Abstract:
The application discloses a noise attenuating system ( 100, 200, 300, 400, 700, 800 ) for use with a positive airway pressure system providing a flow of gas, comprising: an expansion chamber ( 140, 240, 340, 434, 740 ) having a volume; an intake GP tube ( 115, 215, 315, 415, 715, 815 ) having an inlet ( 117, 217, 317, 410, 717, 812 ) and outlet port or portion separated by a length, wherein a portion of the inlet port or portion extends outside of the expansion chamber; and either: a noise attenuator ( 110, 120, 170, 210, 220, 223, 224, 226, 228, 232, 270, 320, 411, 413, 422, 423, 424, 425, 426, 428, 431, 720, 722 ) having a bottom and protruding sidewall forming a cavity, wherein the noise attenuator is positioned near the inlet portion of the intake tube such that a portion of the intake tube extends into the cavity of the noise attenuator; or: an acoustic deflector ( 110, 120, 170, 210, 220, 223, 224, 226, 228, 270, 232, 320, 411, 413, 422, 423, 424, 425, 426, 428, 431, 720, 722 ) positioned near the outlet port or portion of the intake tube, wherein noise is deflected away from the outlet port or portion of the intake tube. The application also discloses positive air pressure apparatus ( 100, 200, 300, 400, 700, 800 ) comprising a housing ( 180, 480, 880, 884 ), first and second acoustic chambers, an intake vent or port ( 125, 225, 410, 812 ) in the first chamber, an inlet port or tube coupling the first and second chambers, a noise attenuator in the first chamber, and a blower unit ( 150, 250, 350, 440 ) in the second chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Application 61/798,367 filed on Mar. 15, 2013; U.S. Patent Application 61/798,541 filed on Mar. 15, 2013 and U.S. Patent Application 61/798,462 filed on Mar. 15, 2013 which are incorporated herein by reference. 
     
