fig1 depicts a speaker 10 of known art intended for mounting in a panel 14 having a mounting pattern consisting of a circular opening 14a and four associated holes 14b , typical of vehicle installation , e . g . in a door panel . for illustrative purposes relating to the following disclosure , speaker 10 can be considered to represent a widely used &# 34 ; 6 . 5 inch &# 34 ; speaker type associated with many vehicles of asian and american design and manufacture , having typically a sheet metal circular basket with an outside diameter of 157 mm ( 6 . 18 &# 34 ;) at the rim 10a . typically the cone has a diameter of 111 . 8 cm , thus a calculated area of 98 . 17 square centimeters . the pattern of the four mounting holes 14b is on a circle 142 mm in diameter . four mounting holes are provided in speaker 10 through the speaker mounting flange around the rim 10a corresponding to the locations of four screws 12 as shown . speaker 10 is typically mounted to panel 14 by the four screws 12 passing through the speaker mounting holes and through the corresponding holes 14b in panel 14 . screws 12 can be self - tapping or machine screws ; holes 14b are sized accordingly , and may be extruded and / or tapped for machine screw engagement . alternatively , e . g . where the material of panel 14 is unsuitable for anchoring screws reliably , screws 12 may be machine screws retained by rear nut fastenings such as tinnerman nuts , tee nuts or by machine nuts typically each accompanied by a flat washer and a lockwasher ; for this type of mounting holes 14b are dimensioned to clear the screws . fig2 shows the speaker 10 mounted in place against panel 14 by four screws whose recessed heads can be seen . fig3 is an enlarged cross - section taken at axis 3 - 3 &# 39 ; of fig2 showing the shape of the speaker edge region including rim 10a forming one wall of a u - shaped channel with a rounded channel bottom 10f bearing against the front of panel 14 . the channel &# 39 ; s opposite side 10g supports a flat landing region on which a surround flange 10c , extending from resilient arched suspension 10d , is adhesively attached to the speaker frame via a spacer 10b , typically made from a cardboard material . the inner flange of the resilient arched suspension 10d is attached to the outer edge of speaker cone 10e . resilient suspension 10d and cone 10e are shown in solid lines in the normal quiescent position , and are shown in dashed lines 10d &# 39 ; and 10e &# 39 ; at an extreme limit of travel , where sufficient clearance must be provided to prevent striking the corner 10h of the speaker frame . the edge of the region of panel 14 above the speaker cutout opening 14a ( fig1 ) is seen retained against the inside of corner 10h . when , instead of the self - threading sheet metal screw type shown , screws 12 are implemented as machine screws with rear nut fastenings , there can be a serious problem accessing the opposite side of panel 14 to hold and / or tighten the nuts since the speaker 10 occupies the mounting opening 14a ( fig1 ); two workers may be required . in thick non - metallic panels , tee - nuts are sometimes utilized , anchored into the rear of panel 14 ; however these tend to work loose and / or become cross - threaded , thus causing costly rework in manufacturing and in field repair . fig4 is a three - dimensional view of a versatile speaker 16 of the present invention , shown in a pre - installed disposition with a metal mounting ring 18 that enables twist - lock mounting to panel 14 . in this illustrative embodiment , the frame of speaker 16 is generally shaped and dimensioned for interchangeability with the &# 34 ; 6 . 5 inch &# 34 ; standard described in connection with fig1 and may actually utilize the same basic speaker frame part with some additional machine rework involving material removal : e . g . the region of rim 16a is configured with four slots at the channel bottom ( not visible in this view ) which engage four corresponding tabs 18a formed on mounting ring 18 , so as to provide twist - lock speaker mounting in accordance with this embodiment of the present invention . speaker 16 , along with ring 18 , is intended to be interchangeable with conventional speaker 10 of fig1 - 2 , being mountable in the &# 34 ; 6 . 5 inch &# 34 ; standard mounting pattern , i . e . cutout 14a and four holes 14b provided in panel 14 . ring 18 may be fastened to panel 14 , prior to mounting speaker 16 , by four screws 12a , typically self - tapping screws engaging suitably sized holes 14b in panel 14 . if the ring 18 is to be left mounted permanently in place on panel 14 , it can be fastened in place by rivets rather than screws . if nut fastenings are required , these can very easily be placed , started and held or tightened from the front ( top as shown ) through the main mounting opening 14a , since the ring 18 is attached to panel 14 prior to mounting speaker 16 , this accessibility eliminates any possible need for a second worker . fig5 shows the verstile speaker 16 of the present invention mounted into panel 14 of fig4 where it is held in place by engagement of the tabs 18a with the previously - mentioned slots in the speaker rim region . with ring 18 fastened in place on panel 14 , the initial mounting of speaker 16 and any subsequent removal and reassembly thereof are easily performed in a twist - lock manner enabled by the present invention . fig6 is an enlarged cross - section of an edge region of speaker 16 taken at a mounting screw location at axis 6 - 6 &# 39 ; of fig5 typical of the four locations of