Patent Publication Number: US-10327086-B2

Title: Head related transfer function equalization and transducer aiming of stereo dimensional array (SDA) loudspeakers

Description:
PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to related and commonly owned U.S. provisional patent application No. 62/491,009, filed Apr. 27, 2017, the entire disclosure of which is incorporated herein by reference. The subject matter of this invention is also related to the following commonly owned Stereo/Dimensional Array® (“SDA®”) patents: (a) U.S. Pat. No. 4,489,432, (b) U.S. Pat. No. 4,497,064, (c) U.S. Pat. No. 4,569,074, (d) U.S. Pat. No. 6,937,737, and (e) U.S. Pat. No. 7,231,053, the entireties of which are incorporated herein by reference, for purposes of providing background information and nomenclature. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to reproduction of sound in audio playback systems generically known as “stereo” systems and more specifically to the application of psychoacoustic and acoustic principles in the design of a multi-driver loudspeaker system configured for use in a stereo pair, traditionally located in front of a listening space. 
     Discussion of the Prior Art 
     Recorded music consumers or listeners often use two-channel “stereo” systems when listening to music recordings. Most commercial recorded music is provided via online music streaming or download services or via distribution of physical recording products such as Compact Discs (“CD”s) which provide listeners with two-channel or stereo recordings. In the parlance of stereo recording and playback, a sound which seems to come from the central space between a left and right speaker (e.g., a single frequency tone having equal amplitude in both left and right channels) is said to be “centered” in the “stereo image” as perceived by the listener. Music recording producers have become very adept at producing wonderful stereo recordings which (when played back under ideal conditions) seem to place performer&#39;s instruments in a space which is recreated or synthesized in front of the listener during music playback. Very few listeners were treated to this ideal playback (with palpable, stable sonic images) however, which is why Mathew Polk developed the original Stereo/Dimensional Array® loudspeaker systems such as those illustrated in  FIGS. 1A-1D . 
     Matthew Polk&#39;s “SDA” Patents: 
     Generating a broad and stable acoustic image was the desired goal of Polk Audio&#39;s work as described and illustrated in the commonly owned (and now expired) U.S. Pat. Nos. 4,489,432, 4,497,064 and 4,569,074, among. others.  FIG. 1A  is a diagram taken from U.S. Pat. No. 4,497,064 illustrating Polk&#39;s “SDA” loudspeaker system and method, with a stereo pair of “main” left and right channel speakers (LMS, RMS) each placed beside a corresponding “sub” or SDA dimensional effect speakers (LSS, RSS), where all four speakers are aligned along a speaker axis in front of a listening location. 
     Referring to  FIGS. 1A-1D , an SDA™ stereophonic sound reproduction system  50  includes an amplifier  54  having a left channel output (“L”)  60  and a right channel output (“R”)  70 , each with positive and negative connections. Right loudspeaker system  80 R includes a right main speaker (RMS or, as seen in  FIG. 1B , stereo mid-woofer) and Left loudspeaker system  80 L includes a left main speaker driver (LMS or stereo mid-woofer) at right and left main speaker locations which are equidistantly spaced from the listening location. The listening location (shown in the diagram of  FIG. 1A  centered in a listener&#39;s head) is defined as a spatial position for accommodating a listener facing the main speakers and having a right ear location R e  and a left ear location L e  which are aligned along an ear axis, with the right and left ear locations separated along the ear axis by a maximum interaural sound distance of Δt max  and the listening location being defined as the point on the ear axis equidistant to the right and left ears. Polk Audio&#39;s SDA speaker system model SDA 1  is shown in  FIGS. 1B, 1C and 1D , and these are exemplary of many other Polk Audio speaker systems made using the SDA™ technology. Right dimensional effect or sub-speaker (RSS or, as seen in  FIG. 1B , dimensional mid-woofer) and left dimensional effect or sub-speaker (LSS or dimensional mid-woofer) are provided at right and left sub-effect speaker locations which are equidistantly spaced from the listening location, in the listener&#39;s space or room (as best seen in  FIG. 1A  and  FIG. 1D ). The right and left channel outputs from Amplifier  54  ( FIG. 1C ) are coupled respectively to the right and left main speakers (RMS, LMS). The crossover networks of right speaker  80 R and left speaker  80 L are connected and an inverted right channel signal (“−R”) with the low frequency components attenuated is developed and coupled to the left dimensional effect or sub-speaker (LSS) via an SDA interconnect cable  66 . And an inverted left channel signal (“−L”) with the low frequency components attenuated is developed and coupled to the right dimensional effect or sub-speaker (RSS) via SDA interconnect cable  66 . 
     The distance between the main speakers and sub-speakers (W) was then selected (as a function of Δt max ) to render an expanded acoustic image with no reduction of low frequency response as perceived by a listener located at the listening location. In effect, the spacing “W” between the main and dimensional SDA effect or “sub” speakers was chosen to approximate the space between the ears of the listener, which allowed an interaural crosstalk cancelling inverted signal from each “sub” speaker to diminish or eliminate cross talk from the left main speaker to the right ear and from the right main speaker to the left ear, and this interaural crosstalk cancellation created the desired audible “SDA” effect for the listener. But, as shown in  FIG. 1D , this system was able to render a wide and stable sonic image and pleasing tonal balance only for those listeners in or just behind the “sweet spot.” When early SDA™ speaker system playback was successful, the left-to-right sound field was easily heard to extend past the physical loudspeaker&#39;s locations (so, for example, stable sonic images were audibly perceived as coming from outside and to the left of Left SDA speaker  80 L). But this effect depended on sitting or standing in the “best listening area” as seen in  FIG. 1D , and phasiness could be a problem, if the listener&#39;s head was turning or moving. 
     In Polk Audio&#39;s early SDA speaker systems (e.g., the SDA 1  system  50 ), these and other limitations in the efficacy of the SDA effect were noted. The SDA effect was created with a band-limited interaural crosstalk cancelling inverted signal from each “sub” speaker which was typically not effective for crosstalk at frequencies above 2 Khz., but this choice was a compromise. Referring again to  FIGS. 1A, 1B and 1D , users were instructed to avoid setting up the SDA speakers with “toe-in” because creating the dimensional or SDA effect required the speakers to fire “forward” or perpendicularly to the “speaker axis” line upon which the loudspeaker enclosures are arranged to achieve the proper time delay between the main and crosstalk cancelling arrays of transducers. Users of Polk&#39;s original SDA™ system and method (like the SDA 1  shown in  FIGS. 1B-1D ) sometimes noted the perceptible “phasiness” as a tonal balance that could change in an unnatural way. 
     There is a need, therefore, for an improved structure and method to more reliably render the SDA effect for users listening to two channel recordings which eliminates perceived “phasiness” and enlarges the SDA effect “sweet spot” in which users experience greater image stability and specificity and greater satisfaction with the loudspeaker system&#39;s sound reproduction. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to overcome the above mentioned problems with phasiness and the narrow sweet spot by providing a method and system for implementing a new form of Stereo Dimensional Array (“SDA™”) signal processing which is effective when used in a pair of loudspeakers configured for placement is a listener&#39;s room or listening space. 
     Another object of the present invention is providing an enhanced SDA™ loudspeaker system with a more natural spectral response where tweeters are used in the SDA or dimension-effect generating transducers without any increase phasiness or image confusion, and which, in use, generates more stable sonic images for the listener. 
