BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention provides a loudspeaker system having a primary driver and an active radiator sealed within an enclosure where the sound pressure level generated by the primary driver is tunable by adjusting the operational characteristics of the active radiator. 
     2. Related Art 
     A loudspeaker system, also known as an audio transducer, converts electrical energy into acoustical energy to generate sound. A loudspeaker system includes at least one “primary” transducer or driver that is mounted into an enclosure. The term “primary” generally indicates that the driver is connected to a signal source such as an amplifier or a crossover network.  FIG. 1  shows a cutout view of a typical driver  100  illustrating some of its electromagnetic components. The driver  100  includes a magnet  102  and a voice coil  104  with two leads  106 . The voice coil  104  is wound cylindrically around a tube like cylinder  108  and placed within an air gap  110 . The tube like cylinder  108  is coupled to a diaphragm  112  that is supported by a suspension  114  and a spider  116 . A dust cap  118  may be provided over the cylinder  108 . The outer ends of the suspension  114  and the spider  116  may be coupled to a basket  120  to ensure that the voice coil  104  moves back and forth substantially along the axial direction. The two leads  106  from the voice coil  104 , for example, may be connected to an audio amplifier that provides current through the voice coil  104  that is a function of the electrical signal to be transformed by the driver  100  into an audible, sub-audible or subsonic pressure variation. As the electrical signal from the amplifier passes through the voice coil  104 , the interaction between the current passing through the voice coil  104  and the magnetic field produced by the permanent magnet  102  causes the voice coil  104  to oscillate in accordance with the electrical signal and, in turn, drives the diaphragm  112  and produces sound. As such, the driver  100  converts the electrical signal source into acoustical energy to produce sound. 
     A loudspeaker system typically has a driver housed in a ported enclosure or a sealed enclosure. The ported enclosure has an opening to allow sound waves to push in and out of the enclosure as the diaphragm of the driver oscillates back and forth. With the sealed enclosure, however, air inside the sealed enclosure compresses and expands as the diaphragm of the driver oscillates back and forth. In some instances, the sealed enclosure may be provided with a primary driver and a passive radiator. As discussed above, the primary driver has electromagnetic components to convert the electrical signal source into acoustical energy to produce sound. In contrast, the passive radiator has a diaphragm but no other electromagnetic components. This allows the diaphragm of the passive radiator to freely vibrate based on the pressure differential inside the sealed enclosure imparted by the primary driver. As the diaphragm of the passive radiator expands the net internal volume of the sealed enclosure increases to ease the pressure differential inside the sealed enclosure. The passive radiator may be incorporated in the sealed enclosure to improve the low frequency extension of the primary driver. This allows the diaphragm of the primary driver to extend further to increase the low frequency response. 
     With a sealed enclosure, the passive radiator and the primary driver share the same enclosure or the same acoustic-internal volume of the enclosure. The air compression and rarefaction caused by the primary driver push and pull on the diaphragm that is freely coupled to the passive radiator. Operating characteristics (excursion properties) of the passive radiator indicate how much force may be needed to push and pull on the diaphragm of the passive radiator. Many factors may define the operating characteristics of the passive radiator such as mass of the diaphragm, surface area of the diaphragm, material, etc. The operating characteristics of the passive radiator may partly determine the characteristics of the pressure changes within the enclosure and may have an effect on the overall performance of the primary driver. In other words, the passive radiator&#39;s resistance to push and pull movement may affect the overall performance of the primary driver. For example, if the passive radiator is very massive, then there may be greater resistance. If such is the case, the enclosure may be subject to a higher pressure, thereby affecting the overall performance of the primary driver. 
     One of the problems with a passive radiator is that its operating characteristics are fixed. In other words, once the loudspeaker system is constructed with a passive radiator, the operating characteristics of the passive radiator may not be changed without changing the mechanical properties of the passive radiator. Put differently, in the design phase of the loudspeaker system, appropriate design parameters are selected for a desired operating characteristic, such as mass, surface area, compliance of suspension, and material for the passive radiator. Once the design parameters of the passive radiator have been selected, however, they cannot be later changed. 
     Accordingly, there is a need for a loudspeaker system that may vary the operating characteristics of a passive radiator without altering mechanical properties of the passive radiator. This way, by varying the operating characteristics of the passive radiator, the overall output of the primary driver may be varied as well to improve the performance of the loudspeaker system. 
