Abstract:
A speech transmission adapter and a respirator mask comprising a speech transmission adapter. The respirator mask comprises an inhalation port, an exhalation port, and a speech transmission adapter in detachably sealed engagement with the inhalation port. The adapter comprises a peripheral housing, a speech reception means supported by the peripheral housing, and a speech transmission means operably coupled to the speech reception means. The speech reception means receives sound pressure generated by a wearer of the respirator mask, and the speech transmission means conveys signals representative of such sound pressure to an external speech transducer. The adapter mates to the inhalation port of a respirator mask and expands the clean air envelope defined within the mask to include the speech reception means within the clean air envelope without requiring structural modification of the respirator mask. The speech transmission adapter comprises a central aperture which is adapted to accommodate the passage of air therethrough and engaging means at each of its ends.

Description:
This is a continuation of application Ser. No. 08/494,305 filed Jun. 23, 1995, now abandoned which is a continuation of application Ser. No. 08/130,299 filed on Oct. 1, 1993, now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a speech transmission adapter for use with both full facepiece and partial facepiece respirator masks. More particularly, the invention relates to a speech transmission adapter that is contained within the clean air envelope that is defined by the mask and the face of the wearer, but does not require penetration of the mask structure. 
     BACKGROUND OF THE INVENTION 
     Respirator masks are used in a wide variety of hazardous environments. Such environments include paint booths, grain storage facilities, laboratories with hazardous biological materials and environments containing certain chemical fumes. Respirator masks are typically adapted to receive a variety of filter units and other attachments that are designed specifically for the hazardous environment in which the mask is to be used. As such, the same mask body can be used in a variety of different hazardous environments simply by changing the filter. This ease of changing filters makes the masks very cost effective by permitting the manufacture of a single mask for multiple environments. 
     Respirator masks define a clean air envelope with the face of the wearer. The clean air envelope includes the clean air source and is bounded by the mask, the mask&#39;s seal with the face of the wearer, and the exhalation valve of the mask. 
     There are two general designs of respirator face masks: the partial facepiece mask and the full facepiece mask. A partial facepiece mask typically encloses the wearer&#39;s mouth and nose and forms a seal with the portion of the wearer&#39;s face that is contiguous to the nose and mouth. The eyes are left unprotected when using the partial facepiece mask. The full facepiece mask is a much larger unit and encloses the wearer&#39;s eyes in addition to the wearer&#39;s nose and mouth. Such masks include a transparent viewing portion to permit the wearer to see while wearing the mask. 
     Respirator masks can additionally be distinguished by being either a positive pressure or negative pressure device. A positive pressure device typically includes an external pump or pressurized vessel, with or without a filter, that is the clean air source and that forces air into the mask. Such a mask creates a more positively sealed clean air envelope about the wearer since the internal pressure in the clean air envelope created by the mask and the wearer&#39;s face is at a higher pressure than the environment around the mask. In this case, environmental air is not allowed to seep into the clean air envelope because it is restrained by the higher pressure inside the clean air envelope. 
     A negative pressure respirator mask functions on the negative pressure generated by the wearer inhaling. The inhalation generates a negative pressure inside the clean air envelope and draws air into the respirator mask. Generally, ambient air is drawn through a filter or filters by the negative pressure. The filters clean the air and the air is then drawn into the clean air envelope of the mask for inhalation by the wearer. 
     In the past, there has been substantial work performed in attempting to provide a means for the wearer of a breathing apparatus to communicate orally. Inactive devices are purely mechanical devices and active devices involve some form of enhancement by powered amplification. The most common inactive communication device is the voice diaphragm. This is a sealing diaphragm that is designed to vibrate in response to the pressure waves in the mask that are generated by the wearer&#39;s speech The prior art comprises two general categories of active speech transmission devices: internal devices and external devices. Internal devices are typically constructed integral to the mask itself. Such devices comprise microphones, light transmission, and magnetic transmission devices. The devices are mounted within the clean air envelope defined between the mask and the wearer&#39;s face. A desirable feature of the internally mounted devices is that they, in general, provide a louder volume and truer, more distinct reproduction of the speech of the wearer when compared to the externally mounted devices. 
