Abstract:
A flush mountable ceiling speaker ( 10 ) with individual coaxial waveguides ( 20, 22 ) for both the lower and high-frequency transducers ( 11, 12 ). The lower frequency radiation is combined with the sonic energy radiated by the high-frequency transducer ( 12 ) and shaped by the high-frequency waveguide ( 20 ) to create a coherent, uniformly controlled coverage pattern. The loudspeaker ( 10 ) creates a well defined sound dispersion pattern over a relatively large bandwidth, resulting in increased vocal intelligibility and more accurate reproduction of music at relatively great distances from the loudspeaker, as is particularly useful in association with high ceiling installations.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of loudspeaker systems, and more particularly it relates to loudspeaker systems for ceiling mounted applications. 
   BACKGROUND OF THE INVENTION 
   A typical loudspeaker is difficult to mount within a ceiling structure. Special ceiling loudspeakers exist which include some sort of mounting device that allows them to be affixed to a ceiling. An example of such a loudspeaker system is disclosed in U.S. Pat. No. 5,088,574, entitled CEILING SPEAKER SYSTEM, issued on Feb. 18, 1992 to Kertesz. Flush mountable ceiling speakers are loudspeakers that are mounted within a hole in a ceiling such that the front of the speaker is substantially coplanar with the surface of the ceiling. An example of such a loudspeaker is disclosed in U.S. Pat. No. 4,123,621, entitled ACOUSTICAL SPEAKER DEVICE, issued to Walker on Oct. 31, 1978. 
   A typical ceiling loudspeaker is a two-way system having a lower-frequency transducer that reproduces the lower frequencies and a high-frequency transducer that reproduces the higher frequencies. 
   One method to increase the lower-frequency output of the lower-frequency transducer is by the addition of a port to the enclosure of the lower-frequency transducer. Low frequencies are then produced not only by the movement of the lower-frequency transducer but also by the movement of air through the port. In a flush mounted ceiling speaker, the port must be on the front of the speaker in order to project the lower-frequency energy in a downward direction toward the audience rather than into the airspace above the ceiling where it will not be heard. 
   Another feature often incorporated into a ceiling speaker is a line transformer, which allows many speakers in a room to be powered by one amplifier. Such a loudspeaker system often includes an adjustable switch that must be accessible in order to permit the user to change the setting of the line transformer. This adjustable switch should be easily accessible at the point of speaker installation. In the case of a flush mounted ceiling speaker, the most convenient place to access this switch once the speaker is installed is on the front of the speaker. 
   In some loudspeaker systems the lower-frequency transducer and high-frequency transducer are mounted in a spaced apart relationship in which their various axes and planes are neither coaxial nor coplanar. An example of such a loudspeaker system is disclosed in U.S. Pat. No. 6,411,718, entitled SOUND REPRODUCTION EMPLOYING UNITY SUMMATION APERTURE LOUDSPEAKERS, issued on Jun. 25, 2002 to Danley et al. In other types of loudspeaker systems the high-frequency transducer is mounted coaxially with the lower-frequency transducer. This coaxial mounting method saves space and often provides a relatively smoother transition between lower frequencies and high frequencies when the listener is positioned off axis from the loudspeaker. In some instances the high-frequency transducer will include a horn, also known as a waveguide, in order to control the dispersion pattern of sound emanating from the loudspeaker system. An example of a coaxial speaker system including a waveguide is disclosed in U.S. Pat. No. 6,431,309, entitled LOUDSPEAKER SYSTEM, issued on Aug. 13, 2002 to Coffin. 
   The higher frequencies at which high-frequency transducer waveguides are effective contain only a portion of the frequencies where intelligible speech is typically present. The human voice produces sounds that appear in the frequency spectrum from between around 100 Hz to 10,000 Hz, with the majority of the vocal intelligibility residing between 500 Hz and 8000 Hz. The typical ceiling speaker includes a lower-frequency transducer that will reproduce a range of frequencies from below 100 Hz up to between 2000 and 4000 Hz (the lower and medium frequencies). The high-frequency transducer in such a speaker will typically reproduce the frequencies from between around 2000 and 4000 Hz up to 20,000 Hz (the high frequencies). The high-frequency transducer often does not produce high levels of sound in the frequency band below 2000 Hz. The high-frequency waveguide that controls the high-frequency transducer dispersion pattern is only effective over the frequency range of the high-frequency transducer to which it is coupled. Such an arrangement leaves the low and medium frequencies produced by the lower-frequency transducer, including those encompassing a significant portion of the human vocal spectrum, with an uncontrolled dispersion pattern. 
   The resultant −6 decibel beamwidth as a function of frequency for a typical prior art loudspeaker is depicted in  FIG. 1 . The main area of interest is from about 800 Hz to approximately 2.5 KHz, above which the high-frequency transducer&#39;s waveguide begins to control its dispersion pattern. As seen in  FIG. 1 , the beamwidth between point  1  (800 Hz) and point  2  (2.5 KHz) remains at a value of approximately 200 degrees, which is undesirably large compared to a beamwidth between 50 and 100 degrees for the frequency band above 4000 Hz. When the listener is located beyond some relatively minimal distance from the loudspeaker, the high frequencies occupying the spectrum at 3000 Hz and above will be focused on the listener to a greater degree than the band of frequencies below 3000 Hz, resulting in a large portion of the vocal intelligibility and musical detail being lost. 