     SUMMARY 
     This invention provides a loudspeaker system having an active radiator that can vary its operating characteristics to tune the sound pressure level generated by a primary driver. The loudspeaker system includes a primary driver and an active radiator sealed within an enclosure so that the primary driver and the active radiator share the same acoustic volume of the enclosure. In other words, the primary driver and the active radiator share a common acoustic compliance of the enclosure. The primary driver has electromagnetic components designed to oscillate a flexible cone or diaphragm along the longitudinal axis of the primary driver. The primary driver is provided with an audio signal from an audio signal source such as an amplifier. The primary driver converts the audio signal source to sound waves by rapidly oscillating the flexible cone or diaphragm forwards and backwards along the longitudinal axis corresponding to the audio signal. As the diaphragm of the primary driver oscillates back and forth, the active radiator may also radiate as a result of sharing the same acoustic volume with the primary driver. 
     The active radiator has electromagnetic components that may be controlled by a number of electrical configuration settings. Each electrical configuration setting may affect the operating characteristics (excursion properties) of a diaphragm of the active radiator. With the primary driver and the active radiator sharing the same acoustic volume or compliance, varying the excursion properties of the diaphragm for the active radiator in turn affects the excursion properties of the diaphragm for the primary driver. As such, the sound pressure level generated by the primary driver can be tuned by varying the configuration setting provided to the active radiator. This allows a user or processor to tune the operating characteristics of the loudspeaker system by varying the electrical configuration setting provided to the active radiator rather than through altering the mechanical properties of the active radiator. 
     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 FIGURES 
       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 sectional view illustrating a typical primary driver. 
         FIG. 2  is a cross-sectional view of a loudspeaker system having a primary driver and an active radiator system housed in a sealed enclosure. 
         FIG. 3  is a circuitry that substantially represents a loudspeaker system having one driver housed in a sealed enclosure. 
         FIG. 4  is a circuitry equivalent to a loudspeaker system having a primary driver and an active radiator both sealed within a sealed enclosure. 
         FIG. 5  is a cross-sectional view of a loudspeaker system having a primary driver and an active radiator facing away from each other housed in a sealed enclosure. 
         FIG. 6  is a cross-sectional view of a loudspeaker system having two primary drivers and one active radiator, where the active radiator faces away from the two primary drivers within a sealed enclosure. 
         FIG. 7  is a graph showing a first plot line of sound pressure level (SPL) generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is shorted. 
         FIG. 8  is a graph showing a first plot line of SPL generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is provided with a resistor. 
         FIG. 9  is a graph showing a first plot line of SPL generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is provided with a resistor and a capacitor. 
         FIG. 10  is a graph showing a first plot line of SPL generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is provided with resistor, capacitor, and inductor in series. 
         FIG. 11  is a graph showing a first plot line of SPL generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is provided with resistor, a different capacitor, and inductor in series. 
         FIG. 12  is a graph showing a first plot line of SPL generated by a loudspeaker system of  FIG. 5  when the input terminals for an active radiator is open and a second plot line when the input terminal for an active radiator is provided with capacitor and inductor in series. 
         FIG. 13  is a flow chart illustrating a process that may be used to tune the loudspeaker system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  is a cross-sectional view of a loudspeaker system  200  having an active radiator  208  designed to tune the operational characteristics of a primary driver  204  housed within a sealed enclosure  202 . The primary driver  204  converts audio signal to corresponding audible sound. The primary driver  204  has electromagnetic components adapted to convert electrical audio signal to acoustical energy to produce sound. The electromagnetic components of the primary driver  204  include a voice coil disposed within a voice coil gap. Two leads from the voice coil may be communicably coupled to input terminals  206  of the primary driver  204 . Audio signals from an amplifier or a crossover network (not shown) may be provided to the input terminals  206  to drive the primary driver  204  to produce sound. The active radiator  208  has electromagnetic components with input terminals  210 . The input terminals  210  are adapted to communicably couple to a configuration unit  212  having a number of electrical configuration settings such as: (1) an active network  214 ; (2) a wire  216  that bridges the two input terminals to short the two input terminals  210 ; (3) an open terminal  217 , and (4) passive network  218 . Each of the electrical configurations can vary the performance of the loudspeaker system  200  depending on the application of the loudspeaker  200  as further explained below. 