     The internally mounted voice receivers generally require structural modification of the mask itself to mount the device within the mask. The devices typically require penetration of the mask to transmit the wearer&#39;s voice outside of the clean air envelope, involving further modification of the mask structure. This penetration is not necessarily a drawback where the voice transmission is required to be used in all cases when the mask is worn. Such instances include, for example, masks worn by the operators of high performance aircraft and masks worn by fire fighters. Structural modification and physical penetration of the mask are a distinct disadvantage in instances where the speech transmission is desired to be an optional feature to an existing mask design. 
     The active external devices are mounted outside the clean air envelope defined by the mask. Such devices typically have poorer quality sound transmission since the sound energy must penetrate a voice diaphragm or the like before being received by the speech transmission device. Such devices do not however penetrate the clean air envelope of the mask. These devices typically involve the use of transducers attached to the exterior of the mask to amplify the sound that is transmitted through a voice diaphragm. The diaphragm is a gas tight seal and may be a vibrating voice diaphragm or may be the exhalation diaphragm of the mask. Such external devices have the advantage that they can be designed to readily added to existing masks by clip-on features and the like and thus may not require structural modification of the mask itself. 
     Examples of internally mounted active speech amplification units are typified by the devices of U.S. Pat. Nos. 4,989,596 and 4,980,926, and one embodiment of U.S. Pat. No. 4,508,936. Externally mounted speech transmission adapters are exemplified by the devices of U.S. Pat. Nos. 4,352,353, 5,138,666, 5,224,473, and 5,224,474. 
     It would be a decided advantage to have an enhanced speech transmission device that is readily adaptable to be attached to an existing mask that is produced in large quantities. The speech transmission adapter should produce excellent quality voice transmission. This requirement means that the adapter should be mounted inside the clean air envelope defined by the mask on the wearer&#39;s face. In order to minimize the cost impact of the adapter, it is highly desirable that the design not require any structural modifications to the basic respiratory mask as it is produced without an enhanced voice transmission device. 
     SUMMARY OF THE INVENTION 
     The present invention is a speech transmission adapter designed to be optionally included with existing respirator masks that do not have an active speech enhancing transmission capability. The adapter of the present invention expands the clean air envelope defined within the mask, placing the speech reception device within the clean air envelope in order to capture the high quality sound available within the envelope. The adapter accomplishes this without structural modification to the mask or penetration of the mask body. 
     Briefly, the present invention is a speech transmission adapter for use with a respirator mask in receiving the sound pressure generated by the speech of a wearer of the respirator mask. The respirator mask is designed to be worn in sealing engagement with a portion of the face of the wearer of the respirator mask (also commonly known as a protective respirator) and has a compliant body that includes at least one inhalation port through which clean air is admitted to the respirator mask and a clean air source coupled to the inhalation port. The mask further includes an exhalation port through which exhaled air is expelled from the mask and a sealing portion generally at the periphery of the respirator mask that is held in sealing engagement with the face of the wearer. The respirator mask defines a clean air envelope between the body of the respirator mask and the face of the wearer bounded by the sealing portion of the respirator mask, the clean air source and the exhalation port. The speech transmission adapter includes a peripheral housing which functions as a ‘spacer’ between an inhalation port and an air filter otherwise attached thereto, and a speech receiver supported by the peripheral housing that is in communication with the sound pressure generated by the speech of the wearer of the respirator mask for receiving such sound pressure. A speech transmission device is connected to the speech receiver and adapted to be coupled to an external speech transducer for conveying signals representative of the received speech energy to the external speech transducer. The peripheral housing is adapted to mate to the respirator mask in a manner that expands the clean air envelope defined therein to include the speech reception device within the clean air envelope without requiring structural modification to the respirator mask. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art full facepiece respirator; 
     FIG. 2 is a perspective view of a prior art partial facepiece respirator; 
     FIG. 3 is a perspective view of the respirator depicted in FIG.  1  and including the sound transmission adapter broken out; 
     FIG. 4 is a perspective view of the respirator depicted in FIG.  2  and including the sound transmission adapter broken out and interposed between the air filter and the inhalation port of the respirator; 
     FIG. 5 is a sectional view showing the sound transmission adapter utilizing bayonet type attachment devices; 
     FIG. 6 is a sectional view showing the sound transmission adapter utilizing threaded type attachment devices; and 
     FIG. 7 is a chart depicting the attenuation of sound with various respirator configurations. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the Figures, similar features have been given similar reference numbers. 
