Abstract:
The invention provides method and apparatus that utilize a plurality of port sub-arrays, in which each port sub-array comprises a plurality of acoustical ports. The ports of each port sub-array are spaced so that each port sub-array responds to acoustical signals that are generated by acoustical sources within an associated frequency range. In an embodiment of the invention, associated frequency ranges are related in a harmonic manner, in which each port sub-array corresponds to different frequency octaves. The associated frequency range is a portion of the total frequency range of an acoustical system. Received acoustical signals from each of the port sub-arrays are coupled over acoustical pathways and are converted into electrical signals by capsules that may be mounted in a capsule mounting. The electrical signals may be filtered, such as to reduce spatial aliasing, and post processed to further enhance the characteristics of the signals.

Description:
[0001]    This application claims priority to provisional U.S. Patent Application. No. 60/402,185, filed Aug. 9, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to multi-element microphones, and more particularly microphones used in conjunction with digital signal processing for telematics applications.  
         BACKGROUND OF THE INVENTION  
         [0003]    Single-element microphones have been used for telematics speech-enabled applications. As an example, these microphones have been used in automotive hands-free cellular applications where good microphone performance is characterized by a combination of high speech recognition scores and high signal-to-vehicle-noise ratio under a variety of vehicle, road, and other noise conditions the driver is likely to encounter. In other words, the more the talker&#39;s voice stands out from the background noise produced by the automotive environment itself, the better the performance of the microphone is considered. The target recognition rate for the industry for these telematics applications exceeds 99% under all conditions. Also, teleconferencing and installed sound applications may suffer from similar problems when single element microphones are used in environments that are associated with reverberation and ventilation noise.  
           [0004]    In the automotive environment, a typically used microphone is a first order gradient, in which a single-element microphone is employed in a surface mount configuration designed to minimize pickup of vehicle noise and reverberation originating in a direction away from the talker. These microphones often have a bi-directional or cardioid polar response pattern. However, these microphones have a relatively wide maximum response window (corresponding to an acceptance angle), in which reflective surfaces on all sides of the passenger compartment, such as windows and leather upholstery, degrade performance and result in a low talker-to-vehicle-noise ratio when noisy driving conditions are encountered.  
           [0005]    Alternatively, a dual-element microphone system in an array configuration may be employed in conjunction with digital signal processing to eliminate the undesired signal from the talker&#39;s voice. Such a solution makes use of time-of-arrival information in identifying and amplifying a talker whose voice is received within an acceptance angle of a two-element array in order to reject noise from outside of the acceptance angle. With the array configuration, the talker&#39;s voice may be isolated satisfactorily from undesired speech or speech-like noise (such as a passenger&#39;s voice) in the horizontal plane. However, the system does not perform well with noise in the vertical plane, such as acoustical signals that emanate from audio speakers located in the vehicle. In addition, these systems require multiple microphone elements, as well as expensive hardware and software systems for performing the digital signal processing. A microphone arrangement coupled to a digital processor is typically expensive for automotive applications. Moreover, these systems have not demonstrated high speech recognition scores.  
           [0006]    The approaches of the prior art, as described heretofore, provide acoustical systems having acoustical response characteristics that are not amenable for directive automotive acoustical applications. Thus, it would be an advancement in the art to provide method and apparatus that supports increased directivity and environmental rejection for a variety of applications including hands-free mobile phone use and telematics applications. Furthermore, it is desired that an acoustical system be cost effective, while having the capability of selectively processing distant acoustical sources.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The inventive method and apparatus overcome the problems of prior art by utilizing a plurality of port sub-arrays, in which each port sub-array comprises a plurality of acoustical ports. The ports of each port sub-array are spaced so that each port subarray responds to acoustical signals generated by acoustical sources within an associated frequency range. In an embodiment of the invention, associated frequency ranges are related in a harmonic manner, in which each port sub-array corresponds to different frequency bands. The associated frequency range is a portion of the total frequency range of an acoustical system. Received acoustical signals from each of the port sub-arrays are coupled over acoustical pathways and are converted into electrical signals by capsules that may be mounted in a capsule mounting. The electrical signals may be filtered, such as to reduce spatial aliasing, and post processed to further enhance the frequency response of the array microphone.  
