Abstract:
An acoustic waveguide with at least two portions coupled by vibration damping structure. The vibration damping structure may be a conformable material such as closed cell foam. The vibration damping structure may further include structure for inhibiting motion in a direction transverse to the interface between the vibration damping structure and a portion of the waveguide.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority of, U.S. patent application 12/388,723, now U.S. Pat. No. 8,002,078, filed Feb. 19, 2009 by Chan, et al. 
    
    
     BACKGROUND 
     This specification describes an acoustic waveguide. Acoustic waveguides are discussed in U.S. Pat. No. 4,628,528. 
     SUMMARY 
     In one aspect, an acoustic waveguide includes at least two portions coupled by vibration damping structure. The vibration damping structure may include a conformable material. The conformable material may include foam. The foam may include closed cell foam. The vibration damping structure may be conformably mated to a first portion and mechanically attached to a second portion. The vibration damping structure may be adhesively attached to the second portion. The acoustic waveguide may further include a structure for inhibiting relative motion between a first portion and the vibration damping structure in a direction transverse to an interface between the vibration damping structure and the first portion. The relative motion inhibiting structure may include a protrusion of the first portion for mating with an opening in the vibration damping structure 
     In another aspect, an acoustic system includes a chassis; an acoustic waveguide including a first portion; a second portion rigidly attached to the acoustic assembly chassis; and a third portion coupling the first portion and the second portion in a manner that damps the transmission of vibration from the first portion to the chassis. The acoustic system may further include a vibration damping connector for connecting the waveguide second portion to a base plate. The waveguide third portion may include a conformable material. The conformable material may include foam. The foam may include closed cell foam. The waveguide third portion may be conformably mated to the first portion and mechanically attached to the second portion. The waveguide third portion may be adhesively attached to the second portion. The waveguide may further include a structure for inhibiting relative motion between the first portion and the third portion in a direction transverse to an interface between the third portion and the first portion. The relative motion inhibiting structure may include a protrusion of the first portion for mating with an opening in the third portion. 
     Other features, objects, and advantages will become apparent from the following detailed description, when read in connection with the following drawing, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic top and side plan view of an acoustic waveguide assembly; 
         FIGS. 2A-2D  are a diagrammatic views of a portion of the acoustic waveguide assembly of  FIG. 1 ; 
         FIG. 3  is a diagrammatic view of a portion of the acoustic waveguide assembly of  FIG. 2 ; 
         FIG. 4  is an assembled view of an actual implementation of the acoustic waveguide assembly of  FIG. 1 ; and 
         FIG. 5  is an exploded view of an actual implementation of the acoustic waveguide assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Acoustic waveguides are frequently used to radiate low frequency acoustic energy at high amplitudes. The radiation of acoustic energy results in mechanical vibration of the waveguide. Mechanical vibration can result in annoying buzzes and rattles. Additionally, if the acoustic waveguide is mechanically or acoustically coupled to a vibration sensitive component such as an LCD television panel, the operation of the component may be adversely affected. It is desirable to damp the vibration of the waveguide to prevent adverse effect on vibration sensitive components and to prevent buzzing and rattling. Typically, vibration damping permits some relative movement between the waveguide and the device chassis. 
     The exit of an acoustic waveguide is typically through an opening in the cabinet enclosing the waveguide. If the cabinet is heavy (for example if the device is a large screen television), a user might employ the opening as a handling point. However, if a user uses the opening as a handling point, and if the device includes vibration damping structure, relative movement between the waveguide and the cabinet could pinch the user. Additionally, the use of the waveguide exit as a handing point could cause stress which could result in damage to the waveguide. 
       FIG. 1  shows a top view and a side view of a diagrammatic representation of a portion, including a waveguide assembly  10 , of an acoustic or multimedia system such as an audio system, a television, a gaming system, or the like.  FIG. 1  shows the mechanical relationship of the elements and is not drawn to scale. A first portion  12  of the waveguide assembly  10  is coupled to a mounting element  16  by one or more non-rigid vibration damping connectors  17 , each including a fastener  18  and a grommet  20  of forty to fifty durometer viscoelasticity. The fastener  18  extends through an opening in a flange  19  of the acoustic waveguide and is attached to the mounting element  16  to couple the acoustic waveguide assembly  10  to the mounting element  16 . The fastener  18  is separated from the flange  19  by grommet  20  which damps vibration from the flange  19  to the mounting element  16 . 
