Abstract:
A highly compact loudspeaker which produces high fidelity, omnidirectionally propagated sound from only two sound drivers. The loudspeaker has a cylindrical, sound tight housing in which are mounted a relatively high frequency sound driver and a relatively low frequency sound driver, and optionally, an intermediate frequency sound driver. The high frequency driver is fixed at the top of the cylindrical housing, and is oriented to direct sound upwardly, away from the housing. The low frequency driver is fixed to the housing at the interior thereof, thereby dividing the housing into two sound resonating chambers. The low frequency driver directs sound downwardly into the lower of the two chambers. The bottom of the lower chamber is closed by a floor which bears a crossover network conventionally connected to the two sound drivers. The sound drivers are both coaxially centered within the housing. The loudspeaker optionally has two pairs of input signal terminals and a switch for selecting between the two pairs. In a further option, the loudspeaker incorporates an amplifier for compatibility with input signal sources such as personal computers.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a Continuation-In-Part of Ser. No. 09/209,838, filed Dec. 12, 1998, now U.S. Pat. No. 6,186,269. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention sets forth a loudspeaker which propagates coherent sound waves spherically in the manner of point source. The speaker has a relatively high frequency driver and a relatively low frequency driver, both mounted in a housing that in addition to being a structural support performs the additional function of directing and delivering sound. Applications of the invention include consumer, commercial, and institutional systems for reproducing and broadcasting sound, especially musical sound. 
     2. Description of the Prior Art 
     In the field of sound reproduction, and more particularly in the field of musical reproduction, it is desirable to reproduce sound in a manner as close to the original sound as is possible. Most sound reproduction systems employ one or more drivers both as transducers for generating sound from electrical signals, and to propagate the reproduced sound. The drivers, as combined into a self-contained speaker, must reproduce sound as faithfully as possible and project that sound universally in all directions. 
     The prior art has proposed speaker arrangements for achieving omnidirectional sound propagation. Examples are seen in U.S. Pat. No. 3,483,945, issued to Stanley Michael on Dec. 16, 1969, U.S. Pat. No. 3,961,684, issued to Stanley H. Michael et al. on Jun. 8, 1976, U.S. Pat. No. 5,115,882, issued to D. Grier Woody on May 26, 1992, U.S. Pat. No. 5,086,871, issued to Alain Barbe on Feb. 11, 1992, U.S. Pat. No. 5,227,591, issued to Timo Tarkkonen on Jul. 13, 1993, U.S. Pat. No. 5,436,976, issued to Donald J. Dougherty on Jul. 25, 1995, and U.S. Pat. No. 5,451,726, issued to Ted L. Haugum on Sep. 19, 1995. In each case, the subject speaker lacks the precise arrangement of drivers and chambers contained within a cylindrical housing, as seen in the present invention. 
     None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. 
     SUMMARY OF THE INVENTION 
     The present invention sets forth a construction for a very small loudspeaker for producing sound waves from electrical signals which sound waves are propagated in time and phase coherent manner. The novel loudspeaker reproduces with great fidelity sound which is to be directed to a human audience inside a building or other enclosure. In particular, the novel loudspeaker is suited for consumer sound systems including audiovisual equipment, music reproduction equipment, and sound synthesizing equipment, employing sound chambers which are remarkably small for the quality and volume of the sound produced. 
     The novel loudspeaker has, in various embodiments, two or three speakers mounted in a common cylindrical enclosure. The enclosure serves both as a structural member and also to form resonant chambers for influencing and propagating sound. Configuration and characteristics of the enclosure and its components are selected to maximize effectiveness of the loudspeaker. 
     The enclosure is a sound reflective cylinder divided into resonant chambers. These chambers are separated in one embodiment by the lower frequency sound driver of two sound drivers provided in the loudspeaker. In an embodiment incorporating three sound drivers, resonant chambers are separated by the lower two sound drivers and an open intermediate chamber. The relatively low frequency sound driver directs its sound downwardly into the lowermost of the chambers. This chamber optionally opens to the outside atmosphere by a port in the lateral wall of the chamber. Optionally, the speaker is mounted on legs, and the port is formed in the floor of the chamber. 
