In primo luogo, tre diversi algoritmi di simulazione, usati nei software ODEON, RAVEN e CATT-Acoustic, sono stati confrontati e successivamente è stata analizzata l'applicazione del coefficiente di scattering in ognuno di essi.

In seguito,esperimenti relativi alla convalida dei metodi di simulazione sono stati eseguiti in un caso studio con condizioni al contorno controllate, ossia la camera riverberante presso The Institute of Technical Acoustics (ITA), Aachen. Quattro diverse alternative sono state indagate: (1) una stanza riverberante 'vuota', (2) una stanza riverberante con una parete acusticamente assorbente, (3) una stanza riverberante con una parete acusticamente assorbente e una diffondente geometricamente costituita da aste verticali in legno e (4) una stanza riverberante con una parete acusticamente assorbente e una di tipo diffondente con una maglia composta da una griglia di aste orizzontali e verticali. I risultati delle simulazioni come i tempi di riverberazione e le risposte all'impulso monaurali vengono discussi e confrontati. Una corrispondenza molto buona è stata trovata tra le simulazione e le misure effettuate per il modello della camera riverberante 'vuota', tuttavia notevoli differenze sono state individuate per gli altri modelli.

L'ultima parte della ricerca riguarda la valutazione oggettiva e soggettiva del suono riflesso in modo diffuso nel caso di una sala da concerto virtuale. Sei diverse alternative sono state modellate e simulate. In ogni modello 6 differenti coefficienti di scattering sono stati applicati alle superfici interne del soffitto, delle pareti laterali e della parete posteriore. L'analisi è stata condotta confrontando i risultati dei parametri acustici oggettivi da un lato e da un'indagine sulla percezione soggettiva del suono diffuso tramite test d'ascolto, dall'altro.

Test di ascolto, con il metodo 3AFC, sono stati eseguiti con stimoli presentati ai soggetti tramite cuffie usando segnali auralizati in uno dei software, Odeon. I risultati hanno mostrato diversi valori di JND-s per i tre motivi riprodotti e le due posizioni analizzate, rispecchiando cosi

con coerenza il grado di difficoltà espresso dagli ascoltatori per ogni campione di segnali.

In conclusione, siccome lo scattering è fortemente correlato alle caratteristiche geometriche delle superfici e degli oggetti all'interno degli ambienti, sembra essere il parametro che influenza più di ogni altro l'interior design degli spazi dedicati a diverse performance acustiche. Questo lo fa diventare un elemento interessante per gli architetti e i designer, e un mezzo di collaborazione multidisciplinare relativo a soluzioni ottimali riguardanti sia acustica che gli aspetti visivi del design.

3.1 Introduction

3.2 ISO Method: scattering coefficient

3.2.1 Some limitations of the ISO

3.2.2 Other Methods: scattering coefficient

3.3 AES Method: diffusion coefficient

3.4 Contrasting scattering coefficient with diffusion coefficient

4 Diffusion and scattering in concert halls

4.1 Introduction

4.2 Diffusion as a rating scale for concert halls

4.3 Diffusers: state of the art

5 Room acoustic computer simulation

5.1 Introduction

5.2 Hybrid models for room acoustics simulations

5.3 Odeon

5.3.1 Odeon: simulation method

5.3.2 Odeon: Scattering coefficient implementation

5.4 Catt-Acoustics

5.4.1 CATT-Acoustic: simulation method

5.4.2 CATT-Acoustic: Scattering coefficient implementation

5.5 Raven

5.5.1 Raven: simulation method

5.5.2 Raven: Scattering coefficient implementation

5.6 Comparison of the three tools

6 Software validation

6.1 Introduction

6.2 Model: ITA Reverberation Chamber

6.2.1 Geometry

6.2.2 Materials properties

6.2.3 Experiment set-up

6.3 Simulations

6.4 Results

7 Objective evaluation of scattering coefficient

7.1 Introduction

7.2 Objective acoustical parameters

7.3 Model: Virtual Concert Hall

7.3.1 Geometry

7.3.2 Materials properties

7.3.3 Experiment set-up

7.4 Simulations

7.5 Results

8 Subjective assessment of scattering coefficient

8.1 Listening tests: 3AFC method and psychometric function

8.2 Stimulus preparation

8.3 Experiment arrangement

8.4 Results

9 Conclusion

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Licenses and use permission

[1] Odeon 10.1, Unlimited education/research version, Laboratorium Bouwfysica K.L. Leuven, BE. [2] CATT-Acoustic v 8.0, Unlimited education/research version, Laboratorium Bouwfysica K.L. Leuven, BE. [3] Raven: Room acoustic simulation software developed at the Institute of Technical Acoustics at RWTH Aachen University. [4] ITA-toolbox: Data acquisition and post processing has been realized by using the ITA-Toolbox for MATLAB developed at the Institute of Technical Acoustics at RWTH Aachen University. [5] Psignifit toolbox 2.5.6: Statistical data processing has been realized by using the free software Psignifit toolbox for MATLAB developed by Jeremy Hill 1999-2005.