       FIG. 3  illustrates a circuitry  300  that substantially represents the operational characteristics of a loudspeaker system having one driver housed in a sealed enclosure. The circuitry  300  divides the electromagnetic components of the primary driver into three equivalent circuits: (1) an electrical equivalent  302 ; (2) a mechanical equivalent  304 ; and (3) an acoustical equivalent  306 . An audio electrical signal may be provided to the input side of the electrical equivalent  302 . The electrical equivalent  302  factors in electrical resistance (Re), inductance (Le), and capacitance (Ce) of the loudspeaker system. For instance, Re and Le may factor in the resistance and inductance in the voice coil of the driver, respectively. The mechanical equivalent  304  may factor in mechanical resistance (Rm), mass (Lm), and compliance (Cm) of the loudspeaker system. For instance, Rm may factor in the inherent resistance to vibration of the diaphragm due to the spider and suspension. The acoustical equivalent  306  may factor in the acoustical resistance (Ra), acoustical mass (La), and acoustical compliance (Ca) of the loudspeaker system. The Ra may factor in the resistance to vibrating the diaphragm due to the size of the diaphragm, and the Ca may factor in the acoustical compliance due to the space within the enclosure. The transfer function F(Sd) between the acoustical equivalent  306  and the mechanical equivalent  304  may represent a function of the surface area of the diaphragm (Sd). The transfer function F(BL, Sd) between the mechanical equivalent the electrical equivalent may represent a function of Sd and magnetic field strength defined as the (BL) product. 
       FIG. 4  illustrates a circuitry  400  that substantially represents the operational characteristics of a loudspeaker system  200  having a primary driver  204  and an active radiator  208 , both sealed within the enclosure  202 . The primary driver  204  may be represented by an electrical equivalent  402 , mechanical equivalent  404 , and acoustical equivalent  406 . The active radiator  208  may be represented by an electrical equivalent  408 , mechanical equivalent  410 , and acoustical equivalent  412 . The acoustical compliance (Ca)  414  may be common to the primary acoustical equivalent  406  and the active acoustical equivalent  412 . That is, the Ca  414  is an equivalent circuit element representing acoustical compliance of the enclosure volume shared by both primary and active radiators  204  and  208 , respectively. The electrical equivalent circuit  408  of the active radiator  208  has input terminals  210  that are adapted to communicably couple to the configuration unit  212 . 
     The function F(Nr)  416  corresponds to the setting in the configuration unit  212  such as the active circuit  214 , short circuit  216 , open circuit  217 , and passive circuit  218 , where each setting may vary the operating characteristics of the primary driver  204 . The electrical equivalent  408  of the active radiator  208  is represented by capacitor Cer, the inductor Ler, and the resistor Rer. The function F(BLr, Nr)  418  represents the product of the electrical equivalent  408  and the function F(Nr)  416  corresponds to the setting in the configuration unit  212 . If the configuration unit  212  is set to an open circuit  217 , then the active radiator  208  operates as a passive radiator, such that there is an acoustical contribution from the active radiator. In other words, with the open circuit  217 , other than the additional mass due to the voice coil and the compliance of the spider in the active radiator  208 , the active radiator  208  may perform more like a traditional passive radiator without the electromagnetic components and which shares the same acoustic volume with the primary driver  204 . 
