Abstract:
An instrument panel is structured to separate a main cabin of a vehicle from a volume behind the instrument panel. The instrument panel has multiple leak paths through which air can travel between the main cabin and the volume behind the instrument panel. An electroacoustical transducer is mounted in the instrument panel and operable to radiate low-frequency acoustic energy into the volume behind the instrument panel. The low-frequency energy radiated by the electroacoustical transducer in the volume behind the instrument panel propagates into the main cabin via the multiple leak paths.

Description:
CLAIM OF PRIORITY 
       [0001]    This application is a continuation of and claims priority to U.S. patent application Ser. No. 11/551,410, the entire contents of which are incorporated here by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Automotive sound systems typically include multiple loudspeakers positioned in various locations around the passenger compartment of the vehicle. Typical loudspeaker locations include the vehicle door panels and the interior trim panels. Low-frequency reproducing speakers, also known as woofers, are typically located in the rear package shelf of a vehicle. The rear package shelf acts as a baffle between the passenger compartment and the trunk of the vehicle. 
       SUMMARY OF THE INVENTION 
       [0003]    In one aspect, the invention is embodied in an apparatus for generating low frequency acoustic signals in a vehicle having an instrument panel. The apparatus includes a baffle that is located at least partially within the instrument panel. An electroacoustical transducer is mechanically coupled to the baffle. The electroacoustical transducer generates low frequency acoustic signals that radiate into a cavity within the instrument panel and leak into the passenger compartment of the vehicle through one or more mechanical openings in the instrument panel. 
         [0004]    In one embodiment, the mechanical openings do not include dedicated acoustic radiation paths for guiding the acoustic signals to the passenger compartment from the electroacoustical transducer. In one embodiment, the baffle is integrated with the instrument panel. In one embodiment, a structure is located within the instrument panel and the baffle is mechanically coupled to the structure to create an enclosure for the electroacoustical transducer. The enclosure can be a ported enclosure, a sealed enclosure, or a bass reflex enclosure, for example. 
         [0005]    The apparatus can further include a transducer that is mechanically coupled to the electroacoustical transducer. The transducer generates acoustic signals in phase with the acoustic signals generated by the electroacoustical transducer. The transducer generates a mechanical vibration that at least partially cancels a mechanical vibration generated by the electroacoustical transducer. 
         [0006]    The apparatus can also include an audio source having a user interface and an electronics unit that is remotely located from the user interface. The electroacoustical transducer can be located at least partially behind the user interface. 
         [0007]    In one embodiment, the electroacoustical transducer radiates energy in a frequency range of between about 60 Hz to 80 Hz. In another embodiment, the electroacoustical transducer radiates energy in a frequency range of between about 20 Hz to 100 Hz. The baffle can be coupled to the instrument panel through at least one mechanical isolator. 
         [0008]    The apparatus can also include a bass radiating transducer that is remotely located from the instrument panel. The bass radiating transducer radiates acoustic energy into the passenger compartment of the vehicle. The bass radiating transducer can be located in a rear package shelf, a vehicle door, a rear corner post, or a rear hatch of the vehicle, for example. 
         [0009]    The electroacoustical transducer can include a radially magnetized cylindrical magnet transducer. The radially magnetized cylindrical magnet transducer can include a solid magnet or a segmented magnet. The electroacoustical transducer can include a moving magnet transducer. The electroacoustical transducer can include a cup-type motor structure. 
         [0010]    In another aspect, the invention is embodied in an audio system for a vehicle. The audio system includes a user interface that is located in a passenger compartment of the vehicle. An electronics unit is remotely located from the user interface. The electronics unit controls the audio source. The audio system also includes a baffle that is located substantially behind an instrument panel of the vehicle. An electroacoustical transducer is mechanically coupled to the baffle. The electroacoustical transducer generates low frequency acoustic signals that radiate into a cavity within the instrument panel and leak into the passenger compartment of the vehicle through one or more mechanical openings in the instrument panel. 
         [0011]    In one embodiment, the electroacoustical transducer radiates all the low frequency acoustic signals into a cavity within the instrument panel that leak into the passenger compartment of the vehicle only through one or more mechanical openings in the instrument panel. In one embodiment, the one or more mechanical openings do not include dedicated acoustic radiation paths for guiding the acoustic signals to the passenger compartment from the electroacoustical transducer. 