           [0008]    In an embodiment of the invention, an acoustical system is configured to process acoustical signals within a desired horizontal angle and a vertical angle, while suppressing acoustical signals lying outside the angular ranges. The embodiment is configured such that voice recognition performance is enhanced. With a variation of embodiment, which may be applicable to automotive telematics, the port sub-arrays are mounted in a mirror casing so that a rear-view mirror may be tilted according to a talker&#39;s line of sight through a rear window of an automobile, while providing desired directional acoustical characteristics for the talker. Variations of the embodiment support mounting the port sub-arrays in other locations of an automobile such as a steering wheel or instrument cluster. Other embodiments of the invention may process acoustical signals in different acoustical media, such as water, in order to support sonar applications. Further embodiments of the invention may process acoustical signals for controlling speech-enabled devices such as appliances. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows an acoustical delay network with two harmonic sub-arrays according to an embodiment of the invention;  
         [0010]    [0010]FIG. 2 shows a front view of an automotive mirror configuration that supports the acoustical delay network that is shown in FIG. 1;  
         [0011]    [0011]FIG. 3 shows a top view of an automotive mirror configuration that supports the acoustical delay network that is shown in FIG. 1;  
         [0012]    [0012]FIG. 4 shows a capsule mounting that supports the acoustical delay network that is shown in FIG. 1;  
         [0013]    [0013]FIG. 5 shows an architectural configuration of the acoustical delay network that is shown in FIG. 1;  
         [0014]    [0014]FIG. 6 shows a polar plot of the horizontal directivity of the acoustical delay network that is shown in FIG. 1;  
         [0015]    [0015]FIG. 7 shows a polar plot of the vertical directivity of the acoustical delay network that is shown in FIG. 1;  
         [0016]    [0016]FIG. 8 shows a polar plot of the horizontal directivity of the acoustical delay network that is shown in FIG. 1 with quarter wavelength damping applied;  
         [0017]    [0017]FIG. 9 shows a mirror-tilting configuration in conjunction with the acoustical delay network that is shown in FIG. 1; and  
         [0018]    [0018]FIG. 10 shows an acoustical pathway configuration that steers the reception of a transmitted acoustical signal in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 shows an acoustical system  100  with two port sub-arrays according to an embodiment of the invention. A first port sub-array comprises ports  101 ,  103 ,  105 ,  107 ,  109 , and  111 , acoustical pathways  125 ,  127 ,  129 ,  131 ,  133 , and  135 , a plenum  151 , and a capsule  155 . Acoustical pathways  125 - 135  meet at plenum  151 . A second port sub-array comprises ports  113 ,  115 ,  117 ,  119 ,  121 , and  123 , acoustical pathways  137 ,  139 ,  141 ,  143 ,  145 , and  147 , a plenum  149 , and a capsule  153 . Acoustical pathways  137 - 147  meet at plenum  149 . In the embodiment, capsules  153  and  155  each comprise a transducer. (Other embodiments of the invention may utilize more than two port sub-arrays, as will be apparent to one skilled in the art.) In the embodiment, pathways  125 - 135  and  137 - 147  correspond to tubes having the same length (within a tolerance of error), although other embodiments may utilize other forms of acoustical pathways.  
         [0020]    For benefits of describing the embodiments of the invention, the following definitions are used. A “port” refers to an opening that functions as an acoustical ingress for a pipe, tube, capillary, mold passageway, waveguide or other such physical pathway that carries pressure variations from a point outside acoustical delay network  100  to capsule  153  or  155 . A “capsule” (e.g. capsule  153  and  155 ) is a section or subsection of a physical microphone assembly that may include a diaphragm and any additional hardware such as spacers, washers, ports, capillary tubes, resonators that are associated with the transduction of acoustical energy to electrical energy.  
         [0021]    Referring to FIG. 1, acoustical signals arriving at each port ( 101 - 123 ) of the port sub-arrays arrives with approximately constant phase with respect to frequency when originating from a particular direction (in this embodiment, perpendicular to the plane or line of the acoustical system  100 ), whereas acoustical signals arriving at different angles do not possess constant phase relationships. The signals arriving perpendicular to system  100  add coherently (constructively) creating a gain in the acoustical signal strength, referred to as “array gain.” Signals arriving from other angles add incoherently (destructively), resulting in attenuation, notches, and nulls in the beampattern as a function of frequency. This principal is typically referred to as “stacking” and the resulting array gain is a function of the number of ports in each harmonic sub-array. Because of these principles, arrays achieve highly directive beams and pick-up patterns. The result is that the array acts as a spatial filter, and acoustical system  100  discriminates between acoustical signals, or sources of acoustical signals, based on direction and signal frequency while a single microphone typically receives acoustical signals from many different directions. The desired sound results in a main beam with a 0° azimuth called the Maximum Response Axis (MRA).  
