Standardization of procedures and calculation models for the numerical simulation of acoustics of enclosed spaces

The present work is an exploration of the feasibility and the accuracy of a hybrid FDTD/GA simulation model when applied to broadband acoustic simulations of large-scale environments. The model selected, which has been developed by the Acoustics and Audio Group research team of the University of Edinburgh (UK), combines a wave-based method, a finite-difference time-domain (FDTD) code, with a traditional GA approach, the ray-tracing method. During the investigation, the attention is focussed on the possibilities recently achieved in the wave-based part of the model thanks to the increasing computational power and to new efficient algorithms adopted. The present thesis concerns the method employed to test and assess these new potentials through various application contexts. Moreover, a thorough analysis of the most significant factors affecting the simulation process is carried out with specific assessments of the outcomes. A sample of four large environments is employed in this study, each one of them for specific peculiar reasons: a traditional opera house, a modern theatre, a multipurpose elliptical hall, and a historical university lecture hall. All the simulation process steps and the method adopted to validate the models are reported and described in detail: the 3D modeling phase, the input data, the setting of proper calculation parameters, the time cost, and the acoustic metrics considered time by time in the halls assessed. The thesis allows defining an objective benchmark between the state-of-art of acoustic simulation in medium and large-scale environments and the new advances allowed by recent research in wave-based methods. Finally, the work outlines theoretical and practical remarks on the effectiveness of the hybrid simulation method adopted, enhancing the existing scientific literature with further data and case studies for an increasingly thorough benchmark of computational acoustics techniques

Acoustical comfort in university lecture halls: simulating the dynamic role of occupancy

The acoustic comfort in teaching environments is generally determined through requirements concerning reverberation time, speech intelligibility and HVAC noise. The presence of students reduces the reverberation time but concurrently increases the background noise, that undermines the focus of students and the vocal effort of teachers. A double set of measures were acquired in two university lecture halls in unoccupied and occupied state to investigate the consequences of occupancy variations. Acoustic simulations allowed to assess the dynamic effects of the occupancy detecting the differences of speech intelligibility. Predicting the student activity may return reliable outcomes improving the quality of lessons

Acoustic design of a multipurpose hall inside a former church

The present work is about an acoustic design for a former church converted into a multi-purpose auditorium. The current status of the hall has been classified by means of an acoustic measurements campaign complying with technical standards requirements. A numerical model, which has been calibrated through the measured values, led to the development of the acoustic design that includes sustainable and not-invasive interventions. In contrast with the practical habits, which would use a large amount of sound absorbing materials, an array of suspended reflecting panels over the musicians positions has been introduced. Exploiting the reflecting and scattering properties of those objects, sound clarity and speech definition improve. All the treatments are validated using numerical simulation softwares in order to estimate the efficiency of the whole improvement proposal

A trial acoustic improvement in a lecture hall with MPP sound absorbers and FDTD acoustic simulations

Sound absorbing micro-perforated panels (MPPs) are being increasingly used because of their high quality in terms of hygiene, sustainability and durability. The present work investigates the feasibility and the performance of MPPs when used as an acoustic treatment in lecture rooms. With this purpose, three different micro-perforated steel specimens were first designed following existing predictive models and then physically manufactured through 3D additive metal printing. The specimens\u2019 acoustic behavior was analyzed with experimental measurements in single-layer and double-layer configurations. Then, the investigation was focused on the application of double-layer MPPs to the ceiling of an existing university lecture hall to enhance speech intelligibility. Numerical simulations were carried out using a full-spectrum wave-based method: a finite-difference time-domain (FDTD) code was chosen to better handle time-dependent signals as the verbal communication. The present work proposes a workflow to explore the suitability of a specific material to speech requirements. The measured specific impedance complex values allowed to derive the input data referred to MPPs in FDTD simulations. The outcomes of the process show the influence of the acoustic treatment in terms of reverberation time (T30 ) and sound clarity (C50 ). A systematic comparison with a standard geometrical acoustic (GA) technique is reported as well