         [0012]    The audio system can also include non-dedicated acoustic radiation paths that guide the acoustic signals to the mechanical openings in the instrument panel. The user interface can be coupled to a steering wheel of the vehicle. The user interface can alternatively be coupled to the instrument panel of the vehicle. The baffle can be located behind the user interface. The baffle can be coupled to the instrument panel through one or more mechanical isolators. The audio system can radiate bass signals from both front and rear of the vehicle. The audio system can radiate all bass signals from a single unit front low-frequency loudspeaker. 
         [0013]    In one embodiment, the audio system can include an enclosure that is located within the instrument panel. The baffle is mechanically coupled to a structure to create the enclosure for the electroacoustical transducer. The enclosure can be a ported enclosure, a sealed enclosure, or a bass reflex enclosure, for example. In one embodiment, the enclosure includes an acoustic waveguide. A volume of the enclosure can be less than two liters. The enclosure can radiate acoustic waves in a frequency range of between about 60 Hz to 80 Hz. The enclosure can be mounted to the instrument panel through at least one mechanical isolator. 
         [0014]    In one embodiment, the audio system also includes a bass radiating transducer that is remotely located from the instrument panel. The bass radiating transducer radiates acoustic energy into the passenger compartment of the vehicle. The bass radiating transducer can be located in a rear package shelf, a vehicle door, a rear corner post, or a rear hatch of the vehicle, for example. 
         [0015]    In yet another aspect, the invention is embodied in a method for generating low frequency acoustic signals in a vehicle having an instrument panel. The method includes locating a baffle at least partially within the instrument panel. An electroacoustical transducer is mechanically coupled to the baffle. Low frequency acoustic signals are radiated from the electroacoustical transducer into a cavity within the instrument panel. The low frequency acoustic signals leak into the passenger compartment of the vehicle through one or more mechanical openings in the instrument panel. 
         [0016]    The method can also include reducing a vibration in the baffle caused by the electroacoustical transducer with a transducer mechanically coupled to the electroacoustical transducer. The transducer is driven mechanically out of phase with the electroacoustical transducer and acoustically in phase with the electroacoustical transducer. 
         [0017]    In one embodiment, non-dedicated acoustic radiation paths guide the acoustic signals to the mechanical openings in the instrument panel. The baffle can be integrated with the instrument panel. The baffle can be coupled to a structure to create an enclosure for the electroacoustical transducer. The enclosure can be substantially isolated from the instrument panel. The baffle can be substantially isolated from the instrument panel. A bass radiating transducer can be remotely located from the instrument panel. The bass radiating transducer radiates acoustic energy into the passenger compartment of the vehicle. The bass radiating transducer can be located in a rear package shelf, a vehicle door, a rear corner post, or a rear hatch of the vehicle, for example. 
         [0018]    One aspect of the invention is embodied in an apparatus for generating low frequency acoustic signals in a vehicle having an instrument panel. The apparatus includes an electroacoustical transducer that is located behind the instrument panel. The electroacoustical transducer generates low frequency acoustic signals that radiate into a cavity within the instrument panel and leak into the passenger compartment of the vehicle through one or more mechanical openings in the instrument panel. The apparatus also includes a low frequency transducer that is located in a rear section of the passenger compartment. The low frequency transducer radiates low frequency acoustic signals to the passenger compartment of the vehicle. 