screws 12a and tabs 18a of ring 18 . ring 18 is secured directly and possibly permanently to panel 14 by screws 12a . the speaker frame cross - sectional shape can be the same as in fig3 except that screw clearance holes ( fig3 ), being no longer required in the landing 16k , are now eliminated , and slots 16g are configured in the rim channel trough region 16f . speaker 16 is secured to 14 panel by tabs 18a , passing through slots 16g and , upon twist - locking , retained by detent means ( to be described in more detail below in connection with fig8 a and 8b ). cone 16e is made larger than the cones described above as ordinarily utilized in speaker 10e of fig1 ; spacer 16b and surround flange 16c are seen to be displaced upwardly on landing 16k in comparison to their counterparts 10b and 10c of fig3 . suspension 16d and cone 16e are shown in the quiescent condition , located as indicated by solid lines , and in a limit travel condition , displaced as indicated by dashed lines showing cone 16e &# 39 ; and suspension 16d &# 39 ; maximally - displaced downwardly to the extent that the surround 16d &# 39 ; is stretched almost flat and yet there is sufficient clearance with regard to corner 16h . attaching ring 18 to panel 14 by screws 12a as shown allows the elimination of all holes in the region of landing 16k , and also , referring to fig1 and 3 , mounting holes in the surround flange 10c and spacer 10b are eliminated , thus providing in speaker 16 of the present invention a more complete and uniform interface surface at landing 16k , unobstructed by the screw heads , for adhesively attaching the surround flange 10c and spacer 10b . fig7 is a three - dimensional view showing the versatile speaker 16 of the present invention in a pre - installation position , to be mounted to a nonconventional panel 20 according an embodiment of the present invention which provides twist lock mounting in a manner that does not require a separate mounting ring 18 ( fig4 ): this is accomplished by forming mounting tabs 20a , shaped the same as tabs 18a of fig4 integrally in the mounting panel 20 . if panel 20 is part of a vehicle , tabs 20a would need to be formed in original manufacture , and mounting holes 14b ( fig4 ) would not be required . alternatively , panel 20 could be provided as a removable panel in the vehicle design , enabling exchangeability of different panel configurations . after twist - lock installation in the same manner as described above in connection with ring 18 , speaker 16 and panel 20 would appear as in fig5 . fig8 a , illustrating twist - lock mounting embodiment of the present invention in reference to fig7 and also generally applicable to fig4 - 6 , is a cross - section taken at axis 8 - 8 &# 39 ; of fig7 after initial assembly , showing a mounting tab 20a that has entered a slot 16g in the lower rim portion 16f of speaker 16 . fig8 b shows the items of fig8 a after the speaker 16 has been rotated clockwise to a locked position such that detent 16k at the rear of the rim channel has moved upwardly as shown to where it engages the hooked tongue portion of tab 20a , thus providing twist - lock mounting of the versatile speaker 16 according to this embodiment of the present invention . for subsequent speaker removal , speaker 16 is simply rotated counterclockwise so as to move slot 16g downward to the location shown in fig8 a , thus disengaging tab 20a from detent 16k and aligning slot 16g as shown so that the speaker 16 can then be easily moved to the right clear of tabs 20a and thus removed from the panel 20 . fig9 is a three - dimensional exploded pre - installation view of a panel 22 having an oversize mounting hole pattern , a versatile speaker 16 of the present invention , and mounting hardware comprising four spring clips 24 and four screws 12b that enable speaker 16 to be mounted in the oversize hole pattern , utilizing four clearance notches 16l provided in the rim 16a of speaker 16 . in this embodiment of the present invention , the oversize hole pattern in panel 22 into which speaker 16 is to be mounted , is the standard mounting pattern for the aforementioned &# 34 ; 170 mm &# 34 ; european style speaker frame , found in many vehicles of european origin . the main circular opening 22a is larger than openings 14a in fig1 and 20a in fig4 while the four mounting holes 22b are located on a circle 157 cm in diameter , which is the same dimension as the outside diameter of speaker 16 . therefore , to enable speaker 16 to be mounted in the &# 34 ; 170 mm &# 34 ; pattern , the rim region is made to have four clearance notches 16l at the four mounting locations , providing sufficient clearance for mounting screws 12b to enter the existing holes 22b available in panel 22 . at each mounting location , a steel spring clip 24 engages the head of the screw 12b with speaker rim 16a : clip 24 is made substantially longer than notch 16l , so that clip 24 overspans notch 16l enabling screw 12b , engaging hole 22b , to secure the speaker rim 16a against panel 22 . fig1 shows the verstile speaker 16 of the present invention mounted into panel 22 of fig9 where it is held in place by screws 12b retaining clips 24 which engage rim 16a at the location of the notches 16l ( fig9 ). fig1 is an enlarged cross - section taken at axis 11 - 11 &# 39 ; of fig1 with speaker 16 mounted into the front of panel 22 utilizing spring clip 24 which bears onto rim 16a when screw 12b is tightened into mounting hole 22b of panel 22 , thus pressing the bottom 16f of the speaker rim channel against the front side of panel 22 