   The directivity index (DI) and directivity factor (Q) for a typical prior art loudspeaker is depicted in  FIG. 3 . The directivity factor expresses the gain in the peak on axis direction with reference to a theoretical omnidirectional source having the same radiated power, while the directivity index is ten times the logarithm of the directivity factor, in decibels. As seen in  FIG. 3 , the DI and corresponding Q between point  3  (800 Hz) and point  4  (2.5 KHz) is relatively low compared to the higher frequencies, indicating relatively poor directional focus at these frequencies. 
   Ideally, a flush mounted coaxial ceiling speaker should utilize a waveguide optimized for the medium and lower frequencies produced by the lower-frequency transducer in addition to a waveguide designed for the higher frequencies produced by the high-frequency transducer, thereby increasing vocal intelligibility and the accuracy of musical reproduction when utilized in a high ceiling application. The ideal speaker system should also include a port to increase the lower-frequency output of the speaker, and include a line transformer switch accessible from the front of the speaker. 
   SUMMARY OF THE INVENTION 
   The present invention includes a flush mountable coaxial ceiling speaker with a lower-frequency transducer waveguide coaxially aligned with a high-frequency transducer waveguide. The dual waveguides focus a wider spectrum of sound into a relatively narrower pattern, thereby projecting the sound further than a ceiling speaker with only a high-frequency waveguide or no waveguide at all. The projected sound is both louder and more intelligible within a well-defined listening plane at relatively greater distances. This characteristic allows the coaxial loudspeaker with multiple waveguides to be placed relatively farther away from the listener, thereby permitting the use of the present invention in association with relatively high ceiling (18′–25′) applications. The present invention also incorporates a forward facing port and transformer switch, both of which are housed within the lower-frequency waveguide in order to facilitate access by the speaker installer while minimizing the overall diameter of the speaker system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph depicting the typical horizontal and vertical beamwidth as a function of frequency for a prior art flush mounted ceiling speaker; 
       FIG. 2  is a graph depicting the typical horizontal and vertical beamwidth as a function of frequency for a loudspeaker system constructed according to the principles of the present invention; 
       FIG. 3  is a graph depicting the typical directivity index and directivity factor as a function of frequency for a prior art flush mounted ceiling speaker; 
       FIG. 4  is a graph depicting the directivity index and directivity factor as a function of frequency for a loudspeaker system constructed according to the principles of the present invention; 
       FIG. 5  is a block diagram of a coaxial loudspeaker and crossover network used in the system of the present invention; 
       FIG. 6  is a first perspective view of a loudspeaker constructed according to the principles of the present invention; 
       FIG. 7  is a second perspective view of the loudspeaker depicted in  FIG. 6 ; 
       FIG. 8  is a side elevation of the loudspeaker depicted in  FIG. 6 ; 
       FIG. 9  is a perspective view of the lower-frequency waveguide utilized in the loudspeaker depicted in  FIG. 6 . 
       FIG. 10  is a top plan view of the loudspeaker depicted in  FIG. 6   
       FIG. 11  is a sectional view taken along line A—A of the loudspeaker depicted in  FIG. 10 ; and 
       FIG. 12  is a sectional view taken along line B—B of the loudspeaker depicted in  FIG. 10 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 3  have been described above in connection with conventional flush mounted ceiling loudspeaker systems. Such speakers may utilize a single waveguide optimized for improved high-frequency transducer performance at the higher frequencies. The lack of a mechanism to control lower-frequency dispersion pattern limits the distance that intelligible sound may be projected over this lower frequency range. 
     FIG. 2  is a graph showing the beamwidth as a function of frequency for the loudspeaker of the present invention. At point  5  (800 Hz) the beamwidth is approximately 160 degrees, but begins to decrease steadily to a value of 50 degrees before reaching point  6  (2.5 KHz). This narrowing of the beamwidth between points  5  and  6  enables the lower-frequency range to be projected to greater distances than the relatively wider beamwidth shown between points  1  and  2  in  FIG. 1 . Such increased listener distances are typically encountered when mounting the loudspeaker of the present invention in a relatively high ceiling, such as might be encountered in a church or school. 
     FIG. 4  is a graph showing the directivity index (DI) and directivity factor (Q) as a function of frequency for the loudspeaker of the present invention. The DI value at point  8  (800 Hz) is approximately five decibels, but steadily increases until the DI value is approximately 12 decibels prior to reaching point  9  (2.5 KHz). This is in contrast to the directivity index and directivity factor graph depicted in  FIG. 3 , which shows a DI value of approximately 3 decibels at point  3  (800 Hz), increasing to a maximum of 10 decibels at point  4  (2.5 KHz). The average directivity index value between points  3  and  4  is relatively lower than the average DI value between points  7  and  8 . The present invention has a narrower beamwidth than the loudspeaker characteristics depicted  FIG. 3  due to the presence of the lower-frequency waveguide which tends to focus the radiated sound within the lower frequency range, thereby projecting a relatively greater portion of the radiated sound for a relatively greater distance from (below) the loudspeaker. 