     As noted above, Polk&#39;s prior Stereo Dimensional Array (SDA™) loudspeakers were attempting to widen and stabilize sonic images within an apparent sound stage between of a set of loudspeakers by sending a band-limited crosstalk cancelling signal from the opposite side of the primary speaker. Using prior art SDA methods, the applicants observed that the sound that reaches the opposite (e.g., right) ear from the primary (e.g., left) speaker is acoustically altered or effected by the head and torso of the listener. This effect is often referred to as the “head shadow” or “head related transfer function” (“HRTF”). In revisiting the challenges to making an improved SDA product, applicants noted that the SDA effect generating cancellation signal could be improved to better account for the head shadow (“HRTF”) effect. After some experimentation, it was discovered that an improved cancellation effect could be accomplished not just in the frequency domain, but also in the time domain (or in “phase”). As noted above, in prior art SDA systems (e.g., 50) the SDA effect was created with a band-limited interaural crosstalk cancelling inverted signal from each “sub” speaker which was typically not effective for crosstalk at frequencies above 2 Khz., so the compromise in this choice was reconsidered in this development effort. 
     The method and structure of the improved SDA loudspeaker system of the present invention were developed by evaluating and manipulating three factors, namely 
     (a) controlling delay from the crosstalk cancelling speaker due to its physical location on the loudspeaker system enclosure or baffle surface, 
     (b) aiming the cross talk cancelling speaker&#39;s radiation and using the speaker&#39;s inherent dispersion characteristics and 
     (c) electronic equalization as cooperative elements which, together, produce or generate an enhanced crosstalk cancelling signal which is more effective in cancelling crosstalk at frequencies in the range of 2 KHz-about 5 KHz. 
     The previous SDA loudspeakers (e.g., the SDA 1 , described above) did not adequately address these considerations. 
     By considering (a) delay from the crosstalk cancelling speaker due to its physical location on the loudspeaker baffle, (b) its inherent dispersion characteristics and (c) electronic equalization in a new way, using the method of the present invention, the operative frequency range of the crosstalk cancelling transducers was increased. SDA effect generating or crosstalk cancelling “Dimensional” midrange and tweeter drivers are configured in an array on specially aimed baffles and provided with SDA cancellation effect signals which combine to extend higher in frequency without introducing issues with phasiness and the narrowing sweet spot. This extension in higher frequencies causes the overall tonality of the loudspeaker system of the present invention to be more natural and increases the listener&#39;s sense of envelopment. 
     As shown in  FIGS. 1A-1D , traditional SDA speakers (e.g.,  80 L,  80 R) fired forward from planar front baffles, perpendicular to the “speaker axis” line upon which they are arranged, to achieve the proper time delay (Δt max ) between the main and crosstalk cancelling arrays of transducers. This configuration aims the radiation pattern of the main array&#39;s tweeter and midrange straight ahead and thus 15-30 degrees away from the listener&#39;s head (when centered between the L and R speakers). At this angle, tweeters in each loudspeaker have unacceptable amount of high frequency attenuation due to their natural dispersion or radiation pattern characteristics. 
     In the new SDA system of the present invention, this problem is overcome by configuring a tower-shaped loudspeaker enclosure with a front baffle having first and second diverging angled upper segments or facets. An upper left segment is oriented to aim a selected angle (e.g., 15 degrees) to the left and an upper right segment is oriented to aim at the same selected angle (e.g., 15 degrees) but diverges to the right, so neither baffle segment points straight ahead. The angled facets or baffle segments aim the drivers with angled upper baffle segments or facets such that the “main” or stereo tweeter for each channel is now pointing almost directly at the listening location. The “main” or stereo midrange is also mounted on the same angled baffle (or slanted planar surface) and aimed at the listening location so that the combination of the main tweeter and main midrange create a better dispersion pattern with a more pleasing overall tonal balance due to that baffle being effectively “toed in” toward the listening location. 
     The left speaker system enclosure has it&#39;s “main” tweeter and midrange drivers aligned vertically in an array aimed from the upper right inwardly angled baffle segment (aimed at the listening location) and also has an “effects” or SDA dimensional cancellation effect generating midrange and tweeter driver array on the upper left segment, where the SDA dimensional baffle is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listening location. 
     Following the same acoustic principles, the mirror-imaged right speaker system has it&#39;s “main” tweeter and midrange drivers aimed from the upper left angled segment (aimed at the listening location) and also has an “effects” or SDA dimensional midrange and tweeter driver array on the upper right segment, where the SDA dimensional baffle is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listening location. 
     One issue which commercial product manufacturers must consider is how to make something that customers actually want to buy and retailers actually want to offer. Modern retailers for audio products are part of a distribution channel which includes wholesalers and very large retail businesses (e.g., “big box” retail store operators) which have pre-conceived biases or requirements which make some products easier to market and other products more difficult to market. Distribution channels for loudspeakers strongly discourage and will not often carry loudspeakers products that have different left and right speaker products (e.g., with differing product or Stock Keeping Unit “SKU” identifiers). This means that in some commercial channels there is likely to be to a Stereo SDA loudspeaker system which has distinct left and right channel products, meaning a “left” speaker (with a right-slanted baffle, to aim at the listener) which differs from it&#39;s paired “right” speaker (with a left-slanted baffle, to aim at the listener). The addition of a tweeter on the crosstalk cancelling side of the new SDA loudspeaker now allows the speaker (as a product or “SKU”) to be symmetrical, thereby providing an option for resolving this issue. The result is a loudspeaker system front baffle with two diverging arrays, each mounted on conjoined, preferably planar left and right side baffle segments or facets which diverge a selected angle (e.g., 15 degrees) from a transverse vertical plane defined along what, in  FIG. 1A  would otherwise been have been the “speaker axis”. The symmetrically angled conjoined intersecting left and right side baffles can intersect in a forward-facing or distal edge to define left and right side angled baffle planes or facets meeting at an acute angle of, preferably 150 degrees (as seen from within the loudspeaker enclosure) or defining an outside corner of two planes which meet at an angle of 210 degrees, as seen from the listener&#39;s position, in front of the speaker(s). This baffle aiming angle is described and illustrated in these embodiments as being (preferably) 15 degrees to the left and right of a listening axis, but could be rendered (effectively enough, with crossover changes) using baffles angled symmetrically back from a horizontal plane in any angle within the range of 10 degrees and 30 degrees. 
     The angled first and second arrays are then are then fed signals from a new crossover which is optionally configurable using switches or jumpers such that either (e.g., left baffle or right baffle) array can be selected by the user or installer as being (a) the main array or (b) SDA/effects array by rerouting signals through a switch or jumper block. 
     The method and system of the present invention preferably implements a new broader spectrum SDA signal processing method in a “stereo pair” of traditional standalone loudspeakers, which, during playback, more effectively presents a wide sweet spot, a pleasing tonal balance and reduced “phasiness”, as compared to prior art SDA systems (e.g., as shown in  FIGS. 1A-1D ). Optionally, each loudspeaker may be configured as an identical product or SKU (e.g., a single enclosure SDA loudspeaker system) which achieves a surprisingly effective psycho-acoustically expanded image breadth by implementing a new type of cancellation signal generation for sources of undesirable inter-aural crosstalk. 