     The upper chamber serves as a reverberation chamber for both the relatively high frequency sound driver, which is upwardly directed, as well as for a relatively lower frequency sound driver. High frequency sound passes through the high frequency driver, and escapes upwardly to the outside. 
     Sound quality and propagation characteristics arise from resonance and other phenomena resulting from relationship of sound drivers to one another and to the housing, and from acoustic properties of cylindrical configuration of the housing and its division into upper and lower chambers. 
     Optionally, the loudspeaker includes two pairs or sets of input signal terminals and a switch for selecting between the two pairs or sets of input signal terminals. In a further option, the loudspeaker incorporates an amplifier so that input signal sources such as personal computers are compatible with the loudspeaker. 
     The novel loudspeaker includes a crossover network, which is mounted on the floor of the lower chamber. Interior surfaces of the chambers of the speaker are preferably lined with acoustic padding. The exterior of the housing is covered with grille cloth which passes sound with minimal dampening and distortion. 
     Accordingly, it is one object of the invention to provide a loudspeaker which reproduces sound in time and phase coherent waves. 
     It is another object of the invention to provide a high fidelity speaker which is very small and compact for its sound output. 
     It is a further object of the invention that the novel loudspeaker be capable of ready connection to different input signal sources. 
     Still another object of the invention is to provide a high fidelity compact speaker which is compatible with personal computers as sources of sound input signals. 
     An additional object of the invention is to provide high fidelity sound employing only two sound drivers. 
     It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes. 
     These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
     FIG. 1 is a front perspective view of one embodiment of the invention, partially broken away to reveal internal detail. 
     FIG. 2 is an exaggerated side elevational diagrammatic view of the embodiment of FIG.  1 . 
     FIG. 3 is an environmental, diagrammatic view of electrical components of an alternative embodiment of the invention. 
     FIG. 4 is a side elevational, diagrammatic view of a further alternative embodiment of the invention, partially broken away to reveal internal detail. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1 of the drawings, novel loudspeaker  10 , which propagates coherent sound waves spherically in the manner of point source is seen to comprise a cylindrical housing  12  having a lateral wall  14 , an upper end  16 , and a lower end  18 . Housing  12  is fabricated from a sound reflective material such as polyvinyl chloride or acrilonitrilebutadiene styrene, which materials provide magnetic shielding by virtue of their chemical constituents. A relatively high frequency sound driver  20  is mounted within housing  12  at upper end  16 . An annular plate  22  provides a supporting surface. Plate  22  is annular in that it is generally disc shaped, having a central opening for passing sound upwardly from sound driver  20 . Plate  22  projects radially inwardly from lateral wall  14 . High frequency sound driver  20  is oriented to propagate sound upwardly, away from housing  12 . High frequency sound driver  20  is preferably a one inch, silk soft dome driver of power in a range of thirty-five to fifty watts, with sound volume capability up to ninety-four dB and frequency capability of two thousand to twenty thousand hertz. 
     A relatively low frequency sound driver  24  is mounted within housing  12  such that low frequency driver  24  divides housing into an upper chamber  26  located between and closed by high frequency driver  20  and low frequency driver  24 , and a lower chamber  28  located below low frequency driver  24 . Sound driver  24  is oriented to project sound downwardly in the depiction of FIG. 1, into chamber  28 . Low frequency sound driver  24  is preferably a pole piece vented, midbass carbon fiber cone driver, with sound volume capability up to ninety-four dB and frequency capability of fifty hertz to twelve thousand hertz. Characteristics of drivers  20 ,  24  are generally conventional, and drivers of these specifications are readily commercially available. High and low frequency drivers  20 ,  24  are coaxially centered within housing  12  along longitudinal axis A (see FIG.  2 ). 
     Chamber  28  has a port  30  for allowing sound to escape. Low frequency sound driver  24  is oriented to propagate sound downwardly into chamber  28  and out through port  30 . Chamber  26  is sealed at upper end  16  by high frequency driver  20 , and is sealed at the bottom by low frequency driver  24 . Low frequency driver  24  is provided with a support plate  32 . Plates  22 ,  32  may, for example, adapt overall diameter of each driver  20  or  24  to bridge the distance, if such distance exists, between the outer diameter of the driver  20  or  24  and the interior surface of housing  12 . Each plate  22  or  32  has a central opening (concealed from view in each case by its associated driver  20  or  24 ) for passing sound through the air. 
