Patent Publication Number: US-8111858-B2

Title: Supra-aural headphone noise reducing

Description:
This application is a Divisional Application of, and claims priority of, U.S. patent application Ser. No. 11/139,045 incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     This specification describes a noise reducing headphone and more particularly a noise reducing supra-aural headphone. Supra-aural headphones are discussed in U.S. Pat. No. 6,567,525. According to a supra-aural design, each earphone has a cushion that rests on the ear when the headphone is being worn by the user. Supra-aural headphones are typically lightweight, compact, and comfortable. However supra-aural headphones have not been as popular as other headphone designs, particularly circum-aural headphones, for high performance noise reduction headphones and particularly for active noise reduction headphones. Circum-aural headphones, which are typically larger than supra-aural headphones, have larger front cavities (which will be discussed below) which aids in passive noise attenuation. Additionally, circum-aural headphones can seal against the side of the head, which aids in passive noise attenuation. Sealing against a relatively even surface, like the side of the head, is simpler than sealing against an uneven surface, such as the ear. For that reason, there typically needs to be more sealing surface in a supra-aural headphone than sealing surface in a circum-aural headphone. 
     SUMMARY 
     In one aspect of the invention an earphone for a supra-aural headphone earphone includes a cup-shaped shell and a cushion mounted to the shell. The cushion includes a portion of an acoustically open foam having an inside surface and an outside surface, the inside surface defining and acoustically coupled to a passageway. The passageway has a cross-sectional area and a volumetric dimension. The earphone also includes a cushion cover of a high acoustic impedance material enclosing a portion of the outside surface of the portion of foam, wherein the cushion cover and the shell define an interior volume having a volumetric dimension. The earphone further includes a baffle assembly, including a baffle plate. An acoustic driver having a diaphragm is mounted in the baffle plate. The baffle assembly is mounted in the earphone to divide the interior enclosed volume into a front enclosed volume portion and a rear enclosed volume portion. The front enclosed volume portion includes the passageway and the foam. The volumetric dimension of the front enclosed volume is greater than 10 cc and wherein the volumetric dimension of the passageway is less than 10 cc. The earphone is constructed and arranged to be positioned against the ear of a user so that the passageway acoustically couples the diaphragm to the user&#39;s ear canal. 
     The passageway cross-sectional area may be smaller than the acoustic driver radiating surface area. The volumetric dimension of the front volume may be about 25 cc, and wherein the volumetric dimension of the passageway may be about 5 cc. The foam may be a fully reticulated, slow recovery material. The rear enclosed volume portion may be acoustically coupled to the environment by an acoustic mass and an acoustic resistance in parallel. The passageway may have an elongated cross-sectional shape. 
     In another aspect of the invention, an earphone for an active noise reduction headset, includes a generally planar baffle having two surfaces, with an opening therethrough; a first enclosed volume portion, that includes the first baffle surface, a foam structure having two generally planar surfaces and sides and an opening therethrough. The opening has two ends. The first planar surface of the foam structure mounted against the first baffle surface so that the baffle opening may be adjacent the first end of the cushion opening. The foam structure opening may be acoustically coupled to the foam structure. The earphone may further include a cushion cover of acoustically closed material, covering the second planar surface of the foam structure, except for the second end of the cushion opening. The earphone may also include a second enclosed volume portion that includes the second baffle surface, and a cup-shaped shell. The cushion cover may be constructed and arranged to seal against the external portion of a user&#39;s ear. 
     The earphone may further include an acoustic driver, mounted in the baffle opening. The volumetric dimension of the cushion passageway may be less than 10 cc. The volumetric dimension of the cushion passageway may be about 5 cc. The volumetric dimension of the foam structure may be about 20 cc. The rear enclosed volume portion may be acoustically coupled to the environment by an acoustic volume and an acoustic resistance in parallel. The foam structure opening may have an elongated shape in cross section. The foam structure opening may have a racetrack shape in cross section. The foam structure planar surfaces have an elongated shape. The foam structure planar surfaces may have an oval shape. 
     In yet another aspect of the invention, an earphone for an active noise reduction headset, includes an acoustic driver, a volume having a volumetric dimension, enclosed by high acoustical impedance material, acoustically coupling the acoustic driver and a user&#39;s ear and sealed to the user&#39;s ear. The earphone also has an open passageway between the acoustic driver and the ear inside the volume. The open passageway has a volumetric dimension. The earphone also has a portion of substantially acoustically open foam in the volume. The foam having a volumetric dimension. The foam is acoustically coupled to the passageway so that the volumetric dimension of the foam significantly acoustically increases the volumetric dimension of the passageway to better passively attenuate noise that enters the volume. The foam volumetric dimension is greater than the passageway volumetric dimension. The foam volumetric dimension may be more than twice the volumetric dimension of the passageway. The foam volumetric dimension may be more than four times the volumetric dimension of the passageway. The volumetric dimension of the foam may be 25 cc and the volumetric dimension of the passageway may be 5 cc. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Other features, objects, and advantages will become apparent from the following detailed description, when read in connection with the following drawing, in which: 
         FIG. 1  is a front plan view of a supra-aural headphone; 
         FIGS. 2A and 2B  are cross-sectional views of an earphone; and 
         FIG. 3  is an inside plan view of an earphone. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a supra-aural headphone  10 . The headphone includes two earphones  12 , connected by a headband. Each earphone  12  includes a cup shaped shell  14  and a cushion  16 . The headband  17  exerts a force in an inward direction as represented by arrows  19 . 