     The new SDA system and method of the present invention was designed and configured to provide four advantages, namely (1) a more natural spectral response of the loudspeakers, (2) allowing tweeters to be used in the SDA effects or dimensional speaker array without increased phasiness or image confusion, (3) improving the imaging of SDA, and optionally (4) removing commercial concerns around having separate left and right loudspeaker products (or SKUs). 
     In the new SDA system, a stereo pair of loudspeaker enclosures is configured in a listening space with a listening location, each loudspeaker system&#39;s enclosure has the dual array aiming beveled or faceted front baffle which carries and aims first and second midrange driver and tweeter arrays, with the new crossover which provides appropriately filtered signals to the each of the drivers in each array. 
     In an early prototype embodiment, a first midrange driver is mounted on a first angled baffle surface or facet and a second midrange driver is mounted on a second angled baffle surface or baffle, and a single tweeter is mounted near (e.g., just above) both angled baffle surfaces on the loudspeaker&#39;s front baffle. 
     In a second (preferred) embodiment, a first midrange driver and first tweeter are mounted on a first angled baffle surface or facet and a second midrange driver and second tweeter are mounted on a second angled baffle surface or baffle, where both angled baffle surfaces are part of the loudspeaker&#39;s front baffle. This second embodiment provides an enhanced SDA “main stereo pair” loudspeaker product which more effectively overcomes the problems/issues with the original SDA (including perceived phasiness and a narrow sweet spot) in a loudspeaker system having a left speaker tower and a right speaker tower which can be easily set up in a listening space by a listener, user or installer. 
     The acoustic centers of the drivers on left angled baffle and the right angled baffle are preferably approximately 6.5″ apart. In a preferred embodiment, each tweeter/midrange array is aligned along a substantially vertical axis which is centered on an angled baffle, so, for the left loudspeaker tower enclosure, the “main” tweeter is mounted directly above the “main” midrange driver on the upper right angled segment (aimed at the listener) and the “effects” or SDA dimensional tweeter is above and vertically aligned with the effects or SDA midrange on the upper left segment, where the SDA dimensional baffle is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listener. The acoustic centers separating the left angled baffle tweeter and right angled baffle tweeter are preferably approximately 6.5″ apart, and the acoustic centers separating the left angled baffle midrange and right angled baffle midrange drivers are also that same distance (e.g., preferably approximately 6.5″) apart. 
     When two of the loudspeaker system towers of the present invention are placed in a typical stereo-listening arrangement in a listener&#39;s space or room, the inner-baffle set of drivers (aiming on an axis toward the centered listener or listening location) play the standard (or main stereo) left and right signals from an amplifier (e.g.,  54 ). The outer-baffle set of drivers (aiming on an axis away from the centered listener) play the crosstalk cancellation or SDA dimensional effect signals. Crosstalk cancellation (or SDA dimensional effect) signals are generated by crossover circuits connecting the loudspeakers to the amplifiers such that the left tower gets an “L-R” signal and the right tower gets an “R-L” signal. An electrical crossover network is used to make the crosstalk cancelling signals used to drive the dimensional or SDA effect tweeter/midrange driver array by matching the main tweeter/midrange driver array&#39;s signal and compensating for the headshadow. In the prototype a simple R-L shelf circuit was used to achieve this. 
     The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a diagram illustrating Mathew Polk&#39;s original “SDA” loudspeaker system and method, with a stereo pair of “main” left and right channel speakers (LMS, RMS) each including a corresponding “sub” speaker (LSS, RSS), where all four loudspeaker drivers are aligned along a speaker axis in front of a listening location, in accordance with the prior art. 
         FIG. 1B  illustrates Polk Audio&#39;s original “SDA 1 ™” loudspeaker system and setup method, with a pair of loudspeaker enclosures including the “main” left and right channel speakers (LMS, RMS) each including a corresponding “sub” or SDA effects speaker (LSS, RSS), where all four loudspeaker drivers are aligned along a planar front baffle surface aligned on the speaker axis in front of a listening location, in accordance with the prior art. 
         FIGS. 1C and 1D  illustrate the setup method for Polk Audio&#39;s original “SDA 1 ™” loudspeaker system, in accordance with the prior art. 
         FIG. 2A  is a spectral plot illustrating plots received at the listener&#39;s left ear, right ear and the acoustic sum, for an SDA effect generating speaker which does not include a head shadow compensating filter in the speaker&#39;s crossover. 
         FIGS. 2B and 2C  are diagram illustrating the new approach for generating a head shadow filter enhanced SDA effect for a listener, in accordance with the structure and method of the present invention. 
         FIG. 3  illustrates an SPL v. frequency plot for an exemplary HRTF curve (or head shadow) target response curve developed as part of the present invention for a crosstalk cancelling (or dimensional SDA effect) loudspeaker, in accordance with the structure and method of the present invention. 
         FIG. 4  illustrates an SPL v. frequency plot for a prototype crosstalk cancelling driver array or SDA effect section of the loudspeaker, in accordance with the structure and method of the present invention. 
         FIG. 5 . illustrates a crossover circuit schematic for an initial prototype wherein the rightmost section illustrates connections for the crosstalk cancelling or dimensional SDA effect speakers and where R 6  and L 6  define a “shelf” filter section which comprises the head shadow mimicking portion, in accordance with the structure and method of the present invention. 
         FIGS. 6A and 6B  illustrate early prototypes for a preferred embodiment of the user or installer configurable, single SKU, multi-faceted or multi-baffle SDA loudspeaker system, in accordance with the structure and method of the present invention. 
         FIG. 7  is a diagram and schematic which, taken together, illustrate how the user or installer configurable multi-faceted or multi-baffle SDA loudspeaker system of  FIGS. 2-6B  may be set up for use as either a left main stereo speaker or a right main stereo speaker, in accordance with the structure and method of the present invention. 
         FIG. 8A  illustrates another preferred embodiment of the system of the present invention including left and right multi-faceted or multi-baffle SDA loudspeaker system enclosures, in accordance with the structure and method of the present invention. 
         FIG. 8B  is a diagram illustrating the new “SDA” loudspeaker system and method, with a stereo pair of left and right channel loudspeaker system enclosures, where both loudspeaker system enclosures are aligned along the speaker axis in front of a listening location and each loudspeaker system enclosure faces forward and in so doing, orients one baffle surface toward the listener and another baffle surface laterally outside of and away from the listener 
         FIGS. 9A-9E , are several views of the new “SDA” loudspeaker system and method, in accordance with the present invention. 
         FIG. 10  illustrates a crossover circuit schematic for another embodiment of the new SDA loudspeaker system and method wherein the middle section illustrates connections for the crosstalk cancelling or dimensional SDA effect signals for the SDA tweeter and SDA midrange speakers including a “shelf” filter section which comprises the head shadow mimicking portion, in accordance with the structure and method of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to  FIGS. 2A-10 , the present invention comprises an enhanced or improved SDA “main stereo pair” loudspeaker system  250  including a left tower enclosure  280 L and a right tower enclosure  280 R which overcomes the issues encountered with the original SDA system (e.g.,  50 ). 
