Abstract:
This invention provides a speaker enclosure that minimizes or defuses standing waves and minimizes resonance within the operating frequency range of its transducers. To minimize standing waves, the speaker enclosure has no two surfaces that are parallel to each other thus preventing the propagation of standing waves. The interior surface of the speaker enclosure may have ribs spaced apart on any surface that is prone to resonate so that the surface is strengthened such that it resonates at a predetermined frequency that is typically outside of the operating frequency range of the transducers.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a non-provisional application claiming priority of U.S. provisional application Serial No. 60/302,830 filed Jul. 2, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a speaker housing that minimizes standing waves and configured to resonate above an operating range of its transducers. 
     2. Related Art 
     In most loudspeaker systems, drivers or transducers are housed in a speaker enclosure. The speaker enclosure serves a number of functions. These functions include easier set up of transducers (or drivers) in one unit and keeping the transducers in the correct position while working together. At the same time, speaker enclosures often affect the quality of sound produced by the transducers. As the transducers vibrate the diaphragm, sound waves are emitted in the back and forth direction relative to the transducer. In other words, sound is produced behind the diaphragm as well as in front of the diaphragm. In a sealed enclosure, no air can escape and therefore back waves are trapped within the enclosure. Because no air can escape, the interior air pressure of the sealed enclosure changes as the diaphragm vibrates. With today&#39;s sealed enclosures, these back waves can significantly affect the quality of sound produced by the transducers. 
     One of the problems with back waves is that standing waves may be formed within the enclosure. For example, within rectangular-like box enclosures, there are a number of parallel surfaces, and as back waves emanate within the parallel surfaces, the standing waves simply propagate back and forth causing negative audible artifacts. The anomalies caused by standing waves are typically one-note based and are objectionable to the listener. 
     Another problem associated with back waves is viration of the waves against the sidewalls of the enclosure. Depending on the size and structural integrity of the sidewalls, the back waves may resonate at approximately the same operating frequency of the transducers. In such a case, the vibration of the sidewalls can interfere with the quality of sound produced by the transducer. Thus, the overall loudspeaker system may operate at less efficiency because some of the energy is used to vibrate the sidewalls instead of the diaphragm. Accordingly, there is still a need for a speaker enclosure that can minimize or defuse standing waves and prevent the enclosure from resonating within the operating frequency range of its transducers. 
     SUMMARY 
     This invention provides a speaker enclosure that minimizes or defuses standing waves and minimizes resonance within the operating frequency range of its transducers. This is accomplished by providing a speaker enclosure formed from a number of inner surfaces where no two surfaces are parallel with respect to another surface. In other words, none of the inner surfaces of the enclosure are parallel with respect to each other minimizing the propagation of standing waves. If standing waves do occur, they are diffused quickly by the elimination of parallel surfaces. Furthermore, a sidewall or inner surface that is prone to resonate within the operating frequency of its transducers may be strengthened, via ribs or any other methodologies known to one skilled in the art, to prevent that sidewall from vibrating. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
     FIG. 1 is a perspective view of a speaker enclosure. 
     FIG. 2 is a front view of a speaker enclosure according to FIG.  1 . 
     FIG. 3 is a cross-sectional view along the line  3 — 3  in FIG. 2 of the speaker enclosure illustrated in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a speaker enclosure  100  having a grill  102  covering a front cover  104  that is adapted to hold one or more transducers. The speaker enclosure  100  also includes a back cover  106  configured to enclose the transducers. To accomplish this, the back cover  106  may have a plurality of receptors  130  adapted to receive screws coupling the front cover  104  to the back cover  106 . In this embodiment, the front cover  104  and the back cover  106  may form a sealed speaker enclosure  100 . The transducers within the speaker enclosure  100  may be mid-range transducers, operating between 100 Hz and 2.5 KHz. The speaker enclosure, however, may also hold high frequency transducers that operate above 20 KHz, and low frequency transducers that operate below 300 Hz. 
     The back cover  106  may be formed of a plurality of sidewalls including a top surface  110  and an opposing base surface  112 . The base surface  112  may be substantially planar so that the speaker enclosure  100  may rest on any flat surface such as a stand, table or above a television set. In contrast, the top surface  110  may be substantially curved, such as in the form of a dome shape. Thus, the two opposing surfaces  110 ,  112  may be structured in a non-parallel relationship with respect to each other. Moreover, two sidewalls  114 ,  116  may be substantially non-parallel with respect to each other as well, along with the top surface  110 , and the base surface  112 . In addition, the back surface  120  may also be structured with a non-parallel relationship with the front cover  104 , along with the top surface  110 , the base surface  112 , and the two sidewalls  114  and  116 , respectively. 
     By minimizing the number of parallel surfaces in the speaker enclosure  100 , the back waves generated by the transducer may be prevented from propagating into standing waves. On the other hand, if some of the back waves do propagate into standing waves within the speaker enclosure  100 , the standing waves may be quickly diffused without a pair of parallel walls causing the standing waves to bounce back and forth from within the speaker enclosure  100 . Standing waves may cause audible artifacts in the loudspeaker system that may be propagated, in part, through the transducer. These artifacts may appear as dips and peaks in the loudspeaker system performance. Put differently, the standing waves within the speaker enclosure may interfere with the performance of the transducer so that sound does not seem natural as originally intended. 