       FIGS. 2A and 2B  show a side cross-sectional view of an earphone  12  in position against a user&#39;s ear. The cushion  16  deforms slightly ( FIG. 2B ) to form a seal against the user&#39;s ear  18 . The seal significantly reduces the amplitude of external acoustic energy reaching the concha  34  and the ear canal  36  of the user. 
     The cushion  16  includes a foam portion  20  and a cushion cover  22 . The foam portion  20  is made of a type of foam that is acoustically open, that is, it is capable of propagating pressure waves. A suitable type of foam is a fully reticulated, slow recovery foam such as CFNT foam, supplied by the E-A-R Specialty Composites business unit of Aeraro Company of Indianapolis, Ind. In the figure, air cells  21  are shown to indicate that the material is foam but do not represent to actual structure of the foam. The shell portion  14  may be made of a rigid and plastic having high acoustic impedance such as an ABS plastic. Together, the shell  14  and the cushion cover enclose an interior volume  23 . 
     An acoustic driver  24  is mounted in a baffle  26 . The acoustic driver  24  includes a diaphragm  25 . The baffle  26  and the diaphragm  25  separate the enclosed internal volume  23  into a front enclosed volume portion  23 F and a rear enclosed volume portion  23 R. The front enclosed volume portion includes a passageway  40  that acoustically couples the diaphragm  25  to the concha  34  and the ear canal  36  of the user&#39;s ears without creating a significant pressure gradient between the ear and the diaphragm, as would an earphone that acoustically couples the diaphragm with a user&#39;s ear through a foam portion. The foam portion  20  is acoustically coupled to the passageway  40  and is sufficiently acoustically open that it volumetrically supplements the passageway  40  and therefore increases the volumetric dimension of the front enclosed volume portion  23 F. The volumetric dimension of foam portion  20  is greater, and preferably much greater, for example greater than four times, the volumetric dimension of the passageway  40 . In one embodiment, the total volumetric dimension of the front enclosed volume portion may be in the range of 30 cc, of which 5 cc is the passageway  40  and 25 cc is the foam portion  20  The passageway  40  may have a smaller cross-sectional area than the diaphragm  25 . The cushion cover  22  has high acoustic impedance, so sound waves passing through the cushion cover are significantly attenuated. The cushion cover  22  forms a seal with a user&#39;s ear and forms a portion of a boundary of the enclosed acoustic volume  23 . A suitable material for the cushion cover is protein leather. The opening  42  between the passageway and the concha  34  may be covered with an acoustically transparent material to protect the diaphragm and to prevent debris from entering the interior of the earphone. The rear enclosed volume portion  23 R may be acoustically coupled to the environment by an acoustic mass, such as acoustic port  44  and an acoustically resistive opening  46 , as described in U.S. Pat. No. 6,894,835. The acoustic resistance in the acoustically resistive opening could be a portion of polyester material, as shown in  FIGS. 2A and 2B , or may be a wire mesh, or some other acoustically resistive material. 
     An earphone in which the foam acoustically open to the passageway, supplements the volumetric dimension of the passageway, and is greater, preferably significantly greater, than the volumetric dimension of the passageway is advantageous because the front enclosed volume can be larger than the front enclosed volume of conventional headphones, while still providing a large compliant surface to provide a good seal with the ear. Such an earphone is especially advantageous for supra-aural headphones, because the earphone can be made relatively small while having the large front enclosed volume for passive noise attenuation and the large compliant sealing surface. 
       FIG. 3  shows the a plan view of the earphone  12  of  FIG. 2 , The foam portion and the cushion cover  22  provide a substantially flat area  27  that seals against the ear of the user. The flat area  27  is sufficiently large so that the earphone provides a good seal against a wide variety of different ear shapes, sizes, and contours. The earphone cushion  16  and the opening  42  have an elongated shape, such as an oval shape or a “racetrack” (two semicircles connected by substantially straight lines) shape. The oval or racetrack shapes match the typical shape of the human ear and the concha better than do earphones having circularly shaped openings. 
     Numerous uses of and departures from the specific apparatus and techniques disclosed herein may be made without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features disclosed herein and limited only by the spirit and scope of the appended claims.