         [0019]    In one embodiment, the one or more mechanical openings do not include dedicated acoustic radiation paths for guiding the acoustic signals to the passenger compartment from the electroacoustical transducer. In one embodiment, the electroacoustical transducer and the low frequency transducer are driven with identical audio signals. In another embodiment, the electroacoustical transducer and the low frequency transducer are driven with different audio signals. In one embodiment, at least one of the electroacoustical transducer and the low frequency transducer radiates energy in a frequency range of between about 60 Hz to 80 Hz. In another embodiment, at least one of the electroacoustical transducer and the low frequency transducer radiates energy in a frequency range of between about 20 Hz to 100 Hz. The low frequency transducer can be located in a rear package shelf, a vehicle door, a rear corner post, or a rear hatch of the vehicle, for example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    This invention is described with particularity in the detailed description. The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
           [0021]      FIG. 1  is a perspective view of the interior of a vehicle having a vehicle instrument panel; 
           [0022]      FIG. 2  is a perspective view of the interior of the vehicle with the control interface removed from the instrument panel; 
           [0023]      FIG. 3A  through  FIG. 3F  illustrate various configurations of low-frequency transducers according to the invention; 
           [0024]      FIG. 4  is a perspective view of the interior of the vehicle according to another embodiment of the invention; 
           [0025]      FIG. 5  illustrates a vehicle audio system according to one embodiment of the invention; and 
           [0026]      FIG. 6  is a diagram of a multiple channel surround sound system for a vehicle according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    It is advantageous in a vehicle audio system to generate low frequency acoustic signals from the front area of the passenger compartment. This improves the overall quality of low frequency acoustic signals compared to those that are generated purely only in the rear area of the passenger component. For example, a bass transducer located in the front of the passenger compartment can generate low frequency acoustic signals that enhance the various low frequency modes in the passenger compartment. 
         [0028]    Unfortunately, the volume required to produce adequate low frequency acoustic signals from the front of the vehicle is generally not available. For example, the instrument panel in most vehicles contains instruments, stereo equipment, computer electronics and climate control electronics, mechanics, and air conditioning duct work. 
         [0029]      FIG. 1  is a perspective view of the interior of a vehicle  100  having a vehicle instrument panel  102 . The instrument panel  102  contains displays  104  that show the speed of the vehicle, fuel level, coolant temperature, speed of the engine, as well as other vehicle parameters. The instrument panel  102  also includes the climate control system  106  and the audio system  108 . Most factory-installed audio systems include a control interface  110  that is accessible to the driver and front passenger and an electronics unit (not shown) that is controlled by the control interface  110 . For convenience, the control interface  110  is usually located near the center of the instrument panel  102  but is not limited to this location. For example, audio controls may be located on the steering wheel or on a console between the driver and passenger seats. 
         [0030]    The electronics unit can include amplifier circuits, tuners, equalization circuits, memory as well as other circuitry. The electronics unit is typically located behind the control interface  110  within a volume space of the instrument panel  102 . 
         [0031]    In one embodiment, the electronics unit is positioned in a location other than behind the control interface  110 . For example, the electronics unit can be remotely located from the instrument panel  102 . Alternatively, the electronics unit can be located in the instrument panel  102 , but in a location that is not directly behind the control interface  110 . 
         [0032]    In one embodiment, the volume of space behind the control interface  110  that is normally occupied by the electronics unit can be used by a low frequency transducer. The low frequency transducer can be coupled to a baffle. The low frequency transducer can alternatively be coupled to an enclosure. In one embodiment, a baffle having a transducer can be coupled to a separate structure which creates an enclosure to contain or alter the back wave radiation from the transducer. The baffle can be located at least partially within the instrument panel  102 . A low frequency electroacoustical transducer is mechanically coupled to the baffle. The low frequency electroacoustical transducer generates low frequency acoustic signals that radiate into a cavity within the instrument panel  102  and leak into the passenger compartment of the vehicle through mechanical openings (see below for more details) in the instrument panel. The path length between the acoustic waves propagating from the back of the transducer and the acoustic waves propagating from the front of the transducer is chosen to reduce acoustic wave cancellation. 
         [0033]    Low frequency acoustic signals are generally non-directional due to the wavelength at which they propagate. These low-frequency acoustic signals do not require dedicated transmission paths to effectively transmit acoustic energy into the passenger compartment of the vehicle. Instead, the low frequency acoustic energy is allowed to leak through the instrument panel into the passenger compartment. A typical instrument panel is not air-tight due to the many gaps in the instrument panel. For example, the instrument panel may be comprised of several sections joined together into a single panel. The seams between the sections are usually not air-tight and air can move through the instrument panel through these gaps. A gap may be created when a display or control does not tightly fit its cutout in the instrument panel. Other gaps in the instrument panel may be designed into the panel as vents or access holes to provide easy access during installation. These gaps are not intentionally designed to provide an acoustic path through the instrument panel and are hereinafter referred as non-acoustic paths. The inventors have discovered that these non-acoustic paths are sufficient for transmitting the low-frequency acoustic signals through the instrument panel into the passenger compartment. Furthermore, using the non-acoustic paths through the instrument panel eliminates the need for specifically-designed acoustic elements such as ducts, tubes, and waveguides. Elimination of these acoustic-specific elements frees up the space behind the instrument panel and also allows greater freedom in aesthetic design of the instrument panel. As used herein, “leak” refers to a non-acoustic path through the instrument panel. As used herein, “leaking” refers to the transmission of acoustic signals from an electroacoustical transducer to a listening area by the exclusive use of a non-acoustic path. 