     Referring first to FIG. 1, there is shown a prior art full facepiece respirator mask  10 . Mask  10  has a rubberized body  12  that is adapted to enclose the wearer&#39;s eyes, nose, and mouth. Body  12  is designed to form a seal at its periphery with the face of the wearer. Special sealing material may be attached proximate the periphery of body  12  to contact the skin of the wearer to form a better seal therewith. Body  12  is formed of a material that is selected to be substantially impermeable to the types of airborne environmental hazards that mask  10  is designed to offer a barrier to. 
     A series of cooperative straps  14  are affixed to mask  10  to provide a means by which the wearer is able to forcibly bring mask  10  into contact with the wearer&#39;s face to effect a seal therewith. Straps  14  may be elasticized to ensure a continuing seal, notwithstanding movement of the wearer. 
     In the embodiment shown, straps  14  include slip clamps  16 . Slip clamps  16  have a toothed portion that is oriented such that the toothed portion bears on the strap  14  in a directional manner and thereby limits motion of strap  14  with respect to clamp  16  that would tend to loosen the fit of mask  10 . The toothed portion of slip clamp  16  is so oriented to permit strap  14  to be readily drawn through slip clamp  16  in the direction that tightens mask  10  to the face of the wearer. 
     A single transparent facepiece  18  is provided in mask  10 . In an alternative embodiment, two individual eye pieces are provided in the front of the mask  10  corresponding to the visional ranges of each of the wearer&#39;s eyes. Facepiece  18  and the alternative eyepieces are preferably formed of a clear, non-permeable, shock resistant, plastic material in order to provide a good seal and to afford some protection to the wearer&#39;s eyes. 
     Mask  10  is provided with two inhalation ports  20 ,  22 . Inhalation ports  20 ,  22  typically have a periphery formed of a circular hard plastic material and are adapted to receive a variety of interchangeable devices that affect the clean air within the mask  10 . In the embodiment shown, inhalation port  22  is connected to positive pressure line  24 . Positive pressure line  24  is in turn connected to a pump or a pressurized vessel (not shown) that may include a filter. Such pump or pressurized vessel is a source of clean air and provides the clean air under pressure to mask  10 . In this embodiment, mask  10  is a positive pressure device having a higher pressure inside the clean air envelope of the mask  10  than the ambient pressure outside the mask  10 . In this configuration, inhalation port  20  is sealably closed by means of a sealing insert  26  that is detachably affixed to inhalation port  20 . Insert  26  may be attached by a threaded engagement therewith, by the use of bayonet fittings, or by like devices that provide for ready sealing and unsealing. 
     Mask  10  further includes an exhalation port  28 . Exhalation port  28  is typically formed of a hard plastic material and has structure defining an aperture therethrough. A flexible diaphragm (not shown) is inserted in the aperture and opens responsive to an increase in pressure in the clean air envelop of the mask. The diaphragm that is positioned in exhalation port  28  is biased to be self-sealing and thereby creates a gaseous seal that helps establish the clean air envelope within the mask. The diaphragm prevents ambient air from entering the mask  10  when it is closed and the expelling of exhaled air prevents ambient air from entering the mask during the periods that the diaphragm is open. 