The coupled rooms of Odeo Cornaro (1534) as support for Renaissance musicians and soloists

The Odeo Cornaro in Padua (Italy) is a well-preserved XVI Century octangular music space (from Latin the ottangulo) surrounded by communicating smaller halls. Inspired by Roman classicism, the Renaissance architect Falconetto designed such coupled volume system for the private villa of the Venetian nobleman Alvise Cornaro. With the aim of assessing the acoustics of the Odeo by means of a contemporary approach, acoustic measurements were performed, and the room acoustic criteria were derived from the acquired impulse responses. Experimental results were employed to quantify the acoustic coupling effects throughout the environments and to outline the acoustic features of the central space. Numerical models were used to assess the free path distribution and the support given by the ottangulo to the singers’ voices. The main outcomes confirm the different use of the spaces suggested by historical research: while the main hall was probably employed for singing and playing instruments, the adjoining rooms were intended for erudite conversations and symposia. The symmetrical shape and the moderate volume of the central octangular space contribute to creating a neat modal behaviour that accentuates the sound propagation, highlighting the outstanding value of the Odeo as one of the “loci resonantes” of the past

Acoustic comfort in a worship space made of cross-laminated timber

The construction of a new worship space in cross-laminated timber provides a good opportunity to include acoustic needs in the whole design development. The surface porosity and the lightweight of wooden elements may be carefully considered in order to improve the intelligibility of priests\u2019 voice. In this work, a practical approach for obtaining a global acoustic comfort using sustainable materials is provided, using geometrical acoustic simulations. Material properties and architectural geometries were taken into account in order to evaluate subjective reverberation, speech intelligibility, and spatial perception over the whole audience. Results show how the sound energy distribution in the case study follows the sound field models proposed by scholars and how the ceiling shape\u2014inspired by industrial sheds\u2014contributes to the acoustic comfort of the faithfuls

Acoustic of a chamber music hall inside a former church by means of sound energy distribution

The present work concerns the acoustic design for a former church converted into a chamber music hall. The current status of the hall was classified with an acoustic measurements campaign according to technical standards requirements. Focusing on literature theories, an accurate sound energy spatial distribution analysis led to the development of an acoustic intervention, not-invasive from a volumetric point of view. An array of hanging reflecting panels over the musicians positions improves sound clarity C80 and sound strength G trends giving to the church an acoustic quality worthy of a concert hall. All the acoustic treatments were validated using a Geometrical Acoustic (GA) numerical model, calibrated through the measured values, in order to estimate the effect of the whole improvement proposal

Numerical simulations of Italian opera houses using geometrical and wave-based acoustics methods

The acoustics of opera houses represents an interesting topic in scientific literature due to their architectural and morphological characteristic traits (shape, materials, coupled volumes). A way to exploit the outstanding value of Italian theatres acoustics is to perform different typologies of music while adding or removing acoustically significant elements on the stage. Numerical simulations may be used as useful tools for designing distinct layouts and for optimising such performances. The present study investigates strengths and weaknesses of two different room acoustics modelling approaches: geometrical acoustics (GA) and wave-based methods. The commercial GA software ODEON and a hybrid ray-tracing and finite-difference time- domain (FDTD) approach are applied in this work. Measurements carried out in a sample of Italian Opera houses provide reference data for 3D virtual models calibration. Preliminary comparisons between room acoustical simulation methods are shown and discussed

Predicting Speech Intelligibility In University Classrooms Using Geometrical Acoustic Simulations

In university classrooms a suitable acoustic condition is necessary to enhance the productivity of students and the vocal comfort of lecturers. With this purpose international standards recently introduced new requirements on the quality of verbal communication. The goal of this work is to propose a procedure for predicting speech intelligibility in large learning spaces through geometrical acoustic simulations. The performance of the present approach is investigated using analytical prediction models as well as the measurements results in six university classrooms surveyed