     The configuration unit  212  may provide an option of selecting a short circuit  216  so that the input terminals  210  can be closed, thereby closing the electrical equivalent circuit  408 . The function F(BLr, Nr)  418  is a function of F(Nr) and the electrical equivalent circuit  408  of the active radiator  208 . With the configuration unit  212  set to the short circuit  216 , or zero resistance, F(BLr, Nr)  418 =the electrical equivalent circuit  408  of the active radiator  208 . Likewise, the function F(Sdr, BLr, Nr)  420  is a function of F(BLr, Nr)  418  and the mechanical equivalent  440  of the active radiator  208 . In general, the mechanical equivalent  440  of the active radiator  208  may be associated with the surface area of the diaphragm (Sdr) of the active radiator  208 . As such, the function F(Sdr, BLr, Nr)  420  is a function of F(BLr, Nr)  418  and Sdr of the active radiator  208 . That is, the combined electrical equivalent  408  and the mechanical equivalent  410  of the active radiator  208  is represented by the equivalent function F(Sdr, BLr, Nr)  420 . Likewise, the combined electrical and mechanical equivalent F(BLr, Nr)  418  and the acoustical equivalent  412  of the active radiator  208  and the acoustical equivalent  406  of the primary driver  204  may be represented by the equivalent function F(Sdp, Sdr, BLr, Nr)  422 . Note that Sdp represents the surface area of the primary driver  204 . The function F(BLp, Sdp, Sdr, BLr, Nr)  424  may be represented by combination of F(Sdp, Sdr, BLr, Nr)  422  and the mechanical equivalent  404  of the primary driver  204 . The function  424  can be combined with the overall output of the loudspeaker system  200 . Note that the Ca  414  representing the acoustical compliance of the enclosure volume shared between the primary driver  202  and the active radiator  204  is a variable of the overall function  424 . A user and/or designer may selectively choose a circuit from the configuration unit  212  to tune the performance of the primary driver  204  contained in the enclosure  202 . 
     As illustrated in  FIG. 2 , the configuration unit  212  includes a number of circuit configurations such as an active network  212 , short circuit  216 , open circuit  217 , and passive network  218 . With the active radiator  208  having electromagnetic components, the input terminals  210  of the active radiator  208  may be connected to the variable configuration unit  212  to provide an active circuit  214 , short circuit  216 , open circuit  217 , and/or passive circuit  218  to the active radiator  208  to vary the operating characteristics of the active radiator  208 . For example, the active circuit  214  may provide an electrical signal to the active radiator  208  to adjust the excursion range of its diaphragm. Adjusting the operating characteristics of the active radiator  208  in turn influences the overall output of the primary driver  204  because the primary driver  204  and the active radiator  208  share a common enclosure  202  or Ca  414 . For instance, as the primary driver  204  radiates back and forth, compression and rarefaction occur inside of the enclosure  202 . The pressure variations inside of the enclosure  202  cause the active radiator  208  to vibrate back and forth as well. The excursion properties of the active radiator  208 , however, depend on the circuit configuration that is provided to the input terminals  210  of the active radiator  208 . Accordingly, varying the circuit configuration provided to the input terminals  210  of the active radiator  208  can influence the performance of the primary driver  204 . 
     The configuration unit  212  may also provide the short circuit  216  to the input terminals  210  of the active radiator  210  to complete the circuit in the active radiator  208  such that the oscillation of the voice coil in the magnetic gap of the active radiator  208  induces current through its voice coil. The induced current through the voice coil of the active radiator  208  in turn generates an opposing magnetic flux in the magnetic components of the active radiator  208  to resist the oscillating movement of the voice coil of the active radiator  208 . As such, the configuration unit  212  includes a number of circuits to allow a user or processor to select a desired circuit provided to the active radiator  208  to change its operating characteristics in order to tune the operating characteristics of the primary driver  204 . 
     The loudspeaker system  200  may include one or more primary drivers  204  arranged in a variety of ways with respect to the active radiator  208 . Likewise, two or more active radiators  208  may be incorporated into the enclosure  202 . For instance,  FIG. 5  illustrates a primary driver  204  and an active radiator  208  facing away from each other within the sealed enclosure  202 .  FIG. 6  illustrates two primary drivers  204  facing the same direction but in opposite direction of the active radiator  208  within the sealed enclosure  202 . As such, more than one primary driver and active radiator may be positioned in a variety of ways within a sealed enclosure. 
       FIGS. 7 through 12  illustrate two sound pressure level (SPL) plots generated by a loudspeaker  200  based on two different settings in the configuration unit  212  for comparison purposes. The SPLs were measured using a loudspeaker system  200  having one primary driver  204  and one active radiator  208  facing in opposite directions within a sealed enclosure  202 , as illustrated in  FIG. 5 . A microphone was placed perpendicular to the primary driver  204  to measure the SPL generated by the primary driver  204 .  FIGS. 7 through 12  illustrate a plot line  702  representing the measured SPL from the primary driver  204 , when the setting for the configuration unit  212  was left opened, i.e., the input terminals  210  to the active-radiator  208  was provided with the open circuit  217 . With the input terminals  210  being open, the active radiator  208  behaved more like a traditional passive radiator without the electromagnetic component. For comparison purposes, a second plot line is provided in  FIGS. 7 through 12  to analyze the differences between the plot line  702  and other plot lines when the configuration unit  212  provides different type of passive circuits to the input terminals  210  of the active radiator  208 . 