as shown . fig1 is a three - dimensional exploded pre - installation view of a panel 26 having an oversize mounting hole pattern , a versatile speaker 16 of the present invention , and mounting hardware comprising four spring clips 24a and four screws 12b that enable speaker 16 to be mounted against the rear of panel 26 in the oversize hole pattern , utilizing four clearance notches 16l provided in the rim of speaker 16 . fig1 shows the verstile speaker 16 of the present invention mounted against the rear of panel 26 of fig1 , where it is held in place by screws 12b retaining clips 24a which engage rim 16a at the location of the notches 16l ( fig1 ). the steel spring clips 24a are made wide enough to encompass the u - shaped speaker rim channel , so that when screw 12b is tightened into the panel mounting hole from the rear of the panel 26 as shown , the open edge of the speaker rim becomes pressed against the rear of panel 26 . this mounting arrangement could be utilized for example in a bulkhead of a vehicle behind a rear cushion , mounting the speaker 16 with its cone facing toward the front of the vehicle . fig1 is an enlarged cross - section taken at axis 14 - 14 &# 39 ; of fig1 with speaker 16 mounted against the rear of panel 26 utilizing spring clip 24a which bears onto rim channel region when screw 12b is tightened into the corresponding mounting hole of panel 26 , thus pressing the rim 16a of the speaker against the rear side of panel 26 as shown . a factor of merit for comparing inherent lf ( low frequency ) capability vs size for different speaker designs can be defined as the ratio of the cone area to the frame area , both areas being calculated from diameter . four speaker types , i . e . the popular &# 34 ; 6 . 5 inch &# 34 ; speaker type # 1 with its standard cone and # 2 with a custom oversized cone , the &# 34 ; 170 mm &# 34 ; speaker type and the versatile speaker of the present invention , are compared in table 1 , as follows : table 1______________________________________lf size efficiency comparison - cone / frame areadimensions : diameter in millimeters , area in square centimeters . speaker type : 6 . 5 &# 34 ;# 1 6 . 5 &# 34 ;# 2 170 mm subject______________________________________cone diameter dc 111 . 8 115 . 3 119 . 3 119 . 3cone area ac 98 . 2 104 . 4 111 . 8 111 . 8frame diameter df 157 157 166 157frame area af 193 . 6 193 . 6 216 . 4 193 . 6lf merit : ac / af 50 . 7 % 53 . 9 % 51 . 7 % 57 . 7 % ______________________________________ from table 1 it is seen that the subject versatile speaker configuration of the present invention rates higher than the other three speakers of known art that it can replace , with regard this factor of merit . with regard to the &# 34 ; twist - lock &# 34 ; embodiment illustrated in fig4 - 8b , the four notches shown in the rim 16a are not utilized in this twist - lock mounting arrangement , which is generally associated with the smaller mounting pattern , e . g . the &# 34 ; 6 . 5 inch &# 34 ; type , and thus this &# 34 ; twist - lock &# 34 ; embodiment could be implemented and practiced without the notches . similarly in the embodiment illustrated in fig9 - 11 the notches 16l are utilized but the slots 16g and tabs 18a / 20a of fig4 - 8b are not utilized in this mounting arrangement , which is generally associated with an oversize mounting pattern , e . g . the &# 34 ; 170 mm &# 34 ; type , and thus this &# 34 ; clip mounted &# 34 ; embodiment could be implemented and practiced without the slots and tabs . while in the foregoing descriptions of illustrative embodiments the particular well known &# 34 ; 6 . 5 inch &# 34 ; and &# 34 ; 170 mm &# 34 ; speaker types and panel mounting patterns have been shown as examples of practicing the present invention , the principles of the invention as disclosed herein are generally applicable to the attainment of interchangeability between various speaker types having moderately different sizes , especially in circumstances where the speaker must be truly &# 34 ; versatile &# 34 ;, i . e . readily installable into at least two different mounting patterns that cannot themselves be altered , for reasons of vehicle warranty , and since they were originated independently for distinctly different speaker types that are ordinarily non - interchangeable with regard to physical and / or performance characteristics . the invention may be practiced with any designated number of tabs 18a / 20a and corresponding slots 16g , typically within a range from 3 to 8 . ring 18 of fig4 may be provided with any desired number of optional spare ring mounting holes 18b , as illustrated in fig4 and any desired ones of these , corresponding to various available panel mounting holes , can be selected for receiving fastening screws 12a , typically but not necessarily in one or more uniform circular arrays . the detented twist - locking action of the present invention can be implemented with tabs 18a and protrusion 16k configured in alternative shapes that can provide detented twist - lock speaker mounting that is functionally equivalent to that of the illustrative embodiment shown . the invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof . the present embodiments are therefore to be considered in all respects as illustrative and not restrictive . the invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof . the present embodiments are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than by the foregoing description ; and all variations , substitutions and changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .