An environmental control unit, such as an HVAC or heat pump unit, includes an insert disposed within the device housing that provides noise attenuation features. The insert defines air flow paths within the housing. The insert may be formed of a foam material and may include multiple foam blocks that cooperate to form a serpentine passageway therein. The passageway includes multiple turns. The features further include perforated sheet metal panels disposed in the passageway at strategic locations. The perforations are shaped and dimensioned to correspond to the frequencies to be attenuated.

Provided is a soundproof structure body including an opening member that forms an opening tube line having a cross-sectional area S, and at least two resonance structures for sound waves that are installed inside the opening tube line, and in a case where a cross-sectional area of the resonance structure is defined as Si, a width thereof is defined as di, an interval between the two resonance structures is defined as L, an impedance of the two resonance structures is defined as Zi, and a synthetic acoustic impedance is defined as Zc, a condition of Expression (1) is satisfied at a resonance frequency f0 at which a theoretical absorption value At is a maximum value. This soundproof structure body can realize high absorption using a plurality of resonance structures.

At (f0, L, S, Si, di, Zi)>0.75(1),

Here, L>0, S>0, Si (i=1, 2)>0, di (i=1, 2)>0

An air-sending device includes a housing including an inlet air passage communicating with an air inlet and an outlet air passage communicating with an air outlet, a first partition plate partitioning an interior of the housing into the inlet air passage and the outlet air passage, a bell mouth disposed around an opening defined in the first partition plate, and an impeller disposed over the first partition plate across the bell mouth and having a rotation axis that extends in a direction that intersects the first partition plate. The impeller suctions air into the inlet air passage from the air inlet, and blows out air from the air outlet through the outlet air passage. The inlet air passage guides air from the air inlet to the opening along the first partition plate, and has an air-passage wall.

A soundproof structure has two or more soundproof units. Each of the soundproof units has an outer shell having a cylindrical shape, has a hollow inner space inside the outer shell, and has a first opening portion opened to outside on a surface that is one end portion of the outer shell in an axis direction of the cylindrical shape. The two soundproof units adjacent to each other are disposed in the axis direction such that the first opening portions face each other. The first opening portions facing each other are spaced apart from each other in the axis direction. An average distance in the axis direction between the first opening portions facing each other is less than 20 mm. Accordingly, there are provided a soundproof structure and a soundproof system which can insulate sounds on the low frequency side with a simple configuration, are small and lightweight, and can easily change the frequency characteristics.

A sound level reducing apparatus and method for reducing the outdoor sound level produced by a high efficiency gas furnace. The apparatus comprising a muffler having an internal length determined by an identified target pure tone frequency producing an undesirable sound level. The internal length may be optimized to reduce the sound level across a range of operational frequencies.

A soundproof structure body includes a first tube structure and a second tube structure connected to the first tube structure and having a cross-sectional area different from the first tube structure, in which a structure body having a cross-sectional area smaller than a cross-sectional area of the first tube structure is installed in the first tube structure, and a transmission loss in a case where the structure body is installed in the first tube structure with respect to a case where the structure body is not installed in the first tube structure is positive at two frequencies adjacent to each other and difficult to generate an air column resonance mode in the first tube structure. This soundproof structure body generates a soundproof effect even at frequencies other than air column resonance of a tube structure such as a duct or a muffler, has a small size, and can obtain a high transmission loss in a wide-band.

A first ventilation duct line has a first portion having a first sectional area, a second portion having a second sectional area larger than the first sectional area, and a third portion having an inclined inner face connecting the first portion and the second portion to each other. Further, there is a second ventilation duct line having an opening portion positioned on an inner side of the first portion of the first ventilation duct line.

An air conditioner includes: a main body having an air outlet; a fan provided in the main body; a heat exchanger provided in the main body; and a first member rotatably supported on the main body and opening and closing the air outlet, wherein the first member includes a first casing having a first surface facing an inner side of the main body while operation is stopped and a second casing attached to the first casing; on the first casing, a recess is formed on the first surface and a protrusion protruding toward the second casing is formed, and the recess is positioned on an opposite side to the protrusion.

A multifunction panel for use in a building defines an interspace, optionally for the passage of air, and includes a first layer having a plurality of first shaped through-holes of a first predetermined diameter; a second layer having a plurality of cells defining a honeycomb or ribbed structure; a third layer having a plurality of second shaped through-holes of a second predetermined diameter, the first and the second holes being selectively open at the opposite ends of respective cells, so as to create a first configuration of a cell providing for the transit of air between the interspace and the internal environment, or vice versa, when a first hole opens at a first end and of a cell at a second hole opens at a second end of the cell, and further generating a Helmholtz resonator.

A soundproof system includes a tube structure having one or more opening ends and a soundproof structure having an opening portion or a radiation surface. The following Expression (1) is satisfied in a case in which a phase difference between sound incident on the soundproof structure and sound re-radiated from the soundproof structure is defined a phase difference as 1; for one or more maximum values of the pressure of sound formed in the tube structure, a distance between the opening portion or the radiation surface and a position where the sound pressure has a maximum value in the tube structure is L; a wavelength of the incident sound is ; and a phase difference 2 is defined as 22L/:

|12|/2(1).

The soundproof system with a small size can obtain high transmission loss in a wide band.