    
     COPYRIGHT STATEMENT 
       [0002]    A portion of the disclosure of this patent application document contains material that is subject to copyright protection including the drawings. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a positive airway pressure [PAP] devices, such as continuous positive airway pressure [CPAP] devices, and more particularly a method for attenuating the noise released therefrom. 
         [0005]    2. Description of the Prior Art 
         [0006]    It is known that applying a CPAP device to a patient may prevent upper airway occlusion during sleep. CPAP devices have become the apparatus of choice for the treatment of chronic sleep apnea, chronic pulmonary obstruction and snoring. Many CPAP machines are readily available in the marketplace. 
         [0007]    A typical CPAP system generally includes a bedside generator comprising, a blower unit powered by an electric motor. The blower unit, the motor, and associated controls are usually encased together within the bedside generator. A delivery tube, usually a flexible plastic tube having a proximal end and a distal end, is used to deliver pressurized air or other gasses to the patient. The proximal end of the delivery tube is connected to the bedside generator and the distal end of the delivery tube is fitted to the face of a patient. The patient interface may include features that allow the patient interface to be affixed to the patient and maintain a proper orientation with respect to the patient. 
         [0008]    Bedside CPAP machines are typically large and heavy. They are usually plugged into a wall outlet for power or have a large external battery. The size, weight, and power constraints can interfere with patients&#39; ability and willingness to use the machine. For example, these constraints can make it difficult to utilize the CPAP apparatus in areas away from their bedside or while traveling. Additionally, these constraints can also prohibit patients from moving freely during sleep, thereby inducing further discomfort. 
         [0009]    Furthermore, typical CPAP devices are relatively loud and can interfere with a patient&#39;s sleep or the sleep of other people nearby. In a typical CPAP device, sound may be propagated from various locations and actions of the device, such as the flow of air the flow of air into and out of the device or the operation of the motor and fan. Because the apparatus is used mainly in a bedroom or other place having a low ambient noise level to facilitate sleep, it is important that the blower operates quietly so as not to disturb the patient or others in close proximity while they sleep. 
         [0010]    A need therefore exists for PAP devices with size, weight, and sound characteristics that provide improved usability for patients. 
       SUMMARY OF THE INVENTION 
       [0011]    The system and methods described herein provide a CPAP apparatus that can be held and operated in one hand, is portable, and is quieter than 30 decibels (dBA) while in operation. 
         [0012]    In an exemplary embodiment, the current application discloses a CPAP apparatus having an air intake attenuator comprising: an intake attenuation chamber defining at least one intake slot; an acoustic chamber having an inlet port and at least one acoustic deflector; a motor or blower that is placed within the acoustic chamber, wherein vibrations from the motor or blower are isolated or substantially isolated from the single chamber; and in some embodiments a dissipative element that may be added to further attenuate the amount of noise heard by the patient. 
         [0013]    A noise attenuating system for use with ventilation or other systems providing a flow of gas comprising an expansion chamber having a volume; an intake tube having an inlet and outlet port separated by a length, wherein a portion of the inlet port extends outside of the expansion chamber; and a noise attenuator having a bottom and protruding sidewall forming a cavity, wherein the noise attenuator is positioned over the inlet portion of the intake tube such that a portion of the intake tube extends into the cavity portion of the noise attenuator. 
         [0014]    The system may further include the intake tube having a length that ranges from 0.25 inches to 3.5 inches. 
         [0015]    The system may further comprise a plurality of acoustic deflectors disposed within the cavity portion of the noise attenuator. 
         [0016]    The system may include at least one deflector that extends from the sidewall and is aligned substantially parallel to the bottom of the noise attenuator. 
         [0017]    The system may further include at least one deflector that extends from the sidewall and is angled into the cavity of the noise attenuator. 
         [0018]    The system may further comprise a noise dissipating element disposed within the cavity portion of the noise attenuator. 
         [0019]    The system may further include a noise dissipating element that is a porous material and at least one acoustic deflector that is covered by a noise dissipating material. The expansion chamber may have an acoustic deflector positioned near the outlet portion of the intake tube the acoustic deflector is angled with respect to a plane defining the outlet portion of the intake tube. In some cases the system include positioning the back-side of the acoustic deflector to deflect noise emanating from a region within the expansion chamber having the greatest noise intensity, wherein the noise is deflected away from the outlet port of the intake tube. 
         [0020]    These and other embodiments are described in more detail herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The foregoing and other objects, aspects, features, and advantages of the disclosure will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIG. 1  illustrates the interior of a portable PAP apparatus; and 
           [0023]      FIG. 2A  depicts an interior view of a portable CPAP apparatus; and 
           [0024]      FIGS. 2B-D  illustrate configurations of chamber configurations; and 
           [0025]      FIG. 3  depicts an example of the interior of a portable PAP apparatus; and 
           [0026]      FIG. 4A  illustrates a perspective view a portable dual-chamber PAP apparatus; and 
           [0027]      FIGS. 4B-D  illustrate additional embodiments of possible attenuator configurations; and 
           [0028]      FIG. 5  illustrates the relationship between the area of an inlet port and a tube or chamber for reducing noise; and 
           [0029]      FIG. 6  illustrates a configuration of a PAP device; and 
           [0030]      FIG. 7A  and  FIG. 7B  illustrate additional embodiments of possible configurations of a PAP device; and 
           [0031]      FIG. 8A  and  FIG. 8B  illustrate a PAP device with an acoustically invisible cover; and 
           [0032]      FIGS. 9A-B  depict an acoustically invisible cover. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    To provide an overall understanding of the systems, devices, and methods described herein, certain illustrative embodiments will be described. Although the embodiments and features described herein are frequently described for use in connection with CPAP apparatuses, systems, and methods, it will be understood that all the components, mechanisms, systems, methods, and other features outlined below may be combined with one another in any suitable manner and may be adapted and applied to other PAP apparatuses, systems, and methods, including, but not limited to, automatic positive airway pressure devices [APAP], variable positive airway pressure devices [VPAP], bi-level positive airway pressure devices [BPAP], and related apparatuses, systems, and methods. 
         [0034]    Bedside CPAP machines are typically large, heavy, and noisy. The systems and methods described herein are directed towards a small, quiet, light-weight, and portable CPAP device to overcome these current limitations and disadvantages. For example, the systems and methods described herein provide a PAP apparatus that is quieter than 30 decibels (dBA) while in operation. In certain approaches, the PAP apparatus can be held and operated in one hand and is portable. 
         [0035]      FIG. 1  depicts the interior of a PAP apparatus, such as a CPAP device. CPAP device  100  has a lower housing component  180 , which together with an upper housing component (not shown) defines a sealed chamber  140 . PAP apparatus  100  includes an intake chamber  110  positioned on a side or back of apparatus  100 . 
         [0036]    Intake chamber  110  serves to prevent the occlusion of inlet port  122  during use of device  100 . Intake chamber  110  may also reduce the acoustic output or noise of apparatus  100 . For example, intake chamber  110  includes foam  170  to reduce acoustic output of apparatus  100 . Although foam is described, any dissipative element could be used. Dissipative elements may include anechoic materials such as foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. Additionally or alternatively, apparatus  100  includes intake vents  125 , through which air may flow. In the depicted example, intake vents  125  are positioned at the side, top, and/or bottom of apparatus  100 . 
         [0037]    Both the attenuation intake chamber and the acoustic chambers may be designed to reduce the amount of noise released from the CPAP device during operation. Intake chamber  110  includes sound attenuators  120  positioned within intake chamber  110 . For purposes of the systems and methods described herein, an attenuator may refer to any of a plane, bar, circular, semi-circular, sphere, cone, or other mechanism configured to deflect, absorb, weaken and/or reduce a sound wave. 
