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 fracturing apparatus may include a first plunger pump including a first power end and a first hydraulic end; a prime mover including a first power output shaft; and a first clutch including a first connection portion and a second connection portion. The first power end of the first plunger pump includes a first power input shaft, the first connection portion is coupled to the first power input shaft, the second connection portion is coupled to the first power output shaft of the prime mover.

Abstract: Architectures and techniques are presented that can facilitate improved design and function of certain air handler devices. Architectures directed to an improved air handler device can be designed to improve temperature control demands such as, e.g., concurrently heat and cool air and reducing device dimensions (e.g., size, weight) that can reduce costs and mitigate shipping and installation difficulties.

Abstract: A sound attenuating baffle device has a baffle casing supported within a duct such that a boundary wall of the baffle device is oriented in the flow direction from the leading end to the trailing end of the baffle casing. The baffle casing includes a sound attenuating structure therein, and a trailing member protruding outwardly beyond the trailing end of the baffle casing towards a free trailing edge of the trailing member which is non-linear in profile. As compared to a continuous, straight trailing edge as found on most silencer outlets, a non-linear profile, for example a V-shaped or saw-toothed edge, improves the flow distribution along the height of the baffle or perimeter of the centerbody. The distribution of airflow across the resulting extended tail edge represents an improvement in the flow recovery.

Abstract: A sound absorber includes at least one cavity and at least one mouth to communicate the at least one cavity with an outside of the sound absorber. The at least one cavity includes a top surface, a bottom surface, and a side wall. The top surface includes the mouth. The bottom surface opposes the top surface. The side wall is extended to connect the top surface with the bottom surface. At least one of the top surface and the bottom surface is inclined with respect to the side wall.

Abstract: Disclosed is an air cleaner having independent fluid paths and a home appliance having the air cleaner. The air cleaner includes a front panel having a plurality of air inlets formed thereon for air to flow in from outside of the case, first and second blower devices arranged inside the case to allow air to flow in through the plurality of air inlets, first and second filter units arranged to filter the air flowing in by the first and second blower devices, a first outlet located on the case to release the air, a second outlet formed at a different location from that of the first outlet, a first fluid path formed between one of the plurality of air inlets and the first outlet; and a second fluid path formed between another of the plurality of air inlets and the second outlet.

Abstract: A ventilation device comprises a body (11) having first and second ports (14, 15) and a ventilation passage (13) that extends through the body between the ports to allow airflow through the body. The ventilation device also comprises a noise attenuation device (21) arranged to attenuate noise transmission through the passage in at least one direction from the first to the second port. The noise attenuation device comprises at least one array (22, 23) of noise attenuation tubes disposed in the ventilation body. In one form, the noise attenuation device (21) include two arrays of attenuator tubes disposed on respective opposite sides of the passage (13). The tubes each have a mouth (27) that opens to the passage and a central axis that extends from the mouth in the direction of elongation of that tube.

Abstract: A blower assembly for an automotive heating, ventilation, and air conditioning system includes a housing having an opening and a blower wheel supported by the housing that directs air through the opening of the housing. A plurality of ribs are disposed within the opening of the housing and define a plurality of channels for directing air through the opening of the housing and toward the blower wheel.

Abstract: A device for reducing sound from an air treatment unit includes, in one embodiment, an air treatment system, including a wall mount HVAC unit with a supply air opening and a return air opening. A supply air sound reducer is provided in communication with the supply air. The supply air sound reducer includes a housing defining a supply interior provided with sound reducing material. The sound reducing material is overlaid with a layer of perforated material. A return air sound reducer is provided in communication with the return air opening. The return air sound reducer includes a housing defining an interior return volume provided with sound reducing material applied to one or more inside surfaces of the interior return volume and a layer of perforated material disposed over the sound reducing material. Mid-structure including sound reducing material is disposed in each of the supply and return air assemblies.

Abstract: This is an environmental unit useful in a xerographic system that reduces or eliminates pulsation and vibration in the system. This is accomplished by the use of flexible bladders on a wall of the air duct work pumping air into the print housing. When the vibration is abated, the banding problems on images are eliminated.

