe shape)

Auditorium build with plastered bricks (no wood in the balconies)

Last restoration work of 1980 brought to light traces in the plasterwork of the personalisation of the balconies.

Sezione longitudinale

34 m 22 m

16 m

33 m

Capacity: 420 seats in the stalls 480 in the balconies

Stage area: 460 m2

Sezione trasversale

15,6 m

Auditorium has seats in the stalls, in the four

tiers of balconies and in the gallery

Experimental analysis

Criteria for the choice of measurement positions :

Good spatially distribution

Research on half auditorium (symmetry hypothesis)

Omni directional sources not centered to avoid focus points

Measurement points

Omni directional Array of loudspeakers

Instrumentation

Microphone Soundfield & Amplifier/processor

Binaural Dummy Head Neumann (Senneheiser mic headset)

Personal Computer P4 Software Adobe Audition

Sound board ”Echo” Event

Measurement chain

Test signal “sweep”

Sound propagation

Stage complex & auditorium Acoustic

Omni directional speaker

Mic Soundfield Dummy Head

PC & sound board

Data post processing

audio signals (WY, XZ, Bin L/R)

IMPULSE RESPONSE (IR)

Impulse response (IR)

Measurement in a particular seat

EXPERIMENTAL MESAUREMENT

Inverse filter

Impulse response

Direct Sound

Reflected Sound

Sound sourceReceiver

Direct Sound

Reflected Sound

Acoustical Parameters - Strength

• Strength represents amplification effect of the auditorium.

• Strength is correlated to Loudness and consequently to the sound quality.

• difference between strength measured on the stage and this one measured in the pit represents the BALANCE.

Acoustical parameters

C80 - CLARITY INDEX

D50 – DEFINITION INDEX

502

050

2

0

( )

( )

ms

p t dt

D

p t dt

802

080

2

80

( )

10log

( )

ms

ms

p t dt

C dB

p t dt

Acoustical parameters

Early decay is responsible of sensation of reverberation

Time necessary to the signal to decrease from -5dB to -35dB

EDT – EARLY DECAY TIME

T30 – REVERBERATION TIME

EDT

0.0

0.5

1.0

1.5

2.0

2.5

31.5 63 125 250 500 1000 2000 4000 8000 16000

[ Hz ]

[s]

Palco Buca

Acoustical parameters

Is possible to calculate by Sounfield microphone using omni directional and Y signal

Is possible to calculate by Dummy head signals (corresponding to two different ears)

LF – LATERAL FRACTION

IACC – INTERAURAL CROSS CORRELAION INDEX

802

580

2

0

( )

( )

ms

L

msms

p t dt

LF

p t dt

segnale mic figura 8Lp

segnale mic omnidirezionalep

max( )IACC

2 2

1lim ( ) ( )

2( )

1lim ( ) ( )

2

T

d sT

T

T T

d sT

T T

h h t dT

h d h t dT

Numeric Model

The Ramsete calculation software, based on the pyramid tracing method (a variant of the “cone-tracing” algorithm) was used for processing.

3D CAD Model

A 3D cad model was made of the theatre’s auditorium and stage complex behind, using present day plan and elevation views

Numeric model elaboration

Ramsete was run and the simulation repeated several times

The associations between the properties of the materials and the flat elements (22000 flat el.) were entered and the

same grid of 25 receiver points used for the experimental investigation was

reconstructed.

File ramsete.mat: each 3D face is part of a group and group has a set

of coefficient of absorption (1/3 octave) associated

Numeric model elaboration

Obtained a good numeric model is possible to calculate the acoustical parameters , as before, correspondent to a receiver point chosen, trough the extrapolation of his IR.

Impulse response (receivers num. 5 e 8 at 125 Hz) Acoustical parameters (receivers 5 e 8)

Auralisation

A anechoic recording of an excerpt from Torna a Surriento was processed by means of the experimentally and numerically obtained impulse response of a seat in the stalls

(20d).

Trough auralisation everyone can ear how the acoustic properties of the theatre change a sound reproduced in it.

Experimental IR

Numeric model IR

Anechoic excerpt (tenor singer)

Takes deconvolved with IR

STOP

Conclusions

-Make an experimental analysis is useful also to do a “Backup” of the acoustic of a theatre (for ex. La fenice)

-Acoustic map as important as plan and elevation plan

-Estimate space project trough a numeric model is of great use in many different fields: from brand-new projects to restoration.

-Acoustic render

The EndThe End

Thank you

The crew

Authors:

Ing.Enrico Reatti

Prof. Ing. Lambeto Tronchin

Prof. Ing. Valerio Tarabusi

Special thanks to:

Dott. Ryota Shimokura

Mr. Gerardo Pece

Web sites:

www.ciarm.ing.unibo.it

www.deacustica.it

AMTA 08 - 24-26 June 2008 Bucharest