         [0038]    Although two attenuators  120  are depicted in  FIG. 1 , any number of attenuators may be used. In some embodiments, the upper and lower housing components and/or the chamber wall  130  define a plurality of attenuators  120  extending therefrom. For example, the flow path defined by attenuators  120  in  FIG. 1  includes one right-angle turn. In additional embodiments however, the upper and lower housing components may define a variety of attenuators. For example, the housing components may be configured such that the flow path defines any number of turns each of any angular dimension (e.g., sixty degrees, ninety-degrees, one-hundred-eighty degrees, etc.) and any combination of vertical and horizontal turns. While the attenuator  120  may divert the airflow pathway and thereby create additional broadband noise, the primary purpose of the attenuator(s) is to reduce the amount of noise exiting the CPAP device. In embodiments having more than one attenuator  120 , each of attenuator  120  may have the same size and length, and may be defined by the housing components to have the same or substantially similar angles relative to the inlet port, chamber wall, and/or housing components. Alternatively, each attenuator  120  may have different sizes, shapes, and/or lengths. Further, each attenuator  120  may be oriented having varying angles relative to the inlet port chamber wall, and/or housing components and in some instances one or more attenuators  120  may partially or substantially surround the inlet port  122 . In certain approaches, one side of chamber  110  may have more attenuators  120 . Additionally or alternatively, chamber  140  may include attenuators  120 . 
         [0039]    Sealed chamber  140  has an inlet port  122  and an outlet port  139 . Inlet port  122  is positioned in wall  130 , which separates intake chamber  110  and sealed chamber  140 . A motor or blower  150  is placed within the chamber  140 . An intake tube  115  extends from intake chamber  110 , through inlet port  122 , and into acoustic chamber  140 . Intake tube  115  includes opening  117  to enable air flow from intake chamber  110  into acoustic chamber  140 . Although depicted as straight, intake tube  115  may include any number of turns. 
         [0040]    In some embodiments, foam or another anechoic material may be placed within chamber  130  to further attenuate noise produced during the operation of device  100 . The anechoic or noise attenuating material may be secured at specific locations within each chamber. In additional embodiments, the lower and/or upper housing components may be lined with an anechoic or noise attenuating material. In such embodiments, the anechoic or noise attenuating material may include foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. 
         [0041]    In certain embodiments, blower  150  is secured to chamber  140  using one or more mount connects  154 . In some embodiments, the mount connects may further comprise pivoting cone connectors, circular donut shaped mount connects, a silicone cradle, or any combination thereof. For example, the mount connects may comprise pivoting cone connectors that connect the top of blower  150  within chamber  140  and circular donut shaped mount connects that connect the bottom of blower  150  within chamber  140 . In addition to connecting blower  150  to the housing, mount connects  154  may reduce or eliminate transfer of vibrations from the blower to other components of device  100 . In certain embodiments, blower  150  is a brushless air-bearing motor. 
         [0042]    In certain embodiments, inlet port  122  includes an intake tube  115  having a first end  112  through wall  130  and a second end  124  that extends into chamber  140 . Intake tube  115  may have either a constant or varying internal diameter ranging from approximately 0.25 inches to approximately 0.75 inches and may have a length ranging from approximately 0.25 inches to approximately 3 inches, although any appropriate diameter and length may be used. The length and diameter of intake tube  115  affect the overall noise attenuation of the CPAP device, as will be further discussed below, for example, in relation to  FIG. 2  and equation 1 and equation 2. Accordingly, in some approaches, the dimensions of intake tube  115  are proportionally related to the volume of chamber  140 . 
         [0043]    Intake tube  115  may be formed using rigid materials, flexible materials, or any combination thereof. For example, intake tube  115  may be formed using a hard plastic. In certain embodiments, intake tube  115  is composed of flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. 
         [0044]    In certain approaches, outlet port  139  includes outlet tube  155 , which extends from blower outlet  152  and through the housing, such as lower housing  180 . An adapter  160  may be used to connect the blower outlet tube  145  to a patient interface, such as mask that can be coupled to the airways (e.g., nose and mouth) of a patient. In embodiments having adapter  160 , adapter  160  may be solitary in construction. Additionally or alternatively, adapter  160  may be configured so that a proximal portion of adapter  160  is secured and sealed to the housing of device  100 , while a distal portion of the adapter  160  extends outward from device  100 . In such an embodiment, lower housing component  180  and the upper housing component may each include a detent capable of accepting a portion of the adapter, whereby the two housing components together form a seal around the circumference of a portion of the adapter. 
         [0045]    Outlet tube  155  may also vary in length and diameter. The length of the blower outlet tube  155  is long enough to connect to outlet  152  of blower  150  through outlet port  139 . Outlet tube  155  provides a sealed airway between blower  150  and adapter  160 . Additionally, depending on the dimensions of the blower  150 , the inner diameter of the outlet tube  155  may vary so long as the diameter is large enough to fit over and seal with outlet  152  and adapter  160  and/or a patient interface system, such as tubing and a delivery mask. Outlet tube  155  may be formed using rigid materials, flexible materials, or any combination thereof. For example, outlet tube  155  may be formed using a hard plastic. In certain embodiments, outlet tube  55  is composed of flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. 
         [0046]    In certain embodiments, intake chamber  110  may include a filter to clean the air of particulate matter. In certain embodiments, intake chamber  110  is removable from chamber  140  and other components of device  100  so that chamber  110  may be cleaned, replaced, or adapted for a particular need. For example, various types of filters may be used depending on a patient&#39;s health needs. A filter may not be required for all patients, may be replaceable, or may be cleaned. 
         [0047]    During operation, PAP device  100  creates positive air pressure through outlet port  139 . For example, when a patient interface, such as a mask, is attached, PAP device  100  creates positive air pressure, which can be provided to the patient when the patient places the patient interface at his or her airways (e.g., nose or mouth). Blower  150  includes intake  156 . When blower  150  is powered on, blower  150  intakes air through intake  156  and pushes out that air through outlet  152 . The reduced pressure at intake  156  causes air to flow through vents  125 , into chamber  110 , through inlet port  122  via tube  115 , and into chamber  130 , where it then flows into intake  156  of blower  150 . Blower  150  then pushes air through outlet  152 , through outlet tube  155 , and through outlet port  139  to thereby provide positive air pressure through outlet port  139 , for example, through hole  162  of adapter  160 . In certain approaches, the pressurized air is delivered a pressure ranging from approximately 2 centimeters (cm) of water to approximately 40 cm of water above atmospheric pressure at the point of use, although any appropriate pressure may be used. 
         [0048]      FIG. 2  depicts the interior of a portable PAP apparatus  200 . PAP apparatus  200  includes an attenuation intake chamber  210  with sound attenuators  220  positioned within intake chamber  210 . In certain approaches, intake chamber  210  includes foam  210  to the reduce acoustic output or noise of apparatus  200 . Although foam is described, any dissipative element could be used. Dissipative elements may include anechoic materials such as: foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. Additionally or alternatively, apparatus  200  includes intake vents  225 , through which air may flow. 
         [0049]    PAP apparatus  200  has an acoustic chamber  240  with an inlet port  222  coupled to intake chamber  210 . An intake tube  215  extends from intake chamber  210 , through inlet port  222 , and into acoustic chamber  240 . Intake tube  215  includes opening  217  to enable air flow from intake chamber  402  into acoustic chamber  240 . When in operation, blower  150  is powered on and pulls air through vents  225 , into opening  217 , through tube  215 , and into blower  250 . Blower  250  then pushes air through outlet tube  255  and through opening  262  into a patient interface, such as a respiratory mask. 
         [0050]    The size and location of intake tube  215  and opening  217  may be determined based on the location and size of the attenuators  220 . For example, opening  217  may have a diameter of approximately 0.5 inches and intake tube  215  may extend into attenuating intake chamber  210  approximately 0.875 inches beyond attenuators  220 . In certain embodiments, the diameter of opening  217  along the length of intake tube  215  varies in diameter, for example, from approximately 0.25 inches to 0.75 inches. In certain embodiments, intake tube  215  extends into attenuating intake chamber  210  so that opening  217  is substantially even with attenuators  220 . In certain approaches, intake tube  215  extends past attenuators  220  by more than approximately 1 inch. 