     A second portion  13  of the acoustic waveguide  10  is coupled to a device chassis portion, such as the external shell  22  of the cabinet enclosing the waveguide assembly  10 . The coupling is implemented by one or more rigid connectors  21 , such as fastener  24  which extends through an opening in flange  23  in the second portion  13  to external shell  22 . The first portion  12  of the acoustic waveguide and the second portion  13  of the acoustic waveguide are acoustically coupled by a mating portion  26  in such a manner that the acoustic waveguide acts in a conventional manner acoustically while isolating mechanical vibration of the first portion  12  of the waveguide from the device chassis. The mounting element  16  and the external shell  22  are mechanically coupled by structure not germane to this discussion and are represented in the side view as mechanical grounds. Other types of damping connectors include compliant pucks molded around two separate threaded studs, flexible hinges, piston in cylinder shock absorbers, and others. 
     The waveguide may also include conventional elements such as one or more acoustic drivers  28 . The waveguide shown is close-ended. If the waveguide is open-ended, there may be another mating portion similar to the mating portion  26  coupling the first portion  12  and a second exit portion. 
       FIGS. 2A-2D  show other features of one embodiment of mating portion  26 . The mating portion  26  may be constructed of deformable material, such as an open-celled polyether/polyurethane foam. Other suitable materials include silicones, rubbers, solid deformable plastics, soft polyester closed cell foam, low density expanded foams, or stretchable and/or deformable membranes. In one embodiment, a mating surface  32  of the second portion  13  is adhesively attached to a mating surface of mating portion  26 . A mating surface  34  of first portion  12  is adhesively attached to a mating surface of mating portion  26 . The mating portion  26  is held in place relative to a waveguide first portion  12  by mechanical pressure which causes mating portion  26  to deform to seal air leaks. 
     The mating portion can also adjust for dimensional or assembly intolerances. For example,  FIG. 2A  shows a normal intersection of first waveguide portion  12 , second portion  13 , and mating portion  26 , with the first and second portions separated by distance d. In  FIG. 2B , dimensional or assembly tolerances or both cause the first and second portions to be separated by distance d 1  greater than d. The mating portion  26  adjusts for the tolerances by deforming less, but sealing the interface sufficiently to prevent air leaks. In  FIG. 2C , dimensional or assembly tolerances or both cause the first and second portions to be separated by distance d 2 , less than d. The mating portion  26  adjusts for the tolerances by deforming more. In  FIG. 2D , dimensional or assembly intolerances or both cause the first portion to be displaced by distance x from the intended position. The mating portion  26  adjusts for the tolerances by deforming at a different area of the mating surface. The deforming of the mating portion  26  may cause the mating portion to protrude into the waveguide resulting in an airflow obstruction, as indicated by arrow  36 . Obstructions, especially near the exit of the waveguide, are undesirable because the combination of high velocities near the exit and the obstruction may result in turbulence and therefore audible acoustic noise. Empirical tests, however, indicate that the turbulence resulting from the deformation of mating portion  26  is insignificant. 
       FIG. 3  shows another feature of an embodiment of mating portion  26  and one or both of portions  12  and  13 . Over time, the mating portion  26  may tend to “creep” in directions y and z, transverse to the interface between the mating portion  26  and the waveguide second portion  13 . In the embodiment of  FIG. 3 , fingers  38  extend from second portion  13  into openings  40  in the mating portion  26  to oppose movement in the y and z directions. 
       FIGS. 4 and 5  are an assembled view and a partially exploded view, respectively, of an actual implementation of the waveguide assembly  10 . Reference numbers in  FIGS. 4 and 5  correspond to like numbered elements in the previous views. Some elements, such as acoustic drivers  28  and rigid fasteners  21  are not shown in  FIGS. 4 and 5 . The waveguide of the embodiments of  FIGS. 4 and 5  is of the type described in U.S. patent application Ser. No. 12/020,978, incorporated by reference in its entirety. 
     Other methods of providing vibrational isolation of the waveguide while permitting rigid mechanical connection to a device chassis include non-intrusive flexible bands or tapes connected to the mating sections by pressure, adhesives, mechanical fasteners, or the like. 
     A number of embodiments of the invention have been described. Modification may be made without departing from the spirit and scope of the invention, and accordingly, other embodiments are in the claims.