       FIG. 2A  illustrates part of the problem with the SDA systems described above. In this development effort, applicants recognized that, as shown in  FIG. 2A , the SDA effect was created with a band-limited interaural crosstalk cancelling inverted signal from each “sub” speaker which was typically not effective for crosstalk at frequencies above about 2 Khz., so this compromise became a focus of the development effort. An improvement in SDA effect bandwidth was sought to generate an enhanced crosstalk cancelling signal which is more effective in cancelling crosstalk at frequencies in the range of 2 KHz to about 5 KHz.  FIG. 2A  is a diagram which illustrates applicant&#39;s early prototype design considerations for generating an enhanced SDA effect for a listener. The principal differences between the system and method of the present invention (now referred to as the Challenger SDA system  250 ) and the SDA systems of the prior art (e.g.,  50 ) are (a) a new implementation of a “Head-Shadow” filter, optimized for use with (b) first and second angled or divergently aimed baffles carrying a “main” tweeter/midrange driver array on a first baffle beside a dimensional or SDA cancellation effect tweeter/midrange driver array on a second baffle, where each tower enclosure has the paired angled baffles aiming at selected angles from a reference plane projecting in parallel to the listening axis and perpendicularly to the speaker axis (best seen in  FIG. 8B ). 
       FIG. 4  illustrates an SPL v. frequency plot for an improved Headshadow compensating crosstalk cancelling section of the loudspeaker, in accordance with the structure and method of the present invention. The new SDA loudspeaker enclosure configuration includes first and second angled baffles segments or facets (e.g.,  192 ,  194 ) and the SDA baffle midrange driver (e.g., in the prototype illustrated in  FIG. 6B ) is a 4″ midrange while the tweeter is a 1″ ring radiator tweeter. The transducers must have the necessary bandwidth to create the Head Shadow compensating effect as described below. Alternatively, the selected transducers for the Main or SDA baffles could be single full range transducers.  FIG. 5 . illustrates a crossover schematic for an initial prototype crossover  140  where the rightmost section illustrates connections for the crosstalk cancelling speakers and R 6  and L 6  define a “Shelf” filter section which comprises the head shadow compensating (or mimicking) portion, in accordance with the structure and method of the present invention. The “shelf” filter section shown in  FIG. 5  is better suited for use in this system than a Low Pass filter section because it can render the Head shadow compensating filter response shape more effectively (in comparison, a similar Low Pass Filter would roll off high frequencies excessively and change the tonal balance adversely). 
     An Improved SDA system (e.g.,  250 ) includes a matched pair of tower-shaped loudspeaker enclosures,  280  with a front baffle  290  having a first angled upper segment or facet  292  and a second diverging angled upper segment or facet  294  (best seen in  FIGS. 9A, 9C and 9D ). First or upper left segment  292  is oriented to aim a selected angle (e.g., 15 degrees) to the left and second or upper right segment  294  is oriented to aim at the same selected angle (e.g., 15 degrees) but diverges to the right, so neither baffle segment or facet points straight ahead. 
     Each upper baffle segment or facet is preferably substantially planar and includes first and second driver receiving apertures configured to support and aim a pair of mounted loudspeaker drivers which are preferably aligned on a centered vertical axis (as seen in  FIGS. 9A, 9C and 9D ). Each upper baffle segment or facet  292 ,  294  thus aims a tweeter driver  338  and a midrange driver  329  which are aligned on a vertical axis within the baffle segment&#39;s planar surface and the drivers in each array are time-aligned by the orientation of the baffle segment surface and the mounting depth within the mounting baffle&#39;s thickness (e.g., 25 mm thick MDF). So each enclosure  280  has on its front baffle  290  an angled upper left baffle segment or facet  292  which aims a vertically aligned left side driver array including left array tweeter driver  338 L and left array midrange driver  329 L. Enclosure front baffle  290  also includes non-parallel, diverging right baffle segment or facet  294  which aims a vertically aligned right side driver array including right array tweeter driver  338 R and right array midrange driver  329 R. 
     The angled facets or baffle segments  292 ,  294  support and aim their driver arrays such that the “main” or stereo tweeter for each channel (e.g.,  338 R for left speaker tower  280 L) is now pointing almost directly at the listening location. The “main” or stereo midrange (e.g.,  329 R for left speaker tower  280 L) is also mounted on the same angled baffle (e.g.,  294 L for left speaker tower  280 L) and aimed at the listening location so that the combination of the main tweeter and main midrange create a better dispersion pattern with a more pleasing overall tonal balance due to that baffle ( 294 L) being effectively “toed in” toward the listening location. 
     Once the crossovers are installed in the enclosures, the system  250  becomes a pair of matched enclosures  280 L,  280 R, so left speaker system enclosure  280 L has it&#39;s “main” tweeter and midrange drivers  338 ,  329  aligned vertically in an array aimed from the upper right inwardly angled baffle segment  294 L (aimed at the listening location, see  FIG. 8B ) and also has an “effects” or SDA dimensional cancellation effect generating midrange and tweeter driver array  338 ,  329  on the upper left segment  292 L, where the SDA dimensional baffle segment or facet  292 L is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listening location. 
     Following the same acoustic principles, when system  250  is installed in the listening space, the mirror-imaged right speaker system  280 R has its “main” tweeter and midrange drivers  338 ,  329  on the upper left angled segment  292 R aimed at the listening location and also has its “effects” or SDA dimensional midrange and tweeter drivers  338 ,  329  arrayed on the upper right segment  294 R, where the SDA dimensional baffle  294 R is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listening location. 
     Referring again to  FIG. 8B , when setting up the new SDA system  250 , a stereo pair of loudspeaker enclosures  280 L  280 R is configured in a listening space with a listening location, each loudspeaker system&#39;s enclosure  280  has the dual array aiming beveled or faceted front baffle  290  which carries and aims first and second midrange and tweeter arrays, with a new crossover (see, e.g.,  FIGS. 5 and 10 ) which provides appropriately filtered signals to the each of the drivers in each array. 
     In an early prototype loudspeaker system tower  90  shown in  FIG. 6A , a first midrange driver  90 ML is mounted on a first angled baffle surface or facet and a second midrange driver  90 MR is mounted on a second angled baffle surface or baffle, and a single tweeter  90 T is mounted near (e.g., just above) both angled baffle surfaces on the loudspeaker&#39;s front baffle. This early prototype incorporated a crossover network similar to that shown in  FIG. 5  (but without the crossover portion for the SDA effect tweeter) and was not really effective enough at presenting the advantages sought in applicants&#39; development work. 
     In a second early embodiment of the improved SDA loudspeaker system  100  (as shown in  FIG. 6B ), a first midrange driver and first tweeter are aligned along a vertical axis on a first angled baffle surface or facet  192  and a second midrange driver and second tweeter are aligned along a vertical axis on a second angled baffle surface or baffle  194 , where both angled baffle surfaces are part of the loudspeaker&#39;s front baffle  190 . This second embodiment tower  100  provides an enhanced SDA “main stereo pair” loudspeaker product which more effectively overcomes the problems/issues with the original SDA (including perceived phasiness and a narrow sweet spot) in a loudspeaker system having a left speaker tower and a right speaker tower (not shown) which can be easily set up in a listening space by a listener, user or installer. 