Abstract: A packless silencer for a Venturi control valve being a generally rectangular enclosed housing formed by four side walls and having an intake opening and a discharge opening. Four perforated baffles for each of the side walls are positioned inside of the housing, extend the length of the housing and are offset from the side walls to create an empty baffle space between the perforated baffles and the side walls the ends of the baffle space are covered by end caps.

Abstract: A sound attenuator for low frequencies in an air-conditioning duct of paper mills includes a sound attenuator frame insertable in the air-conditioning duct. At least one attenuator member operating according to the plate resonator principle has a first resonator plate, a framework, whereto the first resonator plate is attached by its inner surface, and a second plate, which is essentially parallel to the first resonator plate. The second plate is attached to the framework by its inner surface, whereby the second plate, the framework and the first resonator plate delimit at least one attenuator unit. The first resonator plate, attached to the framework, is a steel plate and is attached to the framework by laser welding and the framework comprises a pressure balancing opening.

Abstract: In a disk array apparatus, by taking note of a first sound of a specific frequency which is a noise element of original sounds generated from a fan, a second sound whose phase is inverted to that of the first sound is generated by a structure of a cooling air flow path passing through the fan, and the second sound is synthesized with the first sound on the cooling air flow path, thereby reducing the noise. For example, an exhaust duct is located on a fan unit in an upper part of the apparatus, two flow paths extending to an exhaust port are formed in an internal structure of the exhaust duct, and the two flow paths are designed so that the difference in the flow path length therebetween becomes equivalent to half wavelength of the specific frequency.

Abstract: A noise suppressor for a straddle-type vehicle provided with a belt type continuously variable transmission having a resin-block-type belt. A portion of an air passage for guiding air to a belt chamber is formed in a closed casing. The closed casing includes a dish-shaped first casing member and a dish-shaped second casing member. An inlet port and an exhaust port are formed in the second casing member. Partition walls in the form of curved plate pieces are formed in the first casing and second casing members. Air flow paths formed by the partition walls are U-shaped, thereby forming a serpentine flow.

Abstract: A sound-baffling arrangement for use in conjunction with an air-handling unit. One or more sound baffle columns are mounted for rolling or sliding movement within the interior of the air handling unit housing. Each baffle column may be selectively moved between a use position proximate to the fan assemblies, and a non-use position more distal from the fan assemblies. The movable sound baffles permit the air-handling unit to be fabricated to fit within a smaller housing, and thus to have a smaller, more economical footprint.

Abstract: An air passage opening and closing device for controlling an air flow for air-conditioning a vehicle compartment which is adapted to reduce an uncomfortable noise generated when the opening degree of a door such as an air-mixing door is small is provided, wherein a plurality of extending portions (7g) are provided on tips of the lip seal (7c). The extending dimension (H) of the extending portion (7g) is more than or equal to substantially 1 mm and less than or equal to substantially 3 mm, the dimension (B) in the width direction orthogonal to the extending direction in the extending portion (7g) is more than or equal to substantially 2 mm and less than or equal to substantially 14 mm, and the gap distance (G) between the adjacent extending portions (7g) is more than or equal to substantially 1 mm and less than or equal to substantially 4 mm.

Abstract: A whole house fan system and installation methods configured to reduce noise generated by the fan are provided. The system generally includes a fan, a register, and a flexible duct extending between the fan and the register. The flexible duct has acoustical insulation properties, which helps to reduce sound transmission from the fan to the register. The fan system is configured to be mounted in the attic space of a house. The fan motor is suspended in the attic so that it does not have direct contact with any part of the building structure.

Abstract: A trickle vent such as might be used in association with commercial windows is formed from PVC tubing in two convoluted paths. One or more expansion chambers are provided at turns or directional changes within the tubing which reduce or eliminate noise transmission through the vent. Where a plurality of expansion chambers are used, each chamber may be of different length to dampen a different portion of the acoustic spectrum. In a preferred embodiment, the expansion chambers are filled with an acoustic-type foam, and the ends are not completely sealed. The tubing preferably bridges two extrusions that form a supporting housing for the vent, and by using two separate extrusions bridged by the tubing, both thermal and acoustic isolation are maintained.