         [0051]      FIGS. 2B-D  illustrate additional embodiments of device  200  with additional or alternative configurations of attenuators for reducing noise output.  FIG. 2B  depicts device  200  with attenuators  223  that are configured approximately parallel to intake tube  215 .  FIG. 2B  also shows an end cap attenuator  224 , which extends partially around intake tube  215 , but does not directly contact intake tube  215 .  FIG. 2C  depicts angled attenuators  226  and  228 . Attenuators  226  and  228  extend at an angle relative to the side walls of device  200  and, in this example, relative to the intake tube  215 . Attenuator  226  also includes an “L” extension  227 , which extends from the distal end of attenuator  226 .  FIG. 2D  shows curved attenuators  232 . Each type of attenuator ( 220 ,  223 ,  224 ,  226 ,  228 , and  232 ) alters the flow of air from vent  225  to blower  250 . They can be used individually or in any combination. Additionally, attenuators of other shapes may also be used, such as those with additional curves, different angles, additional extensions, and combinations of curves and linear portions. The attenuators are used to create unique air flow paths, which also have the important effect of altering and reducing the noise properties of device  200 . 
         [0052]      FIG. 3  depicts the interior of a portable PAP apparatus  300 . PAP apparatus  300  includes an attenuation intake chamber  310  with sound attenuators  320  positioned within intake chamber  310 . In certain approaches, intake chamber  310  includes foam  370  to reduce the acoustic output of apparatus  300 . Although foam is described, any dissipative element could be used. Dissipative elements may include anechoic materials such as: foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. Additionally or alternatively, apparatus  300  includes intake vents  312 , through which air may flow. 
         [0053]    PAP apparatus  300  has an acoustic chamber  340  coupled to intake chamber  310  via inlet port  322 . In certain approaches, apparatus  300  includes a first intake tube  315  extending into intake chamber  310 . Apparatus  310  includes a barrier  321  within chamber  340 , which forms flow space  306 , which is in fluid communication with first intake tube  315 . As depicted, flow space  306  can have turns or bends. Barrier  321  may be configured such that flow space  306  defines any number of turns, wherein each turn has of any angular dimension (e.g., sixty degrees, ninety-degrees, one-hundred-eighty degrees, etc.) and any combination of vertical and horizontal turns. In certain approaches, barrier  321  is firm and inflexible. When in operation, blower  350  is powered on and pulls air through vents  312  into opening  317  of intake tube  315 , through tube  315 , through inlet port  322 , through flow space  306 , into acoustic chamber  340 , and into blower  350 . Blower  350  then pushes air through outlet tube  355  and through opening  362  into a patient interface, such as a respiratory mask. 
         [0054]      FIG. 4  depicts the interior of a dual chamber PAP apparatus  400 . CPAP device  400  has a lower housing component  480 , which together with an upper housing component (not shown) defines a first sealed chamber  430  and a second sealed chamber  434  separated by wall  432 . First sealed chamber  430  has an inlet port  410  with intake tube  415 , which extends through housing  480 , through second chamber  434 , and through wall  432  into first chamber  430 . A first portion  412  of tube  415  is outside housing  480  and a second portion  420  is inside sealed chamber  430 . In some embodiments, the first chamber may further include a noise attenuator  431  positioned within the airflow path from portion  420  of intake tube  415 . 
         [0055]    Device  400  includes an interchamber port  417 , which allows air to flow from the first chamber  430  to the second chamber  434 . In certain approaches, interchamber port  417  includes a tube  416 , which extends from first chamber  430 , through chamber wall  432 , and into second chamber  434 . 
         [0056]    The first and second chambers are separated by a chamber wall  432 . In some embodiments, chamber wall  432  may be formed on lower housing and/or the upper housing (not depicted). In certain approaches, chamber wall  432  is solitary in construction with the housing. Additionally or alternatively, chamber wall  432  may be secured to the respective housing components with an adhesive or glue. Additionally, chamber wall  432  may be formed from an anechoic material such as foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. In certain embodiments, chamber wall  432  may be formed using a rigid material, such as a hard plastic. 
         [0057]    A motor or blower  440  is located within second chamber  434 . In certain embodiments, blower  440  is secured to chamber  434  using one or more mount connects  450 . In some embodiments, the mount connects may further comprise pivoting cone connectors, circular donut shaped mount connects, a silicone cradle, or any combination thereof. For example, the mount connects may comprise pivoting cone connectors that connect the top of blower  440  within chamber  434  and circular donut shaped mount connects that connect the bottom of blower  440  within chamber  430 . In addition to connecting blower  440  to the housing, mount connects  440  may reduce or eliminate transfer of vibrations from the blower to other components of device  400 . In certain embodiments, blower  440  is a brushless air-bearing motor. 
         [0058]    In some embodiments, foam or another anechoic material may be placed within chamber  430  and chamber  434  to further attenuate noise produced during the operation of device  400 . The anechoic or noise attenuating material may be secured at specific locations within each chamber. In additional embodiments, the lower and/or upper housing components may be lined with an anechoic or noise attenuating material. In such embodiments, the anechoic or noise attenuating material may include foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. 
         [0059]    In at least one embodiment, the first chamber  430  further comprises an attenuator  431  which may be placed within the chamber directly across from the proximal end  420  of intake tube  415 . Attenuator  431  is positioned within the airflow path to thereby attenuate noise created by the flow of air through chamber  430 . In certain approaches, attenuator  431  is angled toward the intake tube having an acute angle relative to the housing component. In certain approaches, device  400  includes a plurality of attenuators. In certain approaches, device  400  includes at least attenuator in second chamber  434 . When a plurality of attenuators are included, each attenuator, such as attenuator  431 , within the chamber  430  or chamber  434  may be oriented in varying angles relative to the end of intake tube  415 , interchamber tube  416 , and/or the housing components. While the attenuators may vary in size, length, quantity, shape, angle, and/or location, they may divert the airflow pathway and thereby create additional broadband noise, the primary purpose of attenuators is to reduce the amount of noise exiting the CPAP device. Attenuators may further comprise a dissipative element, noise attenuating coating, and/or a noise attenuating material attached thereto. For example, attenuator  431  may be composed of or coated with an anechoic or noise attenuating material. The anechoic or noise attenuating material may include foam, rubber, clay, silicon, or any other suitable soft and/or porous materials. 
         [0060]    Device  400  additionally includes one or more connector portions  485  to couple lower housing  480  and upper housing together, thereby creating a seal. In the depicted example, the connector portions  485  are around the perimeter of the housing and a fastener, such as a screw, is used to couple the housing. Additionally or alternatively, the edge  482  of the housing may provide a coupling and/or sealing mechanism. For example, edge  482  has a tongue, which may couple to a groove in an upper housing portion. Edge  182  may also include a seal, such as santoprene or silicone. 
         [0061]    Intake tube  415  and interchamber tube  416  may have either a constant or varying internal diameter ranging from approximately 0.25 inches to approximately 0.75 inches and may have a length ranging from approximately 0.25 inches to approximately 3 inches, although any appropriate diameter and length may be used. The length and diameter of intake tube  415  affect the overall noise attenuation of the CPAP device, as further discussed in relation to  FIG. 5  and equation 1 and equation 2. Accordingly, in some approaches, the dimensions of intake tube  415  and interchamber tube  416  are proportionally related to the volume of chamber  430 . 
         [0062]    Intake tube  415  and interchamber tube  416  may be formed using rigid materials, flexible materials, or any combination thereof. For example, intake tube  415  and interchamber tube  416  may be formed using a hard plastic. In certain embodiments, intake tube  415  and interchamber tube  416  are composed of flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. Intake tube  415  and interchamber tube  416  may be composed of different materials. 
         [0063]    In certain approaches, outlet port  439  includes outlet tube  445 , which extends from blower outlet  437  in second chamber  434 , through wall  432 , through first chamber  430 , and through housing  480 . An adapter  460  may be used to connect the blower outlet tube  445  to patient interface  465 . In embodiments having an adapter, the adapter may be solitary in construction and configured so that a proximal portion of the adapter may be secured and sealed to the housing of device  400 , while a distal portion of the adapter extends outward from device  400 . In such an embodiment, the lower housing component  480  and the upper housing component may each include a detent capable of accepting a portion of the adapter, whereby the two housing components together form a seal around the circumference of a portion of the adapter. 