     The vertical axes and aligned acoustic centers of the drivers on left angled baffle  192  and the right angled baffle  194  are preferably spaced apart laterally at a distance (“W”, which is a function of Δt max ) of approximately 6.5 inches. In the preferred embodiment, each tweeter/midrange array is aligned along its substantially vertical axis which is centered on its angled baffle segment, so, for a left loudspeaker tower enclosure, the “main” tweeter was mounted directly above the “main” midrange driver on the upper right angled segment  194  and aimed at the listener and the “effects” or SDA dimensional tweeter was above and vertically aligned with the effects or SDA midrange on the upper left segment  192 , where the SDA dimensional baffle ( 192 , for a left side tower enclosure, similar to  280 L, in  FIG. 8B ) is angled or slanted to aim the SDA midrange and the SDA tweeter away from the listening position. This prototype loudspeaker tower  100  incorporates a crossover network  140  ( FIG. 5 ) and the connections to drivers made in a specific enclosure render that enclosure either a Left channel tower or a Right channel tower. Referring again to  FIG. 5 , for a Right channel tower, the “main array” connections are made (a) from K 2 -LMD to the midrange driver on upper left baffle segment  192  and (b) from K 1 -LTW to the tweeter driver also on upper left baffle segment  192 ; following this method, the “SDA” or dimensional array connections are made (a) from K 5 -RMD to the midrange driver on upper right baffle segment  194  and (b) from K 4 -RTW to the tweeter driver also on upper right baffle segment  194 . 
     In the exemplary embodiment of  FIG. 6B , the angled wall segments recede symmetrically to the rear at an aiming angle of 15 degrees, but these baffles need not be symmetrical and can recede at selected aiming angles in the range of 10-30 degrees, and those angles may vary to accommodate drivers with different radiation patterns. For this exemplary embodiment, the acoustic centers separating the left angled baffle tweeter and right angled baffle tweeter are preferably approximately 6.5″ apart, and the acoustic centers separating the left angled baffle midrange and right angled baffle midrange drivers are also that same distance (e.g., preferably approximately 6.5″) apart. 
     When two of the loudspeaker system enclosures (e.g., towers  100  or  280 ) of the present invention are placed in a typical stereo-listening arrangement in a listener&#39;s space or room (e.g., as seen in  FIG. 8B ), the inner-baffle set of drivers (e.g., on baffle segments  294 L and  292 R) are oriented toward a baffle aiming axis and generally toward the centered listener or listening location. When installed and in use, those inner facing baffle-mounted driver arrays play the standard (or main stereo) left and right signals from an amplifier (e.g.,  54 ). The outer-baffle sets of drivers (e.g., on baffle segments  292 L and  294 R) are oriented away from the listening axis and generate the crosstalk cancellation or SDA dimensional effect sounds. Crosstalk cancellation (or SDA dimensional effect) signals are generated by crossover circuits (e.g.,  140  in  FIG. 5 or 440  in  FIG. 10 ) connecting the loudspeakers to one or more amplifiers (e.g.,  54 ) such that the left tower gets an “L-R” signal and the right tower gets an “R-L” signal communicated via an SDA interconnect (e.g.,  266 ) connecting a crossover in a left speaker (e.g.,  280 L) to a crossover in its paired right speaker (e.g.,  280 R). The crossover networks (e.g.,  440 ) of right speaker  280 R and left speaker  280 L are connected to one another through connections labelled “SDA Out” and “SDA In” and an inverted right channel signal (“−R”) with the low frequency components attenuated is developed and coupled to the left dimensional effect or SDA speaker via the SDA interconnect cable  266 . And an inverted left channel signal (“−L”) with the low frequency components attenuated is developed and coupled to the right dimensional effect or SDA speaker also via SDA interconnect cable  266 , and these connections are used to make the crosstalk cancelling signals used to drive the dimensional or SDA effect tweeter/midrange driver array by matching the main tweeter/midrange driver array&#39;s signal and compensating for the headshadow. In the prototype a simple R-L shelf circuit (see, in  FIG. 10 , parallel circuit elements L 7  and R 8 ) was used to achieve this. 
     Turning now to  FIG. 7  a user or installer configurable multi-faceted or multi-baffle SDA loudspeaker system (e.g.,  100 ) may include a switching or multiplexing system and be set up for use as either a left main stereo SDA speaker or a right main stereo SDA speaker, in accordance with the structure and method of the present invention. This optional feature allows product manufacturers SDA compatible loudspeaker products that can be user configured to be left channel or right channel SDA speakers, but, at the time of sale have a single product or Stock Keeping Unit “SKU” identifiers. The addition of a tweeter on the crosstalk cancelling side of the new SDA loudspeaker (e.g.,  100  or  280 ) now allows the speaker (as a product or “SKU”) to be symmetrical, thereby providing an option for resolving this issue (using, e.g., the system illustrated in  FIG. 7 ). The result is a loudspeaker system front baffle with two diverging arrays, each mounted on conjoined, preferably planar left and right side baffle segments or facets which diverge a selected angle (e.g., 15 degrees) from a transverse vertical plane defined along what, in  FIG. 1A  would otherwise been have been the “speaker axis”. In the illustrated embodiments, the symmetrically angled conjoined intersecting left and right side baffles (e.g.,  192 ,  194 ) can intersect in a forward-facing or distal edge to define left and right side angled baffle planes or facets meeting at an acute angle of, preferably 150 degrees (as seen from within the loudspeaker enclosure) or defining an outside corner of two planes which meet at an angle of 210 degrees, as seen from the listener&#39;s position, in front of the speaker(s). The baffle aiming angle described and illustrated in these embodiments as being (preferably) 15 degrees to the left and right of a central axis parallel to the listening axis, but could be rendered (effectively enough, with crossover changes) using baffles angled symmetrically back from a horizontal plane in any angle within the range of 10 degrees and 30 degrees. The angled first and second upper baffle segment arrays are then are then fed signals from a crossover (e.g.,  140 ,  440 ) which is optionally configurable using switches or jumpers (as illustrated in  FIG. 7 ) such that either (e.g., left baffle or right baffle) array can be selected by the user or installer as being (a) the main array or (b) SDA/effects array by rerouting signals through a switch or a jumper block. 
     Enhanced Crosstalk Cancellation Using the “Head Shadow”: 
     Referring again to  FIGS. 2A, 2B, 2C and 8B , cancellation of cross talk requires computing and accounting for the time delay (Δ) for sound travelling between speakers and the listener&#39;s ears. It is important that the dimensional SDA effect cancellation signal&#39;s acoustical energy arrive at the ear at the same time as the original stereo (e.g., “main”) signal&#39;s acoustical energy, since they are “summed” at the ear. To accomplish this, the distance between main and effects arrays (“W” or “DW”) must be roughly the distance between the ears, or about 6″. In the development process for this invention, the sound arriving at each ear was considered as an acoustic sum where: 
                           ⁢       L   ear     =       L   Main     +       L   SDA     *     Δ   1       +       R   SDA     *       HRTF     -   30         HRTF     +   30         *     Δ   2     ⁢           ⁢   And                 (     Eq   .           ⁢   1     )                 R   ear     =         L   Main     *       HRTF     -   30         HRTF     +   30         *     Δ   3       +       L   SDA     *       HRTF     -   30         HRTF     +   30         *     Δ   2       +       R   SDA     *     Δ   1                 (     Eq   .           ⁢   2     )               
The term (HRTF −30 /HRTF +30 ) is the difference between the signal arriving at the near ear and signal arriving at the far ear. This is often referred to as the “Head Shadow”, so in the following equations, HS=(HRTF −30 /HRTF +30 ).  FIG. 3  illustrates an approximation or modelled spectral response known as the KEMAR Head Shadow (+30 vs −30 degrees) for a standard head shape and this response was used in generating the following. So, for the Right side ear:
 