     Plates  22 ,  32  also provide suitable surfaces for receiving silicone caulk (not shown) which is employed to seal drivers  20 ,  24 . Low frequency driver  22  is sealed by a material such as silicone caulk or an equivalent where it contacts the interior surface of housing  12 . Chamber  28  is closed at its upper end by low frequency sound driver  24  and at its lower end, which coincides with lower end  18  of housing  12 , by a floor  34 . Sealing at the upper end of chamber  26  is essentially sound tight, in that there exists no air passage for conducting sonic vibration. Sealing of the lower end of chamber  26  is preferably accomplished in a similar manner, so that sound, where it passes through the air, exits chamber  28  through port  30 . 
     A crossover network  36  is mounted on floor  30 , and is operably connected to high and low frequency drivers  20 ,  24  to control drivers  20 ,  24  conventionally by sending appropriate bandpass frequency signals to drivers  20 ,  24 . Connections of crossover network  36  to drivers  20 ,  24  is conventional, and incorporates conductors  38 ,  40  which extend to input signal terminals  42 ,  44 . Conductors  46 ,  48  connect crossover network  36  to sound driver  20 , and conductors  50 ,  52  connect crossover network  36  to sound driver  24 . 
     Acoustic padding  54  lines chambers  26 ,  28  at the interior surface of housing  12 . Padding  54  is preferably one quarter inch thick, if formed from a material having acoustic damping characteristics of a layer of cotton batting one inch thick. Padding  54  is broken along the circumference of sound driver  22  so that the latter may be bonded to housing  12  by silicone caulk. 
     Novel loudspeaker  10  achieves remarkable sound quality despite relatively small dimensions. Sound drivers  20 ,  24  are spaced apart such that the distance B from sound driver  20  to sound driver  24  is in the range of two and one half inches to two and three quarter inches. The height C of chamber  28 , taken from plate  32  to plate  34 , is in a range of three and one quarter inches to three and three quarter inches, preferably being three and one half inches. The heights of chambers  26 ,  28  are related to sound frequencies, and must not be varied even if other dimensions of speaker  10  are varied. 
     It is anticipated that the overall diameter of housing  12  can vary from four and one half inches to twelve inches, to accommodate standard commercially available sound drivers having overall nominal diameters of four inches, six inches, eight inches, and twelve inches. In the preferred embodiment, speaker  10  utilizes sound drivers having overall nominal diameters of four inches. In the latter case, the preferred embodiment, housing  12  has length in a range of six to seven inches, preferably six and one half inches, and has a diameter in a range of four to five inches, preferably four and one half inches. 
     Turning now to FIG. 3, the electrical components of FIG. 1 are modified to enable a user to select the source of speaker input signals by a two position switch  56 . Illustratively, speaker input signals are selectively derived from a radio receiver  2  and a personal computer  4 . Sound drivers  20 ,  24  and crossover network  36  are similar to those of the embodiment of FIG.  1  and are connected similarly. However, switch  56  is interposed between input terminals  58 ,  60 ,  62 ,  64  and crossover network  36 . Preferably, terminals  58 ,  60  are formed as part of a terminal assembly  66 , and terminals  62 ,  64  are formed as part of a functionally similar terminal assembly  68 , wherein the terminals of each respective terminal assembly are spaced apart to accommodate standard two conductor terminals (not separately shown). Communication cables  6 ,  8  serving radio receiver  2  and computer  4  typically terminate in two conductor terminals (not shown), such as coaxial conductor terminals. It will be understood that the various cables  70 ,  72 ,  74 ,  76 ,  78 ,  80  depicted in FIG. 3 have sufficient individual electrically isolated conductors to operate sound drivers  20 ,  24 . 
     Switch  56  has an operator  82  movable to two positions (identified as “A” and “B” in FIG.  3 ), each position being operable to connect crossover network  36  selectively to cable  70  or to cable  72 . In each position, that cable  70  or  72  not selected for connection to crossover network  36  is disconnected from crossover network  36 , so that only one source of signals is connected to sound drivers  20 ,  24  at any one time. 