         [0034]    In some embodiments, various electronic devices can be coupled to the audio system. For example, the electronic devices can include CD changers, GPS receivers, navigation systems, MP3 players, DVD players, and/or satellite radio receivers. One or more of these electronic devices can be located behind the control interface  110 . Some vehicle instrument panels can include one or more mounting slots  112 ,  114 . The mounting slots  112 ,  114  can accommodate electronic devices. 
         [0035]      FIG. 2  is a perspective view of the interior of the vehicle  100  with the control interface  110  removed from the instrument panel  102 . The electronics unit (not shown) is remotely located from behind the control interface  110 . In one embodiment, the volume of space  116  behind the control interface  110  houses a low-frequency transducer  118  that can generate low-frequency acoustic signals. In one embodiment, the transducer  118  can be coupled to a baffle. The baffle can be coupled to a separate structure to create an enclosure  120  which can be further mechanically coupled to the instrument panel. The enclosure  120  can be less than two liters. The low-frequency transducer  118  can have a relatively small diameter, such as less than six inches. In other embodiments, multiple transducers can also be coupled to the baffle or enclosure  120 . The enclosure  120  can embody a sealed enclosure, a ported enclosure, an enclosure including a waveguide structure, an enclosure including a passive radiator, or any other type of suitable enclosure. 
         [0036]    The control interface  110  can include various controls, such as pushbuttons, rotary controls, scroll wheels, a touch screen including softkeys, and/or joysticks. An example of such a control interface  110  is described in pending U.S. patent application Ser. No. 10/262,349 filed on Jul. 23, 2003, entitled “System and Method for Accepting a User Control Input.” 
         [0037]    The low-frequency transducer  118  generates low-frequency acoustic signals from the front of the passenger compartment of the vehicle  100 . The low frequency transducer  118  preferably has a small diameter and operates in a frequency range of between about 20 Hz to 300 Hz. The enclosure  120  can have a volume of less than two liters. In one embodiment, the enclosure  120  can be located in the volume of space  116 . 
         [0038]      FIG. 3A  through  FIG. 3F  illustrate various configurations of low-frequency transducers according to the invention. Specifically,  FIG. 3A  illustrates a low-frequency transducer  300  that is mounted in a baffle  302 . The baffle  302  is positioned within an instrument panel of a vehicle such that one side  304  of the baffle  302  is acoustically isolated from the other side  306  of the baffle  302 . In some embodiments, the baffle  302  does not fully isolate one side  304  from the other side  306 . For example, the edges of the baffle  302  can include leakage paths. The baffle  302  increases the effective path length between the front and back sides of the transducer  300 , which may increase radiation efficiency. The baffle  302  can be mounted in any suitable orientation. In one embodiment, the baffle  302  is coupled to an interior structure of the instrument panel thereby enclosing a portion of the interior volume of the instrument panel. In this embodiment, the baffle  302  and the interior structure of the instrument panel together act as an enclosure for the transducer  300 . 
         [0039]      FIG. 3B  illustrates an embodiment of an enclosure  310  including a low-frequency transducer  312  according to one embodiment of the invention. The enclosure  310  is a sealed enclosure that is adapted to receive the low-frequency transducer  312 . In one embodiment, the volume of the enclosure  310  is less than about two liters. In one embodiment, the diameter of the low-frequency transducer  312  is less than six inches. The enclosure  310  is shaped to maximize the interior volume of air, while corresponding to the mounting dimensions of the space provided within the instrument panel. 