       FIG. 7  illustrates a plot line  704  representing the measured SPL from the primary driver  204  when the configuration unit  212  was set to the short circuit  216 . In other words, a wire was provided between the input terminals  210  to close the circuit. The two plot lines  702  and  704  indicate that below about 35 Hz, the plot line  704  (short circuit) has a higher SPL than the plot line  702  (open circuit) and cross-over takes place at about 35 Hz. Between about 35 Hz and about 80 Hz, the plot line  704  (short circuit) has lower SPL than the plot line  702  (open circuit). That is, when the configuration unit  212  was set at the short circuit  216 , the plot line  704  indicates that below about 35 Hz—the SPL from the primary driver  204  is boosted, while dampening the SPL between 35 Hz and 80 Hz as compared to the plot line  702 . Such boosting of SPL below about 35 Hz may be used in a variety of applications. For example, in some instances when a loudspeaker is placed near a wall, the wall may reflect back additional energy to the listener&#39;s position in a frequency range of 40 Hz to 70 Hz. In such instances, a loudspeaker system  200  capable of generating SPL corresponding to the plot line  704  may be utilized to boost the SPL below about 35 Hz, while dampening between 35 Hz and 80 Hz to even out the response in the listening room. 
       FIGS. 8 through 12  show plot lines based on the configuration unit  212  providing a variety of passive circuits  218  to the input terminals  210  of the active radiator  208 . For instance,  FIG. 8  shows a plot line  804  representing the measured SPL from the primary driver  204  with a resistor R 1  provided at the input terminals  210  of the active radiator  208 . The plot line  804  illustrate that the SPL generated by the primary driver  204  appears substantially similar to the plot line  704  of  FIG. 7 . That is, providing a resistor R 1  or a short circuit  216  across the input terminals  210  of the active radiator  208  generates a substantially similar SPL from the primary driver  204 . 
       FIG. 9  illustrates a plot line  904  representing the measured SPL from the primary driver  204  when the passive circuit  218  having a resistor R 1  in series with a capacitor C 1  is provided to the input terminals  210  of the active radiator  208 . Comparing the two plot lines  702  and  904 , the plot line  904  indicates that by adding a simple passive circuit  218  such as R 1  and C 1  to the input terminals  210  of the active radiator  208 , the primary driver  204  generates additional SPL below about 40 Hz a, while SPL is dampened above 40 Hz. In applications where boost in SPL would be desirable below 40 Hz with nominal dampening above 40 Hz, a passive circuit  218  having a resistor R 1  in series with a capacitor C 1  may be provided at the input terminals  210  of the active radiator  208 . 
       FIG. 10  illustrates a plot line  1004  representing the measured SPL from the primary driver  204  when the passive circuit  218  having a resistor R 1 , C 2 , and L 1  in series is provided at the input terminals  210  of the active radiator  208 . Comparing the two plots  702  and  2004 , the plot line  2004  indicates that by providing a simple passive circuit  218  with R 1 , C 2 , and L 1  in series to the input terminals  210  of the active radiator  208 , the primary driver  204  generates additional SPL below about 35 Hz, while generating substantially similar SPL, as the plot line  702 , above 35 Hz. As such, by providing a simple passive circuit having R 1 , C 2 , and L 1  in series to the input terminals  210  of the active radiators  208 , additional boost can be obtained below 35 Hz without losing SPL above 35 Hz. In other words, the plot line  1004  indicates that the loudspeaker system  200  would produce a deeper bass sound without dampening the mid and high end of the bass sound. 
