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 θ1; 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 λ; and a phase difference θ2 is defined as 2π×2L/λ:
|θ1−θ2|≤π/2  (1). The soundproof system with a small size can obtain 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.

A silencer module for an air handling unit includes a first baffle and a second baffle spaced apart from the first baffle to form an air channel between the first baffle and the second baffle. The air channel is configured to receive a fluid flow and direct the fluid flow through the silencer module. The silencer module also includes a reactive acoustic feature formed in the first baffle. The reactive acoustic feature includes an attenuation profile configured to reduce propagation of tonal acoustic waves through the air channel.

Embodiments of the present disclosure provide a diffusion muffling device, a diffusion resonance muffling device, a full-frequency diffusion muffling device, a muffling system for a ventilation channel, and a muffling method using the same, which include a plurality of diffusion muffling units disposed in the ventilation extension direction of the ventilation channel, wherein the plurality of diffusion muffling units are arranged in parallel in a direction with a predetermined angle between the direction and the ventilation extension direction of the ventilation channel, and a muffling passage is formed between each two adjacent diffusion muffling units, wherein each of the diffusion muffling units includes at least one diffuser, and each diffuser includes a plurality of convex portions so that sound waves entering the muffling passage are reflected multiple times in the muffling passage by the plurality of convex portions and then sound is attenuated. In the present disclosure, the diffusers are disposed to diffuse and reflect sound waves, so that the sound is attenuated in a long and narrow passage by multiple times of reflections of the sound waves, thereby improving the low-frequency sound muffling performance in the ventilation channel so as to effectively achieve an effect of sound muffling and noise reduction in ventilation.

A packaged terminal air conditioner unit (PTAC) includes a bulkhead that defines an indoor portion and an outdoor portion. An outdoor fan is positioned within the outdoor portion and a controller is communicatively coupled with the outdoor fan for receiving a command to generate white noise and operating the outdoor fan to create the white noise at a desired decibel level to block out ambient sounds. A user may regulate the outdoor fan speed when the PTAC is not heating or cooling by setting a desired decibel level, e.g., using a control panel of the PTAC.

A silencing device and an air supply system according to an embodiment of the present invention include a resonance silencer provided at a position connected to a space in which the sound source is located within the air supply system in order to silence the noise generated from the sound source in the housing, in which in a case where a resonance wavelength of the resonance silencer alone is denoted by λ, a distance by which the resonance silencer is separated from the sound source is less than λ/2. A fundamental resonance frequency of the resonance silencer is equal to or less than an acoustic upper limit frequency determined according to a size of the housing.

An object is to provide a silencing system that can achieve both high ventilation performance and high soundproof performance, can silence a plurality of pieces of resonant sound, and has high general-purpose properties since the silencing system does not need to be designed according to a tubular member. In a silencing system where silencers are disposed on a tubular member, the silencers silence sound having a frequency of first resonance of the tubular member, each silencer includes a cavity portion and an opening portion, the opening portions are connected to a sound field space of the first resonance of the tubular member, a conversion mechanism for converting sound energy into thermal energy is disposed in each cavity portion or at a position where the conversion mechanism covers the opening portion, a ratio S.sub.1/S.sub.d of the area S.sub.1 to the area S.sub.d satisfies “0<S.sub.1/S.sub.d<40%” in a case where the area of the opening portion of the silencer is denoted by S.sub.1 and the surface area of an inner wall of the cavity portion is denoted by S.sub.d, and the depth L.sub.d of the cavity portion in the traveling direction of an acoustic wave in the silencer satisfies “0.011×λ<L.sub.d<0.25×λ,” in a case where the wavelength of an acoustic wave at the resonant frequency of the first resonance is denoted by λ.

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.

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

Compact sound attenuation systems for fluid ducts are provided having one or more sound attenuation units that can be absorptive or reflective, depending on design. Each sound attenuation unit has one or more encircling Helmholtz resonators that fully encircle the duct in a lateral direction. Sound attenuation units can be coincident with the duct well and either interior or exterior to the duct, or in some instances can be partly interior and partly exterior to the duct. Sound attenuation systems can be tuned for maximum attenuation of a single resonance frequency, or can include multiple units of different frequencies for broadband attenuation.