         [0040]    The enclosure  310  can be a sealed enclosure, a ported enclosure, or any other suitable type of enclosure. The enclosure  310  can also include one or more passive radiators and/or a waveguide structure. In one embodiment, acoustic energy from the transducer  312  as well as the port, passive radiator, or waveguide opening, if present, escapes into the passenger compartment of the vehicle through one or more mechanical openings such as seams, cracks, vents, and/or other voids in the instrument panel. Specifically, in some embodiments, sound from the transducer leaks into the passenger compartment solely through non-dedicated sound transmission paths that guide sound radiation from the transducer to the one or more mechanical openings in the instrument panel. 
         [0041]    Input terminals of the low-frequency transducer  312  are coupled to output terminals of an electronics unit (not shown). The electronics unit can include a band pass filter or a low pass filter that transmits only low frequency audio signals to the transducer  312 . Alternatively, the transducer  312  can include a cross-over network that prevents unwanted frequency signals from being reproduced by the low-frequency transducer  312 . 
         [0042]      FIG. 3C  illustrates a low-frequency transducer  320  coupled to an irregular-shaped enclosure  322 . The irregular-shaped enclosure  322  is designed to fit into a specific space within the instrument panel. For example, the irregular-shaped enclosure  322  can be designed such that its internal volume is maximized. The irregular-shaped enclosure  322  can be a sealed enclosure, a ported enclosure, an enclosure including a waveguide structure, an enclosure including a passive radiator, or any other type of suitable enclosure. In one embodiment, the volume of the irregular-shaped enclosure  322  is less than two liters. 
         [0043]    As previously described, the instrument panel within which the enclosure  322  is mounted can be buzz/vibration-prone. This is due at least in part to the design and materials used to fabricate the instrument panel. For example, an energized transducer driver develops forces which cause the diaphragm of the transducer to move relative to the transducer frame. Some of these forces are transmitted through the frame to the enclosure  322  and through the enclosure  322  to the instrument panel. The energized transducer can cause the instrument panel to vibrate excessively, especially when the forces applied to the instrument panel are around its modal frequencies. This excessive vibration in the instrument panel can be acoustically perceived as unwanted buzzes and rattles causing degraded frequency response of radiated sound. Vibration canceling techniques can be used to mitigate the vibration. One such technique is described with reference to  FIG. 3D . 
         [0044]      FIG. 3D  illustrates an enclosure  330  including two low-frequency transducers  332 ,  334 . The low-frequency transducers  332 ,  334  are positioned on opposing surfaces of the enclosure  330 . In one embodiment, the low-frequency transducers  332 ,  334  are substantially identical. The low-frequency transducers  332 ,  334  can be driven with identical audio signals. In one configuration, the transducers  332 ,  334  can be driven with audio signals having the same polarity. Alternatively, the transducers  332 ,  334  can be driven with audio signals having opposite polarity. The transducers  332 ,  334  are mounted such that they move mechanically out of phase when driven with the audio signals, and also radiate acoustically in phase. For example, the transducers  332 ,  334  can be driven mechanically out-of-phase such that forces generated by the first transducer  332  are at least partially cancelled by forces from the second transducer  334 . This configuration is sometimes referred to as a dual opposed transducer configuration. Examples of dual opposed transducer configurations are described in U.S. Pat. No. 6,985,593 issued on Jan. 10, 2006 entitled “Baffle Vibration Reducing” and pending U.S. patent application Ser. No. 10/623,996 filed on Jul. 21, 2003 entitled “Passive Acoustical Radiating”, incorporated herein by reference. 
         [0045]    The transducers  332 ,  334  do not have to be mounted in a parallel configuration to effectively reduce a resultant force on the enclosure. Transducers  332 ,  334  are not required to be identical to each other. For example, one of the transducers may be a moving mass that reduces the vibration generated by the other transducer but does not radiate a significant acoustic signal relative to the acoustic signal generated by the other transducer. 