     FIG. 5  is a block diagram of the coaxial loudspeaker system  10  of the present invention and including a high-frequency waveguide  20 . The system  10  includes the coaxial loudspeaker  9 , constructed so as to have a lower-frequency transducer  11  and a high-frequency transducer  12 , coupled with the high-frequency waveguide  20 . The crossover network  13  includes a high pass filter  14  which forwards its higher-frequency band output signal  16  to the high-frequency transducer  12 . A low pass filter  15  forwards its lower-frequency band output signal  17  to the lower-frequency transducer  11 . The signal containing the entire frequency spectrum is introduced to the speaker system  10  at terminals  18  and  19 . 
     FIG. 6  is a perspective view showing the assembled loudspeaker system  10  including the lower-frequency transducer  11  and the high-frequency transducer  12 . The high-frequency waveguide  20  is coupled coaxially with the high-frequency transducer  12 . Mounted behind the high-frequency transducer  12  and waveguide  20  is the lower-frequency transducer  11 , which is coaxially aligned with the longitudinal axis  21  of high-frequency transducer  12  and waveguide  20 . Also mounted coaxially with the axis  21  is the lower-frequency waveguide  22 , constructed to include a port  23  and adjustable switch  25 . The port  23  is seen to be an integral part of the lower-frequency waveguide, as is the adjustable switch  25 . The combination of high-frequency transducer  12 , lower-frequency transducer  11 , high-frequency waveguide  20  and lower-frequency waveguide  22  is mounted within a rigid housing  24 . The housing  24  is formed substantially as a cylinder having a diameter  30  ( FIG. 8 ) that is slightly greater than the lower-frequency waveguide diameter  34  ( FIG. 10 ) so as to permit the lower-frequency waveguide  22  to reside within the cylinder  24  in an abutting relationship. 
     FIG. 7  is another perspective view of the coaxial loudspeaker system  10  in which the forwardly facing line transformer switch  25  is best seen. The switch  25  is seen to be an integral part of the lower-frequency waveguide  22 . 
   As seen in  FIG. 8 , the assembled loudspeaker  10  includes a front protective grille  26 . The overall height  28  of the entire assembly  10  is approximately 340 mm. In a preferred embodiment, the housing  24  has a height  29  of approximately 303 mm. The diameter  30  is approximately 303 mm. In this preferred embodiment, the total weight of the assembly  10  is approximately 6.0 kg. 
     FIG. 9  depicts the lower-frequency waveguide  22  without the presence of the other components. Referring also to  FIG. 12 , the port  23  is seen to include a wall  31  that extends in a direction substantially parallel to the longitudinal axis  21 . The trailing edge  32  of the port structure  23  extends to a region behind the leading edge  33  of the lower-frequency transducer  11 . 
     FIG. 10  is a top plan view showing the port  23  and adjustable switch  25  residing within the lower frequency waveguide  22 , thereby resulting in a relatively smaller overall diameter of the loudspeaker assembly  10 . The lower-frequency transducer  11 , lower-frequency waveguide  22 , high-frequency transducer  12  and high-frequency waveguide  20  are concentric with one another. 
     FIGS. 11 and 12  depict the relative positions of the high-frequency waveguide  20  and the lower-frequency waveguide  22 . The lower-frequency waveguide  22  substantially surrounds the portion of the longitudinal axis  21  residing within the housing  24  in the region extending from the leading edge  33  of the lower-frequency transducer  11  to the outer edge  35  of the housing  24 . The angle  36  formed between the waveguide  22  and the longitudinal axis  21  is such that the beamwidth produced by the lower-frequency waveguide  22  is substantially equal to the beamwidth produced by the high-frequency waveguide  20  over a large portion of the vocal intelligibility band. Due to the coaxial placement of the transducers and waveguides, the sonic energy radiated from the lower-frequency transducer  11  is shaped by the lower-frequency waveguide  22 . The lower frequency radiation is then combined with the sonic energy radiated by the high-frequency transducer  12  and shaped by the high-frequency waveguide  20  to create a coherent, uniformly controlled coverage pattern. 
   While the specific characteristics of one embodiment of the present invention have been set forth, numerous adjustments may be made to the invention based on specific requirements of the user. In particular, the frequency spectrum of interest may not be as broad as the entire audible range, and even applications devoted to human speech may have spectral requirements with narrower or broader bandwidths than those described. The profile created by angle  36  could be straight, curved, or have a multi-angular profile to achieve a substantially equal beamwidth for varying frequency ranges and applications. If the beamwidth of a high-frequency transducer is desirable without the aid of a high-frequency waveguide, the lower-frequency waveguide may still be utilized and formed to match the high frequency beamwidth.