Soundproofing | EPFL Graph Search

Soundproofing is any means of impeding sound propagation. There are several basic ways to reduce sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles for absorption, or using active antinoise sound generators. Acoustic quieting and noise control can be used to limit unwanted noise. Soundproofing can reduce the transmission of unwanted direct sound waves from the source to an involuntary listener through the use of distance and intervening objects in the sound path (see sound transmission class and sound reduction index). Soundproofing can suppress unwanted indirect sound waves such as reflections that cause echoes and resonances that cause reverberation. Absorption Sound-absorbing material controls reverberant sound pressure levels within a cavity, enclosure or room. Synthetic absorption materials are porous, referring to open cell foa

Scale Model Evaluation and Optimization of Sodar Acoustic Baffles

Adrien Chabbey, Fernando Porté Agel

A 21: 1 scaled sodar, operating at 40 kHz, has been built and tested in the laboratory. Sodars, which use sound scattered by turbulence to profile the lowest few hundred meters of the atmosphere, need good acoustic shielding to diminish annoyance and to reduce unwanted reflections from nearby objects. Design of the acoustic shielding is generally inhibited by the difficulty of testing on full-scale systems and uncertainty as to accuracy of models. In contrast, the scale model approach described allows for "bench testing" of many designs under controlled conditions, and efficient comparison with models. Measured beam patterns from the scale model were compared with those from a numerical model based on the Kirchhoff integral theorem. Satisfactory agreement has allowed using the numerical model to optimize the acoustic shield design, both for the gross acoustic baffle geometry and for the geometry of rim modulations known as thnadners. Optimization was performed in the specific case of a scaled model of a commercial phased array sodar.

American Meteorological Society2015

Plasma-based Electroacoustic Actuator for Broadband Sound Absorption

Stanislav Sergeev

Environmental noise, mostly related to human activities, has an immense impact on public health. The development of noise reduction technologies is paramount in addressing this problem. Because of practical and economic reasons, a compact, broadband, lightweight, and mechanically robust solution is often compulsory. Existing noise reduction methods typically fall short meeting these requirements. Passive absorbers are bulky and inefficient in the low frequency range or present only a narrowband performance. Active noise reduction methods, including active noise cancellation and acoustic impedance control, appear more promising as they allow extending the bandwidth of operation and remain small compared to a wavelength. An electrodynamic loudspeaker is conventionally a favourable choice for a controlled transducer. However, it limits efficient technology application due to its fragile diaphragm, relatively high weight, and inherent resonant nature, bounding the bandwidth of control.This thesis is devoted to the development of a fundamentally different plasma-based electroacoustic transducer for active sound control applications. The acoustic field is manipulated by the partial ionisation of a thin air layer with an atmospheric corona discharge and its further control with an alternating electrical field. The transducer consists of a set of high voltage wires, separated with a grounded mesh by an air gap. Analytical and numerical models are first developed to design and characterise the corona discharge actuator. Several feedback impedance control strategies are adapted and implemented with the corona discharge actuator, resulting in achieving broadband impedance and sound absorption. A prototype of a plasma-based active acoustic liner for noise reduction under grazing sound incidence is proposed and assessed experimentally in laboratory facilities. A model-based feedforward approach for broadband control of acoustic impedance is then developed. Exploiting the unique physics of the corona discharge actuator with the help of the analytical model, perfect sound absorption and tunable acoustic reflection under normal incidence are achieved over two frequency decades, from several Hz to the kHz range. Such unprecedented bandwidth and compactness of the developed system, along with the simplicity of construction, lightweight, and flexible design, opens new doors in noise control applications, and acoustic metamaterials, among others.

EPFL2022

Development of electroacoustic absorbers as soundproofing solutions for industrial ventilation systems

Victor Desarnaulds, Hervé Lissek, Etienne Thierry Jean-Luc Rivet

In many industrial environments, room and cavity modes may severely strengthen the annoyance of low frequency noises, such as in ventilation equipments. Moreover, there is an obvious technological gap in the state-of-the-art relative to low-frequency soundproofing, and the only potential solutions basically take the form of heavy and bulky bodies, that can be practically impossible to implement in real situations. With a view to reducing the low-frequency annoyance, in the range of 30 Hz, resulting from the general ventilation system of the CHUV (University Hospital of Vaud Canton) in Lausanne, a prototype of electroacoustic absorber has been developed, consisting of closed-box loudspeakers connected to electric shunt networks, acting as efficient low-frequency sound absorbers. A numerical model has first been developed and challenged with in-situ measurements. Then the electroacoustic absorber design has been optimized, and theoretical performances have been verified. Finally, the prototype has been assessed in situ, both in terms of global acoustic performances, and also in terms of perceptual low frequency annoyances relief, based on the satisfactory analysis of the neighbourhood of the hospital.

2013

Plasma-based Electroacoustic Actuator for Broadband Sound Absorption

Stanislav Sergeev

EPFL2022