         [0046]    Other techniques for reducing vibration in the instrument panel according to the invention include mechanically isolating the enclosure  330  from the instrument panel or mechanically isolating a transducer from the baffle of the enclosure  330 . For example, the enclosure  330  can be coupled to the instrument panel through one or more mechanical isolators. A suitable mechanical isolator can include, but is not limited to, an elastomer member, a spring, a dashpot, and a shock absorber. The mechanical isolator reduces the amplitude of the mechanical vibration that is coupled into the instrument panel. Examples of mechanical vibration isolation techniques are described in pending U.S. patent application Ser. No. 10/932,137 filed on Sep. 1, 2004 entitled “Audio System for Portable Device”, incorporated herein by reference. It should be noted that the vibration cancelling techniques described herein can be used with various enclosure configurations and transducers. In addition, a combination of the vibration cancellation techniques described above and mechanical isolation can also be used. 
         [0047]      FIG. 3E  illustrates an enclosure  340  including two low-frequency transducers  342 ,  344  according to another embodiment of the invention. The two low-frequency transducers  342 ,  344  are coupled together through motor structures  346 ,  348 . This configuration is generally more compact than the configuration of  FIG. 3D . In one configuration, the motor structures  346 ,  348  are separated. In this configuration, the baskets of the transducers  342 ,  344  are coupled to opposite sides of the enclosure  340 . 
         [0048]    In one embodiment, the low-frequency transducers  342 ,  344  are substantially identical. The low-frequency transducers  342 ,  344  can be driven with identical audio signals having the same phase. In this embodiment, acoustic energy from the front surface of the transducers  342 ,  344  and acoustic energy from the rear surface of the transducers  342 ,  344  combines to increase acoustic output energy. For example, in one configuration, the front surface of each transducer  342 ,  344  can radiate acoustic energy into the interior of the instrument panel while the rear surface of each of the transducers  342 ,  344  can radiate acoustic energy through the opening  345  indirectly into the passenger compartment of the vehicle through one or more non-dedicated mechanical openings in the instrument panel such as seams, cracks, vents, and/or other voids. The path length between the front and rear surfaces of the transducers  342 ,  344  to the passenger compartment is configured to maximize acoustic efficiency. As previously described, the transducers  342 ,  344  can be driven mechanically out-of-phase such that forces generated by the first transducer  342  are generally cancelled by forces from the second transducer  344 . 
         [0049]      FIG. 3F  illustrates an enclosure  350  including two low-frequency transducers  352 ,  354  according to another embodiment of the invention. The two low-frequency transducers  352 ,  354  are coupled to opposite sides of the enclosure  350 . Acoustic energy from the rear surfaces of the transducers  352 ,  354  radiate into the instrument panel while acoustic energy from the front surfaces of the transducers  352 ,  354  radiates into the enclosure  350 . As previously described, the enclosure  350  can be any suitable enclosure type. 
         [0050]    In one embodiment, the low-frequency transducers  352 ,  354  are substantially identical. The low-frequency transducers  352 ,  354  can be driven with identical audio signals that are substantially in phase. The transducers  352 ,  354  are mounted such that they move mechanically out of phase when driven with in phase electrical signals, and also radiate acoustically in phase. For example, the transducers  352 ,  354  can be driven mechanically out-of-phase such that forces generated by the first transducer  352  are generally cancelled by forces from the second transducer  354 . 
         [0051]    In one embodiment, in the various configurations of low-frequency transducers according to  FIG. 3A  through  FIG. 3F , acoustic energy from the transducer(s) radiate into a cavity of the instrument panel and escapes into the passenger compartment of the vehicle through one or more mechanical openings such as seams, cracks, vents, and/or other voids in the instrument panel without any dedicated sound transmission path for guiding sound radiation from the transducer to the one or more mechanical openings. 
         [0052]    It should be noted that all of the configurations described herein can include transducers having various motor structures. For example, radially magnetized cylindrical motor structures can provide increased motor force for a given size motor structure as compared to standard motor structures. The radially magnetized motor structure can include solid or segmented magnets. Additionally, the motor can include a moving coil or moving magnet structure. Other motor structures can also be used such as a pot type motor structure, a ceramic type structure having a donut shaped magnet, or any other suitable motor structure. 