         [0064]    Outlet tube  445  may also vary in length and diameter. The length of the blower outlet tube  445  is long enough to connect to outlet  437  of blower  440  through outlet port  439 . Outlet tube  445  provides a sealed airway between blower  440  and adapter  460  and/or patient interface system  465 . Additionally, depending on the dimensions of the blower  440 , the inner diameter of the outlet tube  445  may vary so long as the diameter is large enough to fit over and seal with outlet  437  and adapter  460  and/or patient interface system  465 . Outlet tube  445  may be formed using rigid materials, flexible materials, or any combination thereof. For example, outlet tube  445  may be formed using a hard plastic. In certain embodiments, outlet tube  445  is composed of flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. 
         [0065]    Apparatus  400  includes a pressure port  462 . Pressure port  462  is coupled to adapter  460 . Pressure port  462  runs through housing  480  into chamber  430 , where pressure port  462  couples to a pressure sensor, such as a pressure sensor on circuitry board  444 . Pressure port  462  provides fluid communication from the output of device  400  at adapter  460  to a pressure sensor coupled to control circuitry. Circuitry board  444  includes control circuitry and control components for the operation of device  400 . Circuitry board  444  may be positioned over or under outlet tube  445 . In certain approaches, circuitry board  444  includes a power sources, such as a power adapter or battery. In certain approaches, the control circuitry on board  444  of device  400  is configured to display the pressure measured through pressure port  462  at a display, such as display  888  depicted in  FIG. 8 . In certain embodiments, the pressure output of device  400  may be adjusted manually by the user with user interface buttons. In certain approaches, the control circuitry on board  444  is configured to automatically adjust the output of device  400  based on the pressure measurements. The output of device  400  may be adjusted by modulating the power of blower  440 . 
         [0066]    Although not depicted, device  400  may include a cover, such as cover  890 , cover  900 , or cover  910 , described in greater detail below, which covers and prevents the occlusion of inlet port  410   
         [0067]    During operation, PAP device  400  creates positive air pressure through outlet port  439 . For example, when patient interface  465  is attached, PAP device  400  creates positive air pressure, which can be provided to the patient when the patient places the adapter at his or her airways (e.g., nose or mouth). Blower  440  includes intake  435 . When blower  440  is powered on, blower  440  intakes air through intake  435  and pushes out that air through outlet  437 . The reduced pressure at intake  435  causes air to flow through inlet port  410  into chamber  430 , where it then flows through interchamber port  416  into second chamber  434 , and into intake  435  of blower  440 . While in chamber  430 , the air can flow above or below outlet tube  445 . Blower  440  then pushes the air through outlet  437 , through outlet tube  445 , and through outlet port  439  to thereby provide positive air pressure through outlet port  439 . In certain embodiments, air may be initially passed through a pre-intake chamber, such as intake chamber  110  as described in relation with device  100 , before entering inlet port  410 . In certain approaches, the pressurized air is delivered to a patient through a patient interface, such as a respiratory mask, at a pressure ranging from approximately 2 centimeters (cm) of water to approximately 40 cm of water above atmospheric pressure at the point of use, although any appropriate pressure may be used. 
         [0068]    Both the first chamber  430  and second chambers  434  may be designed to reduce the amount of noise released from CPAP device  400  during operation. In such embodiments, the chambers may be designed to operate as a high-pass, low-pass, band filter, or a combination thereof. For example, in one embodiment, first chamber  430  may be designed as a low-pass filter, while second chamber  434  is designed as a high-pass filter. In additional embodiments, first chamber  430  and second chamber  434  may both operate as low-pass filters. 
         [0069]    In certain approaches, first chamber  430  and second chamber  434  have a combined volume ranging from approximately 200 milliliters (mL) to approximately 485 mL. For example, the combined volume of first chamber  430  and second chamber  434  may be approximately 481 mL. The combined volume of first chamber  430  and second chamber  434  may be approximately 362 mL. The combined volume of first chamber  430  and second chamber  434  may be less than 200 mL. 
         [0070]    Additionally or alternatively, first chamber  430  and second chamber  434  may have equivalent volumes. In certain approaches, one of the chambers may have a larger volume than the other chamber. For example, in an embodiment where the combined volume is approximately 270 mL, first chamber  430  may have a volume ranging from approximately 70 mL to approximately 170 mL, and second chamber  434  may have a volume ranging from approximately 100 mL to approximately 200 mL. As an additional example, in an embodiment where the combined volume is approximately 480 mL, first chamber  430  may have a volume ranging from approximately 180 to approximately 240 mL, while second chamber  434  may have a volume ranging from approximately 240 to approximately 300 mL. In some instances, the second acoustic chamber, which houses the blower, is larger than the first acoustic (or expansion) chamber. 
         [0071]    As is shown in both Equation 1 and  FIG. 5 , inlet port  410  and interchamber port  417  may each have an area that is proportionally related to the volume of chambers  430  and  434  respectively. In other embodiments however, inlet ports may be designed without using Equation 1. 
         [0072]      FIG. 4A  illustrates CPAP device  400  that has a lower housing component, which together with an upper housing component (not shown) defines two sealed chambers in series, a first chamber  481  and a second chamber  482 , the chambers being divided by chamber wall  483 . The first chamber has an inlet port  417 , which may further comprise an intake tube  416  that extends from the first chamber to the exterior of CPAP device. In some embodiments, the first chamber may further include an attenuator  420 . The second chamber also has an inlet port  418  which may comprise an intake tube  416  that extends from the first chamber and into the second chamber. In the embodiment shown, the motor or blower is located within the second chamber and may be vibrationally isolated from the second chamber and/or the upper or lower housing component using mount connects  452 . 
         [0073]    As shown, the first chamber in  FIG. 4A  includes an attenuator that is located within the chamber directly across from the proximal end of intake tube  115 , the attenuator is angled toward the intake tube having an acute angle relative to the housing component.  FIGS. 4B-D  illustrate additional embodiments having a plurality of attenuators. In such embodiments, the plurality of attenuators may be located within the chamber oriented in varying angles relative to the end of the intake tubes, the noise source, and/or the housing components. While the attenuators may vary in size, length, quantity, shape, angle, and/or location, they may divert the airflow pathway and thereby create additional broadband noise, however, the primary purpose of the attenuators is to reduce the amount of noise exiting the CPAP device. 
         [0074]    In embodiments having an attenuator, the attenuators may further comprise a dissipative element, noise attenuating coating, and/or a noise attenuating material attached thereto. 
         [0075]    Device  100  additionally includes connector portion  185  to couple lower housing  180  and upper housing together, thereby creating a seal. In the depicted example, the connector portions  185  are around the perimeter of the housing and a fastener, such as a screw, is used to couple the housing. Additionally or alternatively, the edge  182  of the housing may provide a coupling and/or sealing mechanism. For example, edge  182  may have a tongue and groove. Edge  182  may also include a seal, such as santoprene or silicone. 
         [0076]      FIGS. 4B-D  illustrate additional embodiments of device  400  with additional or alternative configurations of attenuators for reducing noise output.  FIG. 4B  shows a “V” shaped attenuator  422  positioned in chamber  430  near tube  415  and angled attenuator  425  positioned in chamber  423  near interchamber tube  416 .  FIG. 4C  depicts curved attenuator  424  positioned in chamber  430  near tube  415  and parallel attenuator  425  positioned in chamber  423  near and approximately parallel to the opening of interchamber tube  423 .  FIG. 4D  depicts attenuator  426  and attenuator  429  positioned in chamber  430  near tube  415 . Attenuator  426  has a first portion  427  that is approximately parallel to tube  415 . Attenuator  426  additionally includes an angled portion  428  that is angled from portion  427  and directs air approximately toward tube  416 . Attenuator  429  is angled from housing  480 .  FIG. 4C  additionally includes an intake chamber  411 , which in certain approaches, is similar to previously described intake chamber  310 . Intake chamber  411  includes attenuators  413 . 
         [0077]    Each type of attenuator ( 422 ,  423 ,  424 ,  425 ,  426 ,  427 ,  431 ) alters the flow of air from through device  400 , for example, from intake tube  415  to interchamber tube  416 . The attenuators can be used individually or in any combination. Additionally, attenuators of other shapes may also be used, such as those with additional curves, different angles, additional extensions, and combinations of curves and linear portions. The attenuators are used to create unique air flow paths, which also have the important effect of altering and reducing the noise properties of device  400 . Although not depicted, similar attenuators may also be used in chamber  434 , for example, near interchamber tube  416  or around blower  440 . 
         [0078]      FIG. 5  illustrates a low-pass acoustic filter system. The equation below describe the effects modifying each geometrical section of the filter system has on the system. 
         [0000]    
       
