Sound reinforcement system | EPFL Graph Search

A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience. In many situations, a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage, typically by using electronic effects, such as reverb, as opposed to simply amplifying the sources unaltered. A sound reinforcement system for a rock concert in a stadium may be very complex, including hundreds of microphones, complex live sound mixing and signal processing systems, tens of thousands of watts of amplifier power, and multiple loudspeaker arrays, all overseen by a team of audio engineers and technicians. On the other hand, a sound reinforcement system can be as simple as a small public address (PA) system, consisting of, for example, a single microphone connected to a 100-

Abutment stability assessment of the Hongrin arch dam using 3D distinct element method

Thierry Bussard, Azad Koliji, Jian Zhao

The Hongrin north dam is a double curvature concrete arch dam located in western Swiss Prealps, which attains 125m high. The right bank abutment of the dam mainly consists of intensively jointed Neocomian limestone and exhibits zones of potential instability.At the time of construction (1965–1969), this slope was reinforced with rock anchors. Subsequent hydrogeological study and groundwater monitoring revealed the presence of water pressure due to a slight seepage flow through the rock joints in the dam foundation. This latter evidence raised an additional concern about the stability of the abutment. In a dedicated study, the stability of the right abutment the Hongrin north dam abutment has been assessed using continuumdiscontinuum numerical analysis. 3DEC (3-Dimensional Distinct Element Code) has been used to model the complicated slope geometry and to explore the role of rock discontinuity in the failure mechanisms. The rock mass is defined as deformable distinct blocks which interact along frictional discrete discontinuities representing the rock joint sets. The water pressure is introduced as fluid pressure boundary condition along the discontinuities, and the rock reinforcement is modeled as structural elements working across the discontinuities. The dam reaction forces, derived from a separate finite element analysis, are evaluated for their possible effects on the stability. The model examines the sensitivity of the abutment stability to the presence of joint water pressure and evaluates the improving effects of rock reinforcement. The results of the analysis allow achieving an enhanced understanding of potential failure mechanisms and helps in proposing further suitable measures to improve the stability of the abutment.

Taylor & Francis Group2012

Sound Field Reconstruction in a room through Sparse Recovery and its application in Room Modal Equalization

Vu Thach Pham

The acoustics of a room often refer to the quality of the room in terms of sound recording as well as sound reproduction. At low frequencies, where the wavelengths are of the same order of magnitude with the dimensions of the room, due to the standing waves phenomena, room modes are formed which can give rise to multiple irregularities and eventually damage the listening experience. In order to effectively address the problem at these frequencies, a thorough knowledge of the sound field in the room is often required. Through numerical studies, the sound field in the room could be simulated based on an FEM room model which would result in certain differences when comparing to the actual situation. On the other hand, the traditional experimental sampling of the sound field in a room often results in an impractical number of microphones.This thesis focuses on the development of a sound field reconstruction framework that makes use of certain sparse representation and recovery algorithm to reconstruct the sound field of the room at low frequencies using a limited set of microphones. The reconstruction framework is then tested under different conditions and scenarios to prove its validity. Once the performance of the framework has been validated through both simulation and actual measurements, the reconstruction framework is investigated in detail regarding its application in the field of active modal equalization. These active absorption methods are of high interest in the field of modal equalization due to the fact that passive absorption method at low frequencies are more often than not ineffective. The reconstruction framework is then used to first assess the spatial performance of the active electroacoustic absorbers which consists of a current-driven system of loudspeakers in enclosures that aims to dampen room modes by achieving optimal target impedance in front of the loudspeaker membranes. In addition, a more complex applications of the reconstruction framework in which its reconstructed sound field can be used to fine tune the control parameters of the active absorbers is also investigated. The research shows promising results in both application of the reconstruction frameworks and open doors to further development in both the field of sound field reconstruction as well as room modes equalization.

EPFL2021

Optimal Co-Planning of ESSs and Line Reinforcement Considering the Dispatchability of Active Distribution Networks

Katarina Knezovic, Mario Paolone, Ji Hyun Yi

The paper presents a method for the co-optimization of energy storage systems allocation and line reinforcement in active distribution networks. The objective is to guarantee the capability of an active distribution network to follow a dispatch plan by appropriately coping with the high uncertainties of loads and stochastic renewable generation while ensuring the secure operation of the grid and minimizing the power grid losses. The proposed formulation relies on a modified formulation of the so-called Augmented Relaxed Optimal Power Flow (AR-OPF) method, which considers the exact (i.e., non-approximated) AC-OPF in a convexified way (the AR-OPF is proven to provide the global optimal and exact solution of the OPF problem for radial power grids). To tackle the complexity and computational burden of the proposed planning problem, the Benders decomposition algorithm is used and, in order to enhance the convergence speed of the numerical solution of the proposed problem, the Benders decomposition has been suitably modified to determine the energy storage systems site and size sequentially. To assess the performance of the proposed method, simulations are conducted on a real Swiss distribution network composed of 55 nodes and hosting a large amount of stochastic photovoltaic generation. The sensitivity analysis with respect to the photovoltaic capacity is also carried out to assess the effectiveness of the proposed method.

2022

Sound Field Reconstruction in a room through Sparse Recovery and its application in Room Modal Equalization

Vu Thach Pham

EPFL2021