     An amplifier such as PMOP amplifier  84  is operably connected by switch  56  to one cable, such as cable  72 . Amplifier  84  amplifies power signals derived from a connected signal source which is inadequately powered to produce audible sound from sound drivers  20 ,  24  directly. Amplifier  84  provides necessary amplification assuring that sound drivers  20 ,  24  produce audible sounds responsive to the input signals. 
     FIG. 4 shows a variation on the prior embodiments, wherein speaker  110  includes a relatively high frequency sound driver  120 , a relatively low frequency sound driver  124 , and an intermediate frequency sound driver  186 . Sound drivers  120 ,  124 ,  186  are mounted on respective annular plates  122 ,  132 ,  188  in a manner similar to that of the embodiment of FIG.  1 . An upper chamber  126  is formed between sound drivers  120  and  186 , and is dimensioned and configured such that spacing between sound drivers  120  and  186  is between two and one half inches and two and three quarter inches. A lower chamber  128  formed between sound driver  124  and floor  134  of housing  112  has a height C, taken between plate  132  and floor  134 , of three and one half inches. A chamber  188  is formed between sound drivers  124  and  186 . Chamber  188  opens to the outside to enable sound to escape by one or more openings such as window  190 . Sound drivers  120 ,  124 ,  186  are operably connected to a crossover network (not shown) and to input signals in a manner similar to that of the embodiment of FIG. 1. A two position switch (not shown) functionally similar to switch  56  of FIG.  3  and an amplifier (not shown) functionally similar to amplifier  84  of FIG. 3 are optionally provided for the embodiment of FIG.  4 . 
     The embodiments of FIGS. 1 and 4 are similar in that respective uppermost chambers  26  and  126  have similar spacing between opposed respective sound drivers  20 ,  24  (FIG. 1) and  120 ,  186  (FIG.  4 ), the spacing being in the range of two and one half to two and three quarter inches. Respective lowermost chambers  28  (FIG. 1) and  128  (FIG. 4) also have similar height of three and one half inches. Chambers  26 ,  126 ,  28 ,  128  influence sound quality due to resonance. Hence, spacing and height are important parameters for sound reproduction. 
     It will be appreciated that in the embodiment of FIG. 1, the uppermost and lowermost chambers are separated by a common component, namely, sound driver  24  and its associated mounting plate  32 . By contrast, in the embodiment of FIG. 4, the uppermost and lowermost chambers are separated by two sound drivers  124 ,  186  and intervening chamber  188 . Nonetheless, the two embodiments share the characteristic that there are in each embodiment an uppermost chamber and a lowermost chamber. Location and orientation (where orientation refers to direction of projection of sound) are also similar for the highest and lowest frequency sound drivers between the two embodiments. 
     The relatively highest frequency sound driver in each embodiment has an adjacent sound driver. In the embodiment of FIG. 1, the adjacent sound driver is the same as downwardly oriented relatively low frequency sound driver  24 . In the embodiment of FIG. 4, the adjacent sound driver  186  is not the same as downwardly oriented relatively low frequency sound driver  124 . Despite these differences, it will be noted that both embodiments have a sound driver adjacent to the relatively high frequency sound driver and a downwardly oriented relatively low frequency sound driver. 
     The invention is susceptible to variations and modifications which can be introduced thereto without departing from the inventive concept. For example, hard wiring of speakers shown herein could be supplanted by wireless connection, such as by radio frequency signals. Any suitable frequency allowed by the Federal Communication Commission would be acceptable, although it is preferred to employ a frequency such as 900 MHz. 
     In another variation, port  30  shown in FIG. 1 could be relocated to floor  34 . This variation would preferably further include legs (not shown) spacing loudspeaker  10  above a floor or other supporting horizontal surface. 
     Where necessary to provide electrical power, such as for amplification, the novel loudspeaker in any of its embodiments may optionally include power conductors connected to any electrical component requiring power beyond that supplied by input signals. Supplementary power circuitry may optionally include an AC-to-DC converter, if desired. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.