         [0022]    There are several issues associated with port sub-arrays. One issue is spatial aliasing that results in grating lobes, comprising undesirable acoustical signals from undesirable angles, that may have a signal power approximating that of the main (desired) beam and whose behavior is unpredictable and difficult to control. (Grating lobes correspond to beams other than the MRA beam, in which the phase shift between ports of a port sub-array arriving from a given angle cannot be distinguished from N radians or N+kπ radians, where k is an integer.) In such cases, the undesirable acoustical signals correspond to a half-wavelength that is shorter (i.e. greater in frequency) than the port spacing of the port sub-array.  
         [0023]    Another issue is the beam pattern that results from a port sub-array. The main beam of a sub-array is formed from the stacked signal of all the ports in the port sub-array. However, each subset of those ports also creates a beam.  
         [0024]    The main beam in acoustical system  100  depends on the desired acoustical signal being received by capsules  153  and  155  at the same time. Thus, identical length tubing (within a tolerance of error) is employed in the embodiment. (However, other embodiments may utilize electronic phase compensation to adjust for different tube lengths.)  
         [0025]    In electronic (non-acoustic) systems, phase shifting may be accomplished by electrical signal processing that creates a delay between ports. The delays allow an array microphone pointed in a particular direction to have a main (desired) beam that is not perpendicular to the array in the azimuth. The MRA, then, is shifted to the angle of the azimuth. Correspondingly, in an acoustic system, a phase shift is achieved by utilizing a second network of tubing with the same or coincident ports and specified staggered lengths to create acoustic propagation delays. (The formation of acoustical phase shifts will be discussed in another aspect of the invention as shown in FIG. 10.)  
         [0026]    It is possible to achieve an approximate constant beamwidth with respect to frequency for an acoustical system (e.g. acoustical system  100 ) by using a plurality of port sub-arrays with increased port spacing such that the spatial aliasing frequency of a port sub-array with larger port spacing is some fraction of the spatial aliasing frequency of another port sub-array with the next-smallest port spacing. Because the beamwidth of a port sub-array becomes smaller for frequencies increasing up to the spatial aliasing frequency, implementing sets of port sub-arrays with gradually decreasing port spacing enables a port sub-array to support a narrow bandwidth for frequencies at which the beamwidth of another sub-array is too wide to be considered desirable. This is typically done at frequencies at double multiples of the of a lower frequency port sub-array (having a larger port spacing), corresponding to port sub-arrays that operate in octaves (e.g. 600-1200 Hz, 1200-2400 Hz, 2400-4800 Hz, and so forth) so that the overall beam pattern of the acoustical system remains essentially constant.  
         [0027]    Referring to FIG. 1, adjacent ports (ports  101  and  103 , ports  103  and  105 , ports  107  and  109 , and ports  109  and  111 ) of the first port sub-array are separated by a first port spacing (d 1 )  161  and adjacent ports (ports  113  and  115 , ports  115  and  117 , ports  119  and  121 , and ports  121  and  123 ) of the second port sub-array are separated by a second port spacing (d 2 )  163 . First port spacing  161  is approximately a half wavelength (λ 1 ) of a first upper frequency of a corresponding frequency response of the first port sub-array and second port spacing  163  is approximately a half wavelength of a second upper frequency of a corresponding frequency response of the second port sub-array. As will be discussed in greater detail in relation to FIG. 5, the first upper frequency is selected as approximately 2,000 Hz and the second upper frequency is selected as approximately 4,000 Hz, which are separated by one octave from each other. Correspondingly, the first distance is approximately 8.6 cm and the second distance is approximately 4.3 cm.  
         [0028]    In FIG. 1, a first electrical signal that is generated by capsule  153  and a second electrical signal that is generated by capsule  155  are provided to an adder  157  through filters  169  and  161 , respectively, in order to form an output  159 . (Operation of filters  169  and  161  are discussed in the context of FIG. 6.) Output  159  may be further processed, as discussed later, and may be utilized by another processing unit such as a telematics processing unit or wireless communications telephone in order to provide hands-free operation.  
         [0029]    In other embodiments of the invention, more than two port sub-arrays may be supported. Each port sub-array may be coupled to a capsule, in which an output of a capsule is coupled to electronic circuitry for bandpass filtering and possibly for further processing.  