 R   ear   =L   Main   *HS*Δ   3   +L   SDA   *HS*Δ   2   +R   SDA *Δ 1   (Eq. 3)
 
     If one assumes there is only left signal (i.e. signal is completely panned left), then, for the right ear, there should be no signal. (so R ear =0). 
     If, for example, if delay Δ 3 =Δ 1  these two assumptions can be plugged into the equation, and upon rearranging terms, one gets:
 
− L   main   *HS*Δ   1   =L   SDA   *HS*Δ   2   +R   SDA *Δ 1   (Eq. 4)
 
     Ignoring the L SDA  term:
 
 −L   Main   *HS*Δ   1   =R   SDA *Δ 1   (Eq. 5)
 
     And this observation lead to how a head shadow effect generating filter may be approximated. If the R SDA  (dimensional or SDA effect crosstalk cancelling) signal can be filtered in such a way as to mimic or compensate for the head shadow, then it will more completely cancel the L Main  signal&#39;s crosstalk. Applicant&#39;s development work has led to the discovery that this can be approximated by a simple filter and one can then effectively multiply SDA array&#39;s signal by the effect of this filter.
 
 R   ear   =L   Main   *HS*Δ   3   +L   SDA   *HS*HS*Δ   2   +R   SDA   *HS*Δ   1   (Eq. 6)
 
Because it is known that R SDA =−L Main  (electrically), the expression for the filter as written in Eq. 6 can be simplified to:
 
 R   ear   =L   SDA   *HS*HS*Δ   2   (Eq. 7)
 
     So, the remainder of the acoustic summation at the right ear is the L SDA  signal, filtered by the electrical filter and also the physical head shadow itself, plus a delay, which means cancellation of crosstalk is more effective than the prior art SDA system. 
     In improved SDA system  250 , the SDA crosstalk cancellation effect is significantly increased by using crossover networks (e.g.,  140  or  340  with Shelf filter sections in the SDA part of the crossover network) that compensate for a listener&#39;s Head Shadow, thereby making the dimensional or SDA crosstalk cancellation more effective over a broader spectrum. 
     Referring next to  FIGS. 8A and 8B , sound reproduction system  250  having a left channel output and a right channel output includes apparatus for reproducing sound having an expanded and more stable acoustic field and acoustic image and includes a first or left loudspeaker system enclosure or tower  280 L disposed in a first loudspeaker system enclosure location ( FIG. 8B ) spaced a selected distance (e.g., 6-20 feet) from a listening location for left channel playback, where the listening location is a place in a space for accommodating a listener&#39;s head having a right ear location and a left ear location spaced along an ear axis. System  250  preferably includes a second or right side loudspeaker system enclosure  280 R which is configured for right channel playback and is wired to function as a mirror image or cooperating loudspeaker. 
     The left loudspeaker system enclosure  280 L has a multi-faceted or multi-planar front baffle surface (see e.g.,  FIGS. 9A-9E ) comprising a first front baffle surface or facet  292 L which is angled rearwardly to recede at a selected (e.g., 10-30 degree, preferably 15 degree) angle from a vertical plane aligned with the speaker axis on the left side, and a second front baffle surface or facet  294 L which is angled rearwardly to recede at a selected (e.g., 15 degree) angle from a vertical plane aligned with the speaker axis on the right side, where the first and second baffle surfaces  292 L,  294 L define loudspeaker driver supporting and aiming structures aligned along substantially vertical planes (e.g., as shown in  FIGS. 9A-9E ). As described above, that first baffle facet  292 L carries and aims a first midrange driver  329 L having a midrange driver acoustic center and a first tweeter driver  338 L having a tweeter driver acoustic center which is preferably substantially vertically aligned with said first midrange driver acoustic center along a vertical axis centered within and in the vertical plane defined by facet surface  292 . The second baffle facet  294  carries and aims a second midrange driver  329 R and a second tweeter  338 R, and that second midrange driver  329 R has its acoustic center spaced laterally from the first midrange driver  329 L by a selected distance DW (see, e.g.  FIG. 9D , about 6-6.5 inches), and the second tweeter driver  338 R has a tweeter driver acoustic center which is preferably substantially vertically aligned with the acoustic center of second midrange driver  329 R and spaced laterally from the first tweeter driver&#39;s acoustic center by the same selected distance DW (e.g., about 6-6.5 inches). First loudspeaker system enclosure or tower  280 L has external terminals (e.g., via input panel  316 ) for Main (+) and (−) signal inputs, and an SDA signal input/output terminal (as shown in  FIG. 10 ) where signal processing circuitry including crossover circuit  440  has bi-amp or bi-wire compatible (HI and LO) input terminals for the Main (+) connection, the Main (−) connection, an SDA In connection and an SDA Out connection, where crossover  440  is configured to generate (i) a “main” tweeter signal (ii) a “main” midrange signal, (iii) a “Head Shadow Filter” compensated SDA dimensional effect tweeter signal, and a “Head Shadow Filter” compensated SDA dimensional effect midrange signal. The signal processing circuitry including crossover  440  (or crossover  140 ) communicates the SDA dimensional effect tweeter signal and the SDA dimensional effect midrange signal to an SDA dimensional effect radiating array (mounted on facet  292 ) including first tweeter  338 L and first midrange  329 L which are aimed by first front baffle or facet  292  away from the listening position and away from the listening axis (as shown in  FIG. 8B ). 
     Sound reproduction system  250  has signal processing circuitry (e.g., in crossover circuit  440 ) that communicates the Main Tweeter signal and the Main Midrange signal to the main radiating array comprising second tweeter  338 R and second midrange  329 R which are aimed by said second front baffle  294  toward the listening position. As shown in  FIG. 8B , sound reproduction system  250  also of claim  2 , further includes a second loudspeaker system enclosure or tower  280 R disposed in a second loudspeaker system location which is spaced laterally from and aligned along a speaker axis with the location of first loudspeaker system  280 L and the spacing between left tower  280  L and right tower  280  R is preferably in the range of 6 to 20 feet. Second tower or right side SDA speaker assembly  280 R is preferably spaced from the listening location by a distance substantially equal to the spacing between the listening location and the first loudspeaker system  280 L. Second loudspeaker system enclosure  280 R, is physically configured as a tower enclosure assembly (e.g.,  280 ,  FIGS. 9A-9E ), and differs from left or first enclosure  280 L in how its crossover (e.g.,  440 ) is connected. 
     Second loudspeaker system enclosure  280 R also has a multi-faceted or multi-planar front baffle surface  290  comprising a first front angled baffle surface or facet  292 R which is angled rearwardly to recede at a selected (e.g., 10-30 degree, preferably 15 degree) angle from a vertical plane aligned with the speaker axis on the left side, and a second front baffle surface or facet  294 R which is angled rearwardly to recede at a selected (e.g., 15 degree) angle from a vertical plane aligned with the speaker axis on the right side, where the first and second baffle surfaces  292 R,  294 R define loudspeaker driver supporting and aiming structures aligned along substantially vertical planes. 
     Turning again to  FIGS. 9A-9E , and specifically to  FIG. 9E  which provides an exploded perspective view of the tower loudspeaker enclosure  280  used in making left side enclosure  280 L and  280 R, it is shown that braced MDF loudspeaker cabinet  301  includes internal 18 mm MDF bracing and is supported upon base  302  which is made of 50 mm thick MDF. The cabinet&#39;s entire front baffle  290  (including facets  292  and  294 ) and top  303  are preferably made of 25 mm MDF. In the preferred embodiment, a pair of 5.25 inch midrange drivers  329  are positioned beside one another on the diverging adjacent baffle or facet surfaces  292 ,  294 . The front baffle  290  is covered by and supports a detachable grill assembly  311  and in the bottom segment includes vertically aligned circular openings configured to support and aim first and second 10″ woofers  304  above an aperture or port defined by port trim insert member  306 . An optional removable top cover  305  allows future installation and use of up-firing (e.g., Dolby® Atmos® system) drivers. As noted above, each tower enclosure assembly  280  includes first and second tweeters  338  mounted with tweeter trim panels  312 . In a bass cavity section behind and in fluid communication with the back side of woofers  304 , a tuned port assembly includes port flare  313  and MDF doughnut  314  on cylindrical cardboard port tube  315 . 
     The connections to the crossover (e.g.,  140  or  440 ) are made through an aluminum input plate  316 . Two SDA interconnect conductors (preferably bundled into an SDA interconnect cable assembly  266 ) are preferably made up as red and black jumper wires, one red, one black, each 12AWG, and each with a gold plated spade terminal on one end and a banana plug pin connector on the opposite end. The crossover assembly  345  is preferably a printed circuit board assembly (e.g., with conductors and circuit elements for crossover circuit  440 , as shown in  FIG. 10 ) and preferably has plastic standoffs for attachment near the bottom of the cabinet&#39;s interior volume. Crossover assembly  345  preferably has polarized Faston-style connectors on all connections. Input plate  316  carries preferably three binding post assemblies  359  for a bi-wireable “main” connection to one or more amplifiers (e.g.,  54 ) and optionally to a source for an elevation module (e.g., Atmos) signal to drive an optional ATMOS assembly (not shown). 
     Turning to the crossover circuit  440  illustrated in  FIG. 10 , the “Main In” portion of the crossover is configured for use with a biwire or biamp setup, and so is divided into Hi and Lo sections which may be used with conductive jumpers connecting terminals shown as “HI In+” to “LO In+” and “HI In−” to “LO In−”, where the terminals labeled “LO In” are connected to the woofer portion of the crossover circuit and the terminals labeled “HI In” are connected to the midrange and tweeter portions of the crossover circuit. Crossover  440  is a three-way crossover with five main sections, namely: 
     1) Main Tweeter—a third order high pass with level resistor and notch; 
     2) Main Midrange—a third order high pass, third order low pass, notch and a level resistor; 
     3) Woofer—a third order low pass; 
     4) SDA Tweeter—a third order high pass with level resistor and notch; 
     5) SDA Midrange—a third order high pass, third order low pass, notch and a level resistor, where 
     6) The SDA sections are preceded by a first order low pass shelf circuit (the paralleled circuit of L 7  and R 8 ). 
     The SDA Input/Output terminals are used to connect the SDA portion of the crossover to the “other” speaker in the stereo pair (e.g.,  280 L and  280 R) and enable the improved head-shadow compensating SDA crosstalk cancellation to function as intended. An optional Elevation module input (not shown in  FIG. 10 , but possibly included in crossover assembly  345 ) connects a set of wires up to an optional elevation module which might be installed in the top of the speaker (e.g., replacing cover  305 ). Returning to  FIG. 10 , the critical passive electrical components shown in crossover  440  have selected tolerances which are typically measured at 1 kHz, and the specifics for those components are included in the Table 1: 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 Power, 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Voltage or 
                   