Abstract: A system and method are disclosed for enclosing electronic equipment in a noiseproofed and ventilated enclosure. This includes supplying air to an enclosure and removing air from the enclosure through acoustic chambers attached to the enclosure. The acoustic chambers can be constructed of materials or be treated with materials that have noise-absorbing or noise-abating properties. In addition, the acoustic chambers can contain baffles that prevent noise that has entered the acoustic chamber from leaving the chamber. And, the system and method can use a cable egress port that allows cables and wiring to pass through the egress port while blocking the transmission of noise through the egress port.

Abstract: A system and method are disclosed for enclosing electronic equipment in a noiseproofed and ventilated enclosure. This includes supplying air to an enclosure and removing air from the enclosure through acoustic chambers attached to the enclosure. The acoustic chambers can be constructed of materials or be treated with materials that have noise-absorbing or noise-abating properties. In addition, the acoustic chamber for exhausting air from the enclosure can contain baffles that help to prevent noise that has entered the acoustic chamber from leaving the chamber. And, the system and method can use a cable egress port that allows cables and wiring to pass through the egress port while blocking the transmission of noise through the egress port.

Abstract: A body exhauster includes a housing defining an opening, at least one louver rotatably supported by the housing, and a sound-absorbing material attached to and extending from the housing to prevent noise from traveling through the housing.

Abstract: There is provided an air conditioner for a vehicle, including an air intake provided on a vehicle compartment inner side of a quarter inner panel and on the side of the quarter inner panel, a fan provided on the side of the air intake port and performs forced ventilation, and a cover provided in front of the air intake port and causes operation noise of the fan emitted from the air intake port to interfere with each other so that the noise can be reduced. With this arrangement, operating noise of the fan emitted from the air intake can be reflected in a direction away from a passenger seated on a seat in a vehicle compartment.

Abstract: A repositionable attenuator for a terminal unit in a heating, ventilation, and air conditioning system is disclosed. The attenuator is positionable between at least a first and a second position. This enables the attenuator to be attached to and shipped with the terminal unit prior to installation of the terminal unit.

Abstract: A system and method are disclosed for enclosing electronic equipment in a noiseproofed and ventilated enclosure. This includes supplying air to an enclosure and removing air from the enclosure through acoustic chambers attached to the enclosure. The acoustic chambers can be constructed of materials or be treated with materials that have noise-absorbing or noise-abating properties. In addition, the acoustic chambers can contain baffles that prevent noise that has entered the acoustic chamber from leaving the chamber. And, the system and method can use a cable egress port that allows cables and wiring to pass through the egress port while blocking the transmission of noise through the egress port.

Abstract: A vehicle ventilation duct includes a duct body, a conduit, a sound absorption chamber, a transmission opening communicating the conduit with the sound absorption chamber, and an air-permeable member closing the transmission opening permeably. The duct body is disposed in a vehicle outer hull, and includes a frame having a ventilation opening opened to the outside of a vehicle and a valve element covering the ventilation opening openably and closably. The conduit is formed integrally with or independently of the duct body, is disposed on a vehicle-passenger-room side of the duct body, is communicated with the ventilation opening of the duct body, and is communicated with the inside of a vehicle passenger room, whereby enabling air inside and outside the vehicle to pass therethrough back and forth. Thus, the ventilation duct lets out air in the vehicle passenger room to the outside of the vehicle or vice versa.

Abstract: Silencing equipment is provided for an air-cooling assembly in a large off-road vehicle having wheels, traction motors for the wheels that operate in a motoring mode to propel the vehicle and a power generating dynamic braking mode, resistor grids for dissipating the dynamic braking power, and a blower for moving cooling air past the grids to cool them. The silencing equipment may include a resistor grid housing 24 and at least one upper inlet 22 for passing cooling air to the interior of the housing. The inlet includes noise-absorbing material. A conduit 28 is provided for directing cooling air from the upper inlet through a transition chamber to reach the blower and at least one resistor grid in the housing. The conduit is lined with noise-absorbing material. A removable cover 30 is provided for the conduit for accessing the air blower in the housing through the transition chamber, whereby servicing of the blower may be performed without removal of the entire upper inlet.

Abstract: A flow straightening grid 30 is provided at an area where the air flow turns about 180 degrees in an air path 23, or in the vicinity thereof. Because of this, the air flow can be prevented from being disturbed in the air path 23 and, therefore, noise caused by the disturbance of the air flow can be reduced effectively.