         
           
             
               
                 
                   
                     T 
                     π 
                   
                   = 
                   
                     ( 
                     
                       1 
                       
                         1 
                         + 
                         
                           
                             ( 
                             
                               
                                 
                                   S 
                                   1 
                                 
                                 - 
                                 S 
                               
                               
                                 2 
                                  
                                 S 
                               
                             
                             ) 
                           
                            
                           kL 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0079]    In Equation 1, T is the power transmission, also referred to as the acoustic output, sound level, or noise level; k is the wavenumber of the sound; S 1  is the area of an acoustic chamber; L is the length of an acoustic chamber; and S is the area of an inlet port or tube. Thus, if S 1  increases in size, L increases in length or S decreases in area, then the power transmission T is reduced. 
         [0080]    In accordance with the present disclosure, the area of the respective acoustic chamber (S 1 ) and the area of its inlet port (S) may have a proportional relationship. For example, the area of the chamber may be larger than the area of the inlet port by a factor of 2. In additional embodiments, S 1  may be larger than S by a factor ranging from a factor of approximately 2 to a factor of approximately 20 or more. In at least one embodiment, S 1  is larger than S by a factor of about 10. Additionally, the length of L may be increased wherein the portion of the tube and the acoustic chamber effectively act as single chamber, thus decreasing the amount of noise emanating from the system. 
         [0081]    Referring to  FIG. 5 , the inlet pathway defined by S is smaller than the upstream portion of the acoustic chamber. In accordance with equation 1, when S is reduced relative to S 1 , then T or the noise level is attenuated. By increasing L (the length of the acoustic chamber), the noise may be further attenuated. In addition, if the inlet pathway is sufficiently long, the effective length of the acoustic chamber increases from L to L 1 , thus also reducing the noise of the system. As illustrated in the Appendix, data supports the increase in length of intake tubes helps decrease the amount of noise escaping the system. Thus, longer inlet or sections of tubes help attenuate the noise of the system. 
         [0082]    There exists a proportional relationship between the length of the inlet tube or port and the cross-sectional area of the inlet port with the volume (and length) of the receiving acoustic chamber. However, by increasing the length of the inlet port and restricting the cross-sectional area of the inlet port causes the resistance to air flow in the system. This may in turn cause a blower disposed inside an acoustic chamber to have to work harder, which may result in an increase in noise generation from the blower (and motor of the blower). Thus, a balancing and optimization step is often required when trying to create a sufficiently portable PAP device that is both quiet and small in size. Equation 2, illustrates this relationship of increasing modifying the various dimensions of the inlet port and the effect it has on the increased motor work and noise. 
         [0000]    
       