                   
               
               
                   
                 Current 
                 DCR(Inductors 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Nominal 
                   
                 Rating or 
                 &amp; Switches) 
                   
               
               
                 Part 
                 Value 
                 Tol. 
                 Wire Gauge 
                 DF (Capacitors) 
                 Material 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 C1, C9 
                 10 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤1% 
                 Polyester metal film 
               
               
                 C2, C10 
                 30 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤1% 
                 Polyester metal film 
               
               
                 C3, C11 
                 2.0 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤1% 
                 Polyester metal film 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 C4, C5, 
                  68 μF @ 120 Hz 
                 ±5% 
                 200 
                 V 
                 ≤5% 
                 Electrolytic 
               
               
                 C12, C13 
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 C6, C14 
                 1.0 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤1% 
                 Polyester metal film 
               
               
                 C7, C15 
                 18 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤1% 
                 Polyester metal film 
               
               
                 C8, C16 
                 30 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤5% 
                 Electrolytic 
               
               
                 C17 
                 4.7 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤5% 
                 Electrolytic 
               
               
                 C18 
                 82 
                 μF 
                 ±5% 
                 100 
                 V 
                 ≤5% 
                 Electrolytic 
               
               
                 L1, L8 
                 0.3 
                 mH 
                 ±5% 
                 1.0 
                 mm 
                 ≤0.25 Ω  
                 Air Core; copper wire 
               
               
                 L2, L9 
                 1.0 
                 mH 
                 ±5% 
                 0.5 
                 mm 
                 ≤2.0 Ω 
                 Air Core; copper wire 
               
               
                 L3, L10 
                 2.0 
                 mH 
                 ±5% 
                 1.0 
                 mm 
                 ≤0.25 Ω  
                 Steel laminate I-Core; 
               
               
                   
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                   
                 bobbin 
               
               
                 L4, L11 
                 1.0 
                 mH 
                 ±5% 
                 1.0 
                 mm 
                 ≤0.15 Ω  
                 Steel laminate U-Core 
               
               
                   
                   
                   
                   
                   
                   
                   
                 (min 9.5 mm square); 
               
               
                   
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                   
                 bobbin 
               
               
                 L5, L12 
                 0.5 
                 mH 
                 ±5% 
                 1.0 
                 mm 
                 ≤0.1 Ω 
                 Steel laminate U-Core 
               
               
                   
                   
                   
                   
                   
                   
                   
                 (min 9.5 mm square); 
               
               
                   
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                   
                 bobbin 
               
               
                 L6, L13 
                 3.0 
                 mH 
                 ±5% 
                 0.8 
                 mm 
                 ≤0.6 Ω 
                 Steel laminate I-Core; 
               
               
                   
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                   
                 bobbin 
               
               
                 L7 
                 1.2 
                 mH 
                 ±5% 
                 1.0 
                 mm 
                 ≤0.2 Ω 
                 Steel laminate U-Core 
               
               
                   
                   
                   
                   
                   
                   
                   
                 (min 9.5 mm square); 
               
               
                   
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                   
                 bobbin 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 L14 
                 3.0 mH @ 120 Hz 
                 ±5% 
                 1.2 
                 mm 
                 ≤0.2 Ω 
                 Steel laminate I-Core; 
               
               
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                 bobbin 
               
               
                 L15 
                 2.0 mH @ 120 Hz 
                 ±5% 
                 1.2 
                 mm 
                 ≤0.15 Ω  
                 Steel laminate I-Core; 
               