     As previously indicated, mask  10  defines a clean air envelope around the wearer&#39;s eyes, nose, and mouth within the body  12  of mask  10 . The clean air envelope is defined by the body  12  (including facepiece  18 ) of mask  10 , the seal at the edges of mask  10  and the face of the wearer, the sealing insert  26  in inhalation port  20 , positive pressure line  24  at inhalation port  22 , and exhalation port  28 . It is within the clean air envelope as just described that the speech energy of the wearer is best received for clarity of annunciation and volume. 
     Referring now to FIG. 2, there is shown a partial facepiece respirator mask  30 . Mask  30  includes a flexible body  32  that is preferably rubberized. The body  32  is designed to conform to the face of the wearer and to sealingly enclose the wearer&#39;s nose and mouth. Portions of body  32  may be constructed of a relatively more resilient material in order to provide a more rigid shape and supporting structure to body  32 . Body  32  is constructed of materials that are selected to be essentially impermeable to the hazardous materials in the environment in which mask  30  is expected to be used. 
     Mask  30  includes elasticized straps  34  designed to be worn around the wearer&#39;s head. Straps  34  include buckles  36 . In this embodiment, buckles  36  include an over-centered device with a tang designed to exert a clamping force on straps  34 . The wearer is able to pull straps  34  to a snug position creating an effective seal between mask  30  and the wearer&#39;s face. When straps  34  are snug, the over-center device of buckle  36  is rotated such that the tang bears firmly against strap  34  and a back plate of buckle  36 . Since the device has an over-center feature, the tang is held in the closed position grasping strap  34  and resisting the movement of strap  34  through buckle  36  in the direction tending to loosen strap  34 . 
     Two inhalation ports  38 ,  40  are included in mask  30 . Inhalation port  38  is depicted in FIG.  4 . The structure of inhalation port  40  is generally the same as inhalation port  38  and inhalation ports  20 ,  22 , depicted in FIG. 1, are of similar construction as inhalation ports  38 ,  40 . Referreing to FIG. 4, inhalation port  38  has a peripheral housing  42  that is preferably formed of a hard plastic material to provide a relatively non-deformable structure to inhalation port  38 . Aperture  43  is formed central to peripheral housing  42  to accommodate the passage of clean air therethrough. 
     Inhalation port  38  is designed for the ready attachment and detachment of mating devices thereto. Accordingly, inhalation port  38  has attaching point  44  included generally peripheral to aperture  43 . Attaching point  44  is more fully described in conjunction with FIGS. 5 and 6 and may be a bayonet fitting, a threaded connector, a press fit connector, or the like. 
     Referring again to FIG. 2, filters  46  are adapted to be readily attached to and detached from inhalation ports  38 ,  40 . The design of the attaching points (not shown) is such that the filters  46  may be readily replaced in the field without special tools or training when the filters no longer perform their desired function by readily mating with attaching point  44  (FIG. 4) of inhalation ports  38 ,  40 . Filters  46  come in a variety of shapes to accommodate various types of filtering material. In some instances, the attaching points are designed to ensure a particular desired orientation of the filter  46  with respect to the mask  30  when filter  46  is installed. By the simple expedient of changing the filters  46 , mask  30  is readily adaptable to a number of different hazardous environments. 
     The previously described inhalation ports  20 ,  22  depicted in FIG. 1 are designed similarly to inhalation ports  38 ,  40 . Accordingly, filters  46  shown in conjunction with mask  30  are readily utilized with mask  10  shown in FIG.  1 . In order to utilize filters  46  with mask  10 , positive pressure line  24  is simply turned, released, and withdrawn from inhalation port  22  and sealing insert  26  is turned, released, and withdrawn from inhalation port  20 . Such action prepares inhalation ports  20 ,  22  to receive filters  46 . The installation of filters  46  on mask  10  converts mask  10  from a positive pressure device to a negative pressure device. A negative pressure respirator mask functions on the negative pressure generated by the wearer&#39;s act of inhaling. Negative pressure generated within the clean air envelope formed by the mask  10  would draw air through filters  46  and into the mask  10  through the inhalation ports  20 ,  22 . It can be seen from this description of the pressure functioning of mask  10  that mask  30  shown in FIG. 2 is also a negative pressure device and relies upon the inhalation of the wearer to generate clean air flow through filters  46  and into the mask through inhalation ports  38 ,  40 . 