     Another embodiment of the invention is to configure the speaker enclosure  100  so that it does not resonate within the operating frequency of the transducers. In general, all surfaces resonate. Typically, a larger, weaker surface wall will resonate at lower frequency than a smaller, stronger surface wall. For example, a 12-inch wide panel inside a speaker enclosure may resonate at 1 KHz. On the other hand, if a rib or stiffener is place at the center of the flat panel, the two 6 inch flat panel may resonate at 2 KHz. As flat panels are divided into smaller segments, they resonate at a higher frequency. Accordingly, the speaker enclosure  100  may be configured so that any surface that is prone to resonate in the operating frequency range of the transducer may be strengthen to increase its resonant frequency above the operating frequency of the transducers. This way, the speaker enclosure does not resonate to interfere with the quality of the sound produced by the complete loudspeaker system because the individual low frequency transducers are operating at a lower frequency range that does not resonate the speaker enclosure. 
     FIGS. 2 and 3 illustrate the back surface  120  having a substantially flat surface and about 0.4191 meters (16.5 inches) wide between the two sidewalls  114  and  116 . This means that the back surface  120  may resonate when the wavelength of the back waves is about 0.4191 meters. As such, the frequency in which the back surface  120  may resonate may be based on the following where: Frequency=speed of sound/wavelength=345 (m/s)/0.4191 m=823 Hz. In one embodiment, the mid-range transducers in the speaker enclosure  100  may operate between about 100 Hz to about 2.5 KHz. Accordingly, the back waves from the mid-bass transducers may cause the back surface  120  to resonate around 823 Hz to interfere with the quality of the sound. 
     To prevent the back surface  120  from resonating within the operating frequency range of the transducers, a number of ribs or stiffeners  200  may be placed on the back surface  120  to divide the back surface  120  into smaller segments such as  200 ,  202 ,  204 ,  206 ,  208  and  210 . That is, each of the segments are sized to resonate above the operating frequency of the transducer. For instance, the longest span between the ribs  200  may be in the segment  210 , with a width “W” of about 0.0572 meters (2.25 inches). This means that the segment  210  may resonate when the wavelength is about 0.0572 meters. As such, the frequency in which the segment  210  may resonate may be about 6.036 KHz, based on the following where: Frequency=345 (m/s)/0.0572 m=6036 Hz or 6.036 KHz. Since the mid-bass transducers operate in the frequency range of between about 100 Hz and about 2.5 kHz, the segment  210  cannot resonate to interfere with the quality of the sound produced by the transducer. Likewise, since other segments in the back surface  120  are narrower than the segment  210 , they too cannot resonate to interfere with the transducers. 
     To optimize the strength of the ribs  200 , they may be curved rather than straight because curved ribs are stiffer than straight ribs. Mechanically, a flat surface bend and flex easier than a curved surface. As such, to further enhance the strength of the ribs  200  and consequently the back surface  120 , the ribs  200  may be curved. Alternatively, ribs  200  may have any other configuration as known to one skilled in the art, including a straight rib. 
     Besides the back surface, the ribs  200  also extend to top surface  110  for added strength, but there may be less ribs  200  on the top surface  110  than on the back surface  120  for the following two reasons. First, the top surface  110  may be dome shape so that it is stiffer than a flat panel, such as the back surface  120 . A flat surface bend and flex easier than a curved surface so that the top surface  110  may be less prone to resonate then the back surface  120 . This means that the top surface  110  needs less ribs  200  then the back surface  120 , if any. Secondly, top surface  110  having a dome shape is generally tangential to the direction of the back wave in comparison to the back surface  120 . This means the back waves have less impact on the top surface  110  than on the back surface  120 . With less impact on the top surface  110 , the top surface  110  is less prone to resonate, and therefore less ribs  200  may be needed on the top surface  110  than on the back surface  120 . 
     In this embodiment, the speaker enclosure  100  is designed to resonate above 6 KHz, which is more than twice the peak operating frequency range of the mid-bass transducer, i.e., 2.5 KHz. Alternatively, the speaker enclosure  100  may be configured to resonates just above the peak operating frequency range of the transducers such as 3 KHz. That is, the speaker enclosure  100  may be configured with ribs  200  spaced apart accordingly on any surface that is prone to resonate so that the speaker enclosure  100  resonate at a higher predetermined frequency than the operating frequency of the transducer. For example, for low-frequency range transducers that operate up to about 300 Hz, i.e., bass, the speaker enclosure  100  may be configured to resonate above 300 Hz. The speaker enclosure  100  may be configured to minimize standing waves and to resonate at a higher frequency to prevent the speaker enclosure from resonating within the operating frequency range of the transducer. This way, the enclosure does not resonate to interfere with the quality of the sound generated by the transducers. 
     While various embodiments of the application have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.