         [0030]    [0030]FIG. 2 shows a front view of an automotive mirror configuration  201  that supports acoustical delay network  100  that is shown in FIG. 1. A glass mirror (not shown and corresponding to a glass mirror  903  as shown in FIG. 9) spans an approximate area of automotive mirror configuration  201 . Ports  101 - 123  are situated around a periphery of automotive mirror configuration  201  (corresponding to a mirror casing  1001  as shown in FIG. 10). Capsules  153  and  155  are typically positioned in the interior of automotive mirror configuration  201  (not typically visible to a user) and behind the glass mirror. Ports  101 ,  113 ,  115 ,  103 ,  117 , and  105  are separated from ports  107 ,  119 ,  121 ,  109 ,  123 , and  111  by a vertical distance (d 3 )  207 .  
         [0031]    [0031]FIG. 3 shows a top view of automotive mirror configuration  201  that supports the acoustical delay network  100  that is shown in FIG. 1. Ports  101 - 123  are positioned in a wall  301  of the mirror casing. Ports  101 - 123  are connected to capsules  153  and  155  through acoustical pathways  125 - 147 . A connection  315  couples capsule  153  to electronic circuitry (e.g. filter  509 , adder  513 , and post-processor  515  as shown in FIG. 5) and a connection  317  couples capsule  155  to electronic circuitry (e.g. filter  511 , adder  513 , and post-processor  515  as shown in FIG. 5). Although FIG. 3 shows the electronic circuitry external to the mirror casing, the electronic circuitry may reside within mirror configuration  201  in other embodiments of the invention.  
         [0032]    The embodiment shown in FIGS. 2, 3, and  9  utilizes a rear-view mirror for housing acoustical system  100 . However, other embodiments of the invention may utilize other locations in an automobile, including a steering wheel and an instrument panel.  
         [0033]    While the embodiment that is shown in FIGS.  1 - 3  support a planar array, other embodiments of the invention may support a three-dimensional array, in which the first acoustical sub-array comprises additional ports that are separated from ports  101 - 111  by a depth distance (perpendicular to the vertical distance and the horizontal distance) and the second acoustical sub-array comprises additional ports that are separated from ports  113 - 123  by the depth distance.  
         [0034]    [0034]FIG. 4 shows a capsule mounting  400  that supports acoustical delay network  100  that is shown in FIG. 1. Capsule mounting  400  houses capsules  153  and  155  and acoustically couples acoustical pathways  125 - 147 . In the embodiment, acoustical pathways  125 - 135  are coupled to one side of capsule  153  and acoustical pathways  137 - 147  are coupled to a same side of capsule  155 . With other embodiments, acoustical pathways  125 - 147  may be located differently with respect to capsules  153  and  155 . In one embodiment, acoustical pathways  125 - 137  may be coupled on different sides for capsule  153 , and acoustical pathways  137 - 147  are coupled on different sides of capsule  155 , where an acoustical barrier between a proximity of capsule  153  and a proximity of capsule  155  provides acoustical isolation between capsules  153  and  155 . In other embodiments of the invention, capsule mounting  400  may vary to accommodate a different configuration such as a different type of capsule.  
         [0035]    For a received voice signal in an automotive environment, experimental results suggest that a relative degree of voice recognition is good if the received voice signal is processed with exemplary filter configurations having limiting frequency characteristics such as with a 1000 Hz to 4000 Hz bandpass filter, a 1000 Hz to 5000 Hz bandpass filter, an octave filter centered at 2000 Hz, or a high pass filter with a corner frequency of 1000 Hz. An experimental configuration utilized an IBM Via Voice Recognition Engine, in which different microphone types were positioned at different points within an automobile.  
         [0036]    [0036]FIG. 5 shows an architectural configuration  500  of acoustical delay network  100  that is shown in FIG. 1. Architectural configuration  500  comprises acoustical port sub-arrays  501  and  503 , capsules  505  and  507 , filters  509  and  511  (corresponding to filters  169  and  161 , respectively, as shown in FIG. 1), an adder  513 , and a postprocessor  515  that provides an output  517 . Output  517  may be used for a number of applications, including hands-free wireless terminals and telematics. Acoustical port sub-array  501  corresponds to ports  101 - 111  (as shown in FIG. 1) and acoustical port sub-array  503  corresponds to ports  113 - 123 . Capsules  505  and  507  correspond to capsules  155  and  153  (as shown in FIG. 1). In the embodiment, filter  509  is a bandpass filter having an approximate pass-band of 1 KHz to 2 KHz and filter  511  is a bandpass filter having an approximate pass-band of 2 KHz to 4 KHz. Filters  509  and  511  reduce spatial grating that may be associated with acoustical port sub-array  501  and  503 , respectively.  