     As shown in FIG. 2, mask  30  also includes an exhalation port  48 . Exhalation port  48  includes a diaphragm (not shown) that is biased in the closed position, thereby creating a seal between the interior of mask  30  and the environment surrounding it. The diaphragm of exhalation port  48  is unseated and opened by the increased pressure within the clean air envelope defined by mask  30  that is generated by the wearer during exhalation. Once unseated, the diaphragm of exhalation port  48  permits the expulsion of exhaled air from the clean air envelope defined by mask  30 . 
     The clean air envelope created by mask  30  is defined by body  32  of mask  30 , the seal formed at the periphery of mask  30  with the face of the wearer, the filters  46 , and the exhalation port  48 . 
     FIG. 3 shows the full facepiece respirator mask  10  utilized with a speech transmission adapter  50  of the present invention. Adapter  50  is formed to mirror the attaching points of inhalation port  20  and sealing insert  26 . As is readily apparent from FIG. 3, adaptor  50  functions as a spacer for separating the inhalation port  20  and the filter  46  by providing a body with a passage extending the entire length thereof through which filtered air may pass from the filter to the inhalation port. Accordingly, speech adapter  50  has a first attaching point  52  that is formed with identical engaging members to that of sealing insert  26 . Speech transmission adapter  50  has a second attaching point  54  that is formed with identical engaging members to those of the attaching point of inhalation ports  20 ,  22 . In the depicted embodiment, the second attaching point  54  has threads that are designed to cooperatively engage the threads of inhalation port  20 . First attaching point  52  has threads that are designed to cooperatively engage the threads of sealing insert  26 . In this manner, speech transmission adapter  50  can be mated to mask  10  simply by mating second attaching point  54  to inhalation port  20  and then by mating first attaching point  52  either to sealing insert  26  or filter  46 , as the case may be. 
     The effect of the above described action is to expand the clean air envelope that is created by mask  10  to include the spacer or speech transmission adapter  50  without making any structural modifications to mask  10 . This unique design accomplishes the goal of placing the microphone within the clean air envelope where quality sound production is possible and at the same time accomplishing this without any structural modification to the mask  10  itself. 
     FIG. 4 illustrates the same functionality of the speech transmission adapter  50  when utilized in conjunction with mask  30 . In the embodiment depicted, the first and second attaching points  52 ,  54  (see FIG. 5) of speech transmission adapter  50  are bayonet fittings that are designed to cooperatively engage cooperatively designed bayonet fittings of filter  46  and inhalation port  38 . The engaging structure of first and second attaching points  52 ,  54  is more fully described in conjunction with the description of FIG.  5 . The same speech transmission adapter  50  is designed to be readily utilized with either mask  10  or mask  30 . In both cases, the speech transmission adapter  50  may be readily utilized with the mask  10 ,  30  in the field to convert the mask  10 ,  30  to have an enhanced speech transmission capability. 
     FIG. 5 depicts the speech transmission adapter  50  configured with bayonet type fittings. The depicted embodiment may be utilized with either the full facepiece mask  10  or the partial facepiece mask  30 . For ease of understanding, only the reference numbers of the partial facepiece mask  30  are included. The body  32  of mask  30  is depicted in sealing engagement with the inhalation port  38 . Inhalation port  38  includes a peripheral housing  42 . The housing  42  is preferably formed of a substantially resilient plastic material in order that the housing  42  is resistant to deformation under conditions of normal use. Housing  42  has structure defining a central aperture  43  therethrough that accommodates the passage of air through inhalation port  38 . 