         [0053]      FIG. 4  is a perspective view of the interior of the vehicle  400  according to another embodiment of the invention. An instrument panel  402  includes a control interface  404 . In this embodiment, an enclosure  406  including a low-frequency transducer  408  is located in a 1-DIN, 2-DIN or any suitably sized slot in the instrument panel  402 .  FIG. 4  illustrates that the enclosure  406  is not required to be located directly behind the control interface  404 . The enclosure  406  can be positioned in any suitable unoccupied internal space within the instrument panel  402 . The enclosure  406  can be a sealed enclosure, a ported enclosure, or any other suitable low-frequency enclosure type. 
         [0054]    The control interface  404  includes at least one rotary control  410 . A display  412  is located above the rotary control  410 . A slot  414  is located below the rotary control  410 . The slot  414  is designed to accept a compact disk (CD) or a digital video disk (DVD), for example. 
         [0055]    The low-frequency electroacoustical transducer  408  located within the instrument panel  402  generates low frequency acoustic signals that radiate into a cavity within the instrument panel  402  and leak into the passenger compartment of the vehicle through mechanical openings in the instrument panel  402 . In one embodiment, there are no dedicated acoustic radiation paths such as ducks, tubes, waveguides which guide the acoustic signals to the mechanical openings in the instrument panel  402 . For example, acoustic signals generated by the transducer  408  only propagate through cracks, seams, and voids in the instrument panel  402 . 
         [0056]    In one embodiment, the acoustic signals can propagate through one or more climate control vents  416  in the instrument panel  402 . This can present design challenges since the air handling ducts are generally well isolated from other components within the instrument panel and will not allow substantial acoustic energy to leak into them. It should be understood, however, that an air handling duct generally would not behave as a tuned acoustic waveguide for any low-frequency acoustic energy that leaks into it. Embodiments of the present invention take advantage of sound leaking through openings not designed for the purpose of conducting sound from inside the instrument panel to the passenger compartment. For example, these techniques do not rely on dedicated acoustic paths from the acoustic source within the instrument panel to the passenger compartment. 
         [0057]      FIG. 5  illustrates a vehicle audio system  500  according to one embodiment of the invention. The vehicle audio system  500  includes a control interface  502  and an electronics unit  504 . The electronics unit  504  can be remotely located from the control interface  502 . The control interface  502  can include one or more rotary  506  and/or push button controls  508 . The control interface  502  may include a slot  510  that is configured to accept a compact disk (CD) or a digital video disk (DVD), for example. In one embodiment, the control interface  502  can also include a display  512 . The display  512  can be a liquid crystal display (LCD), cathode ray tube (CRT), or a plasma display, for example. The display  512  can be a touch screen display. 
         [0058]    The control interface  502  is electrically coupled to the electronics unit  504  through a signal transmission line  514 . In one embodiment, the signal transmission line  514  is a bus that couples various systems in the vehicle together. For example, the signal transmission line  514  can couple the central processing unit (CPU)  516  of the vehicle to the control interface  502  and the electronics unit  504 . Although the connections between components are shown as hard-wired, wireless connections can also be used. 
         [0059]    The control interface  502  and the electronics unit  504  can also be coupled to a power source  518  through one or more power lines  519 . The power source  518  can include the battery and/or alternator of the vehicle. In one embodiment (not shown), the signal transmission line  514  can include a power line that can be coupled to the power source  518 . The power source  518  can also be coupled to the CPU  516 . 
         [0060]    An antenna  520  is coupled to the electronics unit  504 . For example, the antenna  520  can be an AM/FM antenna, a satellite antenna, a Bluetooth antenna, or a combination thereof. 
         [0061]    The electronics unit  504  can also include an optical digital output terminal  522  that outputs an optical signal. The optical digital output terminal  522  is coupled to a signal processor  524  such as a 5.1 channel processor through an optical signal transmission line  525 . The signal processor  524  receives the optical signal. The signal processor  524  can embody a digital signal processor (DSP) or can be fabricated from analog circuitry. The signal processor  524  can operate on the optical signal in various ways. For example, the signal processor  524  can provide decoding, alter the signal gain, and/or mix signals in order to create analog output signals. Analog output terminals  526  on the signal processor  524  output the analog output signals. In another embodiment, a non-optical output terminal can be coupled to a DSP through a wired electrical connection. 
         [0062]    One or more amplifiers can be coupled to the analog output terminals  526 . The amplifiers are connected to loudspeakers located throughout the passenger compartment of the vehicle. One such amplifier  528  is coupled to a low frequency transducer  530  that is located within the instrument panel of the vehicle. 