         [0037]    Adder  513  combines the signals from filter  509  and filter  511  so that the corresponding combined frequency response of architectural configuration  500  is approximately 1 KHz to 4 KHz. (Experimental results, as discussed above, suggests a good relative measure of speech recognition in which a received voice signal is processed with a bandpass filter having a pass-band of 1 KHz to 4 KHz.) A post-processor  515  may modify a signal from adder  513  in order to dampen irregularities in the signal response characteristics that result from a quarter wavelength (λ/4) response of acoustical port sub-array  501  and acoustical port sub-array  503 . (In some embodiments, post-processing unit  515  may also be capable of supporting a post-equalization filter to provide for a flat response with respect to frequency over an operational region of acoustical system  100 . This type of optimized filter is often referred to as a frequency domain “inverse” filter or an optimally converged adaptive/“Wiener” filter.) In other embodiments of the invention, quarter wavelength damping may utilize partial acoustical blockage (e.g. a foam material) in acoustical pathways  125 - 147 . In other embodiments of the invention, quarter wavelength damping may be provided by filters  509  and  511  such that filter  509  dampens (attenuates) the quarter wavelength response of acoustical port sub-array  501  (corresponding to approximately 1000 Hz for the embodiment as shown in FIG. 2), and filter  511  dampens the quarter wavelength response of acoustical port sub-array  503  (corresponding to approximately 2000 Hz for the embodiment as shown in FIG. 2). Additional damping of quarter-wavelength resonances in the tubing network may be implemented using acoustical filters consisting of tubes, pipes, plenums, and resistances that augment or supplant notching as implemented using foam impedances or electronic means.  
         [0038]    In the embodiment, a higher order pickup pattern is defined as a pattern resulting from the combination of low order or “common” pickup patterns that may be adjusted by delay or amplitude weighting (such as a foam impedance in the ports or tubes). Examples of low order patterns include omnidirectional microphones (zero-th order), cardioids (first order), super-cardioids (first order with different path difference delay than cardioids), and hyper-cardioids. Higher order beam patterns result from combining these inputs in various combinations, such as a second order finite difference (two cardioids separated by a half wavelength with the second delayed by the travel-time between the two).  
         [0039]    In some embodiments, it may be advantageous to include some type of analog or digital sub-array processing between capsule  505  or  507  and adder  513 . In the case where digital signal processing is applied, bandpass filters  509  and  511  and sub-array processing may be accomplished on the same processor (e.g. a microprocessor). In some embodiments, bandpass filters  509  and  511 , subarray processing, adder  513 , and post processor  515  may be implemented on the same processor (in which the entire system is behind capsules  153  and  155 .  
         [0040]    Even though the embodiment that is shown in FIGS.  1 - 5  is directed toward automotive applications, other embodiments of the invention may be directed to other acoustical applications such as high fidelity acoustical applications, audio conferencing, speakerphones, podium microphones, in-car intercoms, multimedia computers, drive-through communications systems, security or surveillance systems, speech-controlled appliances, and sonar applications. While some acoustical applications of the present invention may be associated with an air medium, applications (e.g. sonar applications), as may be apparent to those skilled in the art, may be associated with a water medium.  
         [0041]    The embodiment that is shown in FIGS.  1 - 3  support a frequency spectrum from approximately 1 KHz to 4 KHz with two harmonic nests (port sub-arrays) in order to provide a good relative measure of speech recognition accuracy. However, other acoustical applications may require one skilled in the art to consider other design parameters. For example, in some embodiments that support high fidelity acoustical applications, a frequency spectrum from approximately 100 Hz to 16 KHz may be desired. In such a case, seven port sub-arrays may be incorporated, in which a first port sub-array corresponds to a frequency band of 125 Hz to 250Hz, a second port sub-array corresponds to a frequency band of 250 Hz to 500 Hz, a third port sub-array corresponds to a frequency band of 500 Hz to 1 KHz, a fourth port sub-array corresponds to a frequency band of 1 KHz to 2 KHz, a fifth port sub-array corresponds to a frequency band of 2 KHz to 4 KHz, a sixth port sub-array corresponds to a frequency band of 4 KHz to 8 KHz, and a seventh port sub-array corresponds to a frequency band of 8 KHz to 16 KHz. Also, embodiments of the invention may consider different error criteria such as a measure of speech recognition accuracy and mean square error (MSE). Mean square error may be useful in gauging the processing fidelity of non-speech acoustical signals such as musical sounds.  