Abstract: An air conduction element (1), particularly an air conduction channel for a motor vehicle, having a reverberant channel body (2) manufactured from plastic, which has at least one wall region replaced by a sound-absorbing component (10, 11), the sound-absorbing component having an at least partially exposed outer side. An edge region of the sound-absorbing component (10, 11) be extrusion-coated with the plastic of the channel body (2) in such a way that the sound-absorbing component (10, 11) is connected in a form-fitting way to the channel body (2) along at least a section of its circumference.

Abstract: A low noise method and apparatus with the apparatus including a hood for mounting over an exhaust outlet duct to capture a fluid stream and then redirect the fluid stream to a fluid outlet in the hood through the use of smoothly curving duct that maintains the fluid flowing therethrough in a laminar flow condition with the inlet and outlet positioned such that there is no line of sight between the exhaust outlet duct and the fluid outlet duct in the hood.

Abstract: A muffler arrangement includes muffler elements arranged in rows which are oriented in each case transversely to a direction of flow. The muffler elements themselves are oriented in each case longitudinally in relation to the direction of flow. The distance between two adjacent muffler rows in this case amounts to approximately at least four times, or at least six times, the distance between two adjacent muffler elements of the equidistantly arranged muffler elements of a muffler row and/or the flow off edges of the muffler elements of at least one muffler row have guide plates. Equipping of the muffler elements of the last muffler row in the direction of flow may be dispensed with.

Abstract: Duct units for delivery of air to an air supply fan and for connecting this fan to an air heater unit are disclosed. The duct unit for delivering air in one version has a narrow first section, a second, transition-type section and a wide sound attenuating, third section with these three sections extending generally vertically. Spaced apart splitters containing sound attenuating material and having side walls of perforated metal are mounted in the third section. The splitters include a central splitter and outer splitters with the latter converging inwardly towards a central axis of the third section. This duct unit also has an elbow-shaped duct section connected to the third section at its upstream end and connectible to the fan at its downstream end. In another version, the duct unit has a single, elongate splitter that extends longitudinally along at least a major portion of a second duct section and that bends through a smooth curve.

Abstract: An acoustic attenuator includes an intake air duct having an intake air duct opening leading to an outside environment and a blower fan opening leading to a blower fan. Air is drawn through the intake air duct opening towards the blower fan and a primary reflecting panel disposed in the intake air duct. The primary reflecting panel is configured to reflect sound propagated from the blower fan away from the intake air duct opening.

Abstract: An apparatus (10) includes a pressure relief valve (12) for relieving air pressure from a passenger compartment (76) of a vehicle (66). The pressure relief valve (12) enables airflow from the passenger compartment (76) to atmosphere (78). The apparatus (10) also includes a member (14) for reducing noise entering the passenger compartment (76) as a result of a backflow of air through the pressure relief valve (12) from atmosphere (78) to the passenger compartment (76). The member (14) includes structure (112, 114) for attaching the member (14) to the pressure relief valve (12).

Abstract: An acoustic barrier systems that reduces the amount of noise entering the passenger compartment of a vehicle includes a secondary acoustic attenuator that extends from a primary acoustic barrier to a vehicle component case to envelop space around a conduit passing from the engine compartment to the component case. In one embodiment, the secondary acoustic attenuator extends from the primary acoustic barrier to the component case, with the secondary acoustic attenuator enveloping space around the conduit between the vehicle component case and the primary acoustic barrier.

Abstract: A ventilation assembly (10) for a window or door assembly is provided with an anti-sound system (80). The anti-sound system may include a sound generator (82), a noise sensor (88) and an error correction noise sensor (100). A control box (86) is provided for the anti-sound system (80). A solar cell (96) may be provided on a weather canopy (14) of the ventilation assembly for providing power to the control box (86). The ventilation assembly may alternatively comprise a wall vent, chimney or stack vent ventilation system.

Abstract: An aircraft engine run-up hangar comprises a building defining a test chamber capable of receiving an aircraft therein, an air inlet structure, and an exhaust structure. The air inlet structure is formed in a front end part of a roof structure corresponding to a front end part of the building, the exhaust structure is connected to a rear end part of the building and defines an exhaust passage extending obliquely upward from the back end of the building, and one or a plurality of current deflecting members are disposed near a lower end of the air inlet structure to deflect air currents flowing through the air inlet structure into the building toward an aircraft housed in the building. A current-straightening structure is incorporated into the air inlet structure. A current-straightening space is defined under the air inlet structure.