     Spiders  64  emanate inward into aperture  43  from the peripheral housing  42 , culminating at a central hub  66 . The central hub  66  includes an inwardly directed post that provides an attachment point for inhalation diaphragm  68 . In a preferred embodiment there are three such spiders  64  supporting hub  66 . The spiders  64  have a relatively thin cross section so as to minimize the resistance to air flow in aperture  43  presented by spiders  64 . 
     Inhalation diaphragm  68  has a larger diameter than aperture  43  such that the periphery of diaphragm  68  extends beyond aperture  43  to sealingly engage housing  42 . The negative pressure in the clean air envelope generated by the wearer&#39;s act of inhalation draws the periphery of diaphragm  68  away from housing  42  to create an opening and to admit air into the clean air envelope. Diaphragm  68  functions to prevent exhalation through filter  46 . Diaphragm  68  closes upon the act of exhalation by the wearer responsive to the increased pressure within the mask that is generated by the act of exhalation. Under other conditions, diaphragm  68  may be open. In positive pressure units, a diaphragm  68  may not be utilized since the positive incoming pressure acts to prevent exhalation to the clean air source. Diaphragm  68  is generally formed of a thin, highly flexible material. 
     Speech transmission adapter  50  is depicted in registry with inhalation port  38  and disposed exterior thereto. Speech transmission adapter  50  has a peripheral housing  70  that is formed of a plastic material having similar properties to the plastic utilized to form housing  42  of inhalation port  38 . Peripheral housing  70  has a central aperture  72  that is in registry with central aperture  43  of inhalation port  38 . 
     A speech reception device  74  is installed within aperture  72 . In a preferred embodiment, speech reception device  74  is an electromagnetic microphone. As depicted in FIG. 5, the microphone  74  extends from the peripheral housing  70  of the spacer or speech transmission adapter  50 , but not into the interior space of the face mask. Other types of known speech reception devices may also be used. In the depicted embodiment, leads  76  pass through a small bore (not shown) in peripheral housing  70  and are held in place by cement or the like. Alternatively, leads  76  may be brought through housing  70  by being press fit into a slot formed in housing  70 . In another embodiment, quick-disconnect connectors (not shown) of a conventional design are provided to facilitate the ready disconnecting of the leads  76 . 
     Leads  76  are typically connected to a transducer such as a pocket or belt mounted speech amplifier/ speaker or are connected into an existing intercom system utilized by several workers on a job. Leads  76  convey the received voice energy of the wearer from speech reception device  74  to the transducer. 
     Speech transmission adapter  50  is connected to inhalation port  38  by means of bayonet fittings. Generally, bayonet fittings comprise cooperating opposed slots and hooks. The hooks are inserted into the slots of the opposing device and then the devices are rotated a slight amount with respect to one another to engage the hooks. Slight inward pressure and rotation in the opposite direction readily disengages the opposed hooks. Accordingly, as applied to the present invention, hooks  80  formed on housing  42  of inhalation port  38  engage hooks  82  formed on peripheral housing  70  of speech transmission adapter  50 . 
     Filter  46  is attached to the side of speech transmission adapter  50  that is opposed to mask  30 . Attachment is by similar bayonet fittings as described above. The hooks  84  of the filter  46  are designed to cooperatively engage the hooks  86  of speech transmission adapter  50 . Hooks  84  are also designed to cooperatively engage the hooks  80  formed on housing  42  of inhalation port  38  such that filter  46  may as readily be utilized with mask  30  alone or with mask  30  incorporating speech transmission adapter  50 . 
     Seals  88  are disposed between inhalation port  38  and speech transmission adapter  50  and between speech transmission adapter  50  and filter  46  to extend the clean air envelope to the filter  46  when speech transmission adapter  50  is utilized. Clean air then flows from filter  46  through aperture  72  in speech transmission adapter  50  and through aperture  43  in inhalation port  38  to the interior of mask  30  and to the wearer. 