         [0063]      FIG. 6  is a diagram of a multiple channel surround sound system  600  for a vehicle  602  according to the invention. The multiple channel surround sound system  600  includes a low-frequency transducer  604  located in the instrument panel of the vehicle  602 . In one embodiment, the low-frequency transducer  604  can reproduce frequencies in the range of about 20 Hz to 200 Hz. In one embodiment, the low-frequency transducer  604  can reproduce frequencies in the range of about 60 Hz to 80 Hz. Although  FIG. 6  illustrates a multi-channel surround sound system, it should be understood that the principles and techniques described herein can also be used in a traditional stereo system. 
         [0064]    The multiple channel surround system  600  includes a control interface  606  and an electronics unit  608 . As previously discussed, the electronics unit  608  can be remotely located from the control interface  606 . The electronics unit  608  is coupled to a signal processor  610 . The signal processor  610  can perform various functions on audio signals that are received from the electronics unit  608 . For example, the signal processor  610  can provide equalization and/or downmixing to the audio signals. 
         [0065]    In one embodiment, the system  600  includes a plurality of discrete surround sound signals. For example, the plurality of signals can correspond to a front left (FL) channel  612 , a front right (FR) channel  614 , a center (C) channel  616 , a surround left (SL) channel  618 , a surround right (SR) channel  620 , a bass or low frequency effects (LFE) channel  622 , and a specific low-frequency channel  624  to drive the low-frequency transducer  604  located within the instrument panel. Although seven channels are shown and described, any number of channels can be utilized. For example, in one embodiment, the center channel  616  is removed. Alternatively, the system  600  can include a surround center channel (not shown). 
         [0066]    Output signals from the signal processor  608  can be sent to spatially diverse transducers positioned in various locations within the vehicle  602 . The transducers can include a front left speaker (FL-S)  632 , a center speaker (C-S)  634 , a front right speaker (FR-S)  636 , a surround left speaker (SL-S)  638 , a low-frequency rear speaker (LFR-S)  640  also referred to as a bass radiating transducer, a surround right speaker (SR-S)  642 , and the low-frequency loudspeaker  604 . The speakers can be installed in various locations throughout the vehicle  602 . For example, the low-frequency loudspeaker  604  can be installed in the instrument panel and the bass radiating transducer  640  can be located in the rear package shelf of the vehicle  602 . In other embodiments, the bass radiating transducer  640  can also located in a vehicle door, such as a rear vehicle door, a rear corner post, or a rear hatch of the vehicle. The bass radiating transducer  640  and the low-frequency loudspeaker  604  can be driven with the same low frequency signal or can be driven with different low frequency signals. In this implementation, low frequency sound can be generated from both front and rear locations in the vehicle  602 . The front left speaker  632  and the front right speaker  636  can be mounted in the front left and front right door panels, respectively, of the vehicle  602 . Any number of transducers can be installed in the vehicle  602  in various locations regardless of the number of signal channels in the system  600 . 
         [0067]    In one embodiment, low frequency performance is enhanced by radiating low frequency sound from both the front and the rear of the vehicle. This configuration provides greater flexibility for bass imaging management, such as providing enhanced perceived bass imaging or increased maximum low frequency output level, or both to passengers in both the front and rear seats of the vehicle. 
         [0068]    In another embodiment, the bass radiating transducer  640  is omitted and all bass signals are radiated from the single unit front low-frequency loudspeaker  604 . 
         [0069]    Skilled artisans will appreciate that although various openings in the instrument panel are shown and described for radiating low frequency sound from the front of the passenger compartment of the vehicle, the low frequency transducer does not require existing or specifically designed dedicated vent openings for radiating low frequency sound. The low frequency sound can be leaked into the passenger compartment through any voids in the instrument panel. 
         [0070]    While the invention has been particularly shown and described with reference to specific exemplary embodiments, it is evident that those skilled in the art may now make numerous modifications of, departures from and uses of the specific apparatus and techniques herein disclosed. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features presented in or possessed by the apparatus and techniques herein disclosed and limited only by the spirit and scope of the appended claims.