Abstract: An improved sound attenuating device for use in a gas transportation duct, said device comprising a core of acoustically absorptive material substantially enclosed within an impervious film to prevent direct contact between the acoustically absorptive material and gas flowing through said gas transportation duct, wherein said enclosed absorptive material is maintained in position between at least two perforated facing plates and further wherein there is provided between the perforated facing and the impervious film and between the impervious film and the acoustically absorptive material spacing means to allow unrestricted movement of the impervious film in the void between the perforated facing and the acoustically absorptive material, while preventing contact between the film and the perforated facing and between the film and the acoustically absorptive material, and blocking means to impede the internal flow of gas between the film and the perforated facing and between the film and the acoustically absorpti

Abstract: An air duct, in particular for a motor vehicle heating, ventilating and/or air conditioning system, which is acoustically optimized by virtue of the fact that at least one cross-sectional discontinuity is constructed by making use of a phenomena which occur as acoustic scattering processes at the cross-sectional discontinuity. The cross-sectional discontinuity should extend substantially perpendicular to the flow direction in the air duct.

Abstract: A ventilation duct and methods of ventilation are disclosed. The ventilation duct provides a plurality of inner and outer sound absorbing members. The inner and outer sound absorbing members lying in separate planes with portions of the inner and outer sound absorbing members overlapping one another to inhibit the transmission of sound through the duct. The inner and outer sound absorbing members each including a longitudinal cavity filled with a sound absorbing material and having a plurality of sound transmission passages extending through the members to expose the sound absorbing material to incoming sound waves. In addition, the members may be shaped to have a reverse megaphone effect to further reduce the sound transmitted across the duct.

Abstract: A supply air terminal designed for installation in an opening (3) in a wall (5) of a ventilation duct (7). The supply air terminal (1) extends in the duct (7) with a part (9) shaped to be able to take up part of the air flow transported in the duct and transport this for venting outside the ventilation duct (7), where the part (9) of the supply air terminal (1) has a considerable extend in the ventilation duct (7) in order to achieve a drop in pressure and a laminar flow in the supply air terminal (1).

Abstract: A system including a cabinet for intaking or discharging a gas while minimizing external duct noise and a gas duct for attachment to a housing with the gas duct having a smoothly curved passageway therein with each portion of the passageway having a cross sectional area which is sufficiently large so that the ratio of the inertia forces to viscous forces within the passageway is sufficiently small so that a laminar flow condition is maintained throughout the gas duct.

Abstract: An aircraft engine run-up hangar comprises a building defining a test chamber capable of receiving an aircraft therein, an air inlet structure, and an exhaust structure. The air inlet structure is formed in a front end part of a roof structure corresponding to a front end part of the building, the exhaust structure is connected to a rear end part of the building and defines an exhaust passage extending obliquely upward from the back end of the building, and one or a plurality of current deflecting members are disposed near a lower end of the air inlet structure to deflect air currents flowing through the air inlet structure into the building toward an aircraft housed in the building. A current-straightening structure is incorporated into the air inlet structure. A current-straightening space is defined under the air inlet structure.

Abstract: An aircraft engine run-up hangar comprises a building defining a test chamber capable of receiving an aircraft therein, an air inlet structure, and an exhaust structure. The air inlet structure is formed in a front end part of a roof structure corresponding to a front end part of the building. The exhaust structure is connected to a rear end part of the building and defines an exhaust passage extending obliquely upward from the back end of the building. A ceiling included in the building has an inclined section sloping down backward to straighten air currents, and a groove is formed in a middle part, with respect to width, of the inclined section to permit a vertical tail fin of an aircraft to pass when the aircraft is carried into or out of the test chamber.

Abstract: A ventilation duct and methods of ventilation are disclosed. The ventilation duct provides a plurality of inner and outer sound absorbing members. The inner and outer sound absorbing members lying in separate planes with portions of the inner and outer sound absorbing members overlapping one another to inhibit the transmission of sound through the duct. The inner and outer sound absorbing members each including a longitudinal cavity filled with a sound absorbing material and having a plurality of sound transmission passages extending through the members to expose the sound absorbing material to incoming sound waves. In addition, the members may be shaped to have a reverse megaphone effect to further reduce the sound transmitted across the duct.