         
           
             
               
                 
                   
                     Resistance 
                      
                     
                         
                     
                      
                     of 
                      
                     
                         
                     
                      
                     air 
                      
                     
                         
                     
                      
                     flow 
                   
                   ∝ 
                   
                     
                       Length 
                        
                       
                           
                       
                        
                       inlet 
                     
                     
                       Area 
                        
                       
                           
                       
                        
                       inlet 
                     
                   
                   ∝ 
                   
                     Motor 
                      
                     
                         
                     
                      
                     Work 
                   
                   ∝ 
                   
                     Motor 
                      
                     
                         
                     
                      
                     Noise 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0083]    Another way of describing this is a smaller inlet diameter increases air flow resistance, which increases motor noise. Some practical steps have been incorporated to also position inlet ports on the PAP device such that they point away from the ears of the user. For example, in several of the figures the inlet port is on the opposite end of the outlet port and adapters, which lead to the tubing that takes air to the mask placed over the user&#39;s nose and/or mouth. In several instances most of the noise escaping the system leaves through the inlet port. 
         [0084]    Equation 1 can also be used to describe the relationship between length and noise attenuation in an individual tube. In the case of a single, individual tube, S 1  is equal to S. Accordingly, the noise output T is reduced when the tube is lengthened (L is increased). This characteristic is important because the length of the intake tube (such as intake tube  115 ) can be used to decrease the noise of the PAP device (such as device  100  and other systems and methods described herein). 
         [0085]    Equation 3 describes the relationship between the cut-off frequency of the acoustic filtering and the length and areas of the chamber and tube: 
         [0000]    
       
         
           
             
               
                 
                   
                     f 
                     c 
                   
                   = 
                   
                     ( 
                     
                       Sc 
                       
                         π 
                          
                         
                             
                         
                          