               
                   
                   
                   
                   
                   
                   
                 copper wire on plastic 
               
               
                   
                   
                   
                   
                   
                   
                 bobbin 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 R5, R13 
                 15 
                 Ω 
                 ±5% 
                 5 
                 W 
                   
                 Sand Cast 
               
               
                 R6, R14 
                 1.0 
                 Ω 
                 ±5% 
                 5 
                 W 
                   
                 Sand Cast 
               
               
                 R7, R15 
                 4.0 
                 Ω 
                 ±5% 
                 10 
                 W 
                   
                 Sand Cast 
               
               
                 R8 
                 8.0 
                 Ω 
                 ±5% 
                 10 
                 W 
                   
                 Sand Cast 
               
               
                 R16 
                 15 
                 Ω 
                 ±5% 
                 5 
                 W 
                   
                 Sand Cast 
               
               
                 R17 
                 1.0 
                 Ω 
                 ±5% 
                 10 
                 W 
                   
                 Sand Cast 
               
               
                   
               
            
           
         
       
     
     Referring again to  FIGS. 9A and 10 , the connections to drivers made in a specific enclosure (e.g.  280 R) render that enclosure either a Left channel tower or a Right channel tower. So for a Right channel tower (e.g.  280 R), the “main array” connections for the driver array on left facet surface  292 R are made (a) from connector P 2 , terminals  3  (+) and  4  to the midrange driver  329 L on upper left baffle segment  292  and (b) from connector P 2 , terminals  1  (+) and  2  to the tweeter driver also on upper left baffle segment  292 ; following this method, the “SDA” or dimensional array connections are made (a) from connector  2 X 2 , terminals  2  and  4  to the midrange driver  329 R on upper right baffle segment  294  and (b) from connector  2 X 2 , terminals  1  and  3  to the tweeter driver  338 R also on upper right baffle segment  294 . 
     The system  250  and method of the present invention provide specific improvements on this applicants&#39; prior work on the well-known SDA™ speaker systems, and persons of skill in the art will appreciate that those improvements include a new and more effective SDA effect generating apparatus in system  250  with a left speaker (e.g.,  329 R) in enclosure  280 L which is aimed (e.g., by facet  294 L) toward the listening position at a selected main driver aiming angle (diverging from a “straight ahead” line parallel to the listening axis, where the selected main driver aiming angle is between 10 degrees and 30 degrees (e.g., 15 degrees) and where the left sub or SDA effect generating speaker(s) (e.g.,  329 L and  338 L) are aimed away from the listening position at a selected symmetrical mirror-image diverging sub/SDA effect driver aiming angle to that straight ahead reference line which is parallel to the listening axis, where the sub/SDA effect driver aiming angle is substantially equal in magnitude to the main driver aiming angle (best seen in  FIGS. 8B, 9C and 9D ). 
     Another improvement in selected embodiments of new and improved SDA loudspeaker system (e.g.,  250 ) is that a left main speaker may comprise a left main midrange driver which is vertically aligned with a left main tweeter (e.g., on angled baffle surface  292 R) to provide a left main driver array aimed toward the listening position at a selected left main driver array aiming angle from a line parallel to the listening axis (as seen in  FIGS. 8B and 9C ), where that selected left main driver array aiming angle is between 10 degrees and 30 degrees (e.g., 15 degrees) and where the left sub or SDA effects speaker includes a left sub midrange driver  329 R which is vertically aligned with a left sub tweeter to provide a left sub driver array aimed (e.g., by facet  294 R away from the listening position at a selected left sub driver array aiming angle, diverging from that imaginary “straight ahead” line parallel to the listening axis which is substantially equal in magnitude to the main driver aiming angle (as best seen in  FIG. 9C ). 
     Yet another improvement in selected embodiments of new and improved SDA loudspeaker system (e.g.,  250 ) is that the SDA jumper connection  266  connecting the crossovers in each of the speakers (e.g.,  280 L,  280 R) provides a connection to the right and left channel outputs for developing a left channel minus right channel signal and a right channel minus left channel signal which now includes signal processing circuitry included in each crossover (e.g.,  140 ,  440 ) with input terminals for a Main (+) connection, a main (−) connection, an SDA In connection and an SDA Out connection, where that crossover (e.g.,  140  or  440 ) is configured to generate (i) a “main” tweeter signal (ii) a “main” midrange signal, (iii) a “Head Shadow Filter” compensated SDA dimensional effect tweeter signal, and a “Head Shadow Filter” compensated SDA dimensional effect midrange signal. In addition, the left sub (or SDA effect) speaker now comprises an array with an effects generating (or sub) tweeter driver which is spaced from and vertically aligned with a sub midrange driver, so that the “Head Shadow Filter” compensated SDA dimensional effect tweeter signal is communicated with the SDA effect generating (or sub) tweeter. 
     The improved method of operating and using system  250  of the present invention comprises the steps of: disposing a right main speaker (e.g., on baffle segment  292 R) and a left main speaker (e.g., on baffle segment  294 L) at right and left main speaker locations equidistantly spaced from the listening location which, as seen in  FIG. 8B  is a place in space for accommodating a listener&#39;s head facing the main speakers and having a right ear location and a left ear location along an ear axis, with the right and left ear locations separated along the ear axis by a maximum interaural sound distance of Δtmax, and the listening location being defined as the point on the ear axis equidistant to the right and left ears, the listening location being spaced from the main speakers and defining a listening angle with respect thereto to result in an interaural time delay Δt of the right and left ear locations along the listening angle to the left and right main speakers; the next step is disposing at least one right sub-speaker (e.g., on baffle segment  294 R) and at least one left sub-speaker (e.g., on baffle segment  292 L) at right and left sub-speaker locations equidistantly spaced from the listening location; the next step is selecting the right and left sub-speaker locations such that the inter-speaker delay of the right sub-speaker over the right main speaker with respect to the right ear location and the inter-speaker delay of the left sub-speaker over the left main speaker with respect to the left ear location are each approximately the same as the interaural time delay Δt; and then coupling the right and left channel outputs to the right and left main speakers, respectively (via crossovers  140  or  440  and SDA cable  266 ); next, using crossover  140  or  440 , deriving from the right and left channel outputs an inverted right channel signal and an inverted left channel signal for use in generating the cross talk cancellation effect; and coupling the inverted right channel signal to the at least one left sub-speaker and coupling the inverted left channel signal to the at least one right sub-speaker. Here, we note that the Improved Method of the present invention also comprises deriving a head shadow compensated inverted right channel signal and a head shadow compensated inverted left channel signal and coupling the head shadow compensated inverted right channel signal to the at least one left sub-speaker (e.g., on baffle segment  292 L) and coupling the head shadow compensated inverted left channel signal to the at least one right sub-speaker (e.g., on baffle segment  294 R). This improved method also includes selecting main speaker locations and sub-speaker locations to be on non-parallel baffle segments (e.g., on baffle segments  292 L and  292 R) aiming at least one left or right sub-speaker away from a speaker axis which is parallel to the ear axis. Optionally, the method may include high pass filtering the inverted right and left channel signals prior to applying them to the at least one left and at least one right sub-speakers, respectively. 
     Having described preferred embodiments of a new and improved loudspeaker system (e.g.,  250 ) and SDA signal processing method, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as set forth in the following claims.