Abstract: A fluid diffuser and a method for diffusing fluid are provided. In one preferred embodiment, the diffuser comprises a frame adapted to be connected to the end of fluid supply duct. Mounted within the frame is a pore-containing web. The web redirects fluid passing through the pores by changing the direction of the fluid upon exiting the web. Prescribed portions of the web can be blocked to expel fluid preferentially in one direction and expel fluid less in other directions. Other means for controlling the direction and flow of fluid upon exiting the web are provided, including changing the angle of fluid supply to the web, and placing a vane at the entrance to the web.

Abstract: An air duct silencer can be used at the inlet of an air supply fan unit for a building or other large structure. The silencer has an exterior housing with exterior walls forming outer surfaces of the housing and interior walls arranged in the housing, connected to the exterior walls and defining an annular airflow passageway extending between an air inlet located at one end and a circular air outlet adapted for connection to the fan unit. The outlet defines a primary central axis extending through the center of the outlet and perpendicular to a plane in which the outlet lies. A central airflow defining member has a second central axis extending from an outer end thereof to an inner end and this axis is substantially coaxial with the primary central axis. This airflow defining member is substantially circular in transverse cross-section along its length and has a relatively wide bulb like end section at its outer end and a narrow end section at the inner end.

Abstract: An air handling system for use in a building is used in combination with an elevated floor assembly for mounting on a principal floor of the building, this assembly including a working area floor which lies above the principal floor so as to provide an air plenum between the two floors. An outlet attenuator is mounted on the principal floor and extends upwardly through the working area floor, this attenuator including an exterior outlet housing having an air inlet at the top and a lowermost air outlet in at least one vertical side thereof. The air outlet is connected to the air plenum and is connected to the air inlet by a lower airflow passageway defined by interior walls. This attenuator includes sound absorbing material contained in the housing. An axial or centrifugal fan unit is mounted above the outlet attenuator and provides a downward flow of air to the outlet attenuator. There is also an inlet attenuator section mounted above the fan unit and extending upwardly to a ceiling of the building.

Abstract: In a blower unit for a vehicle air conditioner, an inside/outside air switching door opens an inside air introduction port and closes an outside air introduction port when an inside air introduction mode is set. Plural ribs for irregularly reflecting an air-blowing noise generated by a blower fan are provided on an inner surface of the inside/outside air switching door, and top ends of the ribs are arranged along a main flow of inside air introduced from the inside air introduction port during the inside air introduction mode. Thus, the blower unit effectively reduces a reflected noise on the inner surface of the inside/outside air switching door, and effectively prevents a disturbance noise of the main flow of inside air.

Abstract: An air handling system for use in a building is used in combination with an elevated floor assembly for mounting on a principal floor of the building, this assembly including a working area floor which lies above the principal floor so as to provide an air plenum between the two floors. An outlet attenuator is mounted on the principal floor and extends upwardly through the working area floor, this attenuator including an exterior outlet housing having an air inlet at the top and a lowermost air outlet in at least one vertical side thereof. The air outlet is connected to the air plenum and is connected to the air inlet by a lower airflow passageway defined by interior walls. This attenuator includes sound absorbing material contained in the housing. An axial or centrifugal fan unit is mounted above the outlet attenuator and provides a downward flow of air to the outlet attenuator. There is also an inlet attenuator section mounted above the fan unit and extending upwardly to a ceiling of the building.

Abstract: An air handling system for use in a building is used in combination with an elevated floor assembly for mounting on a principal floor of the building, this assembly including a working area floor which lies above the principal floor so as to provide an air plenum between the two floors. An outlet attenuator is mounted on the principal floor and extends upwardly through the working area floor, this attenuator including an exterior outlet housing having an air inlet at the top and a lowermost air outlet in at least one vertical side thereof. The air outlet is connected to the air plenum and is connected to the air inlet by a lower airflow passageway defined by interior walls. This attenuator includes sound absorbing material contained in the housing. An axial fan unit is mounted above the outlet attenuator and provides a downward flow of air to the outlet attenuator. There is also an inlet attenuator section mounted above the fan unit and extending upwardly to a ceiling of the building.