Abstract: A car having: two front wheels; two rear wheels; a bottom wall, which delimits a lower surface, which faces a road surface and, in use, is brushed by an air flow flowing under the car; an internal combustion engine; and an exhaust system, which is coupled to the internal combustion engine and is provided with an exhaust duct, which originates from the internal combustion engine and has an end chamber, which ends with an outlet opening, through which exhaust gases are released into the atmosphere. The end chamber of the exhaust duct has at least one movable partition, which can be moved to different positions so as to change the width of the outlet opening. The movable partition delimits a lower surface of the end chamber, which faces the road surface and, in use, is brushed by the air flow flowing under the car.

Abstract: A method for producing an alveolar soundproofing structure in which a portion of a membrane of a diaphragm including an acoustic outlet is inserted into a hole of a perforated membrane which covers a cell of the alveolar structure, and the diaphragm is pressed into the cell with the perforated membrane becoming deformed and is fixed at that location. It also relates to the alveolar structure. Such a method enables different types of diaphragms to be inserted into different configurations of cells and enables the diaphragm to be fixed therein, in accordance with the sound frequencies to be processed.

Abstract: A recreational vehicle and an air conditioner therefor are provided. The air conditioner includes an indoor cover defining an indoor portion and an outdoor portion with an outdoor heat exchanger and an outdoor fan disposed in the outdoor portion and an indoor heat exchanger and an indoor fan disposed in the indoor portion. The air conditioner also includes an indoor panel defining an air inlet and an air outlet. An acoustic insert includes a solid top wall and at least one permeable side wall. The acoustic insert is positioned between the indoor panel and the indoor fan, whereby the acoustic insert dampens sound transmitted through the indoor panel.

Abstract: A sound absorbing structure includes a panel having a first side and a second side and at least one acoustic scatterer coupled to a first side of the panel. The panel may be at least partially transparent. The at least one acoustic scatterer has an opening and at least one channel. The at least one channel has a channel open end and a channel terminal end with the channel open end being in fluid communication with the opening. The panel may be utilized to separate an interior space from an exterior space.

Abstract: Frequency adjustable quarter-wavelength resonators have a movable end wall defined by a surface of a sphere that is moved within the resonator tube. The sphere can be ferromagnetic, enabling it to be moved by magnetic interactions with moving external magnetic elements, or by a variable external magnetic field, controlled by power modulation to external electromagnets. The resonators can optionally be helical or otherwise curved, and the spherical shape of the structure forming the end wall enables it to navigate curves in the resonator tube.