                         
                           L 
                            
                           
                             ( 
                             
                               
                                 S 
                                 1 
                               
                               - 
                               S 
                             
                             ) 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
         [0086]    In equation 3: f c  is the cutoff frequency; c is the speed of sound; S 1  is the area of the expansion chamber; L is the length of the tube or chamber; and S is the area of inlet port. Thus, as L or S 1  become larger in value, and/or S becomes smaller, the cutoff frequency becomes lower and every frequency above the cutoff frequency is significantly attenuated. In practical terms, the cutoff frequency f c  can be reduced by increasing the ratio of S 1 :S, for example by decreasing the area of the inlet and/or increasing the area of the acoustic chamber. Additionally, lengthening the acoustic chamber (increase L) will also reduce the cutoff frequency. 
         [0087]    In embodiments where the inlet ports include an intake tube, the intake tubes may extend from the furthest attenuator in the attenuating intake chamber and into the acoustic chamber. The length of the intake tube may range from approximately 1 inch to approximately 3 inches or longer. In certain approaches, the intake tube (such as intake tube  115 ,  215 ,  315 , or  415 ) has a fixed diameter of ⅜ inch and is approximately 3 inches long. In accordance with  FIG. 5 , equation 1, and equation 2, the length and diameter of the intake tube may be adjusted to affect the overall noise attenuation of the PAP device. Similarly, the interchamber tube and outlet tube may be adjusted to affect the noise output of the PAP device. 
         [0088]    In order to maximize the length of the intake tube so as to further attenuate the noise of the device, the tube may be angled, have one or more bends or turns in any 3-dimensional direction, or it may have a spiral-like configuration. For example, in  FIG. 2A ,  FIG. 3 , and  FIG. 4D , the intake tube has two bends thereby creating an intake tube having an “S” shape. Similarly, interchamber tubes and outlet tubes may also include bends, turns, angles, spirals, or other configurations. 
         [0089]    As disclosed herein, tubes within the systems described herein may be formed using rigid materials, flexible materials, or any combination thereof. For example, in some embodiments, an intake tube may be formed using a hard plastic. In other embodiments, an intake tube may be formed using flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. In certain embodiments, intake tubes are formed from more than one material. 
         [0090]      FIG. 6 ,  FIG. 7A , and  FIG. 7B  depict simplified drawings to illustrate the sound deflection properties of attenuators, and accordingly, do not include all the element previously described.  FIG. 6  illustrates one example of an attenuator found in previous CPAP devices. Device  600  includes an intake tube  615  leading into chamber  640  with an attenuator  620 . The configuration and angle of attenuator  620  deflects sound (represented by the arrows) back through the device. The sound may be generated, for example, by the blower. Importantly, attenuator  620  is angled such that it opens towards chamber  640 . For example, attenuator  620  may form an obtuse angle α with wall  681  of housing  680 . 
         [0091]      FIG. 7A  depicts an end attenuator  720 , which is positioned near the intake end  717  of intake tube  715 . End attenuator  720  deflects sound (represented by the arrows) generated from device  700  back through tube  715  and into chamber  750  of device  700 , where it can dissipate or be absorbed instead of reaching the user. End attenuator  720  may also absorb some portion of the sound.  FIG. 7B  illustrates a related configuration within device  701 . Device  701  includes attenuator  722 . Importantly, attenuator  722  is positioned such that it does not open directly toward chamber  740 , unlike attenuator  620  does in relation to chamber  620 . The space between tube  715  and chamber  740  is smaller near tube  715  than near wall  781  of housing  780 . For example, attenuator  720  may form an acute angle  13  with wall  781  of housing  780 . Accordingly, attenuator  720  is less likely to deflect sound waves back into tube  715 . As shown by the arrows, sound waves will be deflected primarily away from tube  715  and may dissipate and be absorbed within device  701 , rather than reaching the user. In certain approaches, attenuators  720  and  722  may both be used in a PAP device, and may be used with other attenuators, systems, and methods for attenuating the sound, such as tubes with bends, combinations of attenuators, and anechoic sound-reducing materials. 
         [0092]      FIG. 8A  and  FIG. 8B  depict the exterior a PAP apparatus having an internal pressure sensor. CPAP device  800  is similar to previously described CAP devices and apparatuses, such as devices  100 ,  200 ,  300 ,  400 ,  700 , and  701 . Device  800  has a lower housing component  880 , which together with an upper housing component  884 , define the interior and exterior of device  800 . In certain approaches, the interior of device  800  is similar to those depicted in previous figures. 
         [0093]    Inlet port  810  includes an intake tube  815  having a first end  812  extending through lower housing  880  and a second end (not depicted in this figure) that extends to the interior chamber (not depicted in this figure) of device  800 . Intake tube  815  may have either a constant or varying internal diameter ranging from approximately 0.25 inches to approximately 0.75 inches and may have a length ranging from approximately 0.25 inches to approximately 3 inches, although any appropriate diameter and length may be used. The length and diameter of intake tube  815  affect the overall noise attenuation of the CPAP device, as previously discussed. Accordingly, in some approaches, the dimensions of intake tube  815  are proportionally related to the volume of chamber  830 . 
         [0094]    Intake tube  815  may be formed using rigid materials, flexible materials, or any combination thereof. For example, intake tube  815  may be formed using a hard plastic. In certain embodiments, intake tube  815  is composed of flexible polyvinylchloride (PVC) tubing, silicone tubing, or any other type of tubing commonly used in the art. 
         [0095]    Device  800  includes an outlet port  839 , through which device  800  provides pressurized air. An adapter  860  may be used to connect outlet port  839  to a patient interface, such as a mask. 
         [0096]    Apparatus  800  includes a control panel  886  with digital display  888  and user interface buttons  885  for controlling and using apparatus  800 . For example, a user may be able to turn the power on and off, adjust pressure settings, set a timer, run system diagnostic tests, and control or adjust other functions. Display  888  may be any appropriate display, including, but not limited to an LED or LCD display. Although 1-3 user interface buttons  885  are depicted, any appropriate number of buttons may be used. In certain approaches, a PAP apparatus, such as apparatus  800 , may include between 1 and 10 user interface buttons. In certain approaches, user interface buttons are included in display  888 . For example, display  888  may be a capacitive or pressure sensitive touch screen display. Further, control panel  886  and display  888  may vary in size between different embodiments. For example, some embodiments may include a larger display, while other embodiments may include a smaller display. Display  888  may display data or control functions, such as pressure levels, time, use time, or other information. Display  888  may show one piece of data or function or a plurality of data and functions. 
         [0097]    In certain embodiments, apparatus  800  includes a pressure port  862 . Pressure port  862  has a first end  864  on the exterior of lower housing  880  and upper housing  884 . First end  864  is coupled to adapter  860 . Pressure port  862  provides fluid communication from the output of device  800  at adapter  860  to a pressure sensor within device  800 . In certain approaches, the pressure sensor is coupled to control circuitry (not depicted) within device  800 . The control circuitry of device  800  is configured to display the pressure measured through pressure port  862  at display  888  of control panel  886  on upper housing  884 . 
         [0098]    In certain embodiments, the pressure output of device  800  may be adjusted manually by the user with user interface buttons  885 . In certain approaches, the control circuitry of device  800  is configured to automatically adjust the output of device  800  based on the pressure measurements. The output of device  800  may be adjusted, for example, by modulating the power of the blower. 
         [0099]    During operation, PAP device  800  creates positive air pressure through outlet port  839 . For example, when a patient interface is attached to adapter  860 , PAP device  800  creates positive air pressure, which can be provided to the patient when the patient places an adapter, such as a mask, at his or her airways (e.g., nose or mouth). 
         [0100]    As depicted in  FIG. 8B , device  800  may include an intake cover  890 . In certain embodiments, air may be passed through intake cover  890  before entering inlet port  810 . Intake cover  890  serves to prevent the occlusion of inlet port  810  during use of device  800 . Intake cover  890  includes a vented portion  892  to allow the pass through of air during operation of device  800 . In certain embodiments, intake cover  890  may include a filter to clean the air of particulate matter. In certain embodiments, intake cover  890  is removable so that it may be cleaned, replaced, or adapted for a particular need. In certain embodiments, intake cover  890  includes attenuators, such as those previously described. 
         [0101]    In certain approaches, the pressurized air is delivered to a patient through a patient interface at a pressure ranging from approximately 2 centimeters (cm) of water to approximately 40 cm of water above atmospheric pressure at the point of use, although any appropriate pressure may be used. 
         [0102]      FIG. 9A  depicts one embodiment of an acoustically invisible cover  900 . Cover  900  may be similar to cover  890  and is positioned on the housing over the inlet port (such as inlet ports  122 ,  222 ,  322 ,  410 , or  810 ) to prevent occlusion of the inlet port during use. Cover  900  includes a first portion  904 , which is shaped similar to the housing of a PAP device (such as devices  100 ,  200 ,  300 ,  400 ,  700 ,  701 , and  800 ) so that it can couple directly to the housing. Cover  900  includes a flow portion  902 , which is sufficiently porous so that air can flow through it. In certain embodiments, flow portion  902  is constructed of a mesh material, such as a metal or plastic. For purposes of this application acoustically invisible refers to not increasing the generated noise by more than 3 dBA. Ideally the increase in dBA is less than 1 dBA, less than 0.5 dBA and negligible. 
         [0103]      FIG. 9B  depicts an embodiment of an acoustically invisible cover  910 . Cover  910  may be similar to cover  890  or cover  900  and is positioned on the housing over the inlet port (such as inlet ports  122 ,  222 ,  322 ,  410 , or  810 ) to prevent occlusion of the inlet port during use. Cover  910  includes a first portion  914 , which is shaped similar to the housing of a PAP device (such as devices  100 ,  200 ,  300 ,  400 ,  700 ,  701 , and  800 ) so that it can couple directly to the housing. Cover  910  includes flow portion  912 , which is sufficiently porous so that air can flow through it. For example, flow portion  912  may be constructed of paper or mesh. In certain approaches, flow portion  912  includes vents such as vents  916 . In a design where flow portion  912  is not porous and solid the vents  916  may actually increase the dBA, such that it is no longer acoustically invisible. 
         [0104]    In certain embodiments, intake cover  900  and intake cover  910  include attenuators, such as those previously described in relation to PAP devices  100 ,  200 ,  300 ,  400 ,  700 ,  701 , and  800 . 
         [0105]    In the absence of any additional outside attenuators, the CPAP device disclosed herein, having one interior attenuator, produces noise levels of about 27 dBA. 
         [0106]    The above description is merely illustrative. Having thus described several aspects of at least one embodiment of this invention including the preferred embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawing are by way of example only.