         [0042]    [0042]FIG. 6 shows a polar plot  600  of the horizontal directivity of acoustical delay network  100  that is shown in FIG. 1. Polar plot  600  shows frequency responses for 800 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz, and 3000 Hz corresponding to curves  601 ,  603 ,  605 ,  607 ,  609 , and  611 , respectively. Each curve shows the horizontal directional response for the associated frequency with respect to the zero-degree azimuth of acoustical delay network  100 . Typically, within each harmonic sub-array, the higher the frequency, the greater the directivity (i.e. the narrower the beamwidth) of acoustical delay network  100 . The use of multiple nests maintains approximately constant directivity over the operational range of the device.  
         [0043]    [0043]FIG. 7 shows a polar plot  700  of the vertical directivity of acoustical delay network  100  that is shown in FIG. 1. Polar plot  700  shows frequency responses for 800 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz, and 3000 Hz corresponding to curves  701 ,  703 ,  705 ,  707 ,  709 , and  711 , respectively. Typically, the vertical directivity increases as the frequency increases. The embodiment possesses only one “nest” in the vertical direction, but other embodiments may utilize a plurality of nests in the vertical (Y) dimension or depth (Z) dimension as is applied in the horizontal (X) dimension.  
         [0044]    [0044]FIG. 8 shows a polar plot  800  of the horizontal directivity of acoustical delay network  100  that is shown in FIG. 1 with quarter wavelength damping applied. Polar plot  800  shows frequency responses for 800 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz, and 3000 Hz, corresponding to curves  801 ,  803 ,  805 ,  807 ,  809 , and  811  respectively. As with polar plot  600 , typically the horizontal directivity increases as the frequency increases. However, comparing plot  611  (as shown in FIG. 6) with plot  811  (corresponding to 3000 Hz), the side lobes are reduced with quarter wavelength damping.  
         [0045]    [0045]FIG. 9 shows a mirror-tilting configuration in conjunction with acoustical delay network  100  that is shown in FIG. 1. Acoustical delay network  100  is mounted in mirror casting  901  (corresponding to  201  in FIGS. 2 and 3). Mirror casting  901  is tilted at an angle θ  905  with respect to glass mirror  903 . A talker  907  talks within a main beamwidth  911  of acoustical delay network  100 , over an acoustical path  909  (corresponding to a perpendicular to a plane of acoustical delay network  100 ). Because glass mirror  903  is tilted with respect to mirror casing  901 , talker can also view an object  917  through a rear window  913  corresponding to a view path  915 . View path  915  forms an angle such that a perpendicular to glass mirror  903  bisects the angle.  
         [0046]    [0046]FIG. 10 shows an acoustical pathway configuration that steers the reception of a transmitted acoustical signal in accordance with an embodiment of the invention. Ports  1001 ,  1003 , and  1005  receive an acoustical signal corresponding to a wave front  1017  that is incident to acoustical delay network  100  at an angle θ  1021  with respect to a horizontal reference  1019 . Ports  1001 ,  1003 , and  1005  are openings in acoustical pathways  1007 ,  1009 , and  1011 , respectively. Acoustical pathways  1007 ,  1009 , and  1011  differ in length in order that the Maximum Response Axis (main beam) is tilted by angle θ  1021 . The tilting of the main beam corresponds to a differential length between adjacent acoustical pathways (e.g.  1007  and  1009 ) that is approximately equal to d*SIN(θ), where d is the port spacing between adjacent ports. Tilting the main beam facilitates the mounting of acoustical delay network  100  for mounting entities that are not easily adjusted such as a steering wheel or an instrument panel.  
         [0047]    As can be appreciated by one skilled in the art, a computer system with an associated computer-readable medium containing instructions for controlling the computer system can be utilized to implement the exemplary embodiments that are disclosed herein. The computer system may include at least one computer such as a microprocessor, digital signal processor, and associated peripheral electronic circuitry.  
         [0048]    While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.