Paul Luizard

Sound energy decay in coupled spaces using a parametric analytical solution of a diffusion equation.

Sound field behavior in performance spaces is a complex phenomenon. Issues regarding coupled spaces present additional concerns due to sound energy exchanges. Coupled volume concert halls have been of increasing interest in recent decades because this architectural principle offers the possibility to modify the halls acoustical environment in a passive way by modifying the coupling area. Under specific conditions, the use of coupled reverberation chambers can provide non-exponential sound energy decay in the main room, resulting in both high clarity and long reverberation which are antagonistic parameters in a single volume room. Previous studies have proposed various sound energy decay models based on statistical acoustics and diffusion theory. Statistical acoustics assumes a perfectly uniform sound field within a given room whereas measurements show an attenuation of energy with increasing source-receiver distance. While previously proposed models based on diffusion theory use numerical solvers, the present study proposes a heuristic model of sound energy behavior based on an analytical solution of the commonly used diffusion equation and physically justified approximations. This model is validated by means of comparisons to scale model measurements and numerical geometrical acoustics simulations, both applied to the same simple concert hall geometry.

Self-entrainment of the right and left vocal fold oscillators

This article presents an analysis of entrained oscillations of the right and left vocal folds in the presence of asymmetries. A simple one-mass model is proposed for each vocal fold. A stiffness asymmetry and open glottis oscillations are considered first, and regions of oscillation are determined by a stability analysis and an averaging technique. The results show that the subglottal threshold pressure for 1:1 entrainment increases with the asymmetry. Within that region, both folds oscillate with the same amplitude and with the lax fold delayed in time with regard to the tense fold. At large asymmetries, a region involving several different phase entrainments or toroidal regimes at constant threshold pressure appears. The effect of vocal fold collisions and asymmetry in the damping coefficients of the oscillators are explored next by means of numerical analyses. It is shown that the damping asymmetry expands the 1:1 entrainment region at low subglottal pressures across the whole asymmetry range. In the expanded region, the oscillator with the lowest natural frequency is dominant and the other oscillator has a large phase advance and small amplitude. The theoretical results are finally compared with data collected from a mechanical replica of the vocal folds.

Perceptual thresholds for realistic double-slope decay reverberation in large coupled spaces

Reverberation highly influences sound perception in enclosed spaces. The reverberation time (RT) metric, used to quantify reverberation in single volumes, is inappropriate for coupled spaces characterized by non-exponential double-slope energy decays. Previous research on reverberation perception of double-slope decays has been predominantly based on varying basic impulse response characteristics such as decay times corresponding to reverberation times of individual volumes presented as independent variables. Alternatively, several studies have employed geometrical room acoustic software simulations to generate collections of responses while varying architectural parameters such as coupling area and room volumes. To avoid issues related to geometrical acoustics simulations, such as position dependence and limitations of some software to properly simulate coupled volume behavior, this study examines perception of the variability of reverberation typical of a physical coupled volume system. Employing an established statistical model, the control parameter of coupling area aperture which acoustically connects the volumes serves as the independent variable. Two listening tests were conducted to determine perceptual thresholds using an ABX discrimination task. The range of tested values corresponded to physically realizable variations. Just noticeable differences (JNDs) were derived with an average JND of ≈ 10% variation of the coupling aperture. No significant differences were found between different musical excerpts.

Comparison of sound field measurements and predictions in coupled volumes between numerical methods and scale model measurements

Prediction of sound fields in closed spaces can be achieved by various methods, either physical or numerical, based on different theoretical features. While the benefits and limitations of many methods have been examined for single volume spaces, there has been little effort in examining these effects for coupled volume situations. The present study presents a case study comparing theoretical, experimentally physical measurements on a scale model, and various numerical methods, namely boundary element method (BEM), finite-difference time-domain (FDTD), and ray-tracing through the commercial software CATT-Acoustic and ODEON. Although these numerical methods all use 3D numerical models of the architecture, each is different. Ray-tracing is more suitable to geometries with larger planes; BEM requires a more regular finer surface mesh; and FDTD requires a volumetric mesh of the propagation medium. A simple common geometry based on the scale model is used as a basis to compare these different approaches. Appli...

Coupled volumes and statistical acoustics: preliminary results of an improved analytical model

Reverberation chambers, coupled to the main audience hall, make it possible to change the acoustics of a hall through the size and location of coupling surfaces. This passive device provides an acoustical variability which exceeds the possibilities offered by heavy curtains and moving reflectors. Since architects and acousticians are interested in predicting models as design tools, several approaches have been developed, using different simulation methods. This study proposes an improvement to analytical models of sound energy decay in coupled rooms, integrating temporal aspects proposed by Cremer and Muller as well as spatial components described by Barrons revised theory. Distances from the primary source located on stage as well as from secondary sources, which are the apertures between reverberation chambers and the main room, to the same receiver are included. Results from this analytical model are compared to those from ray-tracing software and scale model measurements, all based on the same simple...

Threshold of oscillation of a vocal fold replica with unilateral surface growths

Among vocal fold diseases, the presence of a surface growth is often encountered and can be considered a public health issue. While more energy is required to achieve phonation than in healthy cases, this situation can lead to a wide range of voice perturbations, from a change of voice quality to aphonia. The present study aims at providing finer comprehension of the physical phenomena underlying this type of pathological phonation process. A vocal fold replica is used to perform measurements of mechanical responses of each vocal fold as well as of the subglottal pressure in both healthy and pathological configurations. Besides these physical measurements, a theoretical model is derived, using the one-mass-delayed model involving asymmetry of mass and geometry in order to simulate pressure signals. The theoretical model parameters are determined according to mechanical measurements on the replica. Results from measurements and simulations show that this unique vocal fold replica behaves in a manner comparable to clinical observations. The energy required to produce sound increases in the presence of a growth as well as with the size of the growth. Further investigation tends to show that the contact of the growth on the opposite vocal fold, considered as additional damping, plays a critical role.

Investigation of the effective aperture area of sliding and hinged doors between coupled spaces

Acoustical coupling between architectural spaces can be implemented by sliding or hinged doors. This study compares the effects of these variable coupling area designs on the sound field using temporal energy decay curve analysis. Varying the aperture size alters the multi-slope decay curve properties such as the decay rate of each slope and their point of intersection (time and level). A predictive model is proposed, based on a geometrical approach and statistical theory for coupled volumes. Differences between scale model measurements and analytical predictions are quantified by means of deviations of acoustical parameters; reasonable agreement is found.