       FIG. 11  illustrates a plot line  1104  representing the measured SPL from the primary driver  204  when the passive circuit  218  having a resistor R 1 , C 3 , and L 1  in series is provided at the input terminals  210  of the active radiator  208 . Comparing the two plots  702  and,  1104  the plot line  1104  indicates that providing a simple passive circuit having R 1 , C 3 , and L 1  in series to the input terminals  210  of the active radiators  208 , additional boost can be obtained below 35 Hz without losing SPL above 35 Hz. In addition, comparing the two plot lines  1104  and  1004  indicates that using C 3  in the active circuit  218  in place of C 2  generates additional SPL from the primary driver  204  below about 30 Hz. 
       FIG. 12  illustrates a plot line  1204  representing the measured SPL from the primary driver  204  when the passive circuit  218  having C 3  and L 1  in series is provided at the input terminals  210  of the active radiator  208 . The plot line  1204  is substantially similar to the plot lines  704  and  804  indicating that a resistor and a capacitor may be needed to minimize the dampening that may occur above 35 Hz. 
       FIGS. 7 through 12  illustrate that by providing simple passive circuits to the input terminals  210  of the active radiator  208 , the performance of the loudspeaker system  200  may be tuned, dampened, or boosted along the low, mid, and high frequency range of the bass. This allows a user to tune the operating characteristics of the loudspeaker system  200  by varying the electrical configuration setting provided to the active radiator  208  rather than through changing the mechanical properties of the active radiator  208 . The SPL generated by the primary driver  204  may vary depending on the type of primary driver  204 , active radiator  208 , and the circuit provided to the input terminals  210  of the active radiator  208 . In addition, a number of different types of active and/or passive circuits may be provided through the configuration unit  212 . For example, active circuits such as operational amplifiers or a series of tuning circuits that require an external power supply may be provided to the input terminals  210  of the active radiator  208 . As another example, when coupling the active radiator  208  to an active circuit  214  such as a partition of an excursion limiting circuit, the active radiator  208  may be used as a mechanical servomechanism to limit the excursion of the primary driver  204 . In addition, a variable active notch filter may be provided at the input terminals  210  of the active radiator  208  to tune the loudspeaker system  200  at one or more frequencies. 
       FIG. 13  shows a flow chart  1300  illustrating a process that may be used to tune the loudspeaker system  200 . In block  1302 , a loudspeaker system  200  may be provided with a common acoustical compliance between the acoustical equivalent  406  of the primary driver  204  and the acoustical equivalent  412  of the active radiator  208 . In a decision block  1304 , a decision may be made as to whether the operational characteristics of the primary driver  204  should be tuned. If no tuning is required, then in block  1306 , an open circuit  217  may be provided to the electrical equivalent  408  of the active radiator  208 . On the other hand, if tuning is required, then in block  1308 , at least a portion of the resistance, capacitance, and/or inductance to the electrical equivalent  408  of the active radiator  208  may be adjusted to tune the SPL generated by the primary driver  204 . The tuning may be accomplished by selecting the active circuit  214 , short circuit  216 , or passive circuit  218  from the configuration unit  212 , for example. 
     The flow chart  1300  also illustrates that a feed back system may be incorporated into the process. In block  1310 , the SPL generated by the primary driver  204  may be measured. In the decision block  1312 , the measured SPL from the primary driver  204  may be compared to a desired SPL range. The desired SPL range may be established by an operator. The desired SPL range may be also stored in a look-up-table for comparison. If the measured SPL is within the desired SPL range, then the process may stop. On the other hand, if the measured SPL is not within the desired SPL range, then the process may go back to the block  1308  to readjust the resistance, capacitance, and/or inductance provided to the electrical equivalent  408  of the active radiator  208  until the measured SPL is within the desired range. 
     While various embodiments of the invention 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.
A loudspeaker system has a primary driver and an active radiator sealed in an enclosure where the active radiator is adapted to vary its operating characteristics to tune the sound pressure level and resultant frequency response generated by a primary driver. The primary driver and the active radiator share the same acoustic volume of the enclosure, i.e., the primary driver and the active radiator share a common acoustic compliance of the internal enclosure volume. The primary driver has electromagnetic components designed to oscillate a flexible cone or diaphragm along the longitudinal axis of the primary driver. The active radiator has electromagnetic components adapted to couple to a number of electrical configuration settings. Each electrical configuration setting may affect the operating characteristics of the diaphragm of the active radiator and is reflected back electro-acoustically, through the shared volume, to the primary driver. This electro-acoustical coupling, in turn provides the tuning mechanism for the primary driver.