     In FIG. 6 the depicted embodiment is similar to the structure depicted in FIG. 5 with two exceptions. Instead of the bayonet fittings depicted in FIG. 5, this embodiment utilizes threaded fittings and the inhalation diaphragm  68  is disposed within speech transmission adapter  50  as opposed to being within inhalation port  38 . 
     Female threads  90  are formed integral to the structure of inhalation port  38 . Cooperating male threads  92  are formed integral to the structure of speech transmission adapter  50 . In the opposing side of speech transmission adapter  50  female threads  94  are formed integral to the structure of speech transmission adapter  50 . Cooperating male threads  96  are formed integral to the structure of filter  46 . Appropriate seals such as gaskets or  0  rings may be incorporated in order to ensure an effective seal at the threaded joints. It can be seen that the male threads  92 ,  96  and female threads  90 ,  94  are selected such that the filter  46  is capable of being connected directly to inhalation port  38  without structural modification when speech transmission adapter  50  is not utilized in conjunction with mask  30 . Likewise, the installation of speech transmission adapter  50  between filter  46  and inhalation port  38  requires no structural modification to either filter  46  or inhalation port  38 . 
     Diaphragm  68  is depicted supported by spiders  100  and a supporting hub  102 . Spiders  100  and supporting hub  102  are preferably formed substantially identical to spiders  64  and a supporting hub  66  so that the position of diaphragm  68  may be readily changed without alteration of diaphragm  68 . The depicted positioning for inhalation diaphragm  68  within speech transmission adapter  50  is illustrative of the fact that incorporating speech transmission adapter  50  with mask  30  expands the boundary of the clean air envelope. It has been found that this location for inhalation diaphragm  68  enhances the quality of the sound as compared to the embodiment in FIG.  5 . 
     FIG. 7 is a graph of sound pressure attenuation that serves to illustrate sound attenuation with three different configurations of microphones on two different masks. The frequency response of the mask speaker system was measured using the cross spectrum method in an anechoic chamber. A 0.5″ random field microphone was used for the source measurement; a 0.5″ free field microphone was used for the reception measurement at 0.9 meters from the source. Analysis utilized a B&amp;K 2144 real time analyzer, ⅓ octave band, in the cross spectrum mode. The frequency response was calculated by the following equation: 
     
       
         log H=log G xy −log G xx  where 
       
     
     log G xy =measured cross spectra of source and received signal, and 
     log G xx =Auto Spectra of source as measured by the random field microphone. 
     The attenuation is shown in units of dB of attenuation. Accordingly, the less dB attenuation in a given configuration, the more sound that is available and the more desirable that particular system is. It should be noted that a 3 dB loss is roughly equivalent to a twofold sound energy loss. The data were taken in an anechoic chamber at 1000 Hz for both the partial facepiece mask and the full facepiece mask. Systems A, B, and C are full facepiece masks and Systems D, E, and F are partial facepiece masks. Systems A and D are representative of the prior art and are a design that includes a microphone mounted exterior to the mask. The present invention is represented by Systems B, C, E, and F. Systems B and E have the inhalation valve mounted as depicted in FIG.  5 . Systems C and F have the inhalation valve mounted in the speech transmission adapter and external to the microphone as depicted in FIG.  6 . 
     It can be seen that the prior art device when used with both the full and partial facepiece masks results in substantially greater attenuation than any of the configurations of the present invention. The inner diaphragm configuration of the present invention, Systems B and E, shows a substantial improvement in sound energy transmission over the prior art, while the outer diaphragm configuration of the present invention as depicted by Systems C and F provides the greatest improvement. 
     The present invention has now been described with reference to several embodiments thereof. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the present invention. Thus, the scope of the present invention should not be limited to the structures described herein, but rather by the structures described by the language of the claims and the equivalents of those structures.