In a soundproof structure body including a tubular tube body having an opening portion, and a resonance type soundproof structure, in which a phase difference θ, at an upstream of the resonance type soundproof structure, between a reflected wave in the resonance type soundproof structure and a reflected wave of a transmitted wave transmitted through the resonance type soundproof structure and reflected by the opening portion satisfies Inequation |θ−π|≤π/3 with respect to a resonance frequency of the resonance type soundproof structure. This soundproof structure body can effectively offset a reflected wave from a resonance type soundproof structure body by opening end reflection by appropriately specifying positions of the resonance type soundproof structure and the opening end portion of a duct, a tube line, or the like to improve an absorbance of a single resonance type soundproof structure.

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.

A noise suppression apparatus for an air handling unit includes an inlet section connectable to a fan of the air handling unit. The inlet section includes a forward wall spaced apart from an aft wall to define an internal chamber, and an inlet wall extending between the forward wall and the aft wall, the inlet wall defining an inlet air opening. A plurality of internal walls in the inlet wall define a plurality of resonator openings that each open to at least one of a plurality of resonator sections within the internal chamber. The plurality of resonator sections include at least one quarter wave tube section and at least one Helmholtz resonator section. One or more resonator sections are configured to attenuate noise generated by the fan at two or more frequencies. At least one resonator opening of the plurality of resonator openings opens to a plurality of resonator sections.

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. The silencing system includes one or more silencers that are disposed in a tubular member provided to penetrate a wall separating two spaces, and satisfies “0<Re[Bn]<1” and “Im[Bn]>0” in a case where a standardized effective modulus of elasticity in an interior space of the tubular member in which the silencers are disposed is denoted by Bn.

An object is to provide a silencing system that includes a silencer disposed in a ventilation sleeve, can suppress the generation of negative pressure in the interior, and can prevent a door or the like of an interior entrance from being difficult to open. The silencing system includes one or more silencers that are disposed in a ventilation sleeve provided to penetrate a wall separating two spaces, and “αA>10.sup.C−(0.1/P)×TL” is satisfied in a case where a gap equivalent area of the ventilation sleeve in which the silencer is installed is denoted by αA and a normalized sound transmission loss in an octave band in which a first resonant frequency of the ventilation sleeve is present is denoted by TL.

C denotes a constant determined by a measurement system in a case where there is no silencer and P denotes a transmission efficiency coefficient.

Provided are conduits for air flow that are capable of reducing noise and related methods. The provided conduits include a first section that is tubular and substantially non-perforated and a second section with at least a portion having a multiplicity of microperforations that provide an average flow resistance of from 50 MKS Rayls to 8000 MKS Rayls therethrough. The second section is either (a) tubular and connected in series with the first section, with an outer surface of the second section being in fluid communication with an outer surface of the conduit, or (b) disposed within the first section.

An air-conditioning apparatus includes a housing having an air inlet and an air outlet, a fan disposed in the housing, and a bell mouth through which a fluid flowing from the air inlet to the air outlet passes in association with rotation of the fan. The bell mouth includes curved part having a curved sectional shape in a fluid flow direction and a vibration-damping element disposed on at least one of a front surface and a rear surface of the curved part. The vibration-damping element is disposed at a position corresponding to a node of vibration of the bell mouth.

Aspects of the present disclosure include a casing comprising an air inlet and an air outlet, a fan configured to move air from the air inlet to the air outlet, and a tunable sound attenuating module having an opening at a first end of the tunable sound attenuating module, a cavity, and a back wall at a second end of the tunable sound attenuating module, wherein: the tunable sound attenuating module is oriented such that the back wall is closer to the fan than the opening, and a length of tunable sound attenuating module is substantially one fourth of the acoustic wavelength of a sound generated by the fan.

A housing for an electric apparatus includes a housing body and a silencer. The housing body has a space provided to house a device that is a noise source and at least one opening communicating the space. The silencer is attached to an outer periphery of the housing body in such a manner as to surround the opening.

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.